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RED  YELLOW  BLUE  CITRINE  PURPLE 


Chart  of   Primary,   Secondary   and   Tertiary   Colors 


SEE    PAGE     37 


Prosthetic  Dentistry 


JAMES  HARRISON  PROTHERO,  D.  D.  S. 

I'ROFESSOR   OF    PROSTHETIC    TKCHNIC.    PROSTHETIC 
DENTISTRY,    AXl)    METALLIRCY 


NORTHWESTERN    UNIVERSITY    DENTAL   SCHOOL 
CHICAGO 


Second   Edition     Revised   and    Enlarged 
1200  Pages     1400  Illustrations 


MeDICO-DkNTAL  PUBLISHINC,   Co. 

c. 

Ash  &  Sons 

CHICAGO 

Distributors 
1916 

London 

\  i\ 


bs 


Entered  according  to  Act  of  Congress,  in  the  year  1916, 

By   J.    H.    PROTHERO 

In   the   office   of   the   Librarian    of  Congress.   Washington.    D.   C. 

Entered  at  Stationers'   Hall. 

London,    England. 


THR    I1I,.\KEI,T     PBINTINO     CO..     TRIXTERS.     CIIICMI 


e 


AS  A  SLIGHT  TOKEN  OF  ADMIRATION 
AND  APPRECIATION  FOR  KINDLY  HELP 
AND  AD\'ICE  RENDERED  THE  WRITER 
THROUGH  YEARS  OF  ASSOCIATION,  THIS 
BOOK  IS  DEDICATED  TO  THE  MEMORY  OF 

GREENE  VARDIMAN  BLACK,  M.D.,  D.D.S.,Sc.D.,  LLD. 
WHOSE  PERSISTENT  AND  UNTIRING  EF- 
FORTS IN  THE  FIELDS  OF  SCIENCE  HAVE 
IMMEASURABLY  BENEFITED  NOT  ONLY 
THE  PROFESSION  OF  WHICH  HE  WAS  A 
MOST  DISTINGUISHED  MEMBER,  BUT  HU- 
MANITY AS  WELL. 


PREFACE 

'I'lic  rcvisiiiii  (if  a  foriiicv  cditidii  (if  tlii>  Imok  lia>  rc>iilli'<l 
in   \cry  nearly  a   t'lmi-rdld  ciilar.iAfincnt. 

I*r('\aiiin,y-  dental  educational  ine1li(Hl>.  altlmuuli  eoxcrin- 
(inly  those  sulijects  I'dlisidered  essential,  leave  little  time  to  I  lie 
he.niiiiH'i-  I'oi'  eollatei-al  readin.ii'.  In  tlie  lionr  to  lioiir  transition 
ot"  his  mind  from  one  recitation  to  another  llie  student  some 
times  fails  to  realize  the  hreadtJJ  and  scope  of  some  iiarticular 
subject,  or  its  relation  as  a  ])art  to  the  whole.  This  is  esjieciallv 
true  in  the  prosthetic  field.  Innumeralile  de\  ices  and  nu'tlio(ls 
of  teolinie  have  been  evolved  Tor  the  replacement  ot  lost  natn 
ral  teeth.  To  bnrdeu  the  student'--  mind  with  all  of  these 
would   he  im])racticable. 

The  writer  has  endeavored  to  introduce  the  essentials  in 
four  main  subjects  of  jjrosthesis.  \i/..,  denture,  crown.  Iu-id,i;c 
and  inlay  construction,  with  sul'licient  elahoratimi  to  enahle 
the  be^'inner  to  acquire  a  ]M-actical  as  well  as  theoretical 
knowledii'e  of  them.  Sti'ess  is  laid  upon  the  fad  that,  althou,i;h 
involvin.i;'  many  ]u-olilenis  in  ])hysics  and  mechanics,  the  call 
ing  of  a  prosthetist  is  nuich  more  than  that  of  a  mechanic. 
The  appliances  which  he  constructs  are  jilaced  in  ajiposition 
to  or  rest  upon  living,  sensitive  tissue  susceiitilile  to  i>atho 
logic  changes  when  substitutes  are  not  well  ]ilainied.  Fre 
(juently,  as  a  result  of  improjjer  itlanning,  many  restorations, 
although  well  executed  from  a  mechanical  standjioint,  result 
in  infinitely  more  harm  than  benefit. 

A  synopsis  of  color  ])rinciples  has  been  included  because. 
without  a  knowledge  of  crude  jirimary  colors  and  their  com 
l)lenients,  it  is  impossible  to  discern  fine  distinctions  between 
attenuated  tints  and  their  comi)leineiits,  as  should  he  done  in 
the  harmonious  selection  of  teeth. 

A  section  on  metallurgy  has  been  incoriiorated,  since  the 
prosthetist  is  constantly  dealing  with  metals  and  alloys  in  one 
form  or  otlier;  conse(iuently  a  knowledge  of  their  pliysical 
properties  is  essential.  The  niifliiw  of  recent  discoveries  has 
been  added,  with  the  idea  of  exciting  further  interest  in  the 
wonderful  phenomena  of  the  elements  and  their  relation  to 
eacli  other. 

A  section  on  the  history  of  prosthesis  has  been  added,  so 
that  the  student  may  form  some  conception  of  the  sequent 


growth  ami  proj-rcss  in  tlii>  licM.  Uriel'  thouiiii  it  is,  the 
subject-matter  lu-eseiiteil  iiixoKctI  a  iMinsidcraMc  cxiiemlituve 
of  time.  It  is  IioikmI  that  i1  ma>  aiil  in  i-nundiiig  nut  the 
beginner's  (•()ncc|)ti()ii  of  the  brca(hli  and  scoiic  dl'  the  hchl  he 
is  entering. 

Tlie  writer  desires  to  e\])ress  iiis  ap]>reeiation  to  various 
individuals,  organizations  and  supply  houses,  as  follows: 

To  the  National  Dental  Assoeiatioii,  tlirougli  its  officers, 
for  the  use  of  cuts  which  appeared  in  Dr.  (Jnerini's  History 
of  Dentistry. 

To  tile  S.  S.  W'iiite  Denial  Aiannfacturing  Conipany  for 
inauy  cuts  throughout  the  text,  and  i)articularly  those  relating 
to  crown  and  bridge  work,  included  in  the  chapter  on  history. 

To  the  Dentists'  Supply  Company  of  New  York  for  Dr. 
.).  Leon  Williams'  typal  forms  of  teeth  and  Dr.  Gysi's  aiipli- 
ances. 

To  II.  D.  .lusti  &  Son,  tiirough -Mr.  IJowe;  Ash  »&  Sons, 
through  Mr.  Sykes;  Lee  S.  Smith  &  Co.,  Samuel  A.  Crocker, 
Ransom  &  liandolj)h,  Cleveland  Dental  Supply  Company, 
J.  W.  Ivor3%  Lea  &  Fel)iger,  Johnson  &  Lund,  Goldsmith  Bros., 
Detroit  Dental  Manufacturing  Com]iany  and  others  for  vari- 
ous cuts  used  through  the  text. 

To  Dr.  A.  J.  Bush  of  Columbus,  Ohio,  for  his  essay  and 
<'harts  on  the  classification  of  fixed  bridgework. 

To  Dr.  L.  J.  Weinstein  of  New  York  for  his  recent  work 
on  alloys  of  gold,  investments  and  fluxes. 

Finally,  thanks  are  due  to  the  untiring  efforts  of  my 
assistant,  Dr.  Joseph  Ridgway,  for  help  in  arranging  text  and 
illustrations  and  in  ]n'oofreading. 

James  Hakkison  Protheko. 
Chicago,  January  25,  1916. 


TABLE    OF   CONTENTS 

CHAi'Tl-:R    1 

PROSTHETIC    DENTISTRY 

General  remarks — The  three  principal  objects  desirable  to  attain  in  den- 
ture construction — Restoration  of  the  function  of  mastication — Restora- 
tion of  disturbed  facial  contour  and  fulfillment  of  general  esthetic  re- 
quirements— The  construction  of  dentures  that  may  be  worn  with  com- 
fort   Pages  I   to  (I 

CllAl'Tl'lR     II 

BODILY    FUNCTION'S    CONCERNED   IN    DIGESTION 

Metabolism — Impairment  of  bodily  functions — The  mouth — The  lips — 
The  vestibule — The  oral  cavity  proper — Mucous  membrane — Epithe- 
lium— The  palatine  vault — The  liony  structure  of  the  hard  palate — 
Palatine  foramina — Thickness  of  the  palatine  process  of  the  maxilla — 
Mucous  membrane  of  the  palate — The  rugae — The  tongue — The  sense  of 
taste — The   salivary    slands Pages    7    to    Ki 

CHAPTKR    III 

EXAMINATION  OF  THE  MOUTH 

Position  of  patient — Examination  of  mouth  when  natural  teeth  are  present — 
Examination  of  edentulous  mouths — Preparation  of  the  mouth  tor  den- 
tures— Spongy  borders — Reduction  of  sjiongy  borders — Temporary  den- 
tures— Permanent  dentures Pages  lii  to  22 

chapt]':r  IV 

ARTIFICIAL  DENTURES 

Physical  and  mechanical  problems  involved  in  their  con'struction — I<'ull  den- 
tures— Adhesion — Atmospheric  pressure — Retention  by  means  of  atmos- 
pheric pressure — Conditions  necessary  for  retention — Relieving  pressure 
over  hard  areas  in  upper  dentures — Vacuum  rhaTiibers — Compensating 
for  expansion  of  the  cast — Position  and  outline  form  of  the  distal  mar- 
gin of  an  upper  denture — Preparation  of  lower  impressions — Soft  alveo- 
lar l)orders   Pages  2"   to  32 

CHAPTI'.R    \ 

IMPRESSION    TKAYS 

Definitions  of  some  commonly  used  terms — Use  of  the  terms  "Cast''  and 
"Model" — Impression  trays — Tray  nomenclature — Tray  adaptation — Con- 
forming the  tray  by  bending — Conforming  by  cutting — Additions  to  the 
tray — Special  trays — Cast — Swaged — Trays  of  ideal  baseplate — Metallic 
extensions  to  stock  trays Pages  ^^'■',  In  4n 

(11  M'TI'.R     \l 

IMPRESSIONS    AND    IMPRESSION    MATERIALS 

Ri'(|uircmenls — Classification — Plaster  of  Paris — Manufacture — Physical 
properties — Setting — Strength  of  hardened  gypsum — Time  required  to 
crystallize — Size  of  crystals — Influence  of  mixing  on  quality — Expansion, 
measurement  of — Contraction — Warpage — Means  of  obviating — Compres- 
sibility of — Advantageous  properties  of — Impression  compounds  similar  to 
plaster — Cement  used  as  an  impression  material — Modeling  compound — 

Beeswax — Beeswax    and    paraffin — Hard    bite    wax — Gutta    percha 

Pages  t1   to  112 


viii  •lAI'.l.l'",    ()!■•    CONTENTS 

CIlAl'Tl'.k  \ll 
TECHNIC  OF  IMPRESSION  TAKINH 
I'lilHT  iiiipressions  indications  for  use  of  plaster — Preliminary  steps — 
I'osition  of  patient — Position  of  operator — Selecting  and  fitting  trays — 
.\Iixins  tlie  plaster— Introduetion  of  filled  tray — Securing  peripheral 
adaptation — Muscle  marking  the  periphery — Dislodgins  and  removal 
of  impression — Lower  impressions — Selection  of  tray — Position  of 
patient — Position  of  operator — Muscle  marking — Partial  cases,  classi- 
fications of — Taking  impressions  of  partial  cases — Combination  ini- 
liressions  of  wax  or  modeling  compound  and  plaster — Removal  of 
impression — Assembling  the  fracturd  pieces — Hreakiug  an  impression 
along  definite  lines — Impressions  of  modeling  compound — Full  cases — 
Manner  of  softening  the  compound — Introducing  the  filled  tray — Secur- 
ing adaptation — Reheating  for  corrective  measure — Summary  of  steps. 
Pages  G:i  to  Sy 

(•ii.\1''I'i-:r   \'iii 

PRODI'CTIOX    OF    CASTS 

I'lcainifnt  and  tillint;  of  impression  in  the  production  of  casis  aiul  models — 
Staining  fluids — Separating  mediums — Classification  of  separating  me- 
diums— Requirements — Alcoholic  solution — Varnishes — Ethereal  solu- 
tions— Collodion — Soap — Aciueous  solutions — Oils — Forms  for  casts  and 
models — For  celluloid  cases — For  cast  metal  bases — Models  for  the 
production  of  dies — Models  with  cores — Materials  used  for  casts — Mag- 
nesium oxychloride — Spence's  plaster  compound — Coarse  building  plas- 
ter— French's  regular  plaster — French's  impression  plaster — Commercial 
plaster — Deleterious  effect  of  accelerators  on  casts — Maniinilation  of 
various  kinds  of  materials  in  cast  production — Filling  impressions — Re- 
moval of  impressions  from  hardened  casts — Full  and  partial  cases — 
Artificial  stone — Description  of — Advantages  and  Disadvantages — Dis- 
covery of Pages  90  to  117 

ciiArrh:!';   ix 

BASES    FOR    ARTIFICIAL    DENTURES 

Re(|uisite  properties — liases  of  gold — Platinum — Aluminum — Tin  Alloy — 
Vulcanite — Celluloid — Thermal  conductivity — Cause  of  oral  inflam- 
matory conditions  under  vulcanite  bases — Deleterious  effect  of  color- 
ing matter  in  vegetable  bases — Mechanical  irritation — Unhygienic 
conditions Pages  IIS   to  12.', 

CHATTER    X 

SWAGED  JIETAL   BASE   DENTURES 

Comparative  results  in  adaptation  of  swaged  and  vulcanite  bases — 
Sequent  steps  in  swaged  base  denture  construction — Sequent  steps  in 
vulcanite  denture  construction — Appliances  and  accessories  used  in 
die  and  counterdie  construction — Molding  flasks — Molding  sand — Sieve 
— Talcum  powder — Straight  edge — Heating  appliances — Melting  ladle — 
Die  metal — Zinc — Shrinkage  of  metals  in  passing  from  liquid  to  solid 
state — Treatmetit  of  plaster  models  to  arrest  expansion — Babbitt  metal 
— Melotte's    metal    and    other    fusible    alloys — Composition    of    fusible 

alloys — Counterdie   metal — Whiting  and  alcohol  solution — Brushes 

Pages   126  to  1 oS 

CHAPTER    XI 

TE'CHNIC  OF  DIE  AND  COUNTERDIE  CONSTRUCTION 

Forming  the  sand  matrix — Various  methods  of  removitig  the  model  from  the 
sand — Necessity  for  the  use  of  cores — Construction  of  sand  matrix  in 
the  Hawe's  flask — Forming  the  die — Melting  the  die  metal — Casting  the 
die — Inspection  and  correction  of  the  die — Construction  of  the  counter- 


TABl.E    OF    CONTENTS  ix 

(iic — .Melting  the  counterdie  metal — Casting  the  counterdie — Construction 
lit  the  counterdie  by  dipping — Separation  of  the  die  and  counterdie — 
I'artial  counterdies,  construction  of — Matrix  counterdies — Parker  shot 
swaser — Counterdies  for  partial   cases F^ages  139  to  lO'i 

CllAl'll'k     XII 

CONSTIilCTION   OF  SWACFD   DENTURE   BASES  OF  COLD— (  Upiier 
Cases)         -^,^^ 

Seciiiiiin  pattern  for  the  gold  plate — Carat  and  gauges  of  .yold  used  for  den- 
lure  liases — Annealing  the  plate — Oiling  the  die  and  counterdie — Cleans- 
ing the  plate — Pickling — Conforming  the  plate  to  die — I'pper  cases — 
Various  steps  of — Use  of  partial  counterdies — Swaging  in  the  counter- 
die — Final  trimming  and  finish — Securing  anchorage  for  the  teeth  to 
'  baseplate — Various  means  employed — Forming  peripheral  shoulder  for 
finish  of  the  vulcanite — Locating  position  of  wire  line  on  baseplate — 
Attaching  wire  anchorage  loops — Swaging  full  lower  denture  bases — 
Various  steps  described — ^Construction  of  jiartial  baseplates  of  gold — 
Various  ways  of  reinforcing  the  baseplate — How  to  estimate  the  proper 
ihickness  of  a  double  baseplate — Soldering  doubled  bases — Application 
of  frictional  appliances  in  partial  cases — .Method  of  securing  exact  rela- 
tionshi]! — Attaching  teeth  to  baseplate  by  soldering.  ...  Pages  ICC  to  IS'.t 

ch.\pt]':r  XI]  1 

ALUMINUM  BASE  DENTURES 

Cast  bases  of  aluminum — Cause  of  warpage  in  cast  bases — Imperfect  den- 
sity of  cast  bases — Action  of  oral  fluids  on  aluminum — Granular  struc- 
ture of  aluminum — Casting  by  the  indirect  method — Technic  of  form- 
ing the  wax  model — Investment  of  the  wax  mode! — Preparing  the  case 
lor  casting — Casting  the  fused  metal — Finisliing  and  swaging — Attach- 
ing teeth  to  base  with  vulcanite — Direct  method  of  producing  a  cast 
base  aluminum  denture — X^se  of  centrifugal  casting  machine — Technic — 
-Vli.xing  and  applying  the  investment  to  the  wax  model  base  and  cast — 
Investing  the  case  in  flask — Drying  out  the  case— iCasting — Important 
projierties  of  aluminum  in  reference  to  casting — Swaged  bases  of  alum- 
inum— Comparative  durability  of  cast  and  sw'aged  bases  of  aluminum — 
Summary  of  causes  of  deterioration  of  swaged  bases — Technic  of  swag- 
ing— Developing  the  vulcanite  shoulders  and  anchorages — Forming  the 
shoulder — Spurring    the    base — Anchorage    by    perforation — Use    of    a 

doubler — Some  facts  on  the  history  of  aluminum   castings 

'. Pages  189  to  22li 

CILVPTF-R     Xl\ 

WEIGHTED  LOWER  DENTURES 

Dentures  of  weighted  vulcanite — Vulcanite  dentures  weighted  by  means  of 
a  metallic  core — ^Cast  metal  bases — Technic  of  a  weighted  cast  base — 
Flasking  the  w-ax  model  base  plate — Casting  the  base — Modification  of 
the  foregoing  method — History  of  the  cheoplastic  process. 

VULCANITE    BASEPLATES    (Double    Vulcanization! 

Technic  of  construction — Construction  of  temiiorary  baseplates — Meal  base- 
plate— "Special" — Temporary   Ijasejilates  of  metal Pages  -21    to  2^.2 

■      ClLM'Tl-.K    X\- 

RETENTION   OF  PARTIAL  DENTURES 

Atmospheric  pressure  and  adhesion — Frictional  retention  of  partial  den 
tures — Specialized  frictional  appliances — ^Clasps — Objection  to  the  use 
of  clasps — Advantages  derived  from  the  use  of  clasps — Reciuisites  of  a 
clasp — Adaptation — Resiliency — Inherent  strength — Gauges  of  metal 
lommonly    employed — Types    of    clasps    most    commonly    used — Partial 


X  TAIil.K    OF    CONTENTS 

Hal  band  clasp — Half  round  wire  t-lasp — Wire  or  loop  clasp — The  stop 
clasp — The  double  stay — The  stay  clasp — Indications  and  contraindica- 
tions governing  the  application  of  clasps — Denture  balance — Fulcrum 
line — Object  in  using  specialized  frictional  appliances.  .  Pages  233  to  24!t 

CHAPTER   XVI 

TECHKIC    OF    CLASP    CONSTRUCTION 

Axial  contour  forms  of  bicuspids  and  molars — Outline  of  steps  of  clasp  con- 
struction— Securing  impression  of  tooth  to  be  clasped — Rebuilding  im- 
pression for  reception  of  molten  die  metal — Casting  the  die — Cutting 
the  clasp  metal  to  suitable  dimensions — Securing  peripheral  adaptation 
of  strip  to  die  with  pliers — Securing  surface  adaptation  with  hammer — 
Final  adaptation  of  clasp  to  die — Soldering  stops  and  anchorage  lugs 
to  clasp — Finishing  the  clasp — Various  methods  of  clasp  construction — 
Combination  of  pure  gold  with  clasp  metal — Cast  clasps — The  wire  loop 
clasp — Continuous  and  open  loop  clasp — Securing  relation  between 
clasps,   the  teeth   they   embrace   and   the   baseplate — Taking   impression 

of  clasps,  teeth  and  baseplate — Soldering  clasps  to  baseplate 

Pages    25(1    to    2fiS 

CHAPTER    X\'H 

THE   MASTICATORY   .MECHANISM 

The  .Masticatory  apparatus — The  maxilla — The  mandible — Functions — Gen- 
eral description — Movements — Tempero-mandibular  articulation — The 
condyles — The  condyle  path — Variations  in  pitch  of  paths — Muscles  of 
mastication — The  masseter — Temporal — External  pterygoid — Internal 
pterygoid — Jluscles  which  depress  the  mandible — Muscles  which  con- 
trol the  position  of  food — Summary  of  muscular  action  on  the  mandible 
— Mandibular  ligaments — Capular — External  lateral — Internal  lateral — 
Spheno-mandibular — Stylo-Mandibular — The  teeth — Occlusal  surface 
markings — The  central  sulci  of  bicuspid  and  molar  teeth — The  bucco- 
lingual  grooves — The  masticatory  or  rectangular  groove — Arrangement 
of  the  teeth  in  the  dental  arches — Occlusal  view — Anterior  curvature — 
Incisal  view — Alignment  of  the  posterior  teeth — Buccal  view  of  upper 
arch — The  plane  of  occlusion — Curvature  of  occlusal  plane — Relation- 
ship of  planes  of  occlusion  to  condyle  paths — Governing  factors  in  man- 
dibular movement — The  incisor  path — Condyle  movement  in  protrusion 
— Function  of  incisor  teeth  in  protrusive  effort — Lateral  movements  of 

the  mandible — ^Centers  of  mandibular  rotation Relation  of  lower  to 

upper  teeth  on  pivotal  side — Side  movements  not  controlled  by  rotat- 
ing centers — Relation  of  lower  to  upper  teeth  on  protruded  or  balancing 
side — The  compensating  curve — The  curve  of  Spee — Modification  of  the 
compensating   curve Pages  2011  to  30?, 

CHAPTER  XVHT 

CONSTRUCTIO.X  OF  FULL  DENTURES 

Anatomic  method — Masticatory  movements  of  the  carnivora.  herbivora  and 
omnivora — Main  features  of  anatomic  methods — Present  methods  of 
technic  in  anatomic  denture  construction — Snow  appliances  and  meth- 
ods— Face  bow — Bite  gauges — General  constructive  steps — Occlusion  and 
contour  models — Requirements  of  a  baseplate — Requirements  of  the 
occlusion  rim — Construction  of  occlusion  models — Approximate  depth 
of  occlusion  rims — Bucco-lingual  position  of  upper  and  lower  wax  rims  in 
relation  to  border  crests — Trial  of  occlusion  models  in  the  mouth — 
Testing  adaptation  of  each  baseplate  to  its  ridge — Establishing  height 
of  lower  occlusion  rim — Restoring  disturbed  facial  contour — Marking 
high  and  low  lip  lines — Jlarking  median  line — Locating  outer  ends  of 
condyles — ^Application  of  bite  fork  to  upper  occlusion  model — Meaning 
of  the  term,  "Taking  the  bite" — Difficulty  encountered  in  taking  the 
bite — Various  methods  of  securin.g  the  bite — A  practical  method  tor 
securing  a  correct  bite — Inserting  bite  fork  in  upper  occlusion  model — 


TABI-E    OF    CONTENTS  xi 

Adjusting  face  bow  to  occlusion  models — Adjusting  face  bow  with 
occlusion  models  attached  to  the  occluding  frame — Attaching  casts  to 
the  occluding  frame — Registering  condyle  paths  of  patient — Christen- 
sen's  method — Technic  of  condyle  registration — Limit  of  protrusive 
mandibular  movement — Adjusting  condyle  paths  of  occluding  frame — 
Developing  compensating  curves — Fundamental  principles — Practical 
steps — The  Ulsaver  method — Omitting  development  of  compensating 
curve  Pages  304  to  354 

CHAPTER    XIX 

ESTHETICS  OF  TOOTH  SELECTION 

General  considerations — Classification  of  temperaments — Harmony  defined — 
Esthetics  defined — Intuitive  and  acquired  esthetics — Facial  outlines — 
Natural  tooth  forms — Reproduction  of  natural  tooth  forms  in  porcelain 
— Observed  outlines  of  natural  teeth  in  the  mouth — The  color  problem 
in  tooth  selection — A  synopsis  of  color  principles — Color — Primary  col- 
ors (pigments) — Secondary  colors — Tertiary  colors — Intermediate  col- 
ors— Complementary  colors — Color  functions  of  the  visual  organs — Colors 
found  in  natural  teeth — Suggestions Pages  350  to  381 

CHAPTER   XX 

ARRANGING  AND  OCCLUDING  THE  TEETH 

Tipper  arch — Arranging  the  six  anterior  teeth — Arranging  the  posterior  teeth 
— Arranging  the  lower  in  occlusion  with  the  upper  teeth — Testing  the 
occlusal  surfaces  for  working  efficiency — Securing  contact  of  the  lingual 
marginal  ridges — Arranging  the  six  lower  anterior  teeth — Developing 
balancing  contact — Final  test  with  carbon  i)aper — Developing  the  con- 
tour of  dentures  in  wax — Artistic  principles  involved — Developing  the 
gum  festoons — Trimming  peripheral  outline  of  the  dentures — Finishing 
touches  in  carving  gums — Finishing  lingual  surfaces  of  wax  model  den- 
tures— Development  of  the  rugae — Trial  of  the  dentures  in  the  mouth 
— Final  finish  of  the  model  dentures — Removing  the  casts  from  occlud- 
ing frame  Pages  382  to  40(; 

CHAPTER    XXI 

REPRODUCTION  OF  THE  WAX  MODEL  DENTURES  IN  PERMANENT 
MATERIALS 

Sectional  molds — Flasks — Fitting  cast  and  wax  model  denture  in  Hask — Flasl\- 
ing  the  wax  model  denture — Separating  the  flask — Preparatory  steps — 
Opening  the  flask — Clearing  the  matrix  of  wax  and  baseplate  material 
— Treatment  of  first  section  of  mold  containing  cast — Providing  for 
escape  of  surplus  rubber — Steps  preparatory  to  packing  the  matrix — 
Heating  the  rubber  before  introducing  it  in  the  matrix — Heating  the 
matrix  previous  to  packing  the  rubber — Preparing  the  rubber  for  pack- 
ing— Basic  rubber — Packing  the  matrix — Packing  the  gum  facing — Pack- 
ing the  basic  rubber — Gauging  the  amount  of  rubber  required — Flask 
closing — Estimating  the  force  exerted  by  the  screw — Test  closing  of  the 
flask — Treatment  of  cast  surfaces  for  vulcanization — Screw  presses.... 
Pages  406  to  435 

CHAPTER    XXII 

VULCANITE 

Rubber — Caoutchouc — Formulas  for  dental  rubbers — Vulcanizable  rubbers 
employed  for  denture  bases — Pink  rubber  employed  for  gum  facing — 
Pink  granular  gum  facing — Chemical  constituents  of  rubber — ^Chemis- 
try of  vulcanization — Porosity  of  vulcanite  and  how  to  obviate  it — Clos- 
ing flasks  with  spring  pressure — Dimensional  changes  occurring  in  rub- 
ber during  vulcanization — Expansion — Contraction — Vulcanizers — Safety 
devices — The  thermometer — Steam  gauge — Table  of  steam  pressure — 
Gas  regulators — Time  regulators — The  safety  valve — Vulcanization  of 
cases  in  whicli  automatic  flask  closing  devices  are  used — Vulcanization 


xii  TAItl.l':    OK    CONTEXTS 

of  cases  in  which  flasks  are  closer!  and  bolted  before  viilciirii/.alion — 
Summary  of  facts  of  importance  in  regard  to  time  of  vulcanization — 
Removal  of  the  flask  from  vulcanizer — Removal  of  denture  from  flask — 
Finishing  the  denture — Reiiroduction  of  the  rugae — Use  of  calipers — 
Final  polishing  of  the  denture — p-inishing  touches — Final  fitting  in  the 
mouth — Finishing  the  palatine  surfaces  of  a  denture — Construction  of 
;i   full  ui)]ier  or  lower  denture — Upper  cases — I>ower  cases. 

THE   GYSl    SYSTEM    OF    ANATOMIC    APPI^IANCES 

Applicaiiou  in  denture  construction — Registering  the  forward  condyle  move- 
ment— -Mounting  casts  on  the  articulator — Registering  the  incisor  jiath 
— Registering  the  lateral  condyle  paths — Angular  inclination  of  the 
lateral  condyle  paths — Subsenuenl  steps  in  denture  construction.... 
Ha.ges  4:jri   to   il^> 

CILM'TI'.R    XXIll 

CONSTRICTION   OF  PARTIAL   OENTl'RKS 

Various  types — Planning  a  partial  denture — Baseplates  for  dcuture.s — Par 
tial  dentures  of  vulcanite — Technic  of  construction  of  partial  upper  den- 
tures of  vulcanite  without  clasps — Taking  the  protrusive  bite — Select 
ing  and  grinding  the  teeth — Waxing  the  case — Flasking — Partial  upper 
dentures  of  vulcanite  with  clasps — Partial  lower  denture  of  vuleanite — 
Mounting  casts  on  occluding  frame — Registering  condyle  paths — Arrang- 
ing teeth — Flasking  case — Partial  lower  gold  base  dentures — Forming 
the  finishing  shoulder  for  vulcanite — Adjusting  the  shoulder  wire — Ex- 
tent to  which  the  wire  is  applied  peripherally — Lingual  bar  dentures — 
Relation  of  lingual  bar  to  oral  tissues — Forms  of  lingual  bars — Technical 
steps  in  lingual  bar  cases — Variation  in  form  of  connection  between 
lingual  bar  and  clasps — Soldering  clasps  and  bar  in  correct  relation  to 
each  other — Taking  the  wax  bite — Taking  the  impression — Artificial 
stone  for  casts  in  partial  case.s — The  lingual  bar  combined  with  gold 
saddles — Settling  of  dentures  from  use — Compensating  for  settling  of 
gold  base  saddles — The  Roach  continuous  loop  clasp — Technic  of  con- 
struction— The  open  loop  clasp — The  Balkwill  clasp — The  Roach  ball  and 
tube  attachment — Application  of  the  Roach  attachment — The  .Morgan 
attachment — Technic  of  application — The  Condit  attachment — The  Gil 
more  attachment — T.echnic  of  application — Adjustment  of  clasps  to  bars 
— The  palatal  arch  bar — The  Kelly  attachment — Technic  of  applica- 
tion— The     Griswold    attachment. 

for:ms  of  porcelain  teeth 

'^lain  teeth — Means  of  anchorage — Plain  teeth  for  vulcanite  work — Advan 
tages — Objections — Diatoric  teeth — Countersunk  pin  teeth — Ash's  tube 
teeth — Plain  plate  teeth — Various  forms  of  plain  teeth — Ash's  flat  back 
repair  facing — Ash's  helix  tooth — Saddle  back  teeth — Continuous  gum 
teeth — Gum  teeth  for  vulcanite  work — Gum  teeth  for  metal  work — 
Proportionate  parts  of  teeth^Ridge  lap — Shut — Bite — The  tooth  shade 
guide — Application   of  the   tooth   shade  guide  in  practice. 

A    NEW    GUM    FACING 

Protesyn — Natural  dentures  reproduced  in  porcelain  teeth  and   wax 

Pages   170  to  .")50 

CHAPTER    XXI\' 

CELIATLOID   DENTURES 

Discovery  of  celluloid — Composition — Manufacture — Advantages — Compara- 
tive strength  of  celluloid  and  vulcanite — Disadvantages — General  meth- 
ods of  manipulation — Construction  of  the  wax  model  denture — Flasking 
— Cutting  the  waste  gates — Clearing  the  matrix — Selection  of  blank — 
Pressing  the  case — Removal  from  flask — Finishing — General  remarks — 
Casts  for  celluloid  cases > Pages  551  to  560 


TAHLI-:    OF    CONTKNTS  xiii 

CHAl'TER    XX \' 

REPAIRING    VULCANITE   DENTURES 

Kractuie  of  vulcanite  base — Reassembling  a  fractured  baseplate — Securing 
cast — Melbod  of  joining  the  fractured  pieces — Forming  a  bevel  joint — 
Technical  steps  in  repairing  a  median  line  fracture — ^Method  of  flask- 
ing  case — Replacing  a  displaced  tooth  by  vulcanization — Replacing  by 
casting — Rei)lacement  by  fusible  metal  in  dovetail — Repairing  with 
amalgam — Repair  involving  substitution  of  new  tooth — Preliminary  dove- 
tailing of  the  denture  base — Substituting  artificial  for  lost  natural  teeth 
in  partial  cases — Repairing  gum  section  cases — Substitution  of  a  base- 
plate— Construction  of  the  matrix — Removal  of  teeth  from  old  baseplate 
— Forming  the  wax  baseplate — Modified  methods  of  reconstruction — 
.Mounting  casts  and  old  denture  on  occluding  frame — Forming  the  matrix 
— Forming  the  wax  baseplate — Correcting  imperfect  adaptation  by  sub- 
stitution of  new  base — Correcting  adaptation  by  addition  of  new  rub- 
ber to  old  base — Correcting  adaptation  with  rubber  paste — ^Correcting 
adaptation  with  Furlong's  plastic  rubber — To  correct  occlusion  when 
adaptation   Is   satisfactory Pages   5C1    to   587 

CHAPTER  XX\1 

CONTINUOUS   GUM   DENTURES 

Advantages — Disadvantages — Technic — Forming  the  baseplate — Fitting  base 
plate  to  mouth — Reinforcing  the  baseplate — Forming  the  finishing 
shoulder  for  porcelain — Reswaging  and  cleansing  the  baseplate — De- 
veloping the  occlusion  and  contour  model — Continuous  gum  teeth — 
Selection  and  arrangement  of  the  teeth — Trial  of  the  wax  model  den- 
ture in  the  mouth — Developing  the  contour  matrix — Investment  of  the 
wax  model  denture — Fitting  metal  support  between  teeth  and  baseplate 
— Supporting  the  teeth  with  wire — Continuous  gum  body  and  enamel — 
Preparation  of  the  body — Application  of  body  to  teeth  and  baseplate — 
Support  for  continuous  gum  cases  while  fusing — Poreclain  furnaces — 
First  baking  of  the  case — Second  baking — Preparation  of  case  for  third 
baking — Application  of  the  gun  enamel — Fusing  the  enamel — Special 
uses  of  porcelain — Interstitial  blocks  of  iiorcelain — Gum  sections — Con- 
struction of  gum  section  blocks  for  special  cases Pages  58S  to  (j24 

CHAPTER    XXVH 

CROWN   WORK 

Preliminary  considerations — Structures  of  the  teeth  and  investing  tissues 
— Physiological  relations — Oral  pathological  conditions — Therapeutic 
methods  of  treatment  of  diseased  conditions — Local  ansesthetics — Treat- 
ment after  setting  a  crown — Anatomic  and  esthetic  forms  of  teeth — 
Flare  of  the  axial  surfaces  of  bicuspids  and  molars — Cutting  molar  and 
bicuspid  bands  by  the  conic  system — Stress — Hygienic  requirements  of 
crowns. 

PORCELAIN-FACED    CROWNS    FOR    THE    ANTERIOR    TEEFH 

Technic  of  construction  of  a  porcelain-faced  crown — Upper  central  incisor 
— Devitalization,  treatment  and  filling  of  root  canal — Removal  of  re- 
maining portion  of  natural  crown — Preparation  of  root — Removal  of  en- 
amel— Smoothing  root  periphery  with  files — General  form  of  |)repared 
root — Testing — Flare  of  root  surfaces — Securing  measurement  of  root 
periphery — Measurijig  and  cutting  band  for  root  cap — Forming  and  solder- 
ing band — Sweating  band — Scribing  band  to  gingival  outline — Fitting 
scribed  band  to  root — Trimming  band  to  proper  width — Construction  of 
root  cap — Soldering  band  to  disc — Removing  peripheral  excess  of  disc — 
Construction  of  cap  by  indirect  method — Taking  impression  of  root — 
Constructing  the  root  die — Imbedding  die  in  swaging  ring — Swaging  root 
cap — Fitting  cap  to  root — Enlarging  root  canal  for  reception  of  dowel 
— Countersinking  canal  opening — Indenting  cap  in  countersunk  area — 
Perforating  root  cap  for  reception  of  dowel — Forcing  dowel  through  cap 


xiv  ■lAltlJO    OF    CCX'IION'IS 

into  root  canal — Maintaining  correct  relation  helwceii  diiwcl  ;inil  ca|i 
while  removing  from  root — Investing  the  cap  and  dowel  lor  soldering 
— Taking  bite  and  impression — Use  o£  face  bow  in  crown  work — Details 
of  taking  bite — Securing  an  impression  in  plaster — Production  of  cast 
from  impression — Attaching  casts  to  occluding  frame — Selection  of  fac- 
ing— Grinding  facing  to  root  cap — Beveling  incisal  edge  of  facing — 
Change  of  color  in  porcelain  due  to  metal  backing — Backing  facing  with 
gold — Perforating  backing  for  pins — The  Mason  spacing  calipers — The 
Young  plate  perforator — Adapting  the  backing  to  facing  by  burnishing 
— Swaging  the  backing — Fixing  backing  to  facing — Fitting  backed  facing 
to  root  cap — Investment  of  the  assembled  crown  for  soldering — 
Trimming  investment  preparatory  to  soldering — Removal  of  wax — Ap- 
plying the  flux — Developing  the  lingual  contour  of  crown  with  solder — 
Finishing  the  crown — Setting  the  crown — Removal  of  excess  cement — 
Setting  a  crown  temporarily — Removal  of  a  ciown  or  bridge  set  with 
gutta-percha. 

DIFFERENT  METHODS  OF  APPLYING  PORCELAIN  FACINGS  AND   RE 

PLACEABLE  TEETH  IN  SINGLE  CROWNS  AND  DUMMIES 

FOR  BRIDGES 

Interchangeable  tooth  facings — Steele's  facings — Application  to  anterior 
teeth — Application  to  posterior  crowns — Technic  for  cast  dummies — 
Construction  of  dummies  with  swaged  cusps — Reflecting  the  backing 
over  cervical  margin  of  porcelain — Utilizing  long  pin  plate  teeth  for  re- 
movable facings — The  Evslin  interchangeable  tooth — Technic  for  anterior 
crowns — Technic  for  posterior  crowns — Technic  for  anterior  dummies  in 
bridgework — Interchangeable  teeth — The  Goslee  tooth — Technic  of  ap- 
plication in  crown  and  bridge  work — The  Gardner  replaceable  tooth — 
Application  in  crown  and  bridge  work — The  Merker  replaceable  tooth — 
Diatoric  teeth  used  as  replaceable  teeth. 

FULL-CONTOURED  PORCELAIN  CROWNS 

Fixed  dowel  crowns — Technic  of  plain  Logan  crownwork — Adapting  crown 
to  root — Securing  peripheral  adaptation  of  crown  base  to  root — Setting 
the  crown — The  banded  Logan  crown — Technic  of  application — As- 
sembling the  several  parts — Investing — Soldering — Finishing — The  Davis 
crown — Application  of  plain  Davis  crown — Reducing  peripheral  shoulder 
— General  modification  of  crown  by  grinding — Setting  I  he  crown — The 
Davis   crown   in   bridgework — The   cast   base   Davis   crown — Technic   of 

a  cast  base  crown — The  banded  Davis  crown — Technic 

Pages  fi24  to  T-'it 

CHAPTER    XXVIII 

THE  GOLD  SHELL  CROWN 

Advantages — Disadvantages — Where  indicated — .Modifications — Technic  of 
construction — Preliminary  preparation  of  tooth  or  root — Restoring  badl.\' 
decayed  natural  teeth  for  ancliorage  purposes — Amalgam  restoration — 
Cast  restoration — Cases  of  excessive  restoration — Wedging — Prepara- 
tion of  tooth  for  band — Reduction  of  occlusal  surface — Reduction  of 
axial  wall — ^General  form  of  prepared  tooth  or  root — Testing  correctnes.'-; 
of  root  preparation — Securing  peripheral  measurement — Determining 
width  of  band — Cutting  band — Cutting  a  cone  band — Soldering — Fitting 
band  to  root — Contouring — Forcing  band  to  position  on  root — Taking 
the  bite — Mounting  the  bite  on  occluding  frame — Developing  cusps  of 
crown  in  plaster — Typical  forms  of  natural  teeth — Upper  right  first 
molar — Lower  right  first  molar — Lower  right  second  molar — Upper  left 
first  bicuspid — Upper  right  second  bicuspid — Lower  left  first 
bicuspid — Lower  left  second  bicuspid — Reproducing  the  cusp  sur- 
faces in  gold — Constructing  the  counterdie — Direct  method — Indirect 
method — Developing  a  counterdie  with  Metalline  compound — Swag- 
ing the  cusps  in  an  open  counterdie — Removal  of  peripheral  sur- 
plus  of  gold — Adapting  occlusal  cap  to  liand — Developing  the  marginal 
ridges    of    crown    on    axial    band — Developing    the    cusp    surfaces    in    a 


TABLJi;    OF    CONTENTS  xv 

swager — Assembling  and  soldering  the  band  and  occlusal  cap — Finisliing 
the  crown — Setting — Casting  the  cusps — Cast  crowns — The  shoulder 
crown — Preparation  of  the  natural  tooth — Construction  of  the  crown — 
Seamless  crowns — The  matrix  method — Swagins  the  crown — The  die 
method — Swaging  the  crown — Finishing — Reproducing  natural  tooth 
tdi'nis  in  inlay  wax   Pages  735  to  782 

CHAPTER   XXIX 

BRIDGBWORK 

Engineering  principles — Application  of  stress  to  substructure  of  a  bridge — 
The  arch  bridge — Girder  or  truss  liridges — Ponton  bridges — Cantilever 
bridges. 

DENTAL  BRIDGEWORK 

(General  classification  of  bridges — Distinction  between  fixed  and  removable 
bridges — Fixed  bridges — Fixed  bridges  so  constructed  as  to  be  remov- 
able— Fixed  saddle  bridges — Individual  saddles — Sanitary  bridges — Ex- 
tension bridges — Important  factors  to  be  considered  in  planning  fixed 
bridges — Abutments  and  piers — Preparation  of  abutment  and  pier  roots 
— Inlay   abutments — Displacement  of  inlay  abutments. 

CLASSIFICATION  OF  FIXED  BRIDGEWORK 
By  Dr.  A.  .1.  Bush 
Multiplicity  of  methods — Prime  object  of  crown  and  bridge  application — 
The  basis  of  success — Advantages  of  classifying  fixed  bridges — Simple 
— Compound — Complex  bridges — Proposed  law — Simple  bridge  defined 
— Compound  bridge  defined — Complex  bridge  defined — Argument  in  sup- 
port of  the  classification  and  law  proposed — Possible  masticatory  stress 
— Various  charts  of  compound  and  complex  bridges  formed  by  joining 
simple  anterior  bridges,  uni-  and  bilaterally  with  simple  posterior 
bridges. 

APPLICATION   OF   FIXED   BRIDGEWORK 

Technic — Requirements  of  dummies — Construction — Variation  in  the  forms 
of  dummies — Assembling  the  bridge — Investment — Soldering — Finishing 
—Setting. 

THE   CARMICHAEL  ATTACHMENT 

Construction — Finishing — :Modified  technic — Application  to  cuspid  and  bi- 
cuspid teeth. 

REMOVABLE   ATTACH.MENTS    FOR    FIXED    BRIDGES 

The  Corcoran  attachment — Application — Construction — The  Heddy  attach- 
ment. 

REMOVABLE   BRIDGES 

Attachments — Telescoping  crown — The  split  dowel  crown — Assembling  the 
parts — Constructing  the  crown  base — Constructing  the  saddle — Attach- 
ing the  teeth — Finishing  the  bridge — Setting  the  root  caps — General  re- 
marks— The  Goslee  inlay  clasp  attachment — The  split  dowel — Lingual 
half  crown — Construction — Finishing  the  attachment — Modification  of  the 
telescoping  molar  crown. 

REPAIRING   CROWNS  AND   BRIDGES 

Replacing  porcelain  facings — The  Ash  fiat  back  repair  facing — The  Dime- 
low  facing — The  Steele  repair  outfit — The  Br\  ant  repair  outfit — Long 
pin  facings  used  in  Repairs — Starr's  method — Riveting  facing  to  back- 
ing— Removing  c  banded  dowel  crown — Replacing  facing  on  crown 
removed  as  described — Removing  dowels  from  root  canals — Little  Giant 
post  puller — The  S.  S.  White  crown  repair  outfit — Removal  of  a  dowel 
from  the  deeper  portion  of  a  root  canal — Removing  a  shell  crown  by 
slitting — Removing  a   shell  crown  by  leverage  force — Repairing  crowns, 

slit  in  the  manner  described — Repairing  a  fractured  bridge 

Pages  7S3  to   872 


xvi  'I'Alil.l':     t)l''    COXTICXTS 

CIIAI'TI'.W    X\.\ 

PORCELAIN    CROWN   AND    RRIDGE    WORK 

I'Dicrliiiii  frown  work — Indications  for  use — The  banded,  liaked  iiortrlaiii 
crown — Constructing  root  cap — Application  of  porcelain  Ijody — Modified 
forms  of  porcelain  crowns — I'orcelain  jacket  crown — Technic  of  con- 
strucljon — Taking  imjiression  of  tooth — Constructing  the  die — Forming 
the  platinum  cap — Constructing  the  casts — Application  of  porcelain — 
Baking  the  crown — The  "Land  Jacket  Crown" — Prei)aration  of  tooth 
— Construction  of  cap — Taking  bite  and  impression — Selection  and  grind- 
ing of  facing — Application  and  fusing  of  porcelain — Porcelain  bridge- 
work — Cleneral  considerations — Porcelain  bridge  construction — Prepara 
tion  of  roots  or  teeth — Construction  of  cap  and  shell  crowns  for  abut- 
ments— Construction  of  saddle — Locating  and  fitting  truss  bars — Solder- 
ing— Application  of  body — Fusing  the  porcelain — Finishing  and  setting 
the  bridge — X'arious  types  of  metal  structures Pages  STH   to  ttoii 

fllAl'Tl'.K    XXXl 

PORCELAIN   AND   .METALLIC   INLAYS 

Porcelain — Eaily  application  of  porcelain  in  denture  construction — Correc- 
tion of  warpage  in  the  all-porcelain  denture — Basic  ingredients  of  por 
celain — Kaolin — Preparation — Feldspar — Preparation  —  Silex — Prepara- 
tion— Properties — Proportions — Oxides  of  metal  used  in  coloring  porce 
lain — Gun  enamel — Crown  bridge  and  inlay  porcelains — High  and  low 
fusing   porcelain   bodies — Comparative  value. 

PORCELAIN    INLAY    WORK 

Advantages — Objections — Friability — Constructive  difficulties —  Inlay  reten- 
tion— ^Warpage  of  the  matrix — Annealing  the  foil — Warpage  due 
to  improper  support — Careless  handling — Locations  favorable  for 
Iiorcelain  inlays — General  rules  for  cavity  i)reparation — Details — Gingival 
third  cavities  in  the  anterior  teeth — Proximal  cavities  in  the  anterior 
teeth  not  involving  angle.s — Buccal  cavities — Proximal  cavities  in  an- 
terior teeth  involving  angles — Bicuspid  and  molar  cavities  involving 
an  axial  and  an  occlusal  surface — Restoration  of  incisal  edges  and 
angles — Production  of  the  matrix — Burnishin.g — Removal — Final  anneal 
ing — Selection — Application  and  fusing  of  the  porcelain — Selection  of 
shade — Mixing  the  porcelain — .Application  to  the  matrix — Furnaces  and 
appliances  used  in  fusing — First  baking — Second  baking — Deleterious 
effect  of  overfusing — The  shadow  |)robIem — Removing  the  matrix — 
Etching  the  cavity  surfaces  of  the  inlay — Setting. 

GOLD   INLAYS 

("!avity  preparation  for  gold  inlays — Outline  form — Resistance  form — Reten 
tion  form — Pin  anchorages — Convenience  form — Removal  of  any  remain- 
ing carious  dentine — Finish  of  enamel  walls — Toilet  of  cavity — Some 
special  methods   of  cavity   preparation. 

THE   MATRIX   METHOD   OF   INLAY   PRODUCTION 

Direct  method  of  producing  a  matrix — Variation  in  method — Indirect  method 
of  forming  the  matrix. 

CAST    GOLD    I.XLAYS 

General  remarks — Physical  properties  of  the  materials  employed  in  castinc 
— Expansive  and  contractile  forces — Principal  sources  of  error  in  inlay 
construction — Waxes — Paraffin — Effect  of  combining  wax  and  paraffin 
— Essential  properties  of  a  wax — Elastic  properties  of  wax — Investment 
materials — Expansion  of  investment  ring  and  investment  material — 
Essential  properties  of  an  investment  material — Dimensional  changes 
in  gold  due  to  temperature  changes — Comiiensating  for  errors  due  to 
contraction  of  gold — Result  of  contraction  of  gold  on  inlay  adaptation 
— Technic    of    cast    gold    inlays — Forming    the    wax    model — Investment 


TABLE    OF    rOXTEXTS  xvii 

ot  llip  wax  model — Drying  out  the  investment  and  eliminating  llie  wax 
— Variation  in  the  method  of  preparing  the  invested  ease  lor  casting — 
The  casting  of  gold — Rough  finishing  the  casting — Settling  the  inlay 
Finishing   Pages  9(il   to  flo!! 

CHAPTER    XXXIl 

AX   OUTLINE   OF   .METALI-fRGY 

Facts,  hypotheses,  theories  and  speculations — Discovery  of  elements  liy 
means  of  the  spectroscope — The  mutability  of  matter — Brief  outline 
of  recent  discoveries — Elemental  gases — Discovery  of  the  X-ray — Dis 
covery  of  radio-active  substances — Decomposition  of  radium  compounds 
Character  of  the  emanations  from  radio-active  substances — The  de- 
gradation of  copper — Debasement  of  various  substances  into  hydrogen 
— Summary  of  statements  presented — The  elements  arranged  in  the 
order  of  their  discovery — Arranged  in  the  order  of  their  atomic  weighti. 
— The  Kinetic  constitution  of  matter — The  viliration  of  matter — The  un 
equal  distribution  of  elements — Elements  and  their  atomic  relation  tn 
each  other — Prout's  hypothesis — The  triads  of  Dobereiner — The  octave. 
of  Xewianrt.s — The  periodic  system  of  Mendeleeff — New  elements— 
The  elements  considered  in  groups — The  elements  considered  in  series. 
Metals — Metalloids — Forms  of  matter — Occurrence  of  metals — Min- 
erals— Xative  metals — Ores — Xoble  metals — Base  metals — Physical  prop 
erties  of  metals — Atomic  weight — Specific  gravity — Melting  points 
Malleability — Ductility — Tenacity — Annealing — Tensile  strength  —  Elas- 
ticity— Flow — Conductivity — Heat  and  electricity — Exceptions — Specific 
heat — Expansion — Co-efficient  of  expansion  of  substances — Color — Weld- 
ing— Welding  copper  to  iron — Aluminothermy — Temperatures  common 
and  extraordinary — Soldering — Conditions  essential  to  successful  solder- 
ing— The  structure  of  flame — The  Bunsen  flame — The  blowpipe  flame — 
Micro-structure  of  metals — Alloys — Matthiessen's  theories  as  to  the 
nature  of  alloys — Affinity  of  metals  for  each  other — Liquation — Object 
in  alloying  metals — Eutectic  alloys^Amalgams — Specific  gravity  of 
alloys — Table  of  some  of  the   physical   pro])prties  of  fifteen   metals. 

GOLD 

Occurrence  and  distribution — Placer  deposits — Placer  mining — Vein  gold — 
Extraction  of  gold  from  ores — Chlorination  process — Cyanide  process — 
Physical  properties — Preparation  of  pure  gold — Treatment  of  scrap  plate 
— Alloying  gold — Reduction  of  gold — Boser's  rule — Gold  solders — Table 
of    mixed    caratation — Clasp    gold — Platinum    solder. 

SOME    RECENT    WORK    CONCERXIXG    GOLD    ALLOYS 
By  Dr.  L.  J.  Weinstein 
Author's    preface — Introduction — Binary    alloy.s — Necessity    of    a    knowledge 
of  binary  alloys. 

Section   I — Gold  and  Silver 
Effect  of  silver  upon  gold — Gold  and  copper — Gold  and  platinum — Gold  ami 
palladium — Gold   and   the    metals    in   .group    11 — Iridium — Osmium — Rho- 
dium— Gold  and  metals  in  group  III — Gold  and  metals  in  group  IV. 

Section  II — A  New  Series  of  Alloys 
Gold  for  crown,  bridge  and  plate  work — Gold  plate  No.  2 — Alloys  for  pros- 
thetic  casting — Gold   for   inlay   casting. 

Section  III— Clasp  Metals 
Composition  ot  clasp  metals — Results  of  rolling  and  annealing  on  elasticity 
of  clasp  gold  of  I'arious  formulte. 

Section  IV — Gold   Solders 
Alloys  of  gold  with  metals  in  group  III — Formulae  for  gold  solders. 

Section  V — Compounding  of  Gold  Alloys 
Difficulty  of  alloying  gold  with  platinum  in  small  quantity — Necessity  for  pre- 
venting  oxidation   in   gold   and   copper   alloys. 


xviii  TABLE    OP"    CONTENTS 

Section  VI — Refractory  Materials 
Investment  compounds  for  soldering — Plaster  of  Paris — Powdered  silex — 
Formula  for  investment  fompound  (soldering) — Investment  compounds 
for  casting — Hot  or  cold  mold,  using  illuminating  gas  and  compressed 
air  blowpipe — Hot  or  cold  mold,  using  illuminating  gas  and  nitrous 
oxide  or  oxygen  blowpipe — Compounding  of  investment  materials — Heat- 
ing of  investments. 

Section  VII — Fluxes  for  Soldering  and  Casting 
Formula  for  soldering  flux — Reducing  flux — Formula  for  reducing  flux — 
Oxidizing  flux — Formula — Formula  for  soldering  flux  (substitute)  — 
Table  No.  4 — Melting  point  of  tbe  new  series  of  alloys  and  standard  den- 
tal golds — Some  of  tbe  applications  of  the  new  series  of  alloys  in  the 
Peeso  system  of  removable  bridgework — ^Construction  of  floors,  bands 
and  inner  caps — Outer  halt  bands  and  telescope  caps — Inlay  abutments 
— Construction  of  saddles — Construction  of  dummies. 

IRON 
Occurrence  in  nature — Reduction  of  iron  ores — Production  of  wrought  iron 
— Production  of  steel — The  Bessemer  process — The  cementation  process 
— Hardening  and  tempering  of  steel. 

PLATINUM 
Discovery — Distribution — Occurrence — Physical    i)ropertie.s — Fusing     point — 
Uses — Alloys — Dental   alloy — Platinum   solder  and   clasp  metal. 

IRIDIUM 
Physical    properties    and    uses — Silver — Ores — Reduction — Amalgamation — 
Wet  method — Lead  method — Uses  in  dentistry — Alloys  of  silver — Uses 
in  photography — ^Chemistry  of  photography. 

COPPER 
Ores — Reduction-uses — Alloys — Brass — Bronze. 

ALUMINUM 
Occurrence — Reduction — Physical  properties — ^Soldering-uses — Alloys. 

ZINC 
Ores — ^Reduction-properties — LIses. 

CADMIUM 
Occurrence — Reduction-uses — Alloys. 

LEAD 
Occurrence — ^Reduction-properties — Uses — ^Alloys. 

TIN 
Occurrence — Reduction-iiroperties — Uses — Haskell's    babbitt    metal. 

MERCURY 
Occurrence — Distribution — Compounds — Alloys — Properties — Reduction. 


Properties — Alloys — Uses. 
Properties — Alloys — Uses. 
Properties — Alloys — Uses. 
Properties — Uses. 


NICKEL 

BISMUTH 

ANTIMONY 

TUNGSTEN 


TABLE  OF  CONTENTS  xix 

MEASUREMENT  OF  PLATE  AND  WIRE 

The  unit  of  measurement  of  gauges — Lack  of  uniformity  of  the  various  gauge 
systems — The  Birmingham  gauge — Discrepancies  of  the  Birmingham 
gauge — The  Brown  and  Sharp  gauge — Forms  of  gauges — The  jeweler's 
gauge — The  plate  and  wire  gauge — The  micrometer  caliper — Various  sys- 
tems of  wire  and  plate  gauges  and  their  equivalents  in  thousandths 
of  an  inch  Pages  960  to  1100 

CHAPTER    XXXIII 

A  BRIEF  HISTORY  OF  PROSTHETIC  DENTISTRY 

The  Ebers  papyrus — Antiquity  of  the  papyrus — Guerini's  History  of  Dentistry 
— The  Phoenicians — Effect  of  Egyptian  civilization  on  Phcenicia — One 
of  the  most  ancient  specimens  of  prosethetic  art — The  Etruscans — 
Etruscan  dental  art — First  references  in  history  to  prosthesis — Dentistry 
among  the  ancient  Hebrews — Slow  progress  of  dental  prosthesis  in  the 
middle  ages — First  reference  to  the  use  of  models — First  reference  to 
full  lower  dentures — First  record  of  application  of  mineral  substances 
for  dentures — Retention  of  partial  dentures  without  the  use  of  ligatures 
or  wires — Fauchard's  writings — Transplantation  of  natural  teeth — Crown 
work  in  Fauchard's  time — Mediaeval  bridgework — Full  dentures — Con- 
struction of  full  dentures  by  Fauchard — Summary  of  Fauchard's  work 
— Beneficial  influence  of  Fauchard's  writings  upon  the  profession — First 
work  confined  exclusively  to  dental  prosthesis — First  mention  of  plaster 
— First  mention  of  gold  bases — Implantation  of  teeth — Berdmore's  ref- 
erence to  artificial  dentures — Principal  materials  used  as  denture  bases 
— First  suggestion  of  porcelain  work — Du  Chateau's  efforts  in  porcelain 
work — The  work  of  Dubois  de  Chemant — Introduction  of  single  teeth 
and  blocks  of  porcelain — Introduction  of  porcelain  in  the  United  States 
— First  manufacturer  of  porcelain  teeth  in  America — Introduction  of 
gold  for  denture  bases — Dies  for  swaging  metal  bases — First  use  of 
cast  denture  bases — Special  forms  of  teeth  for  use  with  cast  bases — 
Dental  vulcanite  litigation — Collodion  and  celluloid  as  denture  bases — 
Vulcanizing  rubber  between  metal  surfaces — Denture  bases  pioduced 
by   electro-deposition  of  gold  and  silver. 

ARTICULATORS 

Casts  extended  distally  to  form  articulating  surfaces — 'Evans  articulator — 
Bonwill  articulator — Plain  line  articulator — Starr  articulator — Hayes 
articulator — ^First  suggestion  of  the  face  bow — Study  of  condylar  move- 
ments— Walker's  research  work — Walker's  anatomical  articulator — 
Facial  clinometer — Gritman  articulator — Snow  face  bow — Kerr  articu- 
lator— Christensen's  work — Snow  anatomical  articulator — Schwarze 
articulator — Gysi's  work  and  anatomical   appliances. 

CROWN   WORK 

Pivot  teeth  of  De  Chemant — The  grooved  flat  back  facing — Ash's  tube 
teeth — The  Wood  pivot  tooth — The  Smith  crown — The  Clark  crown — 
The  Lawrence-Foster  crown — The  Dwindle  crown — The  Wood  crowns 
— The  Morrison  crown — The  Black  crown — The  Bean  crown — The 
Mack  crown — The  Beers  crown — The  Gates  crown — The  Richmond 
crown — The  Gates-Bonwill  crown — The  Biittner  crown — The  How 
crown — The  Weston  crown — The  Logan  crown — The  Brown  crown. 

BRIDGEWORK 

The  Bing  bridge — Webb's  work — Litch's  work — Williams'  work — Starr's  work 
— Basis  of  our  present  system  of  bridgework — Porcelain  bridges — Re- 
movable bridges. 

INLAYS 

First  recorded  attempts  in  filling  teeth — First  mention  of  inlays  in  dental 
literature — Prehistoric  inlay  work — The  beginning  of  modern  inlay 
work — Brief  summary  of  inlay  work  beginning  with  1820 — Land's  method 


XX  TABLE    OF    CONTENTS 

of  porcelain  inlay  work — Bing's  metallic  lacing — Rollins'  method — 
Dunn's  method — Stoke's  method — Ames'  uielhod — Various  methods  of 
inlay  production  in  recent  years — Alexander's  method — Slow  progress 
of  inlay    work — Progress   of  gold    inlay   methods. 

INCEPTION    OF    THE    WAX    MODEL    METHOD 

Analysis  of  the  casting  process — Forming  models  in  wax  of  the  cast- 
ing to  be  produced — Method  of  forming  a  sprue  or  pouring  gate — 
Enclosing  the  wax  model  in  a  single  investment — Eliminating  the 
wax  pattern  by  heat — Fusing  the  metal  in  close  proximity  to  the 
mold — Applying  pressure  to  the  fused  metal  to  induce  sharpness  of  de- 
tail in  casting — Pioneers  in  the  production  of  cast  work — The  Blandy 
process — Bean's  method  of  casting  aluminum — Sauer's  method — Reese's 
method — Hayford's  method — The  Watt's  flask — Martin's  method  of  cast- 
ing— The  Carroll  method — The  Zeller  casting  appliances — The  Fenner 
casting  appliances — Harper's  cast  crowns  and  bridges — The  Alexander 
method — The  HoUingworth  method — Flask  designed  by  writer — Phil- 
brook's  method — Schottler's  clinic — The  Lentz  casting  process — The 
OUendort  casting  process — Summary  of  progress  in  casting  operations 
— Causes  of  failure  in  casting  operations — Taggart's  method  of  casting 
— Recent  appliances — The  Solbrig  casting  pliers — The  Biber  casting  ap- 
pliance— Summary  of  foregoing   facts    Pages    1101   to   1201 


CHAPTER    T 
PROSTHETIC  DENTISTRY 

GENERAL  REMARKS 

The  science  of  dentistry  pertains  to  tlie  recognition 
and  treatment  of  diseases  of  the  teeth  and  oral  tissues,  of  the 
general  neuritic  conditions  of  the  head  and  neck  that  may 
have  their  direct  origin  in,  or  be  indirectly  connected  with, 
the  fifth  cranial  nerve,  and  of  the  repair  and  replacement  by 
operative  or  prosthetic  procedures,  of  the  partial  or  com- 
plete loss  of  the  teeth  through  accident  or  by  disease. 

Prosthetic  dentistry  is  that  braucli  of  dental  science 
which  treats  of  the  various  methods  of  replacing  the  lost 
organs  of  the  mouth  in  whole  or  in  part, -the  artistic  and  me- 
chanical processes  involved  in  such  restoration,  together  with 
a  description  of  the  physical  properties  and  peculiarities  of 
the  various  materials  employed. 

Sjieciiically  considered,  prosthetic  operations  may  be 
classed  as  follows:  Construction  of  crowns,  bridges  and 
dentures,  obturators  and  appliances  for  correcting  defects  of 
the  palate,  appliances  for  correcting  irregularities  of  the 
teeth  and  jaws,  appliances  for  retaining  in  position  fractured 
bones  of  the  face  when  reduced,  and  the  construction  of  me- 
tallic and  porcelain  inlays. 

In  all  prosthetic  procediires  the  attainment  of  three 
objects  is  desirable :  First,  the  restoration  of  the  function  of 
mastication;  Second,  the  esthetic  requirements  should  he 
given  due  consideration  and  ivrought  out  correctly;  Third,  the 
snhstitvte,  of  whatever  character,  should  cause  the  wearer  no 
discomfort.  The  late  Dr.  Pritchett  concisely  stated  this  by 
saying  that  in  prosthetic  procedures  "we  strive  to  give  our 
patients  dentures  that  are  useful,  will  lool-  well,  and  he 
comfortahle." 

RESTORATION   OF   THE   FUNCTIONS   OF   MASTICATION- 
UTILITY 

The  first  consideration  is  the  most  im]iortant.  When 
from  any  cause  the  function  of  mastication  is  interfered  with 
or  impaired,  the  digestive  organs  are  necessarily  required  to 
do  an  extra  amount  of  work  for  which  they  are  unfitted,  and 

1 


2  PROSTHETIC     DENTISTRY 

which  will  (iventually  result  in  impaired  digestion,  systemic 
disturbances  and  general  ill  health  of  a  more  or  less  serious 
character.  Without  doubt,  many  lives  are  shortened  by  years 
because  of  the  partial  or  total  loss  of  this  most  important 
function,  and  in  constructing  substitutes  for  the  natural  teeth, 
they  should  be  made  to  restore,  as  fully  as  possible,  the 
function  of  the  natural  organs.  This  point  is  of  such  im- 
portance as  to  bear  repetition  by  restatement.  Ability  to 
masticate  and  digest  food  means  good  health  and  generally 
normal  bodily  functions,  while  inability  to  do  so  entails  dis- 
comfort, ill  health,  disease  and  a  curtailing  of  the  span  of 
life. 

ESTHETICS 

The  second  consideration — esthetics — relates  to  the 
artistic  pliase  of  i;)rosthesis,  the  ability  to  produce  or  create 
appropriate  and  natural  appearing  devices  and  substitutes 
to  take  the  place  of  the  lost  natural  teeth,  to  reproduce  by 
skillful  teehnic  not  only  a  successful  masticatory  apparatus, 
but  to  restore  lost  facial  contour  as  well. 

The  principal  part  of  the  face  to  suffer  change  by 
the  loss  of  the  teeth,  and  the  consequent  absorption  of  the 
alveolar  process,  is  the  mouth,  although  at  times  a  consider- 
able portion  of  the  lower  half  of  the  face  is  modified  in  out- 
line. The  lips  lose  their  normal  pose  and  assume  an  un- 
natural expression,  more  or  less  marked  in  proportion  to 
the  loss  of  the  bony  substructure.  Premature  wrinkles  form 
upon  and  encompass  the  mouth  and  cheeks,  and  an  appear- 
ance of  age,  not  warranted  by  years,  sets  its  seal  upon  the 
subject. 

It  is  the  province  of  the  prosthetist  to  correct,  as  far 
as  possible,  the  ravages  occasioned  by  disease,  and  time,  as 
well,  and  restore  to  the  patient  his  normal  appearance. 

To  do  this  the  prosthetist  should  be  a  master  of  liis 
ai't — one  who  can,  at  will,  imitate  nature  in  her  ideal,  as  we-U 
as  less  typical  forms  and  moods.  From  the  nature  of  his 
vocation,  he  should  be  an  anatomist,  a  sculptor,  an  artist  and 
an  artisan,  thorough  and  proficient  in  each  field  mentioned, 
in  order  to  fulfill,  in  the  highest  degree,  the  requirements  im- 
posed upon  him  by  his  profession. 

Many  eulogistic  effusions  on  the  beauty,  attractive- 
ness and  importance  of  the  mouth  and  teeth  are  to  be  found. 
They  have  emanated  from  the  artists  and  poets  of  every 
race  and  clime.     They  emphasize  the  high  regard  and  even 


PKOS'IHKTIC     DKXTlSTltV  3 

veiifi'aiioii  in  wliidi  these  features  oi'  the  face  have  been 
held  by  tlie  human  race  in  general  from  time  immemorial. 
The  following  are  some  of  the  selections  referred  to. 

Lavater,  one  of  the  early  writers  on  physiognomy, 
says,  in  reference  to  the  mouth:  "The  mouth  is  the  inter- 
preter of  the  mind  and  of  the  heart.  It  combines,  both  in 
a  state  of  rest  and  in  the  infinite  variety  of  its  motions,  a 
world  of  characters.  It  is  eloquent  even  in  its.  silence."  *  *  * 
"I  conjure  our  painters  and  every  artist  whose  mission  it  is 
to  represent  man,  I  conjure  them  with  all  my  might  to  study 
the  most  precious  of  all  our  organs  in  all  its  varieties;  in  all 
its  proportions;  in  all  its  harmonies." 

"What  shall  I  say,  jjaiuters  and  designers,  that  may 
induce  you  to  study  this  sacred  organ  in  all  its  beauteous 
expressions,  in  all  its  harmony  and  proportions."  "Take 
plaster  impressions  of  characteristic  mouths  (lips)  of  the 
living  and  the  dead:  draw  after,  attentively  examine  them, 
learn,  observe,  continue  day  after  day  to  study  one  only; 
and  having  perfectly  studied  that,  you  will  have  studied 
many.  *  *  *  Among  ten  or  twenty  draughtsmen  to  whom 
for  three  years  I  have  preached,  whom  I  have  instructed, 
have  drawn  examples  for,  not  one  have  I  found  who  felt  as 
he  ought  to  feel,  saw  what  was  to  be  seen,  or  could  represent 
that  which  was  evident."  *  *  *  "I  expect  everything 
from  a  collection  of  characteristic  plaster  impressions  which 
might  so  easily  be  made,  were  such  a  collection  once  formed — 
but  who  can  say  whether  such  observations  might  not  de- 
clare too  much.  The  human  machine  may  be  incapable  of 
suffering  to  be  analyzed;  man,  perhaps,  might  not  endure 
such  a  close  inspection,  and  therefore,  having  eyes,  he  sees 
not."  Lavater  further  lays  down  rules  for  the  guidance  of 
the  artist,  as  follows: 

"Distinguish  in  each  mouth  a  the  ujiper  lip,  singly; 
h  the  under  lip,  the  same ;  c  the  line  formed  by  the  union  of 
both  when  tranquilly  closed,  if  they  can  be  closed  without 
constraint;  d  the  middle  of  the  upper  lip  in  particular,  and  e 
of  the  under  lip ;  /  the  bottom  of  the  middle  line  at  each  end, 
and  lastly  g  the  extending  of  the  middle  line  on  both  sides, 
for  unless  you  disiinguish  you  will  not  be  able  to  delineate 
the  mouth  accurately." 

Herder,  the  eminent  German  poet  and  critic,  says 
of  this  prominent  feature  of  the  face :  "It  is  from  the  mouth 
that  the  voice  issues,  interpreter  of  the  heart  and  soul,  ex- 


1  PROS'I'UKTIC     IJKNTISTRY 

IMTssioii  ((f  JVcliii.ii',  (>r  I'liciulsliip,  and  ol'  tlif  purest  enthu- 
siasiii.  The  upi)er  li])  translates  the  inclinations,  the  appe- 
tite, the  disquietude  of  love;  pride  and  passion  contract  it; 
cunning  attenuates  it;  goodness  of  heart  reflects  it;  de- 
bauchery enervates  and  debases  it;  love  and  the  passions 
incarnate  themselves  there  in  an  inexjiressible  charm." 

(Concerning  the  teeth,  Paolo  Mantegazza,  the  noted 
Italian  anthropologist,  says:  "It  is  a  flaw  in  beauty  to  have 
bad  teeth;  it  is  like  a  spot  on  the  sun.  Since  the  hygiene  of 
the  teeth  is  at  the  same  time  the  hygiene  of  beaut^',  good 
dentists  merit  a  golden  statue,  or  at  least  a  place  of  honor 
among  the  principal  benefactors  of  humanit>'. "  *  *  * 
"The  most  beautiful  teeth  are  not  enough  to  make  a  man 
beautiful ;  but  ugly  teeth  would  spoil  the  beauty  of  the  Venus 
of  Milo  herself."" 

Again  reverting  to  Lavater's  remarks  on  the  teeth, 
he  says:  "Nothing  is  more  certain,  striking  or  continually 
visible  than  the  characteristics  of  the  teeth,  and  the  manner 
in  which  they  display  themselves. "  *  *  *  "Whoever  leaves 
his  teeth  foul  and  does  not  attempt  to  clean  them,  certainly 
betrays  much  of  the  negligence  of  his  character,  which  does 
him  no  honor.  As  are  the  teeth  of  man,  that  is  to  say,  their 
form,  position  and  cleanliness  (so  far  as  the  latter  depends 
upon  himself),  so  is  his  taste." 

The  loss  of  the  teeth  and  consequent  absorption, 
to  a  greater  or  less  extent  of  the  bony  substructure  support- 
ing the  lips  and  cheeks,  results  in  marked  disfigurement. 
The  exterior  of  the  dental  arch,  as  well  as  the  face,  is  con- 
vex. The  lips  form  a  movable  curtain  or  pallium,  to  close 
the  oral  opening.  They  are  supported  by  the  dental  arches 
and  alveolar  borders.  The  loss  of  the  teeth  allows  the  lips 
to  sink  in,  and  the  profile,  as  well  as  contour  of  the  face, 
suffers. 

It  requires  a  keen  artistic  sense  to  determine  the 
correct  lines  of  contour  to  develop  in  order  to  restore  har- 
mony in  each  individual  type  or  cast  of  countenance.  Too 
much  or  too  slight  convexity  of  the  substitute  will  mar  the 
symmetry  and  poise  of  the  patient's  face,  through  improper 
support  of  the  lips.  The  color  of  the  teeth  in  artificial  cases 
must  harmonize  with  the  color  of  the  eyes,  hair  and  general 
tone  of  the  patient's  complexion.  The  form,  size  and  ar- 
rangement of  the  teeth  and  their  general  treatment  by  grind- 
ing to  simulate  wear  appropriate  to  the  age  of  the  patient. 


PROSTHF-TIC     DENTISTRY  5 

must  also  be  determined.  No  two  cases  will  be  exactly  the 
same.  Each  factor  must  be  studied  by  itself,  and  all  of  the 
factors  considered  as  a  whole  in  every  case  that  presents. 

The  prosthetist's  highest  attainment  in  the  esthetic 
field  consists  in  imitating  nature  so  closely  that  his  work 
cannot  be  detected  by  casual  or  even  close  observation,  and 
so  well  done  that  his  patient  does  not  seriously  feel  the  loss 
of  the  natural  teetli,  or  will  not  lie  disturbed  by  the  presence 
of  the  substitute. 

COMFORT 

The  third  desirable  object  sought  in  denture  con- 
struction is  a  most  important  one.  It  is  possible  to  construct 
substitutes  that  fulfill  requirements  from  the  standpoint  of 
utility  and  esthetics  as  well,  and  yet  cannot  be  worn  by  the 
patient  with  ease  or  comfort.  Imperfect  adaptation  of  den- 
ture to  tissues,  causing  undue  or  uneven  pressure  at  certain 
jioints;  extension  of  baseplate  on  palatal  muscles  so  far  as 
to  cause  irritation,  retching,  or  by  the  contraction  of  the 
muscles,  dislodgement  of  the  substitute;  impingement  of  the 
])eri])hery  of  the  denture  on  the  labial  or  buccal  muscles  or 
the  frenae;  rough,  unpolished  surfaces,  particularly  in  the 
palatine  portion  of  the  denture,  are  some  of  the  sources  of 
discomfort  that  impair,  and  at  times  seriously  inhibit  the  use- 
fulness of  otherwise  well-constructed  dentures. 

The  ability  to  recognize  such  annoying  conditions 
as  mentioned,  and  be  able  to  anticipate  and  overcome  them 
during  constructive  processes,  is  a  most  important  attain- 
ment, and  should  be  developed  by  every  prosthetist. 

In  entering  upon  the  study  of  dentistry,  the  student 
should  understand  and  thoroughly  appreciate  the  fact  that 
the  vocation  of  a  dentist  embraces  a  much  broader  field  than 
is  usually  accorded  it  by  the  public  or  the  uninformed  in  gen- 
eral. Dentistry  is  a  specialty  of  the  healing  art — medicine — 
and  has  been  so  recognized  from  ancient  times. 

Herodotus  (500  to  425  B.  C),  in  writing  of  the  prac- 
tice of  medicine  in  Egypt,  says :  ' '  The  exercise  of  medicine 
is  regulated  and  divided  amongst  the  Egyptians  in  such  a 
manner  that  special  doctors  are  deputed  to  the  curing  of 
every  kind  of  infirmity;  and  no  doctor  would  ever  lend  him- 
self to  the  treatment  of  ditferent  maladies.  Thus  Egypt  is 
quite  full  of  doctors;  those  for  the  eyes;  those  for  the  head; 
some  for  the  teeth;  others  for  the  belly;  or  for  occult 
maladies."     (Guerini.) 


6  i'UOSTHEtiC     DKNTiStRY 

lu  tliis  (];iy  tlic  dt-ntisl  is  a  scieutilic  sjx'ciulist  wlio  is 
constantly  called  upon  to  treat  living,  sensitive,  vital  tissue; 
to  recognize  and  treat  obscnre,  as  well  as  plainly  apparent 
disorders  and  diseases  having  their  origin  in,  and  adjacent 
to,  the  oral  cavity.  In  addition  to  such  treatment,  it  is  the 
province  of  the  prosthetist,  through  highly  developed  me- 
chanical skill,  to  replace  teeth  and  parts  of  teeth  that  have 
been  lost  through  accident  or  by  disease. 

The  knowledge,  skill  and  handcraft  necessary  to 
carry  out  the  requirements  mentioned  come  only  with  close, 
long-continued  and  patient  application.  The  artistic  and 
esthetic,  as  well  as  the  mechanical  faculties,  should  be  en- 
couraged and  developed  in  the  course  of  study  laid  down  in 
the  dental  curriculum,  for  the  student's  success  depends  upon 
the  thorough,  harmonious  and  balanced  development  of  all 
of  these  faculties.  lie  gets  out  of  his  course  only  what  he 
puts  into  it.  The  half-hearted  acquirement  of  a  few  smatter- 
ing facts  is  not  sufficient  in  these  days  of  strenuous  competi- 
tion to  fit  one  for  the  practice  of  dentistry  in  general,  or  any 
one  of  its  special  branches. 

Patience,  persistence,  energy  and  enthuiasm  are 
essential  to  success  in  the  acquirement  of  a  dental  education, 
as  well  as  in  other  departments  of  science.  Ecjuipjjed  witli 
these  qualities,  no  one  can  place  a  limit  to  the  heights  attain- 
able by  a  student  or  practitioner  in  his  chosen  work.  The 
field  is  broad.  Many  scientific  problems  are  still  unsolved. 
Investigators  are  few  and  in  demand.  Preventive  measures 
are  being  devised  and  introduced  for  the  benefit  of  the  patient. 
The  public  is  being  gradually  educated  in  the  principles  of 
personal  care  of,  and  attention  to,  the  teeth.  Dental  inspec- 
tion in  public  schools  is  being  realized,  and  the  children  are 
being  taught  that  good  teeth,  good  health  and  good  minds 
go  hand  in  hand,  in  the  order  named,  for  without  good  teeth 
the  health  suffers  and  the  mind  and  mental  processes  are 
disturbed. 


C  n  A  P  T  E  R    1 1 

BODILY  FUNCTIONS 

The  human  body  is  an  organism,  whicli  exhibits  the 
I)henomena  of  life  and  in  and  throngii  wliich  tiie  vital  forces 
act.  The  history  of  a  living  entity,  its  daily  routine  of  life 
from  inception  to  final  dissolution,  is  one  of  perpetual  change. 

The  general  epochs  in  the  life  of  an  individual  are  con  ' 
caption,  liirth,  a  varying  period  of  growth,  a  vaguely  de- 
terminate period  of  existence  unmarked  by  radical  change, 
and  finally,  gradual  or  sudden  diminution  and  cessation  of 
the  vital  functions,  terminating  in  death,  with  ultimate  reso- 
lution of  the  organism  into  primal  chemical  elements  or 
compounds. 

METABOLISM 

In  the  human  body  during  life,  constant  changes  are 
continually  going  on.  Every  mental  effort,  every  movement 
of  the  body  or  any  portion  of  it,  the  normal  or  abnormal, 
voluntary  or  involuntary,  action  of  the  functional  organs 
themselves,  call  for  the  expenditure  of  energy  and  result  in 
loss  of  substance.    These  changes  are  known  as  metabolism. 

Every  normal  living  organism  contains  within  itself  a 
varying  amount  of  reserve  force  or  stored  up  energy  ready 
for  use  on  demand.  To  maintain  equilibrimn  and  consequentlj' 
a  normal  condition  of  health,  the  stock  of  energy  when  de- 
pleted, and  the  loss  of  substance  as  it  occurs,  must  be  re- 
plenished. 

In  the  human  organism  this  repair  of  loss  is  accom 
plished  by  taking  into  the  body  substances  known  as  food, 
capable  of  being  masticated,  digested,  absorbed,  circulated 
and  assimilated.  Food  is  composed,  more  or  less,  of  ex- 
traneous matter.  That  is,  the  intrinsic  or  nutritive  elements 
contained  therein,  capable  of  being  assimilated,  or  replacing 
waste  tissue  and  developing  heat,  energy,  etc.,  represent  in 
bulk  only  a  poi-tion  of  the  juaterial  taken  into  the  body  as 
food. 

liulky  and  in  fart  all  varieties  of  food,  when  lu-okeu  up 
and  finely  divided,  are  more  readily  acted  upon  l»y  the  saliva, 
the   gastric   juice   and   intestinal   digestive   fluids,   and   the 

7 


8  BODILY     FUNCTIONS 

Diitritivi'    elements   more   (jnickly   approijriated    than    when 
taken  into  the  system  unprei)ared  by  mastication. 

IMPAIRMENT  OF  BODILY  FUNCTIONS 

The  bodily  functions  are  carried  on  by  various  organs, 
each  of  which  performs  its  part  in  the  maintenance  of  life. 
Some  of  the  organs  are  of  minor  importance.  Their  functions 
may  cease  or  the  organs  themselves  may  atrophy  or  be  oblit- 
erated by  disease  or  traumatism,  and  yet  the  general  healtli 
of  the  individual  may  not  be  seriously  impaired. 

The  organs  of  the  special  senses  are  examples  of  this 
tyjje,  as  the  loss  of  hearing,  the  sense  of  smell,  taste  or  eye- 
siglit  are  of  common  occurrence,  and  although  the  loss  of 
any  one  of  these  senses  may  be  keenly  felt,  yet  existence  may 
be  prolonged  for  many  years,  with  a  greater  or  less  degree 
of  comfort. 

Other  organs  are  of  vital  importance.  Should  they  from 
any  cause  be  destroyed  or  cease  to  carry  out  their  functions, 
the  result  usually  involves  serious  and  permanent  impairment 
of  health,  or  even  the  cessation  of  life  itself.  The  respiratory, 
circulatory,  masticatory  and  digestive  organs  are  examples  of 
the  type  under  consideration. 

THE  MOUTH 
ITS  IMPORTANCE  IN  THE  HUMAN  ECONOMY 

The  cavity  of  the  mouth  contains  those  tissues  and  or- 
gans which  are  of  special  interest  to  the  oral  surgeon  and 
dentist.  Through  it  all  food  substances  and  liquids  are  taken 
into  the  body.  By  the  organs  contained  therein  the  food  is 
triturated,  insalivated,  and  prepared  for  deglutition.  From  it 
articulate  sounds  proceed. 

In  the  oral  cavity  many  forms  of  bacteria  find  lodgment, 
and,  on  account  of  tlie  heat  and  moisture  present,  it  furnishes 
a  favorable  soil  for  their  propagation  and  growth.  The  aver- 
age mouth  usually  contains  from  twenty  to  fifty  varieties  of 
micro-organisms,  some  harmless,  while  others  are  pathogenic 
in  character.  The  latter,  while  not  always,  are  frequently 
present,  ready  to  exhibit  destructive  energy  when  favorable 
conditions  develop.  For  this  reason  the  mouth,  under  normal 
conditions,  although  a  neutral  focus  of  infection,  is  a  con- 
stant menace  to  the  health  of  tlie  individual,  unless  given 
proper  care  and  attention. 


BODILY     FUNCTIONS  9 

The  mouth  consists  of  two  parts,  viz.,  the  vestibule  aud 
tlie  oral  cavity  proper. 

THE  LIPS 

One  of  the  most  prominent  features  of  the  face  is  the 
external  orifice  of  the  mouth.  This  is  a  transverse  fissure 
bounded  above  and  below  by  the  upper  and  lower  lips,  respect- 
ively. At  their  extremities  they  unite  to  form  the  commissures. 
Internally  they  are  covered  with  mucous  tissue,  and  externally 
with  integument.  The  orbicularis  muscle,  which  largely  de- 
velops mobility  aud  closes  the  lips,  is  situated  between  the  in- 
tei'nal  and  external  surfaces.  Composed  as  they  are  of  two 
thick,  fleshy  folds,  and  containing  within  themselves  no  bony 
support,  they  settle  inward  and  liaekward  when  loss  of  the 
teeth,  and  the  resultant  absorption  of  the  alveolar  process, 
occurs.  It  is  the  province  of  the  prosthetist  to  restore  such 
deformity  of  the  face  by  means  of  suitably  constructed  and 
contoured  substitutes  as  conditions  require. 

THE  VESTIBULE 

The  vestibule  is  that  portion  of  the  oral  cavity  which  lies 
external  to  tlie  teeth  and  alveolar  arches,  and  internal  to  the 
cheeks  and  lips.  It  extends  from  the  space  just  back  of  the 
third  molar  on  one  side,  through  which  it  connnunieates  with 
the  oral  cavity  proper,  around  the  labial  aud  buccal  surfaces 
of  the  teeth  and  arches,  to  the  corresponding  space  on  the  op- 
posite side.  Its  upper  and  lower  boundaries  are  tei-minated 
by  the  attachment  or  blending  of  the  mucous  membrane  of 
the  cheeks  and  lips  witli  that  covering  tlie  upper  and  lower 
alveolar  arches. 

When  the  jaw  and  lips  are  closed,  and  the  teeth  are  in 
normal  occlusion  the  mucous  membrane  of  the  cheeks  and  lips 
rests  against  the  outer  surfaces  of  the  teeth  aud  arches,  and 
no  appreciable  space  between  these  surfaces  is  noticeable. 
By  inflation  from  within,  or  liy  parting  the  lips  and  distending 
the  cheek  walls,  the  cavity  of  the  vestibule  becomes  apparent. 

The  upper  and  lower  peripheral  circumferences  of  the 
vestibule  are  known  as  the  superior  and  inferior  cul  de  sacs. 

The  salivary  secretions  from  the  parotid  glands  are  dis- 
charged into  the  vestibule  opposite  the  second  upper  molar 
through  the  ducts  of  Stenson. 

THE  ORAL  CAVITY  PROPER 

The  oral  cavity  is  bounded  anteriorly  and  on  each  side 
by  the  lingual  surfaces  of  all  the  teeth  and  the  alveolar 


]0  BODILY     FUNCTIONS 

arches;  above  by  tlic  palatal  vault,  iucludiug  both  the  hard 
and  soft  palate;  below  by  the  tongue  and  its  mueous  mem- 
brane reflected  against  the  lingual  surfaces  of  the  lower 
alveolar  arch;  posteriorly  it  merges  into  the  pharyngeal  space 
through  the  isthmus  of  the  fauces.  The  tongue  and  palatal 
muscles  acting  conjointly  form  a  temporary  distal  boundary, 
or  wall,  to  the  oral  cavity  as  occasion  requires,  in  the  act  of 
mastication,  deglutition  or  phonation. 

MUCOUS  MEMBRANE 

The  entire  interior  of  the  oral  space  is  lined  with  mucous 
membraue,  being  "composed  of  a  layer  of  stratified  squamous 
epithelium,  supported  upon  a  tunica  propria,  which  is  usually 
described  as  composed  of  two  parts — the  papillary  layer  and 
the  reticular  layer.  The  epithelium  and  the  tunica  i^ropria 
make  up  the  mucous  membrane  proper,  which  is  supported 
upon  a  submucous  layer  composed  of  a  coarse  network  of 
white  and  elastic  tibres,  containing  the  larger  blood  vessels" 

EPITHELIUM 

"The  stratified  squamous  epithelium  is  provided  with  a 
horny,  or  cornous  layer  only  in  the  portions  covering  the 
alveolar  process  and  the  hard  palate,  or  in  other  words, 
where  the  submucosa  is  firmlj^  attached  to  the  periosteum. 
In  these  positions  the  horny  layer  consists  of  dead  cells  which 
have  lost  their  nuclei,  and  whose  cytoplasm  has  been  con- 
verted into  keratin  or  hornv  material."  (Noves'  Histology, 
p.  323.) 

The  mucous  membrane  is  continuous  over  cheeks  and  gum 
tissue  and  extends  from  the  lips  to,  and  merges  with,  that  in 
the  naso-pharyngeal  space. 

THE.  PALATINE  VAULT 

The  vault  of  the  mouth  is  formed  anteriorly  by  the  hard, 
and  posteriorly  by  the  soft  palate.  The  lingual  surfaces  of 
the  alveolar  arch  form  the  lateral  and  anterior  boundaries 
of  the  vault,  while  the  free  margin  of  the  soft  jjalate  forms 
the  posterior  boundary. 

THE  BONY  STRUCTURE  OF  THE  HARD  PALATE 

The  hard  palate  is  formed  by  the  junction  of  the  palatine 
lirocesses  of  the  superior  maxillae  and  the  horizontal  ]ilates 
of  the  palate  bones.     These  processes  unite  in  the   median 


BODILY     FUNCTIONS  11 

line  to  form  a  suture  or  linear  ridge  called  the  raphe.  tSonie- 
times  this  ridge  is  quite  prominent  and  irrcguhir,  and  renders 
the  fitting  of  dentures  a  difficult  task. 

PALATINE  FORAMINA 

Just  back  of  the  central  incisors  in  the  median  line  is 
situated  the  anterior  palatine  fossa,  in  which  are  seen  the 
orifices  of  four  small  canals.  Two  of  these,  the  foramina  of 
Stenson,  are  located  one  on  either  side  of  the  median  suture, 
and  transmit  the  anterior  i^alatine  vessels  and  nerves.  Sit- 
uated just  inside  the  alveolar  arch  and  about  opposite  the 
location  of  the  third  molars  on  either  side,  two,  and  some- 


THE   MAXJLLA,    WITH   FULL   LOMPLEMEXT   OF   TEETH   SHOWING 
ANTERIOR  ANT)  POSTERIOR  PALATINE  FORAMIN.E 

times  three,  openings  are  seen.  Thc^  larger,  or  anterior  of 
these  canals  transmits  the  posterior  palatine  vessels  and 
nerves,  which  pass  forward  in  grooves  parallel  with  the  inner 
alveolar  plates.  These  bony  grooves  are  nearly  always 
plainly  marked  at  their  beginning,  but  usually  become  indis- 
tinct and  finally  obliterated  about  opposite  the  bicuspid  teeth. 
The  vessels  and  nerves  coming  foi'ward  from  these  canals 
supply  the  mucous  tissues  of  the  hard  palate.  Some  fila- 
ments of  the  nerves  and  liranches  from  the  arteries  pass  for- 
ward and  anastomose  with  the  vessels  and  nerves  transmitted 
through  the  anterior  jialatine  canal. 

When  denuded  of  the  soft  tissues  covering  it,  the  bony 
surface  of  the  palate  presents  a  more  or  less  irregular  ap- 
pearance. Freqvrently  sharp,  well-defined  points  of  bone,  and 
occasionally  nodules  of  varying  sizes,  are  present,  sometimes 


12  liODILY     FUNCTIONS 

along  tlie  margins  of  tlie  grooves  which  transmit  the  pala- 
tine vessels,  but  more  eommonly  at  various  places  on  the 
alveolar  border.  The  sore  spots  and  areas  which  so  often 
develop  on  introducing  a  denture  are  often  traceable  to  the 
presence  of  such  irregular  ])oints  and  nodules,  which,  under 
pressure  of  the  base  plate,  naturally  become  sources  of  irrita- 
tion to  the  overlying  soft  tissues.  It  is  advisable  in  such 
cases  to  relieve  the  pressure  of  the  denture  over  these  areas, 
as  well  as  opposite  the  openings  of  the  posterior  and  anterior 
])alatine  canals,  especially  when  the  mucous  and  su])mucous 
tissues  are  thin,  hard  and  unyielding.  Excessive  continued 
l^ressure  on  the  vessels  and  nerves,  transmitted  through 
those  canals,  will  undoubtedly  lower  the  nutrition  of  the  parts 
sup])lied,  tem]iorarily  at  least,  and  cause  unnecessary  dis- 
conifort  and  pain  to  the  wearer  of  the  denture. 

THICKNESS   OF   THE   PALATINE   PROCESS   OF   THE   MAXILLiE 

The  palatine  processes  of  the  superior  maxilla^  by  their 
upper  surfaces  form  the  floor  of  the  nasal  fossa.  The  thick- 
ness of  the  bony  partition  lietween  the  oral  and  nasal  cavities 
varies  in  different  individuals.  In  some  specimens  of  young 
adults  the  thickness  of  these  plates  scarcely  exceeds  1-100  of 
an  inch  at  a  point  about  midway  between  the  raphe  and  the 
outer  wall  of  the  nasal  fossa. 

The  extreme  thinness  of  the  palatine  processes  in  this 
location  converts  them  hito  sounding  boards,  so  to  speak,  and 
gives  a  finer,  clearer  quality  to  both  nasal  and  oral  sounds 
than  would  be  possible  if  the  bony  floor  were  thick.  Base 
l)lates,  whether  of  metal  or  vulcanite,  frequently  tend  to  im- 
pair tone  quality,  and  therefore  care  should  be  taken  in 
denture  construction  to  avoid  unnecessary  bulk  in  the  vault 
jioj'tion. 

Strength  is  given  to  the  thin,  bony  vault  on  the  nasal 
side  in  its  central  portion,  by  the  junction  of  the  nasal  septum 
with  the  palatine  processes  at  the  median  suture  opposite 
and  above  the  raphe. 

THE  MUCOUS  MEMBRANE  OF  THE  PALATE 

The  mucous  membrane  covering  the  hard  palate  and 
alveolar  arches  is  provided  with  a  horny  or  cornuous  layer, 
as  before  stated.  This  layer  is  less  sensitive  than  the  or- 
dinary mucous  membrane,  as  well  as  firmer,  denser  and  more 
fibrous.     These  charactei'istics  render  it  less  liable  to  injury 


BODILY     B'UNCTIONS 


during  the  mastication  of  liard  varieties  of  food,  and  less 
irritable  to  friction  or  stress  tlian  are  membranes  devoid  of 
the  cornnous  laver. 

THE  RUG^ 
Situated  just  back  of  the  central  incisors  and  slightly  in 
front   of  the   position   of  the   anterior  palatine   canal,   is   a 
small  pear-shaped  eminence  called  the  papUla  of  ihe  pnhiic. 


THK  TONUIE   SIK 


Iltrt'.MVAI.I.ATE   I'AI'ILL.E    (St-e  |).    14) 


Extending  jiosteriorly  from  tliis,  and  folldwiiig  tlic  raphe,  is 
also  a  ridge  of  mucous  tissue. 

A  number. of  smaller  irregular  ridges  pass  out  lateral! \, 
usually  running  obliquely,  but  not  necessarily  paralleling 
each  other,  sometimes  extending  l)ack  as  far  as  the  second 
l)icus])id.  Tliese  are  called  pliav  palutliitr,  or  folds  of  the 
jialate.     The  papilla,  with  its  distal  extension,  together  with 


14  r.ODILY      KIINCTIONS 

llic  hilcials  wliicli  arc  arranged  on  either  side,  are  kuown  as 
the  I'lKjir,  I'ruiJi  inga — a  fold  or  wrinkle.  Oftentimes  when 
well  detiued,  the  central  ridge  and  laterals  present  tlie  ay)- 
pearance  of  a  synnnetrical  tree  trnnk  with  spreading 
branches. 

THE  TONGUE 

The  tongue  is  the  organ  of  the  special  sense  of  taste;  it 
is  one  of  the  principal  organs  of  speech,  and  is  an  indispensi- 
ble  factor  in  mastication  and  deglutition.  When  at  rest  it 
occupies  the  space  between  the  internal  walls  of  the  body  of 
the  mandible,  the  lingual  surface  of  the  lower  alveolar  arch 
and  ]iractirally  all  of  the  teeth  (see  cut,  page  13). 

THE  SENSE  OF  TASTE 

The  special  sense  of  taste  is  located  pi-iiicipally  in  tln' 
circumvallate  paiiilla?  which  are  situated  on  the  dorsum  (if 
the  tongue.    They  are  in  two  rows,  arranged  in  V  form,  the 


V    FIURKS    (IH'    VARKII  S    T()N(iUE    MlISCr.ES 


apex  being  on  the  median  line  and  pointing  distally,  the  rows 
running  forward  and  outward.  They  are  of  large  size  and 
vary  in  number  from  eight  to  ten,  or  even  more.  In  addi- 
tion to  these,  there  are  numerous  other  papilte,  called  fili- 
form papill.T,  distributed  over  the  sides  and  dorsum  of  the 


BODILY     FUNCTIONS  15 

tongue,  which  give  it  a  roughened,  or  furred,  appearance. 
Still  another  variety,  called  fungiform,  are  foiaud  interspersed 
with  tlie  filiform  papilhe,  but  are  less  numerous  than  the  latter. 

THE  SALIVARY  GLANDS 

The  parotid  submaxillary  and  sublingual  glands  to  a  lim- 
ited extent,  empty  the  salivary  secretions  in  the  mouth  at  all 


SYMPHYSIS 


THE    SALIVAKT   GLANDS 


times,  l)ut  more  or  less  profusely  during  the  mastication  of 
food.  The  saliva  is  the  first  digestive  fluid  to  act  on  the  food, 
partially  converting  the  starches  into  sugars,  and  in  conjunc- 
tion with  the  mucous  secretions,  luln-icates  the  bolus  of  food 
and  prepares  it  for  deglutition. 


CHAPTER     III 
EXAMINATION  OF  THE   MOUTH 

GENERAL  REMARKS 

To  render  the  most  skillful  service  to  a  patient  it  is  nec- 
essary for  the  dentist  to  know  the  exact  conditions  of  the 
tissues  and  organs  of  the  mouth  in  detail.  Such  knowledge 
can  only  be  acquired  by  a  close  examination  of  the  parts.  In- 
telligent questioning  of  the  patient  will  assist,  to  a  certain 
extent,  but  the  burden  of  the  diagnosis  rests  upon  the 
operator. 

He  must  be  a  histologist  and  pathologist  as  well,  to  recog- 
nize conditions  of  health  and  disease.  No  detail,  that  has  a 
direct  or  even  a  remote  bearing  on  the  dental  aspect  of  the 
case  in  hand,  should  escape  his  notice.  The  general  method 
of  procedure  for  an  examination,  as  here  outlined,  may  be 
followed  with  good  results. 

POSITION   OF   PATIENT 

Seat  the  patient  and  adjust  the  chair,  first,  so  that  he 
may  feel  comfortable ;  second,  so  as  to  bring  the  mouth  within 
convenient  range  for  examination.  Adjust  a  towel  over  the 
patient's  clothing,  attaching  it  around  the  neck.  A  mouth 
mirror,  probe,  explorer,  tongue  depressor,  pliers,  cotton, 
water  syringe,  and  a  small  electric  mouth  lamp,  are  the  in- 
struments most  useful  for  examination,  and  should  be  placed 
conveniently  at  hand,  although  not  necessarily  in  sight. 

Everything  being  in  readiness,  the  operator  should 
cleanse  his  hands  in  the  presence  of  the  patient,  or  so 
the  latter  may  know  it  is  being  done.  This  is  necessary  for 
two  reasons — first,  to  prevent  possible  danger  of  carrying  in- 
fection to  the  patient's  mouth,  and  second,  to  engender  within 
the  mind  of  the  latter  a  feeling  of  confidence  in  the  operator's 
knowledge  and  ability  to  cope  with  disease.  The  free  appli- 
cation of  tepid  water,  or  normal  salt  solution,  with  the  syringe 
to  the  teeth  and  oral  tissues  is  nearly  always  advisable  be- 
fore beginning  an  examination. 

The  lips  guard  the  entrance  to  the  alimentary  tract,  and 
as  they  are  first  encountered,  the  examination  should  begin 
with  them.    Note  whether  they  are  of  good  color  and  normal 

16 


EXAMINATION     OF     THE     MOUTH  17 

in  appearance,  or  if  lesions  are  present  such  as  fissures,  cold 
sores,  etc.  If  so,  avoid  giving  any  unnecessary  pain 
by  distension,  or  pressure  on  the  parts.  If  in  a  healthy 
condition,  the  index  finger  should  be  passed  around  between 
the  alveolar  process  and  cheeks,  a  general  idea  being  thus 
gained  of  the  distensibility  of  the  lips  and  cheek  walls.  The 
first  glance  in  the  mouth,  in  most  cases,  discloses  to  the  ex- 
aminer something  of  the  character  of  the  patient  and  the 
class  of  operations  required. 

EXAMINATION    OF   MOUTH   WHEN   NATURAL   TEETH    ARE 
PRESENT 

Note  specifically  the  general  appearance  of  the  mouth 
as  to  health  and  cleanliness.  If  any  natural  teeth  are  present, 
look  for  calculus,  pyori'hea  pockets,  alveolar  and  gingival  ab- 
scesses, dead  pulps,  peridental  inflammation  and  gingivitis. 

Note  any  and  all  peculiarities  of  the  mucous  membrane, 
redness,  discoloration  and  swelling  usually  being  signs  of 
some  irritated  or  diseased  condition.  Stomatitis,  leukoplakia, 
mucous  patches,  cancrum  oris,  etc.,  are  liable  to  be  present, 
and  if  so  should  be  recognized  immediately.  If  any  condition 
found  is  infectious  in  character,  the  operator  should  take  due 
precautions  for  his  own  safety  during  the  examination,  and 
thoroughly  sterilize  all  instruments  as  soon  as  the  patient  is 
out  of  the  chair.  If  teeth  are  carious,  observe  the  extent  to 
which  the  disease  has  progressed,  the  teeth  affected,  and  the 
probable  method  of  treatment.  Note  also  the  relation  of  the 
teeth  in  the  same  arch  to  each  other,  and  to  those  in  the  op- 
posite arch,  as  well.  Observe  the  forms  of  the  teeth  them- 
selves, whether  constricted  at  the  neck;  elongated  or  normal; 
whether  tissues  have  receded,  leaving  them  standing  more  or 
less  unsupported;  whether  they  diverge  or  converge  to  an 
unusual  degree;  whether  loss  of  proximate  contact  has  oc- 
curred; the  form  of  the  spaces  where  the  teeth  and  spaces 
alternate.  By  noticing  the  extent  of  abrasion  on  the  occlusal 
surfaces  of  the  teeth,  some  idea  can  be  formed  of  the  stress 
exerted  in  masticatory  effort. 

If  the  patient  is  past  middle  age  and  no  signs  of  occlusal 
abrasion  appear,  as  it  normally  should  at  such  an  age,  try 
to  discover  the  cause,  whether  due  to  mal-occlusion  or  to  a 
diseased  condition  of  the  peridental  membrane  of  one  or  more 
of  the  natural  teeth.  Tenderness  of  the  peridental  mem- 
brane, and  slight  elongation  of  a  single  tooth,  will  often— 


IS  EXAMINATION     OK     THK     MOUTH 

sometimes   I'or  yeurs — inhibit    or    sciiously    iiii])air    proper 
masticatory  eti'ort. 

EXAMINING  EDENTULOUS  MOUTHS 

111  edeiitulous  cases,  note  particular!}-  the  i'oriu  oC  tlir 
alveolar  processes,  or  as  Dr.  G.  V.  Black  has  appropriately 
termed  tliem  the  residual  ridges,  the  amount  of  absorption 
that  has  occurred,  the  extent  and  position  of  muscular  at- 
tachments to  the  labial,  buccal  and  lingual  surfaces.  In  the 
upper  jaw,  determine  the  location  and  extent  of  the  hard 
and  soft  areas,  and  the  thickness  of  the  mucous  and  sub- 
mucous tissues  in  the  vault  portion.  Notice  particularly  the 
form  of  the  raphe  (the  bony  ridge  formed  by  the  union  of 
the  palatine  processes  of  the  upper  maxillae)  and  compare 
the  thickness  of  the  mucous  membrane  which  covers  it  with 
that  covering  the  crest  of  the  borders.  Determine  whether 
there  are  any  sensitive  or  tender  areas  on  which  tlie  pros- 
pective denture  will  rest.  These  areas  usually  will  be  found 
on  either  side  of  the  vault  just  internal  to,  and  a  little  in 
front  of  the  tuberosities,  and  in  the  median  line,  just  back 
of  the  central  incisors,  where  the  four  canals  are  situated 
which  transmit  the  posterior  and  anterior  palatine  vessels 
and  nerves. 

When  the  mucous  and  submucous  tissues  are  sparse  and 
thin  on  these  areas,  the  pressure  of  the  denture  is  at  times 
very  disagreeable,  sometimes  producing  pain.  It  can  be  ob- 
viated by  properly  relieving  the  impression.  Examine  par- 
ticularly the  buccal  aspect  of  the  tuberosities  as  well  as  other 
locations,  to  determine  whether  undercuts  are  present.  If 
so,  what  efifect,  if  any,  tliey  will  have  on  the  removal  of  the 
impression.  When  the  vault  is  deep,  rising  abruptly  back 
of  the  incisor  region,  there  will  frequently  be  an  undercut 
area  in  the  anterior  portion  of  the  mouth,  the  distance  from 
the  labial  to  the  palatine  alveolar  plates  through  the  region 
of  the  incisive  fossa  being  less  than  through  the  border  por- 
tion near  the  crest. 

In  examining  the  arch  and  tissues  of  the  lower  jaw,  ob- 
serve the  amount  of  absorption  and  the  position  and  extent 
of  muscular  attachment  to  the  outer  and  inner  sides  of  the 
alveolar  arch,  whether  the  tongue  and  cheek  muscles,  and 
the  tissues  above  the  submaxillary  glands  are  liable  to  inter- 
fere in  impression  taking;  how  far  distally  and  downward  the 
lingual  wings  of  a  full  denture  case  can  extend  without  impp<l- 
ing  tongue  movements.    Notice  the  relative  size  of  the  arches, 


EXAMINATION     OF     THK     MOUTH  19 

and  the  probable  ease  or  difficulty  of  introducing  tlie  impres- 
sion tray  through  the  oral  opening. 

A  pad  of  charts  having  diagrams  of  the  upper  and  lower 
arches  should  be  on  the  bracket,  and  any  points  of  interest 
should  be  marked  thereon  as  soon  as  found.  While  the  chart 
can,  or  may  not,  be  used  after  the  examination  is  completed, 
the  marking  of  the  important  points  will  fix  them  fii-mly  in 
the  mind.  Every  peculiarity  of  the  teeth  or  tissues  that  may 
have  a  direct  or  even  a  remote  bearing  on  prosthetic  pro- 
cedures, should  be  recognized  and  kept  in  mind  in  order  that 
the  most  efficient  service  may  be  rendered. 

PREPARATION   OF  THE  MOUTH   FOR   DENTURES 

All  operative  procedures,  as  a  rule,  such  as  the  placing 
of  fillings  and  inlays,  removal  of  calcareous  deposits,  and 
treatment  of  the  soft  tissues,  should  be  completed  before  tak- 
ing impressions.  Useless  teeth  and  roots  should  be  extracted, 
and  in  some  cases  the  tissues  should  be  allowed  to  heal  before 
introducing  a  denture.  Further  surgical  procedures  are  at 
times  very  necessary,  such  as  freeing  muscle  fibers  and  tissues 
of  the  cheek  wall  that  may  at  some  previous  time  have  been 
lacerated,  and  in  healing,  have  been  drawn  over  and  become 
attached  to  the  tissues  on  the  process,  in  such  manner  as  to 
interfere  with  the  correct  seating  of  the  denture.  The  late 
Dr.  Burchard's  suggestion  is  a  good  one,  of  taking  an  im])res- 
sion  of  the  mouth,  including  the  cicatrized  tissue,  and  from 
this  securing  a  cast.  This  is  then  trimmed  to  represent  the 
normal  form  of  the  ridge,  that  portion  representing  the 
cicatrized  soft  tissues  being  dissected  away  on  the  cast,  and 
leaving  the  trimmed  portion  rather  more  prominent  than  the 
natural  hard  tissues.  A  denture  of  vulcanite  is  constructed, 
the  margins  rounded  and  polished  smoothly,  which  when  in 
position  holds  the  severed  tissues  apart  until  healed,  and  thus 
the  normal  alveolar  surfaces  are  regained. 

SPONGY   BORDERS 

Often,  when- the  teeth  have  been  lost  from  phagedenic 
troubles,  the  bony  process  is  practically  all  absorbed,  or  de 
stroyed.  The  border  in  such  cases,  although  presenting  a 
fairly  good  form,  is  soft  and  tlabby,  consisting  of  thickened, 
sometimes  fibrous,  mucous  membrane,  devoid  of  bony  sup- 
port.   Such  a  ridge  affords  an  unsatisfactory  foundation  for 


20  EXAMINATION     OF     THE     MOUTH 

a  (It'iitiirc,  without  sonu'  ]ii'('liiiiiiiarv  treatment  of  tlic  iiioutli 
itself,  or  ol'  the  cast  to  lie  used  in  coiistiuetiou. 

REDUCING  SPONGY  BORDERS 

Three  metliods  are  in  \(),!;u<'  for  iniuiiiiiziii.i;'  this  vvvy 
annoying  condition : 

First.  A  metiiod  wliereliy  the  treatment  of  tlie  east  used 
in  denture  construction  will,  in  certain  cases,  correct  the  dif- 
ficulty mentioned.  This  will  be  described  later  in  proper 
order. 

Second.  A  very  satisfactory  method  suggested  by  Dr.  C. 
P.  Pruyn  of  absorbing  excess  tissue — construct  a  temporary 
])asei)late  for  the  case,  or  if  the  patient  is  wearing  an  old, 
even  though  ill-fitting,  denture,  it  will  serve  the  purpose.  Line 
the  interior  with  oxychloride  or  oxyphosphate  of  zinc,  mixed 
to  medium  consistency.  Place  it  labially  and  lingually  of  the 
border  position,  thus  leaving  sort  of  a  groove  for  the  crest 
of  the  ridge  to  enter.  Under  pressure  the  cement  is  com- 
pressed between  the  basej^late  and  the  unyielding  tissues,  and 
is  forced  from  l)oth  sides  against  the  flabby  ridge,  reducing 
its  bulk  without  materially  distorting  or  changing  its  position 
or  depth.  Two  or  three  weeks'  constant  wear,  of  this  cement 
corrected  denture,  will  imjirove  the  density  of  the  border 
very  noticeably.  If  furtlier  absori)tion  is  deemed  advisable, 
the  denture  is  thoroughly  cleansed,  an  additional  layer  of 
cement  is  spread  over  that  already  adapted,  and  the  ridge 
subjected  to  pressure  as  before.  When  the  density  of  the 
border  is  satisfactory,  a  permanent  denture  is  constructed. 

Third.  The  most  severe  method  of  treatment  consists  in 
surgically  removing  such  portion  of  the  spongy  border  as 
may  be  deemed  necessary,  and  stitching  the  margins  of  the 
membrane  together  to  accelerate  the  healing  process. 

When,  in  ])reparing  a  mouth,  extractions  are  performed, 
care  should  be  taken  to  see  that  the  sharp  or  prominent  pieces 
of  alveolar  ]n-ocess  that  frequently  project  from  the  border, 
are  removed.  This  can  easily  be  done  with  a  cutting  forcep 
or  bur  while  the  trauma  is  fresh.  The  border,  if  left  smooth 
and  rounded,  and  free  from  sharp  projections,  will  afford 
a  bettej-  foundation  for  a  denture,  and  the  soft  tissues  will 
heal  more  ra])idly  than  when  this  smoothing  up  process  is 
neglected. 

When  sharp,  bony  jioints  are  ])resent  as  the  result  of 
previous  operations,  it  is  advisable,  in  most  cases,  to  dissect 
away  the  gum  and  periosteum,  remove  the  prominences,  and 


EXAMINATION     OF     THE     MOUTH  21 

if  the  wound  gaps  open,  stitch  the  gum  tissue  together.  If, 
for  any  reason,  it  is  not  advisable  to  remove  the  points  by 
cutting,  then  tliose  areas  in  the  impression  impressed  by 
the  points  should  be  scraped  to  obviate  pressure  and  conse- 
quent irritation,  when  tlie  denture  is  introduced. 

TEMPORARY  DENTURES 

When,  by  i-ecent  extraction,  the  mouth  has  been  cleared 
of  all  remaining  teeth,  the  problem  confronting  the  patient 
and  prosthetist  is — Hoio  soon  shall  dentures  he  fitted  to  the 
edentulous  borders?  Without  qiiestion,  iu  most  cases,  the 
patient  will  be  best  served  by  constructing  dentures  imme- 
diately, that  is  to  say,  within  a  few  days  after  the  loss  of  the 
teeth.  It  is  a  noticeable  fact  that  patients  who  have  never 
worn  dentures  become  accustomed  to  the  presence  of  sub- 
stitutes with  less  effort,  when  introduced  soon  after  the  loss 
of  the  natural  teeth  than  do  patients  for  whom  the  introduc- 
tion of  dentures  has  been  deferred  for  a  varying  period  of 
from  six  months  to  a  year.  Just  why  this  is  so,  is  not  clear. 
Perhaps  the  inconvenience  felt  from  the  introduction  of  the 
temporary  dentures  is  so  slight  as  to  be  nearly  lost  sight  of, 
while  the  cataclysmic  effect,  both  physical  and  mental,  result- 
ing from  the  loss  of  the  natural  teeth  and  the  consequent  in- 
ability to  masticate  food,  is  engrossing  the  attention  of  the 
patient. 

Another  factor  of  importance  is  the  marked  aversion 
most  persons  have  of  presenting  themselves,  toothless,  in 
public,  or  to  their  friends.  Almost  without  exception  they 
will  submit  to  much  inconvenience,  and  pain  as  well,  rather 
than  suffer  the  humiliation  occasioned  by  the  absence  of  the 
teeth.  This  is  the  psychological  moment  and  should  not  be 
neglected  by  the  operator.  The  ability  to  tolerate  the  pres- 
ence of  temporary  dentures  in  the  mouth  is  positive  assurance 
that  the  permanent  substitutes  will  prove  both  useful  and 
comfortable.  Another  point  in  favor  of  temporary  substitutes 
is  that  the  alveolar  processes  absorb  more  uniformly,  as  to 
density  of  tissue,  and  the  ridges  will  maintain  their  form 
for  a  longer  period  with  less  change,  tlian  where  the  intro- 
duction of  the  dentwes  is  deferi'ed. 

PERMANENT  DENTURES 

Usually  the  jcnipdravy  should  be  rcphu-ccl  with  perma- 
nent dentures  in  from  six  to  twelve  months.  The  inequalities 
of  the  borders  will  usually  in  this  period  have  become  smooth 


L'2  KXAMINATION      OK     'J'HE      MOUTH 

and  rounded,  the  alveoli  filled  in,  and  the  soreness  will  have 
disappeared  from  the  soft  tissues.  Since  as  a  result  of  the 
absorption  that  has  occurred  tiie  adaptation  of  the  denture 
to  the  tissues  is  imperfect,  deferring  the  construction  of  the 
permanent  sets  beyond  the  time  mentioned  usually  results 
in  unnecessary  and  deleterious  absorption  of  the  alveolar 
process.  Stress  therefore  should  be  laid  upon  this  fact,  and 
the  patient  advised  accordingly. 

In  the  examination  of  any  mouth  with  a  view  of  carrying 
oi;t  prosthetic  procedures,  certain  tilings  should  be  kept  in 
mind  by  the  operator. 

First,  he  sJiould  carefully  consider  what  class  of  substi- 
tute will  give  the  patient  the  best  service,  as  indicated  by  the 
conditions  in  the  mouth. 

Second,  when  the  class  of  work  indicated  is  not  to  be 
considered  on  account  of  expense,  what  other  method  can  be 
followed  to  the  best  advantage. 

Third,  the  operator  and  not  the  patient  should  determine 
what  class  of  work  is  indicated,  and  how  it  should  be  done. 
This  he  can  do  if  by  his  ability  and  sincerity  he  can  ins]iire 
within  the  mind  of  his  patient,  confidence  in  his  knowledge, 
judgment,  and  honesty  of  purpose,  all  of  which  are  essential 
in  order  to  bring  together  and  hold  a  desirable  clientele. 


CHAP  T  K R    I  V 

ARTIFICIAL    DENTURES 

PHYSICAL    AND   MECHANICAL    PROBLEMS    INVOLVED 
IN   THEIR   CONSTRUCTION 

THE  THREE  ESSENTIAL  REQUIREMENTS 

The  production  of  artificial  dentures,  either  full  or  par- 
tial, is  accomplished  by  the  carrying  out  of  a  series  of  tech- 
nical details  that  follow  each  other  in  sequence. 

The  degree  of  success  attained  in  denture  construction 
is  directly  dependent  on  the  skill  with  which  the  details  are 
wrought  out.  The  test  of  success  lies  first,  in  the  patient's 
ability  to  use  the  dentures  successfully  in  masticatory  effort ; 
Second,  in  the  greater  or  less  complete  fulfillment  of  es- 
thetic requirements;  and  third  in  the  ability  of  the  wearer 
to  use  them  without  inconvenience  or  to  briefly  summarize — 
usefulness — good  looks — comfort. 

FULL   DENTURES 

Perhaps  the  most  difficult  problem  confronting  the  pros- 
thetist  is  that  of  retention  or  securing  stability  of  the  finished 
dentures  when  introduced  and  subjected  to  use.  In  full  cases, 
the  natural  teeth  having  been  lost,  no  mechanical  aids  to  re- 
tention can  be  resorted  to,  such  as  are  used  in  partial  sub- 
stitutes. In  extreme  instances  spiral  springs  can  be  applied 
but  they  are  objectionable,  on  account  of  the  constant  pres- 
sure exerted  to  force  the  mandible  and  maxilla  apart,  also 
on  account  of  unhygienic  conditions  caused  by  their  presence. 
Retention  of  full  dentures  is  largely  a  question  of  physics 
and  not  of  mechanics,  although  good  mechanical  judgment 
and  skill  must  be  exercised  in  developing  the  physical  aids  to 
retention. 

Full  upper  and  lower  dentures  are  retained  in  position 
on  tlio  alveolar  borders  by  adliesion  and  atmospheric  pres- 
sure. In  lower  cases  gravity  also  assists.  Partial  den- 
tures are  usually' retained  with  some  form  of  clasps,  or  me- 
chanical devices,  which  attach  to  some  of  the  remaining  nat- 
ural teeth  or  roots.  In  favorable  cases  both  means  first  men- 
tioned, viz.  adhesion  and  atmospheric  pressure,  are  utilized. 
The  same  general  conditions  which  are  requisite  for  develop- 

23 


:i4  AKTIKUUAL     DENTURES 

ing  good  atmospheric  pressure,  are  also  essential  iDr  develop- 
ing good  adliesive  qualities. 

ADHESION 

(a)  Adliesiou  is  deliued  as  "tlie  molecular  attraction  ex- 
erted between  the  surfaces  of  bodies  in  contact. ' ' 

(b)  This  peculiar  property  is  attributed  to  some  recip- 
rocal action  between  the  contact  surfaces.  The  par- 
ticles must  be  brought,  within  the  limit  or  distance  of 
molecular  attraction. 

(c)  "The  attraction  increases  as  the  contact  is-prolonged 
and  is  greater  in  proportion  as  tlie  contact  is  closer." 

Adhesion  takes  place  between  dissimilar  substances.  It 
is  more  powerful  between  a  solid  and  a  liquid  than  between 
solids,  or  between  the  molecules  of  a  liquid  itself. 

If  a  thin  layer  of  oil  is  interposed  between  two  perfect 
planes  of  metal,  they  will  adhere  firmly,  but  when  pulled 
asunder  each  i^late  is  moistened  by  the  oil,  showing  that  in 
separating  the  plates,  the  cohesion  of  the  liquid  is  overcome, 
but  not  the  adhesion  of  the  oil  to  the  metal.  (Ganot's 
Physics.) 

That  adhesion  plays  a  part  in  the  retention  of  dentures 
is  beyond  question,  but  the  conditions  surrounding  a  denture 
when  in  position  and  in  use  in  the  mouth,  tend  to  reduce  the 
effectiveness  of  adhesion,  viz.,  the  slight  yet  unavoidable 
movement  which  occurs  when  the  denture  is  subjected  to 
stress,  due  to  the  natural  resiliency  of  the  tissues.  This 
movement  is  opposed  to  prolonged  as  well  as  close  contact. 
(8ee  paragraph  c.) 

ATMOSPHERIC   PRESSURE 

The  atmosphere  is  the  aeriform  fluid  which  envelopes  the 
earth  and  extends  outward  from  its  surface  a  distance  of 
almost  50  miles.  It  is  composed  mostly  of  free  oxygen  (21) 
and  nitrogen  (79),  with  about  4  parts  of  carbonic  acid  to 
10,000.  Ammonia,  sulphuretted  hydrogen  and  other  gases  are 
also  present  in  varying  quantities  in  diiferent  places,  due  to 
local  causes. 

The  air  has  weight.  One  hundred  cubic  inches  of  dry  air, 
rmder  ordinary  atmospheric  pressure  of  30  inches,  and  at  a 
temperature  of  62  F.,  weigh  31  grains.  Twelve  cubic  feet  of 
air  under  the  same  conditions,  weigh  1  pound.  The  air  in 
a  room  16x16x10  feet  weighs  210  pounds. 

Since  the  air  has  weight,  and  the  earth's  surface  is  at 


ARTIFICIAL     DENTURES  25 

the  bottom  of  the  aei'ial  sea,  the  outer  layers  of  the  atmos- 
phere are  constantly  pressing  down  upon  the  deeper  layers 
with  a  very  considerable  force,  the  earth's  surface  being  the 
site  of  greatest  pressure. 

This  pressure  is  not  noticeable  under  ordinary  conditions, 
as  the  air  presses  equally  in  all  directions,  and  upon  all  ob- 
jects. If,  however,  it  is  excluded  from  between  two  surfaces, 
the  pressure  is  immediately  apparent.  In  case  of  perfect 
exclusion  of  the  air,  the  pressure  at  sea  level  amounts  to  14.7 
pounds  per  square  inch.  When  two  perfectly  ground  plane 
plates  of  glass  or  metal  are  placed  together,  and  the  air  be- 
tween the  contact  surfaces  is  excluded,  it  will  require  a  force 
equal  to  the  area  of  the  plates  in  square  inches  multiplied 
by  14.7,  to  separate  them.  If  the  plates  are  4  inches  square, 
tiie  formula  would  be  stated  thus:    4X4X14.7=235.2. 

To  summarize,  it  would  require  a  pull  of  235.2  ]>ounds 
to  overcome  atmospheric  pressure  and  separate  the  plates, 
without  considering  the  adhesive  force  which  is  also  present, 
and  which  would  have  to  be  overcome  before  separation 
could  take  place. 

RETENTION  BY  MEANS  OF  ATMOSPHERIC  PRESSURE 

In  ai^plying  the  principle  of  atmospheric  pressure  to  the 
retention  of  an  artificial  denture,  it  is  necessar^^  to  develop 
certain  ^conditions  between  the  denture  and  the  tissues  on 
which  it  rests,  similar  to  those  present  in  the  plane  plates 
mentioned,  viz.,  close  or  uniform  adaptation  of  the  contact  sur- 
faces iiarticularly  peripheral  contact. 

The  denture  is  seated  upon  the  mucous  membrane  of  the 
mouth,  which  in  turn  is  supported  by  and  rests  on  a  bony 
structure  or  foundation.  The  thickness  of  the  mucous  tissue 
varies  in  different  mouths,  and  often  varies  greatly  in  dif- 
ferent areas  of  the  same  mouth. 

For  example,  as  often  happens,  the  central  vault  portion 
of  the  mouth  is  covered  with  a  thin,  un^delding,  and  the  max- 
illary area  with  a  thick  and  yielding,  layer  of  mucous  tissue. 
Unless  precaiitionary  measures  are  taken  to  prevent,  a  denture 
fitted  to  such  a  mouth  will  be  readily  dislodged  under  stress, 
the  hard  central -area  acting  as  a  fulcrum  on  which  tlie  base 
plate  will  tip,  the  side  on  which  stress  is  exerted  being  forced 
upward,  tlie  opposite  side  being  carried  downward  corre- 
spondingly, just  as  the  arms  of  a  lever  rotate  about  the  ful- 
crum.   This  movement  disturbs  the  equilibrium  of  the  denture, 


26  AKTIFICIAT.     DENTURES 

breaks  the  contact  surfaces,  and  the  air,  if  at  first  exchided. 
rushes  in  between  the  denture  and  tissues. 

The  same  condition  would  prevail  were  the  mai'gins  of 
the  plane  plates  previously  alluded  to  soft  and  yieldinc^  and 
the  central  area  hard  and  unyielding.  Pressure  produced 
on  the  margins  of  the  plates  on  one  side,  to  force  them  to- 
gether, brings  the  hard  central  area  into  action  as  a  fulcrum, 
separates  the  opposite  sides  and  destroys  atmosyiheric  pres- 
sure. By  proper  precautionary  measures  the  difficulty  men- 
tioned in  denture  construction  may,  to  a  great  extent,  lie 
obviated. 

NECESSARY    CONDITIONS    FOR    RETENTION 

First,  there  must  be  uniform  contact,  or  lieai'ing,  of  th( 
denture  against  the  tissues  on  which  it  rests. 

Second,  the  peripheral  margins  of  the  denture  at  al/ 
points  should  be  so  formed  that  the  tissues  when  at  rest,  or 
under  muscular  tension,  will  remain  in  close  contact  with  these 
margins,  thus  preventing  the  ingress  of  air  between  the 
denture  and  tissues. 

With  the  first  requirement  realized,  it  is  comparatively 
easy  to  develop  the  second  one.  In  both  cases  the  necessary 
conditions  are  developed,  principally  during  the  taking  of 
the  impression,  the  details  of  which  will  be  given  in  the  chap- 
ter on  this  subject. 

Briefly  stated,  the  principle  involved  in  carrying  out  the 
first  requirement,  viz.,  uniform  bearing  on  hard  and  soft  areas, 
consists  in  exerting  pressure  on  the  soft  areas  by  means  of 
suitable  impression  material,  of  proper  plasticity,  to  com- 
press them  so  that  the  finished  denture  will  bear  firmly  on 
the  soft,  and  lightly  and  in  some  cases  not  at  all  on  the  hard 
areas.  This  condition  can  be  still  further  carried  out  and 
accentuated  by  scraping  the  impression  in  certain  areas,  the 
details  of  which  will  shortly  be  given. 

The  second  requirement,  viz.,  close  peripheral  adaptation, 
is  accomplished  first  by  careful  manipulation  of  the  impres- 
sion materials  against  the  peripheral  areas,  and  second,  by 
having  the  patient  exercise  the  muscles  actively  while  the  im- 
pression material  is  still  soft  and  plastic,  and  thus  mark  their 
form,  direction  and  limit  of  attachment  to  the  alveolar  process. 

The  ol)ject  sought  in  carrying  out  this  step  is  to  seeui'e 
a  iieripheral  outline  to  the  denture  that  will  not  impinge  on, 
or  cause  irritation  of,  the  muscular  or  soft  tissues,  and  yet 


AUTIFK'IAL      DRNTUUKS  27 

will  have  such  close  aila])tiitiuu  as  to  seal  against  the  ingress 
of  air — to  atTord  "relief  without  leak,"  as  Dr.  J.  W.  Greene 
expresses  it. 

RELIEF  FROM   PRESSURE   BY   SCRAPING  THE  IMPRESSION 

When  the  impression  is  secured,  those  parts  imjiressed 
by  the  exceedingly  hard  and  nnjdelding  areas  of  the  month 
shonld  be  scrajied  slightly  to  insure  relief  from  bearing  of 
the  finished  denture  on  these  areas.  It  is  especially  necessary 
to  atford  such  relief  in  the  central  palatine  portion  of  the 
mouth  when  the  raphe  is  distinctly  mai'ked  and  prominent 
and  is  covered  with  oulv  a  thin  laver  of  tissues. 


AN     IMl'RKSSIDX     SHOWING     MBDIIM     AMOINT    OF    liELlEK 

In  relie\'ing  this  area  the  scraping  should  extend  sligldly 
btyo)i(l  the  margins  of  the  hard  outline  in  every  direction. 
Usually  the  relief  should  not  exceed  1/25  of  an  inch  in  depth 
in  the  deepest  part,  and  should  gradually  taper  out  to  a 
thin  invisible  jDeriphery,  losing  itself  in  the  general  contour 
of  the  vault  impression. 

The  idea  in  thus  treating  the  impression  is  not  to  pro- 
duce a  vacuum  chamber  in  the  denture,  but  to  alford  relief 
from  pressure  on  the  raphe  and  adjacent  tissue,  and  thus  pre- 
vent the  hard  areas  from  serving  as  a  fulcrum  to  tip  the 
denture  when  stress  is  applied. 

A  little  experience  will  enable  one  to  readily  detei-mine 
the  outline  and  extent  of  the  hard  areas  by  merely  scanning 
the  impression.  It  is  a  good  plan,  however,  to  make  a  digital 
examination  of  the  mouth,  either  immediately  before  or  after 


28  AUTIKU^IAL      DENTURES 

flic  iiii|ii'cssi(iii  is  taken,  to  he  alisdliitclv'  ccrtHin  (if  tln'  extent 
of  relief  iieeessary  to  pi'ov'idc!  i'or. 

VACUUM   CHAMBERS 

Vacuum  eliambeivs,  oi'teu  incorrectly  called  iilr  chamhern, 
are  shallow,  depressed  areas  with  a  definite  outline,  usually 
formed  in  the  central  palatine  surfaces  of  dentures  during 
the  constructive  steps,  and  which  are  supposed  to  assist  in 
retention.  As  ordinarily  constructed,  they  are  not  intended 
to,  nor  do  they  seldom  afford,  relief  from  pressure.  The  ef- 
ficiency of  a  vacimni  chamber  is  dependent  ujion   its  area, 


AN  IMPItESSION  SIKPWlNi;    SI.IIiHT  AMOIXT  OF  PALATINE  REUEF 

depth,  adaptation  of  its  peripheral  margins  to  the  opppsing 
tissues,  and  the  ability  of  the  patient  to  exhaust  the  air  from 
the  interior. 

Under  the  most  favorable  conditions,  the  usefulness  of 
the  vacuum  chamber  is  questionable.  The  tissues  are  soon 
drawn  into,  and  usually  after  a  time  permanently  fill,  the 
cavity,  thereby  defeating  the  object  for  which  it  was  designed. 
When  the  chamber  is  very  deep,  the  tissues,  while  they  may 
not  fill  it  entirely,  are  kept  in  an  irritated  condition,  more  or 
less  annoying  and  frequently  painful  to  the  patient.  On  the 
other  hand,  when  the  chamber  is  shallow  and  the  tissues  are 
not  drawn  into  it,  it  is  not,  as  its  name  would  indicate — a 
vacuum  chamber — but  merely  a  useless  and  unsightly  de- 
pression which  increases  the  thickness  of  the  dentiire  in  a 


ARTIFICIAL     DENTURES  29 

region  where  Inilk  is  objectionable  on  accoiuit  of  its  tendency 
to  modify  the  resonance  of  the  voice. 

For  more  tlian  fifteen  years  past  the  nse  of  this  very 
questional)le  method  of  retention  has  been  discontinued  by 
the  writer,  both  in  clinical  work  and  in  private  practice.  The 
results  during-  this  time  furnish  convincing  proof  of  the 
greater  advantages  over  vacuum  chamber  for  retention  pur- 
poses of  well  defined  uniform  bearing  developed  in  taking  the 
impression  and  by  scrainng  the  cast  to  secure  peripheral 
adaptation  of  the  denture. 

COMPENSATING  FOR  EXPANSION  OF  THE  CAST— FULL  UPPER 
DENTURES 

Since  all  plasters  expand  in  setting,  to  a  greater  or  less 
extent,  some  means  of  compensating  for  the  enlargement  of 
the  cast  should  be  adopted. 


I'RAriNC    THE    PERIPHERY    OP    A 


The  plan  followed,  and  which  has  proven  very  satisfac- 
tory, is  to  scrape  a  slight  groove,  extending  from  one  tube- 
rosity to  the  other,  on  the  buccal  and  labial  surfaces  of  the 
cast.  This  groove  should  be  made  with  a  discoid  20  or  small 
Kingsley  scraper,  to  avoid  the  formation  of  any  angles,  and 
be  very  shallow, — so  slight  as  to  scarcely  be  noticeable  ex- 
cept on  close  inspection.  -It  should  occupy  a  position  about 
midway  between  the  crest  of  the  border  and  the  peri];)heral 
line  of  termination  of  the  denture,  and  as  before  stated  ex- 
tend from  one  tuberosity  to  the  other  on  the  labial  and  buccal 
surfaces.  This  groove  on  the  cast  produces  a  slight,  rounded 
liead  on  the  iimer  asi)ect  of  the  labial  and  buccal  surfaces  of 
the  denture,  reducing  the  diameter  of  the  latter  by  an  amount 
equal  to  the  elevation  of  the  bead,  thus  insuring  close  peri- 
pheral adaptation,  and  overcoming  any  slight  enlargement  of 
the  cast  due  to  expansion. 


So  AUTIKlCtAL     I)IONTlIHES 

POSITION  AND   OUTLINE  FORM   OF  THE  DISTAL   MARGIN   OF 
UPPER   DENTURES 

The  distal  terminal  inaigiii  of  an  ii]»iier  denture  should 
follow  the  Hue  of  junction  of  the  soft  with  tiie  hard  ])alate, 
or  be  laid  on  tlie  soft  immovable  area,  being  careful  to  avoid 
encroaching  on  the  soft  movable  tissues  or  palate  muscles. 
The  latter  liecome  an  active  cause  of  displacement  when  the 
denture  overrides  them  to  any  appreciable  extent. 

Usually  the  distal  margin  of  the  denture  should  assume 
a  double  compound  curve,  extending  either  way  from  the 
median  line,  to  correspond  in  general  with  the  distal  margin 
of  the  hard  palate. 

In  those  cases  where  the  tissue  between  the  luird  central 
area  and  the  tuberosities  is  soft,  the  terminal  line  on  eitiier 
side  of  the  center  may  be  carried  forward  somewhat,  witliout 


DISTAL    FOItM    (IF    ri'I'EI!    liASEPLATE 


impairing  the  adaptation.  Such  trimming  will  also  relieve 
pressure  to  a  certain  extent  on  the  posterior  palatine  vessels 
and  nerves  which  find  their  exit  from  the  canals  situated  just 
inside  of  the  tuberosities.  Pressure  of  the  denture  directly 
on  the  overlying  tissues  and  indirectly  on  the  nerves  in  this 
region  is  a  frequent  cause  of  nausea. 

The  distal  terminal  line  when  proiDeiij^  laid  will  form 
a  pleasing  symmetrical  curve  which  will  harmonize  well  with 
the  buccal  and  labial  outlines  of  the  denture. 


PREPARATION   OF  LOWER   IMPRESSIONS 

In  full  lower  cases  it  frequently  happens  that  the  al- 
veolar border  is  thin  and  the  crest  of  the  process  is  very 


AKTIFICIAL     DENTURES 


liard.  In  such  cases  the  impression  should  be  trinuued  or 
scraped  in  the  deepest  part  with  a  discoid  instrument  similar 
to  the  one  used  in  the  peripheral  scraping  of  the  upper  cast. 
The  scraping  of  the  impression  of  the  crest  should  not  be 


SCRAI'IXG    THE    DEEPER  PORTION    OF    LOWER    IMPRESSION 
TO    RELIEVE    STRESS    ON   HORUER    CREST 

carried  too  close  to  the  distal  terminals,  for  when  extended 
entirely  back,  a  vent  is  formed,  through  which  the  air  finds 
its  way,  affecting  adversely  the  stability  of  the  denture. 

The  effect  of  scraping  an  impression  as  described,  is  to 


-^ 


i.INEAK    DISTANTE    USUALLY    RELIEVED    ON    LOWER    IMPRESSION 
\ 

increase  the  "'^eight  of  the  crest  of  the  ])order  on  tlie  cast  so 
that  a  denture  when  numlded  on  tlie  cast  will  not  rest  on  the 
extreme  crest,  wJiile  the  labial,  Iniccal  and  lingual  flanges  will 
lie  brought  in  closer  contact  with  their  respective  surfaces, 
the  air  forced  out  and  atmospheric  pressure  utilized  for  re- 


32  ARTIFICIAL     DENTURES 

tention  purposes.  In  many  cases,  a  considerable  amount  of 
adhesion  that  could  not  otherwise  })e  realized,  will  be  devel- 
oped in  this  manner. 

SOFT  ALVEOLAR   BORDERS 

When  the  alveolar  border  in  either  upi^er  or  lower  cases 
is  of  average  form,  but  devoid  of  bony  support  due  to  ex- 
cessive absorption  of  the  process,  it  is  frequently  advanta- 
geous to  pare  the  labial  or  buccal  and  lingual  surfaces  of 
the  cast,  slightly,  being  careful  not  to  reduce  the  height  of  the 
crest,  so  that  these  surfaces  of  the  border  will  be  compressed 
when  the  denture  is  introduced.  In  many  cases  in  practice 
the  carrying  out  of  this  plan  has  added  greatly  to  the  sta- 
bility of  dentures,  the  effect  in  most  instances  being  to  con- 
dense and  render  the  tissues  permanently  harder  without  any 
ill  effects.  A  method  of  correcting  extreme  cases  of  soft  and 
yielding  borders — spongy  or  flabby  gums,  as  they  are  some- 
times called — is  detailed  in  another  chapter. 

Partial  dentures  are  usually  retained  in  position  by 
means  of  clasps,  or  some  of  the  forms  of  frictional  appli- 
ances in  common  use.  In  the  case  of  a  clasp,  the  ]3ressure  of 
the  appliance,  which  is  slightly  smaller  than  the  tooth  it  em- 
braces, is  due  to  the  resiliency  or  springiness  in  the  metal  of 
which  it  is  composed.  When  in  position  in  the  mouth,  the 
clasp  which  is  attached  to  the  denture,  grasps  the  tooth  more 
or  less  firmly  and  prevents  displacement.  So  also  with  the 
various  specialized  appliances,  except  that  usually  they  are 
made  in  two  parts,  one  of  which  is  permanently  attached  to 
a  natural  tooth,  or  crown  set  on  a  root,  the  other  to  the  den- 
ture. They  are  so  adjusted  that  when  in  jiosition  the  friction 
between  the  two  jiarts  holds  the  substitute  in  place.  The 
various  iappliances  used  for  this  purpose  will  be  described 
later. 


CHAP TEE    V 

DEFINITIONS  OF  SOME  COMMONLY  USED  TERMS 

IMPRESSION   TRAYS 

DEFINITIONS 

An  impression  is  a  iicfjatire  copy  or  conntorpart  oi  some 
object  impressed.  In  prosthetic  procediires,  to  which  the  fol- 
lowing definitions  will  refer,  an  imiDression  is  obtained  by 
pressing-  a  plastic  material,  such  as  plaster  or  modeling  com- 
pound, against  some  portion  of  the  oral  tissues  or  teeth. 

A  cast  is  a  positive  copy  or  likeness  of  the  object  im- 
pressed and  is  obtained  by  casting  plaster,  or  some  similar 
plastic  material,  Into  the  impression  or  mold.  Casts  are  used 
for  giving  tlie  negative  form  of  the  month  to  plastic  base 
dentures. 

A  model  is  a  positive  or  duplicate  copy  of  the  mouth  or 
some  portion  of  it,  and  is  used  for  producing  a  similar  posi- 
tive of  itself,  and  consequently  of  the  movith,  in  metal.  A 
model  is  produced  in  the  same  general  manner  as  a  cast,  but 
differs  from  it  in  its  use,  and  slightly  in  its  form,  being  so 
shaped  as  to  be  readily  withdrawn  from  the  sand  in  which  it 
is  imbedded,  in  the  sequent  steps  of  die  construction. 

A  die  is  a  metal  duplicate  of  the  mouth  or  some  portion 
of  it,  also  of  the  model  from  which  it  is  derived.  In  construct- 
ing dentures  with  swaged  metal  bases,  a  die  fulfils  a  sim- 
ilar purjiose  to  that  of  a  cast  in  the  production  of  plastic 
base  dentures,  viz.,  giving  the  reverse  form  of  the  mouth  to 
the  metal  base  denture.  A  die  is  formed  by  pouring  molten 
metal  or  alloy  into  a  sand  matrix  derived  from  the  model, 
or,  in  some  cases,  by  pouring  directly  into  the  impression. 

A  counterdie  is  a  negative  or  reverse  of  the  die,  and  is 
ol)tained  by  pouring  a  similar  or  a  lower  fusing  m(>tal  or  alloy 
directly  against  the  face  of  the  die. 

USE  OF  THE  TERMS  "CAST"  AND  "MODEL" 

Tlie  ioYwvDiodd  has  been  and  is  still  veiy  generally  used 
instead  of  cast  1o  designate  the  ])roduct  obtained  by  filling 
the  impression  with  plaster  or  ])laster  compound.  All  such 
products  so  obtained  are  in  reality  casts.  The  term  cast,  is 
gradually  coming  into  use  to  designate  the  prod^ict  of  the  im- 

33 


c 


34  DI'JKINITIOXS    OK    SOMK    COMMONI^Y    USRI)    TERMS 

prcssioii  wlioii  it  is  used  In  give  tlic  reverse  form  of  tlie  mouth 
to  a  plastie  base,  and  the  term  iiniilfl,  when  it  is  used  as  a 
means  to  reproduce  a  die  which  is  a  duplicate  of  itself. 

The  folhjwing  definitions  of  liie  two  terms  are  given  in 
the  Standard  Dictionary : 

"Cast. — An  ohject  fouiidcil  (ir  run  in,  or  as  iji  a  mold,  as 
of  metal,  plaster,  wax,  etc." 

"A  reverse  copy  of  pUister  of  Paris,  or  simiU\r  material, 
of  a  mold,  usually  distinguished  from  a  casting  whicli  is  of 
iron  or  other  metal  or  alloy." 

"Model. — An  object  usually  in  miniature,  representing 
something  to  be  made  or  already  existing;  a  material  pattern 
of  natural  size;  more  rarely  a  plan  or  drawing  as  a  mode! 
of  an  invention ;  a  model  of  a  building;  to  draw  a  model." 

"Specifically:  In  sculpture  the  plaster  or  clay  original 
of  a  work  to  be  executed  in  stone  or  metal.  A  person  who 
does  duty  as  a  copy  or  pattern  for  sculptors  and  painters." 

"A  pattern  is  always,  in  modern  use,  that  which  is  to  l)e 
copied;  a  model  may  be  either  the  thing  to  he  copied  or  the 
copy  that  has  been  made  from  it,  as  the  models  in  tlie  Patent 
Office.  A  pattern  is  commonly  superficial;  a  model  is  usually 
in  relief.  A  pattern  must  be  closely  followed  in  its  minutest 
])articulars  ])y  a  faithful  copyist.  A  model  may  allow  a  great 
degree  of  freedom;  a  scul]itor  may  idealize  his  living  model; 
his  workmen  must  exactly  copy,  in  marble  or  metal,  the  model 
he  has  made  in  clay." 

Before  the  introduction  of  vulcanite,  the  plaster  cast  de- 
rived from  an  impression  was  used  almost  exclusively  for  the 
making  of  metal  dies  on  which  to  swage  gold,  silver  and 
platinum  bases.  For  this  ]inr])ose  it  is  a  true  model,  since  it 
serves  as  a  co])y  from  which  sometiiing  like  it  (the  die)  is 
Ijrodnced. 

On  the  introduction  of  \ulcani1(',  which  came  into  use 
rather  gradually,  the  same  geneial  form  of  cast  as  was  used 
in  die  construction,  served  as  a  shape  over  which  to  mold  the 
vulcanite.  The  similarity  in  method  of  production  and  form 
of  a  cast  accounts  for  the  retention  of  the  term  model,  even 
though  it  does  not  fulfill  the  pur])ose  of  a  model. 

IMPRESSION  TRAYS 

An  imjjression  tray  is  an  a])iiliance  used  for  conveying 
iTn])ression  material  to,  and  liolding  it  in  position  against,  the 
tissues  of  the  mouth  or  teeth  while  hardening.     It  is  also  of 


DEFIN'ITIOXS    OF    SOMK    COMMOXl.V     I'SEO    TERMS  35 

material  assistance  in  reiiuixiiiii'  the  impression  t'lom  the 
montli,  and  in  holding  the  parts  of  the  impression,  when 
fractured  and  removed,  in  correct  relation  to  each  other  while 
securing  the  cast. 

A  large  assortment  of  trays,  in  vai'ving  sizes  and  forms, 
and  constructed  of  metal,  rubber,  celluloid,  i)orcelain  and 
papier-mache,  are  proeurab](>  at  the  sui)ply  houses.  The 
trays  most  commonly  used  are  nuide  of  Britannia  metal,  brass, 
German  silver  or  aluminum,  all  of  which  uuiy  be  bent  with- 
out much  etfort.  This  latter  feature  is  an  imjiortant  one. 
since  the  stock  tray  will  require  more  or  less  moditication  in 
each  case,  to  meet  some  peculiar  unbalanced  or  abnormal  con- 
dition of  the  alveolar  ridge  or  oral  tissue. 

The  other  classes  of  trays,  l)eing  rigid,  are  incapable  of 
much  change,  and  are  therefore  limited  in  their  application. 
In  difHcult  cases,  special  trays  are  frequently  constructed  of 
block  tin  by  casting,  or  from  sheet  metal  by  swaging,  the  de- 
tails of  which  will  be  given  later. 

TRAY  NOMENCLATURE 

The  various  siirfaces  of  the  oral  cavity  are  definitely 
named  and  those  areas  of  the  inipi-essicm  tray  that  come  in 
close  proximity  to  these  oral  surfaces  are  named  accordingly. 
For  instance,  the  outer  surfaces  (right  and  left)  of  the  ujijier 
and  lowei'  alveolar  arches,  fi-oni  the  distal  of  the  cusiuds  back 
ward,  are  termed  the  JutccdJ  siirldccs  because  of  the  close 
proximil\-  of  the  buccal  muscles  to  these  surfaces.  From  cus- 
pid to  cuspid,  anteriorly,  the  outei'  surfaces  of  the  arches  are 
called  the  labial  surfaces  because  the  labial  muscles  are  in 
close  proximity.  Those  areas  on  the  imier  side  of  the  l)order 
that  are  touched  by,  and  are  in  close  ]u-oximity  to,  the  tongue 
are  termed  lingual  surfaces. 

In  order  to  describe  clearly  the  adjustment  of  the  tray 
and  the  taking  of  im]iressions,  the  tray  nomenclature  as 
given  by  Dr.  G.  IT.  Wilson  in  "Dental  Prosthetics"  will  be 
made  use  of. 

"A  tray  has  a  hitihi  and  a  IuiikUi'.  The  Ixxly  consists  of 
a  ^00/- and  faiigcs.  ITjiper  trays  have  a  raiilf  portion.  There 
are  two  types  cf  floors,  oval  for  edentulous  jaws  and  fat  for 
accommodating  the  remaining  teeth.  The  flanges  are  called 
outer  and  inner.  The  outer  flange  has  two  portions,  the  an- 
terior, or  labial,  and  the  ]iosterior,  or  buccal.  The  dividing 
line  is  the  proximity  of  the  distal  surface  of  the  cuspid  tooth. 


36  DEFINITIONS    OF    SOME    COMMONIA'     ISEl)    TERMS 

TIk'  inner  liange  is  called  tlie  lingual  tiange.  The  surfaces  of 
the  tray  are  named  for  the  surfaces  they  aijproxiniate,  as 
maxillary,  labial,  buccal  and  lingual." 

"The  vault  portion  spans  the  space  described  by  the 
curve  of  the  lingual  flange  of  the  ui)per  tray.  The  handle 
is  an  extension  from  the  union  of  the  floor  and  the  anterior 
flange. ' ' 

A  tray  when  fitted  should  conform  closely  in  general 
outline  and  contour  to  the  mouth.  Since  it  receives  or  par- 
tially encloses  the  oral  tissues,  it  should  be  slightly  larger  to 
accommodate  the  impression  material,  a  uniform  space  of 
about  one-eighth  of  an  inch  or  less  between  the  tray  and 
tissues  being  sufficient  for  this   purpose. 

Conforming  the  tray  to  meet  the  conditions  mentioned, 
viz.,  close  adaptation  and  uniform  space  for  impression 
material,  is  accomi)lished  )iy  liending,  cutting,  or  making 
addition  to  the  tray  at  points  where  deficient.  Occasionally 
all  three  methods  are  resorted  to  in  adjusting  a  tray  to  a 
given  case. 

CONFORMING  THE  TRAY  BY  BENDING 

Trays  are  narrowed  or  widened  by  lieuding  tlie  flanges 
inward  or  outward,  or  by  compressing  or  expanding  the  body 
of  the  tray  across  its  buccal  diameter.  Compression  of  the 
])ody  of  upper  trays  increases  and  expanding  reduces  the 
height  of  the  vault  portion. 

In  lower  trays,  decreasing  the  buccal  diameter  l)y  bend- 
ing the  body  of  the  tray  usually  narrows  the  sjiace  between 
the  labial  and  lingual  flanges  anteriorly.  To  correct  this 
fault  the  lingual  flange  can  be  slit  in  the  median  line  and  the 
adjacent  portions  bent  and  allowed  to  overlap  so  as  to  gain 
the  necessary  space.  The  flanges  are  l)ent  inward  or  outward, 
as  the  position  and  form  of  the  border  indicates,  always  keep- 
ing in  mind  two  points — the  maintenance  of  the  proper  space 
for  the  reception  of  impression  material,  and  freedom  from 
nniscle  impingement  by  the  flanges. 

CONFORMING  BY   CUTTING 

Frequently  it  l)ecomes  necessary  to  reduce  the  height 
of  the  flanges  of  a  tray,  particulai'ly  in  edentulous  cases. 
While  trays  with  deep  or  wide  flanges  may  be  used  in  such 
cases  and  fairly  good  impressions  of  the  mouth  secured,  it 
will,  in  most  eases,  be  found  that  the  labial  or  buccal  muscles, 
or  both,  have  been  distorted  and  forced  out  of  normal  posi- 


DEFI.N'ITIOXS    OF    SOME    COMMOXLY     USED    TERMS  'i1 

tion.  In  fact,  the  i'(iin])r('ssi(>ii  may  Ix'  so  scN'erc  as  to  i)blit- 
erate  the  surface  iudicatioiis  n\'  their  presence  or  jiosition 
on  the  cast  when  secured. 

These  nnisch's  and  the  freinun  frequently  have  their  ori- 
gin near  the  crest  or  maxilhiry  portion  of  the  alveolar  process, 
while  the  border  itself  may  he  deep  or  high,  and  if  not  con- 
sidered in  outlining  the  peripheral  margin  of  the  base  plate, 
may  become  active  causes  of  displacement  by  lifting  the  den- 
ture off  the  crest  of  the  border,  thus  breaking  the  adhesion. 

It  is  foimd  that  by  selecting  trays  with  narrow  flanges 
which  do  not  impede  the  muscular  action,  and  having  the  i)a- 
tieut  exercise  these  muscles  at  the  proper  time,  while  the 
impression  material  is  still  soft,  that  their  ]tosition,  under 
tension,  can  be  (h'ternrmcd  and   indicated  on  the  iin]n'essi(in 


and  the  iieripheral  outline  of  the  denture  ytroperly  laid  on  the 
cast. 

Therefore,  in  selecting  trays  for  edentulous  cases,  the 
Avidtli  of  the  flanges  should  be  noted;  when  too  wide,  the 
excess  should  be  cut  away  with  the  shears,  and  the  margins 
smoothed  with  a  file  to  prevent  tissue  injury,  should  the 
trimmed  margin  be  forced  through  the  impression  material. 
In  very  flat  upper  arches  it  is  at  times  necessary  to  cut  away 
almost  the  entire  labio-buccal  flange,  while  in  lower  cases 
both  outer  and  inner  flanges  are  frequently  to  a  great  extent 
removed.  The  goveruing  factor,  in  all  cases  of  flange  cutting, 
is  the  form  of  the  bony  tissue  or  border  enclosed  by  the  tray 
and  the  muscidar  attachments  to  the  border  with  which  the 
flanges  may  interfere. 

A  commop  location  calling  for  the  iise  of  the  shears  is  in 
the  median  line  of  both  upper  and  lower  trays,  in  notching 
the  labial  flanges  to  relieve  impingement  at  this  point  and  on 
the  lingual  of  the  lower  to  obviate  contact  with  the  lingual 
frenum. 


3S  DEPINITIOXS    OF    SOMP:    COMMONLY     USED    TERMS 

MAKING  ADDITIONS  TO  THE  TRAY 

When  tlie  tray  selected  is  of  correct  outline  form  and 
generally  siiitalile  to  the  case,  but  slightl.v  deficient  in  some 
locations,  additions  may  be  nmde  where  required  by  build- 
ing up  the  deficient  ])ortiou  with  wax  or  modeling  com])ound, 
or  by  splicing  a  ])iece  of  metal  to  the  tray.  The  most  common 
location  for  building  u))  a  tray  is  on  the  vault  portion,  increas- 
ing its  height  and  frequently  extending  it  posteriorly.  This 
applies  almost  exclusively  to  trays  designed  for  plaster  im- 
pressions, both  full  and  i^artial. 

In  most  cases  of  ])laster  impressions,  better  results  can 
l)e  secured  by  taking  a  i)reliminary  impression  in  beeswax  or 
modeling  com|)ound,  cutting  off  the  excessive  surplus  and 
using  this  preliminary  impression  as  a  tray  for  holding  the 
plaster.  In  partial  cases  the  wax  or  compound  is  removed 
from  around  the  impressions  of  the  teeth,  thus  enlarging  the 
ojjenings  to  make  room  for  a  fair  thickness  of  plaster  to  sur- 
round the  teeth,  so  thai  when  fractured  the  parts  may  be 
readily  replaced. 

Where  marked  irregularity  of  the  border  is  noticeable, 
or  in  some  cases  where  a  few  of  the  natural  teeth  are  present, 
it  is  sometimes  advisable  to  construct  a  tray  for  the  case. 
This  may  be  done  by  casting  it  of  block  tin  or  some  fusible 
metal,  or  by  running  a  die  and  counterdie  and  swaging  a  tray 
of  brass,  German  silver  or  aluminum.  Or  by  swaging  a  tra>' 
of  Ash's  metal  over  plaster  casts  in  screw  press  with  rubber 
pads. 

SPECIAL  TRAYS 
CAST 

Secure  as  good  an  impression  as  possible  with  the  trays 
at  hand.  From  this  a  cast  is  formed,  and  over  the  cast  a  sheet 
of  wax  is  molded  to  represent  the  form  of  the  desired  tray, 
including  a  handle.  The  wax  pattern  is  removed  from  the 
cast  and  invested  in  some  suitable  investment  comjiound, 
placing  the  handle  portion  u]iward.  Heat  is  then  applied  and 
the  wax  burned  out,  after  which  the  fusible  metal  is  poured 
in  through  the  gate  left  by  melting  out  the  wax  handle. 

Dr.  Walter  M.  Bartlett  of  St.  Louis  has  followed  a  sim- 
ilar method  for  many  years,  but  has  very  materially  im- 
proved the  efficiency  of  the  tray  by  beading  it.  He  applies  a 
narrow  wax  rim  entirely  around  the  inner  periphery  of  the 
wax  model,  which  is,  of  course,  reproduced  in  the  casting. 
This    rim    or    bead    serves    to    confine    the    impression    ma- 


DEKINITIOXS    OF    SOME    COMMONLY    USED    TERMS  39 

terial  witliin  the  compass  of  the  tray,  and  minimizes  the 
anionnt  required.  A  tray  eonstrneted  in  this  manner,  when 
introduced  in  tlie  mouth  without  any  impression  material 
present,  Avill  fre(|uently  exliihit  a  ninrkcd  amount  of  adhesive- 


ness due  to  close  ])eripheral  adaptation.  In  constructing  the 
tray,  plaster  may  he  used  as  the  matrix  and  the  latter  may 
he  of  the  tliree  or  four  piece  separable  ty]ie,  hut  the  pieces 


MATRIX    OF    ri.ASTKR    IX    nHICH    TRAY    IS    TO    HE    CAST 

should  he  reasoualily  tliin,  and  before  casting-  should  be 
warm  and  dry.  The  several  pieces  are  held  together  with 
binding  wire. 

SWAGED  TRAYS 

A  swaged  tray  may  lie  made  by  securing  a  die  and 
counterdie  from  tlic  cast  ol'  tlic  mouth.  I'rass,  German  silver 
or  aluminum,  usually  L'4  or  Jl'  gauge,  is  cut  to  appropriate 


40  dp:finitio.\s  of  some  commoxly  i'Sed  terms 

si/,(',  Hiid  coiiror-incd  ))y  swaging.  I'lic  sur])lus  is  ji-iiiiiiicd 
away  to  give  the  tray  its  correct  ])eriplieral  outline,  and  a 
liandle  aitaehed  in  the  nsnal  location  1)y  soldering  or  riveting. 

SPECIAL  TRAYS  OF  IDEAL  BASE  PLATE 

A  (|uickly  formed  and  convenient  tray  for  ])laster  im- 
pression work  can  be  made  by  adapting  a  sheet  of  special 
Ideal  base  plate  to  the  cast,  secured,  as  in  the  cases  just 
mentioned.  The  surplus  is  trimmed  off  and  correct  periph- 
eral outline  given  the  base  plate;  a  piece  of  12-gauge  Ger- 
inan  silver  or  steel  wire  is  bent  to  the  form  of  the  border  and 
extended  forward  to  serve  as  a  handle  and  laid  on  the  base 
plate.  With  a  hot  spatula  the  scraps  can  be  melted  over  the 
wire  and  at  various  points  to  strengthen  the  tray  and  give  it 
necessary  rigidity.  Sometimes  a  second  sheet  of  base  plate 
is  added  to  the  first,  the  wire  being  between  the  two  layers. 

METALLIC  EXTENSIONS  OR  ADDITIONS  TO  STOCK  TRAYS 

The  distal  vault  portion  of  a  tray  is  frequently  too  short 
to  suiiport  the  plaster  against  this  area  of  the  mouth.  An 
extension  may  quickly  be  made  by  cutting  a  piece  of  sheet 
metal  of  suitable  form  so  as  to  overlap  the  vault  portion. 
Punch  two  or  three  holes  to  correspond,  through  the  addition 
and  the  tray,  with  the  plate  punch,  and  attach  together  with 
l)inding  wire.  Usually,  however,  additions  to  the  vault  por- 
tion are  made  quite  as  well  and  more  quickly  with  wax  or 
compound. 

In  taking  im]3ressions  where  modeling  compound  is  the 
sole  medium  used,  tray  extension  or  contouring  is  not  so 
essential,  since  the  compound  which  escapes  distally  can  be 
conformed  and  adapted  to  the  tissues  with  the  fingers,  as  well 
in  this  location  as  peripherally. 

The  modeling  compound  tracing  sticks  are  very  con- 
venient for  making  slight  additions  to  trays,  particularly 
along  the  rim  portion.  All  additions,  whether  of  wax,  com- 
l)ouiid  or  metal,  should  be  tested  by  trial  in  the  mouth  before 
introducing  the  impression  material. 

As  a  rule,  trays  that  are  too  large  and  with  labio-buccal 
flanges  much  too  broad,  are  selected  for  edentulous  cases. 
When  it  is  undei-stood  that  with  close-fitting  trays  and  a  mini- 
muni  (piantity  of  im])ression  material,  more  accurate  impres- 
sions can  be  secui-ed  than  when  an  excessive  amount  is  used, 
much  of  the  difficulty  arising  from  lack  of  adaptation  of  den- 
tures will  be  eliminated. 


C  TT  A  P  T  K  R    V  T 
IMPRESSIONS  AND  IMPRESSION    MATERIALS 

GENERAL  REMARKS 

An  impression,  in  its  dental  sense,  is  an  imprint,  a  re- 
verse cojiy  or  connterpart  of  some  portion  of  the  oral  cavity. 
It  is  seenred  by  aiiplying  to  the  parts  involved,  some  plastic 
medium  that  conforms  readily  to  the  surfaces  impressed,  and 
which,  when  adapted,  will  harden  and  retain  its  form. 

The  surfaces  embraced  by  an  impression  may  vary  from 
an  area  involving  only  a  small  portion  of  the  mouth,  or  even 
of  a  tootli,  to  one  containing-  the  full  complement  of  teeth, 
together  with  the  alveolar  border  in  which  they  are  imbedcied, 
and  in  edentulous  cases  (mouths  devoid  of  teeth)  to  the  bor- 
der and  adjacent  areas. 

The  character  and  size  of  the  substitute  or  rejjlacement 
under  construction  determines  the  area  to  be  included  in  an 
impression.  It  is  a  safe  plan  generally,  and  in  partial  cases 
especially,  to  extend  the  impression  beyond  the  areas  actually 
involved  in  an  operation,  since  when  the  cast  is  secured,  a 
better  conce])tion  may  lie  formed  of  the  I'elationship  and  pro- 
liortions  of  the  contem]ilated  sul)stitute  to  the  remaining  nat- 
ui'al  teeth  than  when  the  impression  is  restricted  in  size. 

Absolute  accuracy  of  the  impression  in  representing  tlie 
parts  impressed  is  positively  essential,  except  in  cases  to  be 
noted  later,  and  no  effort  should  be  spared  to  secure  such  an 
end,  since  the  cast,  derived  from  an  impression,  becomes  the 
basis  and  forms  the  ground  work  on  which  most  technical 
procedures  are  carried  out.  If  the  foundation  is  faulty  and 
imperfect,  the  structure  built  thereon  will  lie  pro]iortionately 
inaccurate,  and  a  probable  failure. 

It  does  not  follow,  however,  that  all  impressions  for  any 
purpose  should  be  taken  in  tlie  same  manner  and  under  the 
same  conditions,  nor  do  impressions  always  represent  a  true 
reverse  copy  of  the  parts  im^iressed.  For  instance,  it  is  found 
that  in  certain  caSes  pressure  sufficient  to  distort  or  com- 
press the  soft  and  yielding  tissues  of  the  mouth  is  desirable, 
while  in  other  cases,  siich  compression  is  not  only  uncalled 
for,  but  detrimental  to  tinal  results.  In  any  procedure,  the 
l)rosthetist  must  first  plan  his  substitute,  and  then  thought- 
fully and  skillfully  work  out  the  details  of  the  impression  to 

41 


42  IMPRESSIONS    AND    IMPRESSION     MATERIALS 

uuH't  tlic  i('(|uir('iiiciits  of  tilt'  case  in  hand.  Witliout  doubt, 
most  of  the  misliai)s  and  mi.sfits  in  prostiietic  procedures  are 
due,  in  part,  to  faulty  manipulation  in  impression  taking. 
The  slighting  of  this  o})eration  in  the  carrying  out  of  details 
in  a  perfunctory  and  careless  manner,  is  a  widespread  evil, 
and  cannot  be  too  strongly  condemned. 

It  sliould  be  the  amliition  of  the  student,  and  of  every 
practitioner  as  well,  to  perfect  himself  in  the  technical  details, 
the  art  of  impression  taking,  so  that  he  may  overcome  any 
obstacle  and  meet  every  emergency  that  may  arise.  A  thor- 
ough understanding  of  the  conditions  governing  each  case, 
together  with  painstaking  effort  in  the  handling  of  the  mate- 
erial  employed,  both  in  and  out  of  the  oral  cavity,  will  ac- 
comiilisli  the  desired  results. 

IMPRESSION   MATERIALS 

Since  accuracy  in  impression  taking  is  an  absolute  ne- 
cessity, the  choice  of  the  medium  used  for  this  i)urpose  re- 
quires careful  consideration.  Tlie  following  statement  of  the 
requirements  of  an  impression  material  represents  tlie  ideal, 
rather  than  the  aftaiiinhle,  because  no  sxilistance  has  yet  been 
found  which  is  absolutely  free  from  imperfections.  Several, 
however,  approach  closely  to  the  ideal  requirements,  and  with 
a  knowledge  of  the  desirable  and  detrimental  qualities  of  each, 
fairly  satisfactory  and  accurate  results  may  be  secured  in 
most  instances. 

REQUIREMENTS 

An  impression  material  should  possess,  as  nearly  as  pos- 
sible, the  following  qualities : 

First — It  should  be  composed  of  some  material  that  will 
not  be  unduly  disagreeable  to  the  patient. 

Second — It  shoidd  become  plastic  at  a  temperature  the 
oral  tissues  can  tolerate. 

Third — It  should  copy  accurately  the  fine  lines  and  ir- 
regular surfaces  to  which  it  is*  applied,  and  retain  the  form 
so  coined,  without  becoming  distorted  in  removal  from  the 
mouth. 

Fourth — It  should  harden  in  a  reasonably  short  time — 
from  one  to  three  minutes. 

Fifth — It  should  neither  expand,  contract  nor  war])  at 
ordinary  teini)eratures  to   any   a]i]>recial)le  degree. 

CLASSIFICATION 

Several  varieties  of  impression  materials  are  in  common 
use.  These  may  be  divided  into  two  groups.    First,  those  which 


IMPRESSIONS    AND    IMPRESSION     MATERIALS  43 

are  rendered  plastic  with  a  liquid  and  harden  by  crystalliza- 
tion. This  class  includes  plaster,  impression  compounds,  and 
the  various  dental  cements,  as  oxy-chloride  and  oxy-i)hos- 
pliate  of  zinc,  magnesia,  and  the  silicates. 

The  second  class  embraces  those  materials  that  are  ren- 
dered plastic  by  heat  and  harden  on  cooling.  The  principal 
materials  in  this  group  are  modeling  compound,  beeswax  (both 
pure,  and  combined  with  other  substances),  paraffin  and 
gntta  percha.  The  most  commonly  used,  as  well  as  practical, 
of  these  materials  are  modeling  compound  and  gutta  percha. 

GROUP  I 

Impression  Materials  That  Harden  by  Crystallization 
PLASTER  OF  PARIS 
riastcr   of    Paris   is    so   called   because   in   former   times 
large  (piantities  were  produced   at   the   gyi)sum  (juarries  at 
Montmarte,  near  Paris. 

Plaster  is  made  from  gyjjsum.  a  hydrated  calcium  sulphate 
the  chemical  formula  of  which  is  CaS04  -f-  iH.O.  It  occurs  in 
a  number  of  different  forms,  the  transparent  and  crystalline 
variety  being  called  selciiitc,  from  the  (ireek  word  selene, 
meaning  the  moon,  due  to  its  peculiar  soft  lustre.  This  variety 
sometimes  occurs  in  large  plates,  and  formerly  was  used 
instead  of  glass  for  window  lights.  In  this  form  it  some- 
what resembles  mica,  but  is  much  softer,  and  the  plates,  al- 
though slightly  flexible,  are  brittle  and  inelastic.  When  it 
occurs  in  needle-shaped  crystals  or  in  fibrous  form,  it  is  known 
as  fibrous  gypsum  or  satin  spar.  The  ordinary  massive, 
oi)aque  crystals  are  called  gypsum.  This  form  presents  many 
varying  colors — red,  brown,  black  and  yellow — from  the  en- 
closed coloring  matter,  usually  the  oxides  of  iron.  It  also 
occurs  amorphous,  in  comi>act,  ti'anslucent  and  snowy  white 
masses,  and  is  then  termed  alahasfcr.  This  variety  is  very 
beautiful,  and  as  it  is  easily  carved,  it  is  much  used  for  small 
ornaments  and  statuary. 

Gypsum  frequently  contains  more  t)r  less  foreign  matter, 
such  as  sanck  clay,  oxide  of  iron,  or  calcium  or  magnesium 
carbonate.  These  impurities  are  not  usually  present  in  ex- 
cessive quantities,  and.  when  not  exceeding  three  per  cent, 
do  not  seriously  impair  the  conmiercial  grades  of  ])laster. 
Dental  jilaster,  iiowexcr.  should  be  )>rodu<'e(l  from  the  purest 


■M  IMl'liKSSIONS    AND    I.MI'HKSSIOX     MA'I'KKI  AI.S 

liualily  of  oypsuni  o))tainable,   and  special   care  uslmI   in   it.s 
inaimracturc  to  iiisurp  niiifoi-m  results. 

MANUFACTURE  OF  PLASTER 

Dental  plaster  is  a  half  hydrated  calcium  sul- 
pliate,  formula  CaSO*  +  ]/2H,0.  It  is  formed  by  heating 
gypsum,  CaSoj  +  2H.(),  at  a  temperature  ranging  from  130 
deg.  to  190  deg.  C.  If  heated  above  190  deg.  C,  the  product 
is  uiisuitalile  for  dental  jnirposes,  but  a  plaster  is  produced 
which  has  a  wide  range  of  usefulness  in  the  manufacturing  and 
building  fields. 

Two  general  methods  are  employed  in  the  conversion  of 
gyi)sum  into  plaster.  First,  by  pulverizing  and  then  de- 
hydrating. Second,  by  dehydrating  and  then  pulverizing  the 
rock.  The  first  method  and  the  oldest  is  known  as  the  kettle 
process,  in  which  the  gypsum  is  crushed,  ground,  tlien  placed 
in  large  kettles  and  subjected  to  heat.  This  process  drives 
off  some  of  the  water  of  crystallization,  and  if  conducted  at 
the  right  temperature  and  for  the  proper  length  of  time,  will 
produce  a  fairly  uniform  half  liydrate.  Glasenap,  however, 
says  that  on  account  of  tlie  difliculty  of  maintaining  a  perfectly 
uniform  temperature,  a  small  per  cent  of  the  mass  may  be 
reduced  below  a  half  hydrate  or  become  a  partially  dehydrated 
half  hydrate,  which  renders  the  ])roduct  slower  setting  than 
the  half  hydi'ate. 

The  second  method  is  a  more  recent  one,  made  possible 
by  improved  machinery.  The  gypsum  is  broken  up  into  mod- 
erate sized  pieces,  and  htirned  to  drive  off  a  portion  of  the 
water  of  crystallization,  reducing  it  to  a  half  hydrate.  It  is 
then  led  into  a  rotary  drum  and  pulverized.  In  some  cases, 
by  means  of  a  partial  vacuum,  the  finest  particles  of  the  pul- 
verized ])roduct  are  drawn  out  into  a  suitable  receptacle,  and 
this  constitutes  the  better  grade  of  dental  plaster.  The  qual- 
ity of  the  plaster,  however,  as  before  stated,  is  also  dependent 
upon  the  purity  of  the  gypsum  used  in  its  manufacture,  the 
purer  varieties  producing  the  best  grades. 

PHYSICAL  PROPERTIES 

Regardless  of  the  fact  that  jilastcr  of  Paris  has  been  em- 
ployed for  many  years  in  dentistry,  but  little  knowledge  of 
its  physical  properties  is  current  among  those  who  use  it, 
further  than  that  it  becomes  ])lastic  by  mixture  with  water, 
that  it  sets  or  hardens  quickly,  and  that  it  is  more  or  less  re- 


IMPRESSIONS    AND    IMPRESSION     MATERIALS  45 

sistant  to  stress.  Why  or  how  it  sets,  or  liow  imich  pressure 
it  will  withstand  without  hecomiug  distorted,  are  points  of 
vital  importance,  practically  unknown  \v,  or  at  least  disre- 
garded by,  prosthetists. 

The  entire  bulk  of  jtlaster  used  by  the  dental  profes- 
sion represents  but  a  very  small  per  cent  of  the  vast  output 
of  this  material.  Tlie  greater  ])ortion  is  used  in  the  arts, 
building  trades,  and  in  glass-making  industries.  A  numl)er 
of  investigators,  thoroughly  competent,  by  training  and  with 
suitable  apparatus,  have  made  extended  researches  in  the 
chemical  and  physical  aspect  of  this  material,  and  some  of  the 
results  of  tlieir  findings,  together  with  some  experimental 
work  carried  out  liy  the  writer,  will  here  be  presented. 

Professor  M.  Grlasenapp,  chief  of  the  technical  department 
of  the  University  of  Eiga,  Russia,  an  authority  on  Iniilding 
materials,  has  gone  into  this  subject  exhaustively.  Although 
not  relevant  in  all  respects  to  the  use  of  plaster  in  the  pros- 
thetic field,  the  following  extracts  from  his  writings  will  shed 
much  light  on  the  chemical  as  well  as  the  physical  aspects  of 
this  material.  The  translation  of  Glasenapp's  work  is  by  Dr. 
W.  Michaels  of  Chicago. 

SETTING 

"If  ordinary  plaster  of  paris,  representing  mainly  the 
half  hydrate  C'aSOj  -f  l/^HoO  is  mixed  with  water  and  exam- 
ined under  the  microscope,  a  lively  process  of  crystallization 
can  be  observed  to  set  in  after  five  or  six  minutes.  In  the 
beginning,  very  thin  needle-crystals  form  on  the  cover  glass 
and  shortly  afterwards  also  in  the  liquid  and  on  the  particles 
of  gyi)sum.  After  15  or  20  minutes,  single  needle-crystals 
and  groups  of  them  can  be  seen  in  great  numbers,  and  espe- 
cially the  larger  fragments  of  the  half  hydrate  are  covered 
with  needle-crystals  radiating  from  them,  also  the  character- 
istic twin  crystals  appear  abundantly.  As  fast  as  the  crystals 
form,  the  original  ]iarticles  of  the  half  hydrate  disappear. 
After  an  hour  they  are  completely  used  up  and  transformed 
into  crystajs,  whereby  the  larger  fragments  of  them  be- 
come centers  of  accumulation  of  crystals,  while  the  smaller 
have  been  converted  into  isolated  star-shaped  groujis.  After 
the  same  gyjisnm  was  heated  for  several  hours  to  a  teni])era- 
tnre  of  170  deg.  C.  (whereliy  the  amount  of  water  still  re- 
mained ():2  per  cent,  corres])onding  with  the  half  hydrate) 
crystallization  began  after  •"!  t"  4  iiiiiiutcs,  and  was  prac- 
tically completed  afti-r  half  an  hour;  imly  the  largest  particles 
required  almost  an  hour  to  dissolve  and  re-erystallize." 


4P  IJIPRESSIONS    AND    IMPrtRSSION    MATERIALS 

"Tlie  ])r('Sont  stiili'  ot'  our  knowledge  ol'  llic  liardciiiiif;-  ol' 
liypsmn  is  that,  after  having  l)een  mixed  witli  water,  tlie  hall' 
hydrate,  plaster  of  paris,  and  the  first  anhydrous  modification 
ol'  gyi)siun,  wliicli  is  snp]iosed  to  l)e  formed  hetween  !'.]()  and 
■JDO  deg.  C,  form  over-satnrated  solutions,  from  whieh  the  di- 
liydrate  precipitates  in  the  sliapc  of  small  crystals,  a  process 
which  is  finished  only  aftci-  nil  hall'  hydrate  or  anhydrite  is 
dissolved  and  transformed  into  crystals  of  di-hydrate.  Ap- 
parently tlie  lialf  hydrate  goes  into  solution  more  rai)idly  and 
crystallizes  in  a  shorter  time  than  the  first  modification  of 
anhydrite;  at  least  I  conclude  this  from  the  fact  that  this  first 
anhydrite,  which  is  considered  tn  he  'easily  s()lul)le,'  dis- 
solves the  more  slowly  at  a  higher  tcmiteraturc  than  it  was 
pi'odnced."      *      *      * 

"To  judge  from  excii  llie  most  j-eeent  statemenis  to  he 
found  in  hooks  on  chemical  technology,  only  a  few  chemists 
seem  to  he  aware  of  the  fact  t'.iat  a  complete  transformation 
of  every  particle  of  i)laster  is  an  essential  point  in  its  hard- 
ening. Owing  to  the  greater  soluhility  in  water  of  burnt 
gyi)smn  over  crystallized  gypsum,  the  hardening  of  plaster 
of  paris  has  l>een  attriljuted  to  a  process  of  crystallization  for 
some  time;  yet,  this  crystallizing  has  mostly  been  regarded  as 
of  secondary  importance.  The  ]>r('vailing  explanation  was 
that  the  partly  or  completely  dehydrated  gypsiun  hydrated, 
combined  with  water,  and  hardened  without  changing  its 
form  or  place;  that  is  to  say,  without  previous  going  into 
solution.  The  process,  therefoi'e,  was  considered  to  be  sim- 
ilar to  the  hydration  of  calcined  magnesia,  and  in  many  per- 
sons' opinion  seemed  to  resemble  the  hardening  of  Portland 
cement  and  of  hydraulic  limes.  This  erroneous  conception 
likewise  led  to  the  Itelief  that  the  strength  of  the  casting  de- 
])ended  ui)on  the  hardness  of  the  native  gypsum  from  which 
the  plaster  was  burned.  In  fact,  the  ditference  in  hardness 
between  two  kinds  of  raw  gyi)sum  is  a  matter  of  no  conse- 
(|ncnce. 

THE   STRENGTH   OF   HARDENED  GYPSUM 

The  strength  of  the  liardeiied  gyjisum  depends  solely 
upon  the  shape  of  the  ci'ystals,  upon  their  size,  and  ujjon  their 
more  or  less  close  contact.  The  more  slowly  the  plaster  hard- 
ens, the  larger  and  stronger  the  crystals  of  di-hydrate  grow, 
and  the  less  water  is  mixed  with  the  plaster,  the  denser  and 
less  ]iorous  the  casting  becomes.  Molds  which  absorb  water 
readily,  therefore  rc(|uire  a  jilaster  coiitaining  as  little  an- 
hydrite as  ])ossible;  furthermore,  such  molds  call  foi'  a  lib 


IMPRESSIONS    AND    IMPRESSION     MATERIALS  47 

eral  aiiioiiiit  of  water.  Adinixturtvs  to  the  ])laster,  wliieli  re- 
tard the  setting,  so-ealled  negative  eatalyzers,  create  large 
crystals  and  consequently  are  tlie  cause  of  more  resisting  and 
stronger  castings."     "     '"     * 

"The  microscopical  examination  of  samples  of  powdered 
gyjisum,  burnt  at  temperatures  higher  than  :200  deg.  C,  teaclies 
nothing  essentially  different  from  the  behavior  of  the  half 
hydrate  or  plaster  of  paris  toward  water.  Only  the  ability 
of  this  anhydrite  to  form  over-saturated  solutions  is  impaired; 
it  is  limited  the  more  the  higher  the  burning  temperature  has 
been,  and  the  longer  the  material  was  heated.  Transformation 
into  crystals  of  di-hydrate  takes  place  in  the  same  manner, 
but  more  slowly.  The  following  table  gives  the  various  tem- 
peratures to  which  the  gypsum  was  exi)osed,  as  well  as  the 
time  of  heating  in  many  instances,  and  the  beginning  and  ter 
mination  of  the  process  of  crystallization  corresponding  with 
them : 


Burnino;    Time 


Tt 

Miiperature 

107 

Centigrade 

.130 

" 

170 

200 

( ( 

200- : 

250     " 

250-; 

;!00    " 

400 

" 

450 

" 

hours 


ALLIZATION" 

OF    PLASTER 

Beginning    of 

Crystallization 

Crystallization 

Completed   After 

0-  7   minutes   i  U  hour 

G-  7 

1.,    to    1     houi 

3-  4 

i/o  hour 

30-45 

iZ  day 

00 

7  days 

40 

O          i  I 

l->4  hours 

17     " 

10  davs 

30      ' ' 

14 


1  o  hour 

"As  the  hardening  of  the  castings  of  plaster  is  caused 
mainly  by  the  transformation  into  the  di-hydrate,  and  as  this 
process  of  crystallization  is  the  same  also  for  'overburnt' 
gypsum,  the  lack  of  hardening  in  the  case  of  the  latter  must 
doubtlessly  be  ascribed,  wherever  it  has  I)een  observed,  to  the 
drying  out  of  the  uncovered  castings;  tlie  process  of  crystal- 
lization, therefore,  was  interruj^ted  and  the  casting  could  not 
ol)tain  its  full  strength,  which  it  otherwise  would  have  done. 
This  must  happen,  esjjecially  in  cases  in  which  the  pi'ocess 
of  crystallization.takes  a  number  of  days.  With  gypsum  liurnt 
at  200  deg.  o^ntigrade  the  transformation  into  crystallized 
di-hydrate  is  almost  completed  within  24  hours;  only  the 
larger  particles  take  more  time,  and  as,  especially  in  the  case 
of  large  castings,  still  a  sufficient  amount  of  water  remains 
for  crystallization  after  24  or  even  4S  hours,  this  explains 


48  IMPRESSIONS    AND    IMPRESSION    MATERIALS 

the  fact  tliat  gypsum,  hurlit  at  200  dog.  centigrade  and  even 
above  this  temperature,  unless  heated  for  too  long  a  time,  or 
mixtures  of  this  with  standard  plaster  of  Paris,  show  normal 
hardening  and  high  strength.  Rohland,  who  assumes  that 
only  a  small  portion  of  the  gypsum,  its  active  part,  takes  a 
share  in  the  hardening,  is  therefore  mistaken;  the  entire  mass 
is  active,  if  given  time  and  opportunity  to  exhibit  its  activity, 
which  is  greatly  diminished,  indeed.  'Complete  hydration 
and  transformation  into  di-hydrate  without  hardening,'  as 
Rohland  describes  it,  is  consequently  out  of  tlie  question.  The 
term  "overburnt  or  dead  burnt"  gypsum  is  therefore  mis- 
leading; the  proper  name  for  gypsum  burnt  at  temjieratures 
between  200  deg.  and  300  deg.  centigrade  would  be  'slow 
setting. ' 

"The  process  of  hardening  of  such  slow  setting  jjlaster 
shows  two  distinct  phases.  In  the  first  place,  the  plastic 
dough  assumes  a  dull  surface  and  becomes  stiff  owing  to  the 
transformation  of  the  anhydrite  into  the  half  hydrate.  This 
point  is  reached  after  1  or  2  minutes  in  the  case  of  gypsum 
heated  to  200  deg.  centigrade  and  after  30  minutes  or  more 
with  gypsum  burnt  at  temperatures  between  250  deg.  and  300 
deg.  centigrade.  If  further  absorption  of  water  is  interrupted 
at  this  point  by  a  rapid  drying  process,  the  stiff  jjlaster  is 
found  to  contain  from  6  to  (>.5  per  cent  of  water  of  combina- 
tion, corresi^onding  about  with  the  half  hydrate.  During  the 
second  phase,  which  requires  more  time,  the  half  hydrate 
previously  formed  goes  into  solution  and  crystallizes  as  di- 
hydrate.  Setting  and  hardening  are,  therefore,  two  well  pro- 
nounced processes  in  this  case.  Castings  that  have  only  time 
to  set  yield  insufticient  strength;  they  must  be  given  time  to 
harden.        «     *     *     # 

SIZE   OF   CRYSTALS   OF   ORDINARY    PLASTER 

"The  reason  why  castings  made  from  ordinary  quick  set- 
ting plaster  are  low  in  strength  and  possess  little  resistance 
toward  atmospheric  influences,  is  evidently  to  be  found  in 
the  minute  size  of  the  interlacing  needle-crystals  of  di- 
hydrate,  which,  owing  to  the  rapid  process  of  crystallization, 
have  not  time  to  develop  and  grow  larger.  The  following 
table  illustrates  this  point  by  giving  the  dimensions  of  the 
crystals  in  millimeters  and  the  corresponding  temperatures 
at  which  the  various  kinds  of  quick-setting  and  slow-setting 
plasters  have  been  burned : 


IMPRESSIONS    AND    IMPRESSION    MATERIALS  49 

Largest  Dimensions  of  Crys- 
tals. 


Rurnino- 

Temperature. 

Diameter. 

Length. 

107-130 

centigrade 

0.0025 

mm. 

0.04  mm 

140 

" 

0.012 

" 

0.14     " 

250-300 

(I 

0.075 

" 

0.50     " 

400 

a 

0.050 

( ( 

0.35     " 

450  . 

_    " 

0.035 

" 

0.60     '* 

"Tlie  plaster  burnt  at  400  centigrade  was  heated  only  for 
half  an  hour;  that  burnt  at. 250-300  centigrade,  however,  for 
several  hours.  This  explains  the  ditTerenee  in  the  dimensions 
of  the  crystals.  The  first  two  of  the  plasters  given  in  the  jire- 
ceding  table  are  quick-setting,  the  last  three  slow-setting. 

"The  diameters  of  the  needle-crystals  of  the  plaster  burnt 
at  107-130  centigrade  are  30  times  smaller  than  those  origin- 
ating from  the  plaster  burnt  at  250-300  centigrade;  their  sec- 
tional areas  are,  consequently,  900  times  smaller.  It  is,  there- 
fore, evident  that,  other  things  being  equal,  a  casting  made 
from  slow-setting  plaster  must  show  greater  strength.  Hence, 
whenever  time  has  not  to  be  considered,  and  increased  strength 
of  the  casting  is  desired,  as,  for  instance,  in  the  case  of  stat- 
ues for  art  galleries  and  so  forth,  experiments  with  slow- 
setting  plaster  seem  to  bo  very  adxisablc. 

''In  conclusion,  the  various  calcined  produced  obtainable 
from  raw  gy^jsum  may  be  classified  in  accordance  with  the 
results  derived  from  the  foregoing  research.  The  limits  of 
temperatures  stated  must  only  be  considered  as  approximate 
figures,  of  course,  as  the  change  from  one  kind  to  the  other 
takes  place  very  gradually,  and  because,  as  repeatedly  stated, 
not  only  the  height  of  temperature,  but  also  its  duration,  deter- 
mine the  properties  of  the  calcined  gypsum  product. 

A.  Native   gypsum Di-hydrate  containing  two  mole- 

cules of  water. 

B.  107   centigrade Half  hydrate  containing  lo  mole- 

cule of  water. 

('.     107-170       centigrade.  .  .Consists  mainly  of  half  hydrate. 

D.  170-200  centigrade.  .  .More  or  less  dehydrated  half  hy- 
drate. Combines  with  water 
readily  until  half  hydrate  is  ob- 
tained. 
C.  and  D.  represent  the  commer- 
cial plaster  of  Paris. 


50  IMPRESSIONS    AND    IMPRESSION     MATERIALS 

K.     L'OO-'JaO       centigrade.  .  .(Vmtaiiis  a  very  small  aiiiomit  of 

water.  Sets  more  slowly  tliaii 
tlie  I'oi'mei'. 

F.  L'r)()-400       eeiitii'rade.  .  .(\)iitains  only  a  trace  of  water. 

Slow-setting.  B.,  ('.,  D.,  K. 
and  F.  foi'm  crystals  of  di-liy- 
drate,  if  mixed  with  water. 
Hardening  dne  to  crystalliza- 
tion. 

G.  400-750       centigrade.  .  .Completely     dehydrated,     anhy- 

drite, overhnrnt  from  a  prac- 
tical point  of  view. 

H.     750-800      centigrade.  .  .Gradual  transformation  into  the 

granular  modification  of  anhy- 
drite; heginning  of  the  forma- 
tion of  hydraulic  gyijsum. 
G.  and  H.  show  in  contact  with 
water.  No  hardening,  or  only 
very  imperfect  hardening. 

T.      800  centigrade.  .  .Hydraulic     gypsum      containing 

minute  grains  of  anhydrite. 

K.     900-1000    centigrade.  .  .Genuine     hydraulic     gypsum, 

grains  fully  developed. 

L.     1000-1400  centigrade.  .  .Hydraulic    gypsum     showing 

grains  increasing  in  size  and 
hardness  with  rising  tempera- 
tui"e.  The  i^ercentage  of  "basic 
calcium  sulphate"  likewise  in- 
creases in  the  same  ratio. 
I.,  K.  and  L.  harden  slowly  with 

water  without  crystallizing. 
G.,  H.,  I.,  K.  and  L.  crystallize 
with  alum  solution. 

"A  temperature  of  from  1300  deg.  to  1400  deg.  centi- 
grade, in  my  opinion,  can  be  employed  in  the  manufacture  of 
hydraulic  gypsum  only  in  cases  in  which  gypsum  does  not 
come  in  immediate  contact  with  the  fuel,  as,  for  instance,  in 
laboratory  experiments,  in  which  the  burning  is  done  witli 
gas. 

"Where  coal  is  used,  the  ashes  of  it,  as  well  as  the  reduc- 
ing carbon,  are  bound  to  contaminate  and  R]3oil  the  calcined 
product.  Moreover,  tem]ieratures  as  high  as  these  are  almost 
out  of  the  (juestion  in  ]n"actical  operations." 


IMPRESSIONS    AND    IMPKKSSION     MATERIALS  51 

TIk'  I'on'goiug  extracts  refer  esijeeially  to  the  eliemistry 
of  setting,  and  the  effects  of  varying  temperatures  and  time 
in  burning  on  the  time  of  setting  and  hardness  of  plaster. 
The  metliod  of  nianii)ii!ation  is  not  considered.  This  to  tlie 
prostlietist  is  a  matter  of  imi)ortance  that  cannot  be  over- 
looked. 

INFLUENCE    OF    MIXING    ON    QUALITY 

I'laster  mixi^d  at  a  medium  to  tliick  consisteucy  will  set 
more  rapidly  and  be  of  better  density  when  set  than  if  an  ex- 
cess of  water  is  present.  Too  thick  a  mix,  however,  should 
I)e  avoided,  ])articularly  where  accelerators  are  used,  as 
under  such  circumstances  the  setting  freciueutly  begins  before 
tlie  mass  is  of  uniform  ccmsistency,  and  further  stirring  breaks 
uji  the  already  forming  crystals,  'i'liis  interference  results 
in  a  mass  of  nnccrtaiii  density,  oflcntimcs  willi  nianv  si)ac('s 
present. 

Tlie  other  extreme,  too  much  water,  should  ))e  avoided,  as 
it  retards  the  setting,  and  the  plaster,  when  set,  is  less  resist- 
ant to  stress.  Various  substances  are  added  to  accelerate 
thb  setting,  particularly  in  impression  woi'k.  Common  table 
salt  (NaCl)  is  frequently  used,  but  should  never  be  incor- 
l)orated  in  ])laster  used  for  casts  for  vulcanite  work,  since  its 
atlinity  for  moisture  causes  rapid  softening  and  deterioration 
in  the  presence  of  steam  or  water.  Sulphate  of  i)otassium 
(K0SO4)  is  by  far  the  best  accelerator,  because  it  not  only 
hastens  the  setting,  but  lias  a  controlling  intluence  on  expan- 
sion. This  medium,  however,  should  not  be  used  in  east  con- 
struction for  the  same  reasons  that  apply  to  NaCl.  Potas- 
sium alum  has  lieen  highly  recommended  as  an  accelerator 
and  hardening  medium  for  plaster  in  dental  lalioratory  ])ro- 
cedures,  but  tests  made  with  this  substance  fail  to  verify  the 
claims  made  for  it. 

EXPANSION   OF   PLASTER 

The  tendency  of  plaster  to  ex]iand  during  and  after 
setting  and  the  deleterious  effects  of  this  movement  in  denture 
adaptation  has  long  lieen  recognized  Ity  some,  but  its  im- 
l)ortance  is  not  fully  understood. 

When  freshly  mixed  plaster  begins  to  set,  it  contracts 
slightly,  then  remains  stationary  foi'  a  short  lime,  then  ex- 
pauds,  and  after  assuming  a  thoroughly  dry  condition  it  again 
contracts  to  a  very  slight  degree.  From  fi  deg.  to  10  deg. 
rise  ill  tcnipcratni'c  is  n()ticeal)l('  during  the  setting  proct'ss, 
due  to  llie  clieniical  action  that  oc<'Uis. 


52  I.Vll'KESSIONS    AND    IMPRESSION'     MATKKIAI.S 

111  an  ordimiry  mix  of  iiiipressiuii  plaster  that  harck'us  in, 
say,  3  minutes,  the  first  contractile  period  occurs  between  the 
time  of  mixing  and  that  of  the  beginning  of  setting.  Since 
the  consistency  of  plaster,  when  freshly  mixed,  is  soft  and 
the  mass  yielding,  no  accurate  record  can  be  made  of  any 
change  that  may  occur  within  the  first  minute  after  mixing. 
From  tlie  beginning  of  tlie  second  minute,  usually,  the  mass 
being  hard  enough  to  resist  the  tention  spring  of  the  microme- 
ter, the  contraction  is  perceptible  and  usually  continues  for 
about  2  minutes,  or  until  the  evolution  of  heat  is  noticeable. 
This  would  establish  the  contractile  period  in  the  last  two  of 
the  three  minutes  that  elapse  between  the  time  of  mixing  and 
that  of  setting.  Any  variation  in  the  time  required  for  set- 
ting would  undoubtedly  produce  a  corresponding  change  in  tlie 
contractile  period. 

The  contractile  stage  is  followed  by  a  short  period  of 
inertia  of  usually  about  one-half  minute,  after  which  expan- 
sion sets  in,  slowly  at  first,  then  increases  rapidly  for  two  or 
three  minutes,  then  decreases  gradually,  and  finally  ceases 
altogether.  Usually  the  greatest  expansion  is  over  in  ten 
minutes,  although  the  movement  continues  in  a  gradually 
decreasing  ratio  for  twenty-four  hours  or  more. 

The  rate  and  amount  of  expansion  is  very  greatly  influ- 
enced by  the  manner  in  which  the  plaster  is  mixed  with  the 
water,  and  the  method  and  length  of  time  the  mass  is  stirred 
Long  and  rajiid  stirring  increases  the  rapidity  of  setting,  and 
the  rate  and  amount  of  expansion  as  well,  while  on  the  other 
hand  slight  stirring  for  a  sliort  time  induces  only  moderate 
movement. 

MEASUREMENT  OF  EXPANSION  AND  CONTRACTION  OF 
PLASTER 

For  the  purjtose  of  studying  the  behavior  of  plaster  under 
different  conditions,  the  writer  constructed  a  micrometer 
which  registers  both  the  expansive  and  contractile  movements 
of  this  and  other  materials  as  well. 

This  instrument  is  graduated  to  read  to  the  1/10,000  of  an 
incli  and  the  1/500  of  a  mm.  In  reality  readings  can  be  made 
to  the  1/40,000  of  an  inch.  The  spring  actuating  the  conta<-t 
rod  is  very  delicate  and  offers  but  slight  resistance  to  expan- 
sion, so  that  practically  all  of  this  movement  can  be  noted. 

The  following  records,  taken  from  many  hundreds,  show 
the  results  of  stirring  the  several  mixes  varying  lengths  of 
time.     French's  impression  plaster  was  the  material  used. 


IMPRESSIONS    AND    IMPRKSSION     MATKRIALS  51] 

tilt'  mixes  being  practically  identical  as  to  weight,  aniouiit  of 
water,  temperature  of  room  and  material.  Nothing  was  added 
to  accelerate  setting  or  control  exj^ansion.  The  plaster  was 
sifted  into  the  water  in  the  rubber  bowl.  The  only  api)reci- 
able  difference  was  in  the  length  of  time  each  mix  was  stirred. 

Expansion 
After 
Time  Stirred.   10 
X( 


Time  Stirred. 

10 

Minutes. 

1^4   Hours. 

.r  .Mix. 

Minutes. 

I^)ints. 

Points. 

1 

% 

•) 

(il 

•) 

1 

?>•! 

101.5 

3 

11/4 

fil 

!i:'..5 

4 

114 

!)3 

118.5 

5 

1% 

118 

i;!4 

(5 

2 

137 

157.5 

7 

-"y4 

140 

1()0 

8 

'^^ 

U2 

159 

9 

2% 

147 

165 

10 

3 

145 

162 

The  point  is  1/10,000  of  an  inch. 

Tlic  mixes  were  of  a  consistency  suitable  for  impression 
work. 

Further  experiments  indicate  that  thinly  mixed  plaster 
exhibits  less  expansion  than  when  more  thickly  mixed,  but 
the  density  is  proportionately  less,  as  the  mixes  are  made 
thinner. 

CONTROL    OF  EXPANSION 

Many  experiments  have  been  made  with  different  sub- 
stances, singly,  in  combination,  and  in  varying  proportions, 
in  an  effort  to  control  this  expansive  movement,  but  with  the 
exception  now  to  be  mentioned,  only  negative  results  were 
ol)served. 

Potassium  sulphate  in  definite  pro^jortions  acts  as  an 
accelerator,  and  also  decreases  expansive  movement.  The 
slightest  amount  of  stirring  consistent  with  the  production  of 
a  imiformly  plastic  mass  is  also  important  in  keeping  down  tlie 
expansive  movement. 

WARPAGE 

In  prosthetic  procedures  the  princi]ial  difficulty  resulting 
from  expansion  is  in  the  warpage  of  impressions  and  models 
when  allowed  to  remain  in  the  tray  for  any  length  of  time 
after  the  plaster  has  set. 


54  IMPRKSSIONS    AND     IMPRESSION     MATP.'RIAI.S 

Dr.  I)iickiii.niiain,  in  1860,  first  noticed  the  (;'xi)aiisiv(' 
movement  in  ])liister,  lint  he  failed  to  realize  tlie  deleterions  ef- 
fect of  it.  Dr.  \y.  Txiwrnan  McLeod  of  Kdinl»nr.nii,  Scotland, 
in  1880,  tii'st  calliMl  attention  to  tlie  warpauc  of  plaster  when 


HXI'AXSKIN    MAI  1 1  INK 


coiiliiicd  ill  an  iin|ii'ession  tra\".  Ilis  cxpcrinieiit  consisted  in 
clanipini;'  nietai  liars  td  llii'  edi-cs  of  a  ri.ii'id  iiielal  ]ila1e  and 
tillin,^'  the  enclosed  s]iace  with  jiroperly  mixed  plaster. 


After  twenty-fonr  hours  the  hars  were  removed,  and  the 
slal)  of  plaster  sawed  dia,i;(mally  tlironi;h  the  center,  when  it 
was  found  that  in  the  central  ])or1ion  it  had  arched  up  to  a 
consideralile  extent,  while  the  edges  remained  in  contact  with 
the  plate.    This  was  due  to  the  fact  that  lateral  exjiansion  was 


IMPRESSIONS    AND    IMPRESSION     MATERIALS  55 

prevented  by  llic  fixed  in;u',i;iiial  bars,  whicli,  however,  did  not 
confine  the  material  on  its  npper  surface,  and  movement 
occurred  in  that  direction. 

An  impression  tray  with  its  fixed  sides  cori'esponds  to  the 
shil)  witli  clamped  bars.    Tlie  sides  of  the  tray  prevent  lateral 


C 

WARPED    IMPRESSION    DUB    TO    FIXED    TRAY    FLANGES 

ex])ansion,  so  that  the  movement  is  noticeal)le  by  the  arching- 
up  or  war])ing  of  the  palatine  portion  of  the  impression,  while 
the  sides  inclosed  by  the  buccal  and  labial  fianges  of  the  tray 
remain  in  close  contact  with  them.  The  result  is  that  the  pala- 
tine portion  of  the  ini]iression  raises,  while  no  corresponding 


a>  d' 

WARPED    f'AST    DUE    TO    RESTRICTED    LATERAL    MOVEMENT 

movement  occurs  in  the  alveolar  portion.  Now  if  the  plaster 
for  the  cast  is  introduced  in  the  impression  and  allowed  to  re- 
main for  some  time,  a  similar  error  due  to  a  corresponding 
cause  will  result,  and  thus  establish  an  additional  increase  in 
the  height  of  the  jialatine  arch  of  the  cast. 

ERRORS  DUE  TO  WARPAGE 

Two  errors,  due  to  warpage,  have  therefore  occurred, 
either  one  of  which  might,  and  certainly  both  together  will, 
result  in  the  cast  being  an  imperfect  reproduction  of  the 
mouth  it  is  intended  to  re]>resent.  A  denture  molded  over 
such  a  cast  will  touch  the  palatine  portion  of  the  mouth  before 
it  is  firmly  seated  on  the  alveolar  borders,  and  under  stress 


56  IMPRESSIONS    AND    IMPRKSSION    MATERIALS 

ol'  masticatioii  will  readily  li|t.  In  some  iustaiiccs  tliere  will 
be  no  adhesion  whatever.  The  method  for  reducing  or  par- 
tially controlling  and  overcoming  expansion  of  i)laster  impres- 
sions and  casts  will  he  taken  np  when  considering  the  teclinic 
of  this  work. 

COMPRESSIBILITY    OF   PLASTER    OF    PARIS 

An  object  composed  of  plaster  of  Paris  appears  like  a 
solid  substance  and  is  resistant  to  ordinary  stress  without 
change  of  form.  When  we  examine  this  material  under  a 
microscope,  however,  it  is  found,  as  before  stated,  to  be  com- 
posed of  numerous  crystals  grouped  irregularly  in  masses 
with  many  spaces  between  the  masses  and  between  the  crys- 
tals themselves.  Within  and  below  the  modulus  of  resist- 
ance of  these  crystals,  they  retain  their  form  and  resist  a 
verv  considerable  annnuit  of  stress  witliont  ciushing. 


ronrpRTSSTOx  MAnrpTC 


In  certain  technical  procedures,  particularly  in  vulcanite 
work,  plaster  is  usually  subjected  to  heavy  pressure.  By  ex- 
l)eriment  it  has  been  found  that,  in  many  cases,  an  amount  of 
force  far  in  excess  of  the  modulus  of  resistance  of  this  ma- 
terial is  ordinarily  used  in  laboratory  procedures.  While 
perhaps  in  some  instances  the  physical  change  is  not  apparent 
to  the  eye,  it  can  be  readily  discerned  in  others.  In  many  in- 
stances where  no  visual  change  is  noticeable,  the  adaptation 
of  dentures  is  seriously  interfered  with,  which  can  be  laid  to 
no  other  cause  than  that  of  compvessihility.  Further  discus- 
sion of  this  important  problem  will  be  continued  under  the 
subject  of  the  flasking  of  vulcanite  cases. 

ADVANTAGEOUS  PROPERTIES  OF  PLASTER  OF  PARIS 

Plaster  has,  however,  a  number  of  good  (puilities  which 
commend  it  for  impression  work,  and  notwithstanding  the 


IMPRESSIONS    AND    IMPRESSION    MATERIALS  57 

serious  disadvantages  which  have  already  been  cited,  it  is  an 
indispensable  material  in  prosthetic  procedures.  Its  plasticity 
when  freshly  mixed,  its  tastelessness  and  freedom  from  odor, 
the  facility  with  which  the  most  irregular  surfaces  can  be 
copied,  its  rapid  setting  property,  and  the  fact  that  it  can  be 
introduced  in  the  mouth  at  ordinary  temperatures,  commend 
it  for  general  use.  Being  inelastic  and  brittle,  it  breaks  with 
a  clean  fracture,  and  the  broken  pieces  can  easily  be  placed 
togetlier  again  in  exact  relation  to  each  other,  so  that  liy  its 
use  the  impression  of  any  surface,  however  irregvilar,  may  be 
secured  with  accuracy. 

Only  the  finest  grades  of  dental  plaster  should  be  used 
for  impression-taking,  and  it  should  be  kept  dry  and  in  air- 
tight receptacles  to  retain  its  setting  quality.  When  used 
with  skill  and  in  properly  selected  cases,  it  is  an  excellent 
medium  for  imi^ression  work,  and  indispensable  for  many 
other  purposes. 

In  mixing  plaster,  the  best  results  are  secured  by  plac- 
ing the  required  amount  of  water  in  the  bowl  and  sifting  the 
plaster  into  it  until  a  sufficient  amount  has  been  added  to 
take  up  the  water.  No  excess  of  water  should  be  present, 
while  an  excess  of  plaster  results  in  an  insufficient  amount  of 
water  to  bring  the  half  hydrate  into  solution.  It  should  be 
sul)jected  to  the  slightest  amount  of  stirring — just  enough  to 
make  the  plastic  mass  homogeneous  and  of  uniform  consist- 
ency throughout. 

IMPRESSION   COMPOUNDS 

These  are  manufacturers'  products  intended  for  impres- 
sion work,  and  into  which,  on  drying,  metal  dies  can  be  run 
without  resorting  to  the  usual  steps  in  such  cases.  The  basis 
of  all  such  compounds,  however,  is  plaster  of  Paris,  which 
acts  as  a  cementing  medium  between  the  particles  of  refrac- 
tory material,  usually  pulverized  or  granular  calcium  car- 
bonate, silex,  pumice-stone  or  coarsely  ground  asl)estos.  But 
little,  if  any,  advantage  is  dci'ivcd  from  tlieir  use. 

CEMENTS 

Tlie  various  dental  cements  are  at  times  employed  in 
taking  inqu'essions  of  limited  areas,  as,  for  instance,  of  pre- 
pared teetli  for  inlay  work,  or  in  certain  procedures  in  crown 
and  bridge  work.  They  are  used  to  such  a  limited  extent  as 
not  to  be  considered  as  general  im])ression  materials, 


58  lAII'lUOSSIONS    AND    IMI'KIOSSION    MATIOIUAI.S 

GROUP  II 

IMPRESSION    MATERIALS    RENDERED    PLASTIC    BY    HEAT 
MODELING   COMPOUND 

Modeling  coiiipouiKl,  as  its  iiiunc  implies,  is  iiiiulc  ii])  of 
several  ingrodients  ('()ral)ined  in  sueli  proportions  as  to  pro- 
duce a  material  that  is  plastic  and  workable  at  low  tempera- 
tures, which  will  copy  accurately  the  surfaces  against  which 
it  is  pressed,  and  cool  or  harden  quickly.  Since  the  formulae 
of  the  manufacturers  are  not  jmblished,  it  is  not  possible  to 
give  exact  data  on  this  subject.  The  base  of  this  material, 
in  practically  all  cases,  consists  of  one  or  more  of  the  natural 
resinous  gums  used  in  varnish  making,  such  as  dammar,  copal 
or  kauri.  These  gums  are  more  or  less  hard  when  dry  and 
cold,  but  become  sticky  and  plastic  on  heating.  Stearin  is 
added  to  reduce  the  stickiness,  while  pulverized  soapstone 
is  incorporated  to  give  body  to  the  mass.  Carmine  is  usually 
used  to  tint  the  material,  and  sometimes  a  little  aromatic 
flavoring  substance  is  added  to  render  it  pleasant  in  taste 
and  odor. 

FORMULA    FOR    MODELING    COMPOUND 

A  formula  which  will  serve  to  illustrate  the  compounding 
of  this  material  was  given  to  the  writer  a  number  of  years  ago 
by  Dr.  E.  Lloyd  Williams  of  Ijondon  : 

Kauri   1       part 

French  chalk    1%  parts 

Stearin   1  Vi;  parts 

The  stearin  is  first  melted,  the  kauri  added,  and  the  two 
thoroughly  incorporated,  then  the  chalk  is  gradually  sifted  in 
and  the  mass  kneaded  until  well  mixed.  The  coloring  and 
flavoring  ingredients  should  be  incorporated  in  the  stearin 
and  gum  before  adding  the  soapstone. 

Some  varieties  of  conii)ound  show  a  decided  tendency  to 
contract,  or  warp,  on  cooling,  which  projierties  make  them 
unreliable  in  impression  work,  while  some,  to  render  them 
efficiently  })lastic,  require  a  degree  of  temperature  unbearable 
to  the  oral  tissues.  While  the  tissues  of  the  mouth  can  tol- 
erate temperatures  ranging  from  140  to  170  deg.  F.  without 
much  discomfort,  a  compound  should  be  selected  that  will 
copy  fine  lines  and  irregular  surfaces  at  even  lower  tempera- 
tures than  those  mentioned,  in  order  to  be  efficiently  workable. 

As  a  rule,  modeling  compound  is  heated  in  water  to  soften 
i'oi-  inqiression  work,  but  should  never  be  sul)jected  to  l)oiIing 
temperature,  as  its  quality  is  soon  impaired  and  the  material 


IMPRESSIONS    AND    IMPRESSION    MATERIALS  59 

is  too  sticky  to  liaiidk'  (•(uncniciilly  wIr'U  oNcrlicated.  The 
bottom  of  the  vessel  used  for  lieatiii,i;'  shoukl  be  covered  with 
a  piece  of  rubber  dam,  or  clean  pajjer,  to  prevent  the  compound 
adiiering  to  it.  Softening  in  water  is  preferable  to  dry  heat, 
although  some  use  the  latter  method.  Modeling  compound  is 
inelastic  and  therefore  when  iinjjressed  against  a  surface  it 
should  be  thoroughly  hardened  l)efore  removal  from  the 
mouth,  since  in  the  act  of  loosening  the  impression  or  in  its 
withdrawal,  pressure  upon  the  iirominent  portions  is  liable  to 
distort  it.  This  precaution  also  ai>])lies  to  most  of  the  sub- 
stances made  jilastic  with  heat. 

BEESWAX 

This  material  is  elaborated  by  bees  out  of  substances  col- 
lected from  flowers  and  from  it  the  honeycomb  is  formed. 
The  wax  is  pre})ared  for  use  l)y  melting  the  comb  in  water 
after  removal  of  the  honey.  Impurities  lighter  than  the  wax 
are  skimmed  oiT,  or  if  heavier  are  removed  by  trimming  the 
under  surface  of  the  hardened  cake.  The  natural  color  of 
beeswax  is  yellow.  It  may  be  bleached  by  forming  it  into  thin 
sheets  and  exposing  it  to  l)right  sunlight,  or  by  the  use  of 
dilute  acids  in  the  melting  pan.  It  may  be  given  almost  any 
tint  desired  by  the  addition  of  suitable  pigments. 

It  was  formerly  much  used  as  an  impression  material, 
but  has  been  to  a  great  extent  supplanted  by  modeling  com- 
])ound.  There  are  two  serious  objections  to  the  use  of  bees- 
wax as  a  material  for  general  im|)ression  work:  First,  when 
(lis]>osed  around  the  laliial  and  buccal  portions  of  the  alveolar 
border  unsu]i]iorted  by  the  tray,  in  a  thin  layer,  it  is  very  apt 
to  be  distorted  in  removal  because  of  lack  of  inherent  rigidity, 
even  when  chilled;  second,  there  is  a  tendency  for  it  to  warji 
and  contract  in  changing  from  a  heated,  plastic  condition  to 
a  cold  state.  When  manipulated  with  care  it  may  be  used  to 
advantage  in  some  cases,  although  it  is  difficult  to  say  in  what 
instances  it  would  be  ]ireferable  to  modeling  compound,  since 
in  recent  years  the  quality  of  the  latter  has  been  so  materialh' 
improved. 

Wax  is  furnished  by  the  manufacturers  in  the  form  of 
sheets  and  cakes,  both  in  a  pure  state  and  combined  with 
other  substances, .such  as  paraffin  or  some  of  the  resins,  to 
render  it  harder  or  more  adhesive,  as  desired. 

BEESWAX  AND   PARAFFIN 

The  addition  of  paraffin  to  beeswax  lowers  its  melting 
point  and  renders  it  harder  when  cold,  but  reduces  the  ad- 


liO  IMFRKSSIONS    AND    IMF'Rp:SS10.\     MATKKlALS 

liesivcuess  of  the  wax  if  used  in  cxcctss.  Tallow  is  fr('(|ii('ntiy 
used  as  an  adiiltoiaiit  of  wax.  The  coinhinatioii,  however,  is 
worthless  for  dental  i)nri)oses.  The  sticky  wax,  so  useful  for 
many  purposes  in  tiie  lal)oi'atory,  oonies  in  the  form  of  small 
sticks  or  cylinders,  and  is  made  l)y  combining  some  of  llu- 
I'esins  with  beeswax.  It  is  adhesive  and  hard  wlien  cold, 
and  is  nuicli  used  in  the  assembling  of  parts  in  crown  and 
bi'idge  work. 

HARD   BITE  WAX 

A  material  known  as  hard  hifc  ifax  is  procurable,  which 
is  very  convenient  in  the  making  of  wax  contour  models  for 
use  in  warm  weather.  When  formed  of  this  wax,  the  rims 
withstand  the  stress  of  trial  in  the  mouth,  as  well  as  the  effect 
of  oral  temijcrature,  without  becoming  distorted.  AVax  of 
this  class  usually  contains  rosin. 

Beeswax  is  mani]mlated  much  the  same  as  modeling  com- 
])ound,  being  softened  in  warm  water.  It  should  be  broken 
uj)  in  small  pieces,  if  in  bulk,  or  in  sheets  of  moderate  thick- 
ness, so  that  tlie  heat  may  ])enetrate  readily  at  rather  low 
temperatures,  say  130  deg.  to  140  deg.  F.  When  thoroughly 
warmed,  it  is  kneaded  with  the  fingers  into  a  uniform  ])lastic 
mass  and  pressed  with  a  towel  to  take  up  any  moisture  that 
may  be  present. 

None  of  the  plastic,  non-elastic  impression  materials,  with 
one  exception,  are  suitable  for  taking  impressions  in  under- 
cut spaces,  or  in  partial  cases  where  the  teeth  have  constricted 
services  or  the  embrasures  and  inter]iroximate  spaces  are  de- 
void of  gum  tissue.  Under  certain  conditions  and  by  follow- 
ing methods  to  be  outlined  later,  modeling  compound  may  be 
ri^ed. 

The  difficulty  encountered  in  such  cases  is  due  to  the 
drawing  or  distorting  of  the  impression  material  in  with- 
drawal from  the  teeth  and  spaces  designated. 

Beeswax  is  frequently  employed  as  a  preliminary  im- 
pression material  in  partial  as  well  as  full  cases,  the  impres- 
sion thus  obtained  being  relieved  of  excessive  surplus  and 
used  as  a  matrix  or  improvised  tray  for  holding  the  ])laster 
for  the  final  impression.  By  this  means,  the  wax  having  been 
conformed  to  the  tissues,  a  minimum  quantity  of  plaster  is 
carried  to  every  surface  involved,  with  less  discomfort  to  the 
patient,  while  the  ratio  of  expansion  in  the  plaster  is  corre- 
spondingly less.  In  partial  cases,  however,  the  wax  should  be 
trinuned  well  away  from  around  the  remaining  teeth,  so  that 
the  plaster  enclosing  them  may  be  of  sufficient  thickness  when 


IMPRESSIONS    AND    IMPRESSION    MATERIALS  61 

fractured  iii  renioval,  lo  be  readily  plai-t'd  together  again  in 
the  wax  matrix. 

GUTTA   PERCHA 

This  material  is  ()l)taiued  from  the  juice  of  a  tree,  the 
Isonandra  or  Dichopsis  Gutta,  found  in  the  Malay  Archipel 
ago,  on  either  side  of  the  equator,  for  a  distance  of  two  or 
three  degrees. 

The  word  "gutta"  iu  the  Malay  language  means  "gum" 
and  "percha"  is  the  name  of  the  tree,  so  the  term  means  the 
"gum  of  the  percha  tree."  The  juice  is  collected  by  a  method 
similar  to  that  followed  in  tapping  the  rubber  tree  (Siphouica 
Klastica)  by  making  a  long  diagonal  cut  entirely  through  the 
bark  and  adjusting  a  trough  under  the  incision,  througli 
which  the  escaping  juice  is  carried  into  vessels  to  receive  it. 
As  more  or  less  dirt  and  impurity  is  mixed  with  the  juice,  the 
crude  material  is  nufit  for  use.  It  is  refined  by  first  tearing 
it  into  shreds  iu  a  special  machine,  washing  and  agitating  in 
water,  and  afterward  boiling,  to  bring  it  into  a  coherent  mass, 
in  which  form  it  is  known  as  commercial  gutta  percha.  It 
is  nearly  similar  in  composition  to  rubber,  being  a  hydro- 
carbon, but,  unlike  that  substance,  it  deteriorates  slowly  if 
exposed  to  the  air,  the  oxygen  of  the  air  uniting  with  it  and 
causing  the  gum  to  become  brittle  and  lose  its  elasticity  and 
strength.  It  can  be  mixed  with  sulphur  and  vulcanized,  but 
the  product,  while  more  durable  than  the  crude  material,  is 
not  so  permanent  or  lasting  as  vulcanite,  and  consequently 
is  not  used  iu  this  form  to  any  great  extent. 

The  fresh  commercial  product  is  sometimes  used  for 
taking  impressions  of  the  mouth.  It  becomes  plastic  enough 
for  this  purpose  at  a  temperature  of  130  deg.  to  150  deg.  F. 
and  is  prepared  by  softening  in  water.  It  will  contract,  how- 
ever, unless  dried  and  heated  sufificiently  to  adhere  to  the  sides 
of  the  tray.  In  general,  it  is  manipulated  the  same  as  model- 
ing compound,  except  that  s]iecial  care  must  be  observed  to 
cement  it  to  the  tray  before  introduction  into  the  mouth  and 
to  chill  it  thoroughly  befoi'e  removal.  Being  elastic,  it  will 
readily  draw  away  from  undercuts  and  teeth  with  constricted 
cervices,  and  immediately  resume  its  proper  form  when  pres- 
sure is  relieved. 

CONSTITUENTS  OF  GUTTA  PERCHA 

As  it  is  difficult,  or  almost  imi)ossible,  to  secure  the  fresh, 
unadulterated  product,  its  use  as  an  impression  material  is 
very  limited.     The  base  plate  gutta  percha  furnished  by  the 


62  IMPRESSIONS    AND     IMPRKSSION    MATERIALS 

sii])ply  liduscs  is  not  coiiiiKiscd  of  the  pure  .i4'iiin,  liul  (•(iiitniiis 
chalk,  niannesia  or  oxide  of  zinc,  and  t'rcciuently  coloring  umt- 
ter.  The  addition  of  these  suhstanoes  prevents,  to  a  certain 
extent,  rapid  deterioration,  and  also  renders  the  product  nioi'c 
rig'id.  Wliile  sometimes  used  for  the  base  of  trial  plates, 
gutta  percha  is  not  sufficiently  rigid  to  insure  accuracy  in 
such  procedures.  The  sheet  base  plate  is  frequently  used  foi 
taking  impressions  of  faced  roots  in  cro\Yn  and  bri age  work 
where  it  is  desirable  to  force  the  giiigivie  apically  to  obtain 
an  outline  of  the  root  periphery.- 

(intta  jx'reha  consists  of  a  ('(inihinatioii  of  iixdrocai-bons 
similar  to  caoutchouc. 

Payen's  analysis  shows  the  following: 

Gutta    78  to  82  per  cent 

Albane   16  to  14  per  cent 

Fluavile   (i  to     4  i^er  cent 

Chemical  coin])osition  : 

( "arlion   86.36 

Hydrogen 12.15 

Oxygen   1.4!) 

Since  the  juice  is  coli(M'tcd  from  several  varieties  of  trees 
and  comes  from  dilTerent  localities,  it  is  a  natural  cansequence 
that  the  physical  as  well  as  chemical  proportions  of  constitu- 
ents must  vary  more  or  less,  so  the  above  may  be  considei'ed 
as  representing  the  general  comiiosition  of  this  material  and 
not  an  absolute  unchangeable  chcinical   foi-mula. 


C  If  A  P  T  K  R    V  1 1 
TECHNIC  OF  TAKING  IMPRESSIONS 

GENERAL  REMARKS 

In  i>t'iieral,  tlie  taking'  of  improssioiis  in  plaster  for  full 
and  partial,  njjper  and  lower  cases,  is  similar  in  many  tech- 
nical details.  A  comparatively  fnll  description  of  the  mani])- 
ulative  details  carried  out  in  taking  an  impression  of  an 
upper  edentulous  cast,  will  serve  as  a  basis  for  all  classes 
of  plaster  impressions.  The  difference  in  details  will  be  pre- 
sented as  each  class  is  descrilied. 

INDICATIONS  FOR  THE  USE  OF  PLASTER 

The  value  of  plaster  as  an  impression  material  lies  in 
the  fact  that  it  can  be  readily  adapted  to  the  most  irregular 
surfaces  and  carried  into  deeji  undercuts  and  embrasures, 
from  which  it  can  be  removed  by  fracturing,  and  the  broken 
j^arts  readjusted  with  ease. 

An  outline  of  those  cases  where  plaster  is  most  strongly 
indicated,  is  here  in  order: 

First — In  all  eases  where  any  of  the  natural  teeth  are 
present. 

Second — In  case  undercuts  exist,  either  on  the  opposite 
surfaces  of  the  borders,  or  in  spaces  formed  as  the  result 
of  the  loss  of  the  natural  teeth. 

Third — Where  flabby  ridges  are  itresent,  such  as  have 
jireviously  been  described. 

Fourth — In  edentulous  cases  where  the  nuicous  and  sub- 
nnicous  tissues  are  thick  and  elastic,  i)articularly  in  the  pal- 
atine portion  of  the  mouth.  When  such  a  condition  prevails, 
the  tissues,  if  compressed  uniformly,  as  when  modeling  com- 
pound is  used,  assert  their  resiliency,  on  pressure  being  re- 
lieved, which  breaks  the  jieripheral  adai^tation  of  the  im- 
pression, and  later  on,  of  the  denture  that  may  be  constructed 
when  such  an  iniju'ession  is  used  as  a  basis. 

In  ]iractically  all  of  the  cases  just  cited,  the  use  of  bees- 
wax or  modeling  compound,  as  an  im])ression  material,  is 
contra-indicated,  but  the  use  of  either  of  these  substances  as 
a  preliminary  impression  material,  in  wliich  to  hold  tlic  plaster 
for  the  final  impression,  is  strongly  indicated. 

63 


G4  TECHNIC    OF    TAKING    IMPRKSSIONS 

UPPER  EDENTULOUS  CASES 
PRELIMINARY    STEPS   IN    IMPRESSION    TAKING 

Taking  it  for  granted  that  the  mouth  has  been  previously 
examined  and  is  in  condition  to  receive  prosthetic  substitutes 
the  patient  is  seated  in  tlie  o]ici'ating  chair. 

POSITION   AND   COMFORT  OF  THE  PATIENT 

As  a  general  rule  in  all  plaster  impression  work  the  patient 
should  sit  in  an  upright  position.  The  chair  may  be  slightly 
inclined  backward,  ])ut  not  to  any  marked  degree.  The  chair 
should  be  raised  high  enough  to  ))ring  the  patient's  mouth 
within  convenient  range  for  manipulation.  Further  adjustment 
of  the  chair  should  be  made  for  the  comfort  of  the  patient, 
so  far  as  may  be  consistent  with  the  work  in  hand. 

A  covering  should  be  adjusted  to  protect  the  patient's 
clothing  from  becoming  soiled  with  particles  of  plaster,  or 
the  dripping  or  overflow  of  saliva  from  the  mouth.  When 
possible  to  do  so,  the  saliva  ejector  should  be  used  to  over- 
come this  difficulty.  Before  taking  the  impression,  the  mouth 
should  be  rinsed  with  tepid  water,  or,  preferably,  normal  salt 
solution,  to  remove  the  viscid,  stringy  mucous.  A  glass  of 
water  should  be  placed  on  the  bracket  so  that  the  patient 
may  rinse  the  mouth  after  the  removal  of  the  impression. 

POSITION   OF  THE   OPERATOR 

For  upper  impressions  the  operator  should  stand  on  the 
right  side  of  the  chair,  and  slightly  back  of  the  patient.  He 
should  stand  erect  and  work  with  the  upper  arms  perpen- 
dicular, and  tlie  forearm  horizontal.  In  introdiicing  an  npi)er 
impression,  his  left  arm  should  pass  to  the  left  of  the  patient's 
face,  so  that  the  left  hand  may  manijmlate  that  angle  of  the 
mouth,  and  later,  snjiport  the  tray. 

In  taking  lower  impressions,  the  operator  will  find  it 
more  convenient  to  stand  slightly  in  front,  to  the  riglit  of,  and 
facing  the  patient.  In  this  position,  both  hands  have  more 
freedom  of  action,  and  the  line  of  vision  is  less  obsti-uctcd 
than  when  the  operator  stands  back  of  the  chair. 

SELECTING   AND    FITTING    TRAY    TO    MOUTH 

By  a  glance  in  tlie  nioutli,  the  opcraidr  can  determine  tlie 
approximate  form  and  size  of  Irny  to  use,  and  select  one 
accordingly.     This  is  introduced  in  the  mouth,  and  its  gen- 


TBCHNIC    OF    TAKING     IMPRESSIONS  65 

eral  adaptability  to  the  case  aseertaiued.  If  apiiroximately 
of  the  right  form,  but  not  exactly  adapted  to  the  case,  the 
points  needing  modification  are  noted.  By  placing  the  tray 
in  position  and  subjecting  it  to  a  side-to-side  movement,  th(; 
excess  of  buccal  space  can  be  estimated.  By  holding  the 
distal  margin  of  the  tray  against  the  palatine  vault  in  ap- 
proximately the  correct  mesio-distal  position  that  it  should 
occupy,  and  letting  the  anterior  portion  of  the  tray  drop  down 
below  the  Ixirder  level,  so  that  a  view  above  the  tray  of  the 
vault  and  tray  curvature  may  be  obtained,  the  adaptation  of 
the  vault  portion  of  tray  to  tissue  can  be  determined. 


FULL   ITTKR   Un'RESSlON   TRAV    SlITAiiLE   FOK   EDEXTULOIS   CASES 

The  relative  width  of  the  labio-buccal  flange  to  the  al- 
veolar border,  and  the  several  points  of  muscular  attachment 
can  be  determined  by  holding  the  tray  in  position,  rather 
loosely,  of  course,  since  the  impression  material  is  not  pres- 
ent, and  subjecting  the  lips  and  cheeks  to  outward  and  down- 
ward traction.  If  too  broad,  the  amount  of  excess  width 
can  be  determined  br  alternately  pressing  upward  on  the 
central  portion  of 'the  tray  and  pulling  downward  on  the 
lips  and  cheeks,  the  amount  of  movement  in  the  tray  indicat- 
ing the  excess  present. 

Hold  the  tray  in  normal  position  witli  one  hand  and  pass 
the  index  finger  of  the  other  hand  backward  along  the  central 


66  TKCHNIC    OF    TAKING    IMPRKSSIONS 

vault  portion,  past  tlie  tray  margin,  onto  the  oral  tissue,  and 
determine  whether  this  portion  of  the  tray  extends  to  the 
line  of  junction  of  hard  with  soft  palate.  If  not,  make  an  ex- 
tension, as  descrihed  elsewhere.  The  usnal  syjace  outline  of 
an  eighth  of  an  inch,  or  less,  hetween  tray  and  tissue,  should 
he  closely  adhered  to,  since  a  sjnall  amount  of  impression  ma- 
terial, properly  applied,  will  yield  more  accurate  results  and 
be  less  objectionable  to  the  patient  than  an  excessive  bulk. 

MIXING  THE   PLASTER 

A  clean  rubber  liowl  is  tilled  about  one-fourth  full  of 
slightly  warm  water,  into  which  should  be  sifted  some  im- 
pression plaster  (plaster  which  contains  an  accelerator).  Or, 
if  French's  regular  dental  plaster  is  used,  dissolve  about  one- 
half  gram  of  sulphate  of  potassium  in  the  water  before  sifting 
in  the  plaster.  This  will  hasten  the  setting  and  also  have  a 
slight  control  on  expansion. 

Add  enough  plaster  to  take  up  the  excessive  moisture, 
and  produce  a  plastic  mass,  which,  when  stirred  slightly,  will 
stand  when  piled  upon  itself,  or  in  other  words,  will  not  drop 
from  the  inverted  tray.  Distribute  the  mixture  in  the  tray 
selected,  spreading  it  uniformly  over  the  various  surfaces  and 
building  it  slightly  higher  on  the  vault  portion  than  else- 
where, to  insure  a  sufificient  amount  of  material  being  present. 
The  general  contour  of  the  plaster  in  the  tray  should  be  sim- 
ilar to  the  general  contour  of  the  mouth,  but  reversed,  of 
course. 

INTRODUCING  THE   FILLED   TRAY  IN  THE  MOUTH 

The  tray  handle  is  held  in  the  right  hand,  thumb  on  top 
of  handle,  index  and  middle  fingers  underneath,  to  support 
the  body  on  the  right  side.  The  right  angle  of  the  tray  is 
inserted  well  back  in  the  right  angle  of  the  mouth,  while  the 
o])posite  side  is  rotated  through  the  left  angle  of  the  mouth, 
the  latter  l)eing  distended  with  the  index  or  middle  finger 
of  the  left  hand. 

After  the  greatest  diameter  of  the  tray  has  passed  the 
oral  opening,  its  adjustment,  although  requiring  care,  is 
easily  accomplished. 

See  that  the  tray  is  centered.  The  direction  of  the  handle 
indicates  this  to  a  certain  extent,  although  it  cannot  be  de- 
pended on  in  those  cases  where  the  buccal  alveolar  process 
has  been  absorbed  more  on  one  side  than  on  the  other,  or 


Tkchnic  of  taking   impressions  6? 

where  the  aheuhir  processes  are  not  synunetrieally  related  to 
the  medium  line  of  the  cranium. 

Pass  the  tray  back  until  the  labial  surface  of  the  border 
is  within  about  one-fourth  of  an  inch  of  the  flange,  and  press 
the  tray  upward  until  the  border  is  fairly  well  imbedded  in 
the  plaster,  not,  liowever,  to  the  full  extent,  as  at  this  time 
nmscular  impingement  is  not  yet  relieved.  The  index  and 
middle  fingers  of  l)oth  hands  are  placed  under  the  floor  of 
the  tray  to  carry  the  impression  to  place.  This  is  the  first, 
or  pressure  position  of  the  hands.  Apply  the  index  and  middle 
fingers  of  the  left  hand  to  the  vault  portion  to  support  the 
tray,  and  quickly  pass  the  index  finger  of  the  right  hand 
along  the  Imccal  border  of  the  right  side  of  the  tray,  at  the 
same  time  producing  tension  on  the  buccal  muscles,  drawing 
them  outward  to  prevent  them  from  becoming  caught  by  and 
folded  interiorly  over  the  tray  margin.  Then  reverse  the 
position  of  the  liands  and  carry  out  a  similar  procedure  on 
the  opposite  side,  being  careful  not  to  disturb  the  relation 
of  the  impression  to  the  border  during  this  step.  Now  return 
to  first,  or  pressure  position,  and  apply  sufficient  force  to 
carry  tlie  impression  firmly  to  place. 

SECURING   PERIPHERAL   ADAPTATION 

Eeturn  to  the  second,  or  tray  supporting  position,  and 
with  the  free  hand  press  against  the  lips  and  cheeks, 
directing  the  pressure  from  low  down  near  the  floor  of 
the  tray,  inward  and  upward  against  the  outer  flange,  so  as  to 
carry  the  plaster  that  has  been  forced  outside  the  flange,  up- 
ward against  the  labial  and  buccal  surfaces  of  the  border. 

MUSCLE  MARKING  OF  THE  PERIPHERY 

While  still  supporting  the  impression,  instruct  the  pa- 
tient to  produce  buccal  and  labial  muscular  tension  on  the 
peripheral  plaster  margins,  in  order  to  indicate  distinctly 
the  position  and  form  of  muscle  tendons  and  labial  frenum. 

All  of  these  steps  should  l)e  carried  out  quickly,  before 
the  plaster  has  set  to  any  appreciable  extent,  for  if  allowed 
to  set  too  hard,  the  mu'scle  markings  will  not  show  distinctly. 
Usually  all  of  tlie  details  as  outlined  can  be  carried  out  in  from 
thirty  to  forty  seconds. 

Steady,  moderate  and  uniform  pressure  maintained  on 
the  floor  of  the  tray  with  the  index  and  middle  fingers  of 
both  hands,  until  the  plaster  has  become  well  hardened,  is 


68  TECHNIC    OF    TAKING    IMPRKSSIONS 

essential.  Tlie  liavdness  of  the  plaster  is  determiued  by  break- 
ing some  of  that  i-emaining  in  the  bowl.  When  it  breaks  with 
a  clean  fracture,  and  without  crumbling,  the  impression  is 
ready  for  removal. 

DISLODGING  THE   IMPRESSION 

If  the  impression  is  correct  and  well  adapted,  it  should 
adhere  to  the  tissues  firmly,  and  require  considerable  effort 
to  effect  its  removal.  An  impression  that  requires  but  slight 
effort  to  dislodge  it  can  rarely  be  relied  upon  to  serve  as  a 
basis  for  an  accurately  fitting  denture. 

To  break  the  adhesion,  the  index  finger  is  passed  back- 
ward inside  the  cheek  opposite  the  buccinator  muscles,  and 
pressure  made  outward  and  upward  on  them.  These  regions  on 
either  side  are  the  natural  air  valves  to  the  vault  portion,  and 
with  some  slight  traction  on  the  handle,  at  the  same  time  the 
buccal  muscles  are  lifted  as  described,  the  adhesion  of  the 
impression  will  be  broken  without  much  difficulty.  Should 
this  method  fail,  instruct  the  patient  to  cough,  and  at  the 
same  time  press  upward  on  the  tray  handle.  The  sudden 
muscular  contraction  occurring  in  the  soft  palate  lifts  these 
muscles  up  from  the  distal  margin  of  the  impression,  and  at 
the  same  time  forces  the  air  in  between  the  tissues  and  the 
plaster. 

REMOVAL  OF  THE  IMPRESSION 

When  loosened,  the  impression  is  dropped  down,  clear  of 
the  border,  and  rotated  out  of  the  mouth  in  much  the  same 
manner  as  it  was  introduced,  but  with  reversal  of  movement, 
and  without  the  necessity  for  distending  the  oral  angle  with 
the  finger. 

In  edentulous  cases  where  decided  undercuts  are  present, 
it  is  advisable  to  oil  the  tray  before  introducing  the  plaster, 
and  when  the  impression  is  ready  for  removal,  dislodge  and 
remove  the  tray  first.  The  impression  can  then  be  weakened 
by  cutting,  so  as  to  be  removed  in  pieces,  thus  preventing 
injuries  to  the  tissues  that,  in  some  cases,  would  most  certainly 
follow  its  removal  as  a  whole. 

INSPECTION  OF  THE  IMPRESSION 

On  removal,  the  impression  should  be  carefully  inspected 
to  see  that  all  essential  surfaces  have  been  copied,  and  that 
it  is  intact.    If  fractured  at  any  point,  the  broken  parts  are 


TECHNIC    OF    TAKING    IMPRESSIONS  G'J 

recovered,  placed  iu  their  respective  positions,  and  held  there 
by  melting  a  little  wax  along  the  external  fracture  line. 

The  treatment  of  the  impression  and  the  production  of 
the  cast  will  be  described  in  a  subsequent  chapter. 

EDENTULOUS  LOWER  CASES  IN  PLASTER 
SELECTING  THE   TRAY 

The  tray  in  these  cases  should  be  of  such  size  that  the 
ci'est  of  the  alveolar  process  will  occu]3y  a  central  position 
between  the  outer  and  the  inner  flanges.  The  usual  eighth  of 
an  inch  space  allowance  for  impression  material  should  be 
present.  The  flanges  should  not  impinge  on  the  buccal,  labial 
or  lingual  muscles  or  franse.     This  requirement  is  essential 


I.UUKR    TRAY 


in  order  that  their  subsequent  movements  may  be  unre- 
stricted. 

When  considerable  absorption  of  the  border  has  occurred, 
either  uniform  or  unequal,  a  preliminary  impression  in  wax 
or  modeling  compound  should  be  taken,  the  excessive  surplus 
trimmed  away,  and  this  modified  impression  used  as  a  tray. 

Frequently,  by  extending  the  lingual  wings  of  lower  den- 
tures distally,  when  the  shape  of  the  mandible  permits,  and 
muscular  attachments  do  not  interfere,  much  greater  stability 
of  the  substitute  is  assured.  If  such  a  plan  is  feasible,  a  tray 
with  deep  lingual  wings  should  be  selected,  or  if  the  tray  at 
hand  most  suitable  in  other  respects  is  deficient  in  this,  addi- 
tions of  suitable  length  to  carry  the  impression  material 
against  the  desired  areas  should  be  made  with  wax  or  com- 
pound, and  tested  in  the  mouth  before  attempting  to  take  an 
im])ression. 

The  tendency  in  selecting  trays  for  lower  cases  is  to 
choose  one  with  too  wide  buccal  and  too  narrow  lingual  flanges. 


70  TECIINK"    OF    TAKING    iMPliKSSIONS 

Tilt'  ])lastc'r  is  mixed  as  dcscrilx'd  lur  upitcr  cases.  It  should 
he  distributed  in  the  tray  in  a  uniform  layer  about  one-fourth 
of  an  ineli  thick,  confinins'  it  within  the  tray  flanges. 

POSITION   OF   PATIENT 

'I'he  position  and  elevation  of  the  patient  in  the  chair 
slioidd  Itc  about  tlic  same  as  in  taking  imjiressicm  of  the  upper 
arch. 

POSITION    OF  OPERATOR 

The  operator  should  stand  on  the  rigiit  side,  somewhat 
iu  front  of,  and  facing  the  patient.  Some  prefer  to  lower  the 
chair  a  trifle  below  the  point  designated,  and  stand  back  of 


LOWER    THAV    UlTIl     UKIOl'    LINGUAL    FLAN(iKS 

the  patient  during  the  manipulative  procedures.  The  first  de- 
scribed position  is  to  be  j^referred  iu  most  cases,  for,  as  before 
stated,  the  line  of  vision  is  less  obstructed  and  the  hands  have 
more  freedom  of  movement  than  when  the  operator  stands 
behind  the  patient. 

INTRODUCING  THE  TRAY 

The  operator  holds  the  inverted  tray  between  the  thumb 
and  index  and  middle  fingers  of  the  right  liaud,  the  thumb 
beneath  and  the  index  finger  on  the  handle,  the  middle  finger 
resting  on  the  right  side,  just  back  of  the  first  finger.  The 
index  finger  of  the  left  hand  distends  the  right  angle  of  the 
patient's  mouth.  The  left  angle  of  the  tray  is  inserted  in 
the  left  angle  of  the  mouth,  while  with  a  deft  rotary  movement 
the  tray  is  brought  into  position  over  the  border. 


TECHNIC    OF    TAKING    IMPRESSIONS  71 

When  the  operator  assumes  the  position  back  of  the 
chair,  the  right  angle  of  tlie  tray  is  inserted  in  the  right 
angle  of  tlie  month,  while  its  left  angle  is  rotated  into  position 
throngh  the  left  angle  of  the  montli,  which  is  being  distended 
with  the  ojierator's  left  index  finger. 

SEATING  THE  IMPRESSION 

Tlie  technic  of  carrying  the  impression  to  place  is  as 
follows — the  operator  standing  in  front  of  the  patient:  The 
tray  being  centralized,  the  index  fingers  are  placed  on  either 
side  of  the  body,  the  thumbs  under  the  mandible,  and  pressure 
applied  to  carry  it  partiallj'  to  position.  Now  place  the  thumb 
of  one  hand  under  the  mandible,  the  index  finger  across  the 
tray  body  to  steady  it,  and  grasp  the  cheek  well  back  with 
the  thumb  and  index  finger  of  the  other  hand  and  pull  out- 
ward, to  draw  any  folds  of  the  cheek  or  buccal  muscles  out- 
ward that  may  have  been  caught  under  the  tray  margins. 

Eeverse  the  hands  and  carry  out  the  same  procedure  on 
the  opposite  side.  Grasp  the  lip  in  a  similar  manner,  draw- 
ing it  out  from  under  tlie  tray  margin.  Instruct  the  patient 
to  lift  the  tip  of  the  tongue  up  and  touch  the  high  jjart  of  the 
vault.  These  movements  clear  the  tray  margins  of  all  ab- 
normal muscle  folds.  With  thumbs  under  the  mandible  and 
index  fingers  on  the  sides  of  the  tray,  the  latter  is  forced 
down  to  place.  Now  steady  the  tray  by  placing  the  index  and 
middle  fingers  of  one  hand  across  it  from  side  to  side,  thumb 
under  the  mandible,  and  with  the  other  apply  pressure  on  the 
outer  side  of  the  cheek  and  lip  to  force  the  surplus  plaster 
along  the  flange  margins  into  close  contact  with  the  border. 

Eeverse  the  hands  and  carry  out  similar  steps  on  the  op- 
posite side.  With  each  free  hand,  in  turn,  pass  the  index 
finger  around  the  periphery  of  the  lingual  flange  margin  to 
adapt  the  plaster  in  this  location  also,  particularly  under  the 
tongue  and  along  the  disto-lingual  surfaces. 

"MUSCLE  MARKING"  THE   IMPRESSION 

Steady  the  tray  with  both  hands  and  instruct  the  patient 
to  exert  active  muscular  etTort  with  cheeks,  lower  lip  anof 
tongue,  to  indicate  clearly  in  the  ]ilaster  the  muscular  attach- 
ments. As  before  stated,  the  time  required  to  carry  out  all 
of  these  several  steps  ought  not  to  exceed  thirty  or  forty  sec- 
onds, for  the  final  muscle  viarkiiig  must  l)e  accomplished  while 


72  TECHNIC    OF    TAKING    IMPRESSIONS 

tlie  plaster  is  still  soft  aud  capable  of  yielding  to  moderate 
pressure. 

REMOVAL   OF  THE   IMPRESSION 

Lower  impressions  require  a  little  longer  time  for  hard- 
ening than  do  uppers,  because  of  the  excess  of  moisture  pres- 
ent, the  saliva  usually  accumulating  in  excessive  quantity  and 
retarding  the  crystallization  somewhat. 

When  well  hardened,  the  impression  is  loosened  by  gently 
l)ulling  the  lips  and  cheeks  away  from  the  outer  flange.  Trac- 
tion up  and  down  on  the  tray  handle  is  made  at  the  same  time, 
and  the  air  finds  its  way  readily  between  impression  and 
tissues. 

Should  the  lingual  wings  extend  downward  and  outward, 
the  anterior  part  of  the  impression  should  be  raised  above 
the  border  and  the  tray  carried  back  a  short  distance.  As  the 
space  between  the  lingual  borders  widens  constantly  from  be- 
fore backward,  this  brings  the  flanges  into  more  open  terri- 
tory. By  tipping  or  lifting  one  side  of  the  tray  higher  than 
the  other  and  rotating  the  elevated  side  forward,  the  im- 
pression can  be  disengaged  and  rotated  out  of  the  mouth, 
usually  without  fracture.  Inspect  it  carefully  before  allowing 
the  patient  to  rinse  the  mouth,  and  if  fractured,  recover  the 
broken  pieces,  place  in  position,  and  lute  with  wax. 

PARTIAL  IMPRESSIONS  OF  THE  MOUTH  IN  PLASTER 

Partial  cases  are  those  in  which  some  but  not  all  of  the 
natural  teeth  are  missing.  Substitutes  designed  for  such 
cases  contain  a  less  number  of  teeth  than  are  usually  placed 
in  full  dentures.  For  obvious  reasons,  therefore,  an  im- 
pression of  such  a  case,  although  usually  involving  as  much 
area  as  an  edentulous  one,  is  termed  a  partial  impression. 

While  partial  impressions  may  be  secured  in  plaster 
alone,  as  a  rule  a  preliminary  imjiression  in  wax  or  modeling 
compound,  corrected  before  introducing  the  plaster  by  freely 
enlarging  the  impressions  made  by  the  teeth,  and  cutting  away 
the  excessive  surplus,  will  yield  more  accurate  results  than 
plaster  alone. 

In  practically  all  cases  of  partial  impression  work  where 
plaster  alone  is  used,  the  tray,  having  been  previously  oiled 
on  the  inside,  is  removed  as  soon  as  the  plaster  has  set. 

The  operator,  being  familiar  with  the  undercuts  present 
and  spaces  between  the  teeth,  cuts  the  impression  in  suitable 
places  to  weaken  it,  so  that  with  a  little  effort  it  may  be  frac- 


TECHNIC    OF    TAKING    IMPRESSIONS  Ti 

tured  and  removed  in  pieces.  Sometimes  the  breaking  of  one 
or  two  pieces  is  sufficient  to  release  the  impression  so  that  it 
will  come  away  in  very  nearly  a  whole  condition.  Again,  when 
teeth  and  spaces  alternate,  tlie  teeth  being  long  and  having 
constricted  crevices,  the  impression  must  be  broken  in  a  num- 
ber of  pieces  to  effect  its  removal.  In  all  cases  an  effort 
should  be  made  to  break  away  all  areas  that,  if  not  discon- 
nected, would  either  injure  the  tissue  or  be  marred  or  de- 
stroyed in  the  removal  of  the  impression.  If  the  fractured 
pieces  are  not  too  small,  and  are  of  reasonal)le  thickness,  pre- 
senting clean-cut  fractures,  the  impression  may  be  practically 
restored,  even  though  broken  in  many  i^ieces.  The  accuracy 
of  the  impression  depends  on  how  perfectly  the  broken  parts 
are  reassembled. 

The  wide  flange  trays  designed  by  Dr.  Angle  are  intended 
for  carrying  the  impression  material,  not  only  against  the 
labial,  buccal  and  lingual  surfaces  of  the  teeth,  but  for  holding 
it  in  contact  with  these  surfaces  of  the  alveolar  border  as 
well.  When  a  tray  with  narrow  flanges  is  used  in  partial 
cases,  the  necessity  for  using  wax  or  modeling  compound  as 
a  preliminary  impression  material  for  increasing  the  width 
of  the  flange  is  apparent. 

CLASSIFICATION  OF  COMMONLY  OCCURRING  PARTIAL  CASES 

Partial  cases  may  be  grouped  into  six  general  classes, 
according  to  the  teeth  lost: 

First — Posterior  teeth  on  both  sides  missing;  anterior 
teeth  in  place. 

Second — Posterior  teeth  on  one  side  missing;  opposite 
and  anterior  teeth  present. 

Third — Anterior  teeth  missing;  posterior  teeth  on  both 
sides  in  place. 

Fourth — Anterior,  and  posterior  teeth  on  one  side  miss- 
ing; posterior  teeth  on  opposite  side  in  place. 

Fifth — Teeth  and  spaces  alternating  with  more  or  less 
regularity. 

Sixth — An  occasional  tooth  missing. 

IMPRESSIONS  OF  PARTIAL  CASES 
Combination  Modeling  Compound  and  Plaster — Class  1 

SELECTING  THE  TRAY 
A  tray  of  the  flat-bottom  type,  with  flanges  of  moderate 
width  that  will  not  impinge  on  the  muscles,  is  best  adapted  to 
this  case.     Place  sufficient  softened  compound  for  a  regular 


74  TKCHNIC    OP    TAKING    IMPRESSIONS 

impression  in  the  tray,  luiilding  it  up  thicker  wliere  the  teeth 
are  missing  than  anteriorly.  The  compound  should  be  dis- 
posed in  the  tray  to  conform  as  nearly  as  possible  to  the  sur- 
faces being  copied,  and  be  reasonably  soft. 

TAKING  THE   PRELIMINARY    IMPRESSION 

Introduce  tilled  tray  in  the  mouth,  centralize  and  press 
up  slightly.  Steady  with  one  hand  and  draw  lip  and  cheek 
muscles  outward  to  prevent  them  from  folding  inwardly, 
and  press  to  place. 

Steady  the  tray  and  apply  linger  along  buccal  and  labial 
surfaces,  to  secure  sufficient  height  and  peripheral  adaptation. 


TRAY    FOR    PjVRTIAL    CASES.       FLAT    HOTTDM    TYI'E 

Instruct  patient  to  exercise  buccal  and  lip  muscles  freely 
to  indicate  their  position.  Chill  with  cold  water  applied  with 
napkin,  sponge  or  syringe,  or  with  cold  air,  and  remove. 

PREPARING   THE    PRELIMINARY    IMPRESSION    FOR   THE 
PLASTER 

Trim  off  excessive  surj^lus  buccaily,  distally,  and  periph- 
erally. Enlarge  freely,  both  labially  and  lingually,  the  im- 
pressions made  by  the  teeth.  Frequently  the  larger  part  of 
the  anterior  portion  of  the  impression  is  removed  to  give 
greater  bulk  to  the  plaster  which  surrounds  the  teeth. 

TAKING  THE   FINAL   IMPRESSION 

Mix  the  plaster  to  medium  consistency,  ]ilace  in  the  tray 
to  the  depth  of  an  eighth  of  an  inch  or  so,  quickly  introduce 


TECHNIC    OF    TAKING    IMPRESSIONS  75 

in  file  inoiitli,  partially  carry  to  place,  centralize  and  ))ress 
it  lip  against  the  teeth  so  they  will  occupy  a1)out  the  same  re- 
lation to  the  tray  flange  as  in  the  tirst  impression. 

Steady  the  tray  firmly,  draw  the  lip  over  the  lahial  flange, 
and  the  buccal  muscles  away  from  the  imjiression  margin. 


ritKI.IMINARY     IMPBESSIOX     IX     MODELING 


With  slight  vil)ratory  movement  and  moderate  i)ressure.  carry 
the  tray  to  place. 

With  outside  pressure  against  the  lips  and  cheeks,  adapt 
the  plaster  which  extends  above  the  compound  margin  to  the 
boi'der,  holding  the  tray  firmly  while  doing  so.  Instruct  the 
patient  to  exercise  the  buccal  and  labial  muscles  freely  and 
vigorously. 


76 


TECHNIC    OF    TAKING    IMPRKSSIONS 


REMOVING   THE   IMPRESSION 

Wlit'ii  set,  traction  on  the  tray  handle  will  loosen  tlie  iiii- 
pressiou,  although  if  the  teeth  are  long,  considerahle  force 
may  be  required  to  dislodge  it,  since  in  most  cases  the  plaster 
impression  must  necessarily  be  fractured.  On  removal,  place 
the  impression  within  convenient  reach  on  the  l)racket,  and 
recover  the  fractured  pieces  before  permitting  the  patient  to 
rinse  the  mouth.    As  each  piece  is  removed  it  is  placed  out- 


side of  the  impression  periphery,  but  as  near  to  its  proper 
position  as  i^ossible,  to  simplify  the  adjustment  of  the  several 
parts  later. 

ASSEMBLING  THE   FRACTURED  PIECES 

The  fractured  surfaces  of  both  the  impression  and  the 
pieces  are  cleared  of  small  adhering  particles  with  a  mod- 
erately stiff  camel's  hair  brush.  Care  should  be  taken  to 
clear  the  general  surfaces  of  the  modeling  compound  matrix 
of  debris  at  the  same  time.  The  character  of  the  fracture 
determines  the  order  of  assembling,  those  pieces  in  the  deep- 
est ]iortion  of  the  tray  oi-  comjiound  matrix  being  usually 
first  placed  in  position. 

The  pieces  are  luted  together  by  applying  a  little  wax  to 
the  fracture  lines  at  various  points,  usually  outside,  in  such 


TECHNIC    OK    TAKING    IMPRESSIONS  77 

mauuer  as  not  to  form  an  accretiou  to  tlie  impression  proper 
and  thus  change  its  form.  Wax  does  not  adliere  firmly  to 
damp  plaster  unless  the  latter  is  well  heated.  To  effect  a 
good  union  of  the  pieces,  a  spatula  is  heated  almost  to  redness 
and  applied  to  the  small  piece  of  wax  already  placed  on  the 
fracture  line.  The  spatula  should  be  laid  against  the  plaster 
so  as  to  heat  it  quite  hot.  The  wax  in  the  meantime  is  melted 
and  penetrates  the  substance,  thus  cementing  the  pieces  to- 
gether much  more  fimly  than  when  the  imion  is  superficial. 

CLASS  2 
BICUSPIDS  AND  MOLARS  OF  ONE  SIDE  MISSING 

A  flat-bottomed  tray,  similar  to  No.  16,  is  selected,  and 
wax  or  comiJound  heated  and  adjiisted  for  a  preliminary  im- 


hrSt 

'r-^> 

^ 

^^             ^^^^.^K, 

Wu  ^ri  ^^^^H 

^•^\ 

l^^K  hHB 

JLS" 

3 

ANGLE    TRAY    ADAPTED   TO   BORDER   AND   XATIRAI.    TEETH 

pression,  placing  it  thicker  on  the  one  side  where  the  teeth 
are  missing  than  elsewhere,  to  make  uji  for  loss  of  teeth  and 
tissues. 

The  general  steps  for  securing  the  impression  are  similar 
to  those  in  Class  1.  When  removed,  the  impression  material 
is  freely  cut  away  around  the  impressions  of  the  teeth,  botli 
labially  and  bucally,  as  well  as  lingually,  to  give  ample  space 
for  the  ])laster  which  is  to  enclose  them. 

CLASS  3 

ANTERIOR    TEETH     MISSING;    BICUSPIDS    AND    MOLARS    ON 
BOTH    SIDES    PRESENT 

The  same  general  style  of  tray  is  selected  as  in  the  pre- 
ceding case.    Wax  or  compound  for  preliminary  impression 


78  'nOCIINIC    OK    TAKINC!     IM  l'lil';SSK)NS 

is  introduced  in  llie  form  of  ratlior  a  wide  roll  extending  from 
labial  flange,  over  vault  portion,  to  distal  margin  of  tray. 

The  impression,  when  taken,  will  not  extend  out  to  the 
buccal  surfaces  of  the  teeth,  nor  will  it  usually  be  necessary 
to  include  them  in  the  preliminary  imjiression,  since  the  tray 
flange,  is  UKSually  wide  enough  to  support  the  plaster  against 
the  buccal  surfaces  of  the  teeth  and  the  adjacent  gingival 
margin  of  the  border  as  well.  However,  if  it  is  necessary  to 
secure  an  impression  of  the  entire  buccal  surfaces  of  the 
border,  tlie  tray  flange  can  be  increased  in  width  by  spread- 
ing the  preliminary  impression  material  over  the  entire  tray. 

CLASS  4 

ANTERIOR   AND    POSTERIOR   TEETH    ON    ONE   SIDE   MISSING; 
THE  OPPOSITE  POSTERIOR  TEETH   IN   PLACE 

The  same  general  style  of  tray  can  be  used  as  in  the  pre- 
ceding class.  The  compound  should  be  thicker  on  the  side 
where  the  teeth  are  missing.  The  preliminary  impression  is 
obtained,  trimmed  and  enlarged  at  the  proper  points,  and 
the  final  impression  seciired  in  plaster. 

CLASS  5 

TEETH  AND  SPACES  ALTERNATING  WITH   MORE  OR  LESS 
REGULARITY 

Teeth  and  spaces  alternating,  in  impression  work,  usually 
requires  that  the  impression  will  be  broken  into  several  pieces 
in  order  to  effect  its  removal.  Such  a  case  always  requires 
special  care  to  secure  accurate  results. 

The  usual  routine  described  for  the  preceding  cases  is 
applicable  here,  although  with  a  deep-sided  tray  of  the  Angle 
type,  vase  lined  inside  to  prevent  the  plaster  adhering,  will 
often  times  prove  more  satisfactory  than  the  combined  im- 
pression. In  fact,  the  Angle  tray  can  be  used  for  most  any 
of  the  partial  cases  described,  either  with  plaster  alone,  or 
combined  with  wax  or  modeling  comiiound.  The  one  serious 
objection  to  its  use  is  due  to  the  very  wide  flange,  preventing 
ease  of  finger  adaptation  of  the  impression  material. 

CLASS  6 
AN    OCCASIONAL    MISSING   TOOTH 

These  cases  are  handled  in  a  similar  manner  to  the  pre- 
ceding class.  A  preliminary,  ('om])ound  or  wax,  impression  is 
taken,  enlarged  and  used  as  a  receptacle  for  the  plaster. 


TECHNIC    OF    TAKING    IMPRESSIONS  79 

Frequently,  however,  wliere  teeth  and  spaces  alternate 
throughout  a  considerable  extent  of  the  arch,  a  properly  se- 
lected Angle  tray,  oiled  to  more  readily  part  from  the  im- 
pression, and  with  plaster  alone  used  as  the  impression  mate- 
rial, will  iJrove  as  satisfactory  as  the  combined  use  of  com- 
pound and  plaster.  The  vault  adai^tation  can,  in  most  in- 
stances, be  nuich  improved  with  wax  or  compound  additions. 
On  removal  of  the  tray,  the  plaster  which  fills  the  spaces  is 
notched  and  pried  apart,  to  release  the  impression. 

TO   BREAK  AN  IMPRESSION  ALONG  DEFINITE   LINES 

Strips  of  sheet  wax  are  attached  edgewise  to  the  floor 
of  the  tray,  and  so  adjusted  as  to  pass  into  the  spaces  where 
the  teeth  are  missing.  These  strips,  if  properly  adjusted,  will 
serve  to  divide  the  plaster  in  a  similar  manner,  Init  more  ef- 
fectively than  can  usually  be  done  by  notching  with  a  knife. 
By  inserting  the  knife  blade  into  the  wax  and  prying  slightly, 
the  impression  can  easily  be  broken. 

TAKING    IMPRESSIONS    OF    ELONGATED    AND    LOOSE    TEETH 

It  is  frequently  necessary  to  secure  an  impression  of  one 
or  more  elongated  or  loose  teeth,  which  if  taken  in  the  ordi- 
nary manner  would  very  likely  result  in  injiary  to  the  already 
weakened  peridental  membrane  of  tlie  tooth,  or  at  least  cause 
the  patient  some  discomfort. 


The  following  method,  if  carried  out  as  detailed,  is  con- 
venient, accurate,  and  practically  painless : 

Mix  a  small  amoimt  of  plaster  of  medium  consistency,  and 
apply  to  the  lingual  surfaces  of  the  loose  teeth  and  as  mxich 
of  the  ]»rocess  as  the  final  imjjression  should  cover  in  this  area. 


80  TECHNIC    OP    TAKING    IMPRESSIONS 

If  other  teeth  are  present,  it  may  sometimes  be  best  to  extend 
the  impression  so  as  to  include  them  for  subsequent  support. 
Now  mix  some  plaster  of  medium  consistency,  and  with  the 
point  of  a  spatula  apply  to  the  lingual  surfaces  of  the  teeth, 
making  such  additions  as  to  give  reasonable  thickness  to  the 
body  of  the  impression.  The  plaster  should  be  forced  into 
the  embrasures  and  extend  from  where  ]:)eripheral  plate  line 
will  rest  to  the  incisal  edge.  Should  the  embrasures  be  open, 
the  plaster  contained  in  them,  which  is  forced  labially  to  the 
point  of  shortest  diameter  of  the  space,  should  be  removed 
with  excavators,  so  that  this  half  of  the  impression  may  be 
removed  lingually  without  difficulty. 

When  set,  this  portion  is  removed  and  trimmed  smoothly, 
so  as  to  flare  from  gingival  to  incisal  or  occlusal  surfaces. 
It  is  then  entirely  coated  with  separating  fluid  and  re- 
turned to  its  former  position  in  the  mouth.  Another  mix  of 
plaster  is  applied  to  the  labial  or  buccal  surfaces,  securing 
good  adaptation  to  those  surfaces,  and  against  the  lingual 
body  of  plaster  presenting  in  the  embrasures  and  at  the  in- 
cisal or  occlusal  surfaces.  When  the  plaster  is  hard,  insert 
the  point  of  an  instrument  between  the  two  halves,  carefully 
pry  them  apart,  and  remove.  Trim  them  so  that  when  again 
returned  to  the  teeth  and  set  in  position,  they  form  a  trun- 
cated cone,  the  base  of  which  rests  against  the  alveolar  pro- 
cess, the  smaller  end  coming  evQn  with  or  covering  the  incisal 
or  occlusal  surfaces,  as  the  case  demands.  Usually  the  two 
pieces  will  be  retained  firmly  in  position  without  tying,  but 
they  can  be  ligated  together  if  necessary.  In  trimming,  re- 
duce the  jjieces  labio  or  bucco-lingually  as  much  as  possible, 
yet  without  weakening  them,  so  that  there  will  be  no  excessive 
bulk  to  interfere  with  the  next  step. 

Now  fit  a  tray  over  this  matrix,  or  in  reality,  the  core-to- 
he,  and  see  that  it  also  conforms  elsewhere  to  the  tissue  to  be 
included  in  the  impression.  Either  plaster  or  modeling  com- 
pound can  be  used  for  the  impression  material,  as  the  case 
requires.  The  impression  is  obtained  in  the  ordinary  manner, 
and  removed.  When  the  matrix  or  core  has  been  properly 
flared,  the  impression  will  part  from  it  without  difficulty.  The 
two  halves  of  the  matrix  are  now  removed  from  the  teeth 
they  enclose,  placed  in  their  respective  positions  in  the  im- 
pression, and  luted  firmly  with  wax. 

This  method  is  especially  valuable  in  taking  impressions 


TECHNIC    OF    TAKING    IMPRESSIONS  81 

of  teeth  in  pyorrhea  cases.  It  is  also  capable  of  application 
to  a  variety  of  difficult  conditions  that  are  frequently  met  with 
in  practice. 

IMPRESSIONS    IN    MODELING   COMPOUND 

When  manipulated  properly,  in  well  selected  cases,  mod- 
eling compound  is  a  most  reliable  impression  material.  By 
reference  to  the  "Indications  for  the  Use  of  Plaster,"  it  will 
readily  be  seen  when  to  avoid  the  use  of  modeling  compound. 


taIjAtim;  \ii:\v  of  keiui  thw  uic.movakj.e  handle 

In  probably  70  per  cent  of  edentulous  cases  presenting,  com- 
pound can  be  used  to  better  advantage  than  plaster. 

FULL  UPPER  EDENTULOUS  CASES  IN  MODELING  COMPOUND 

The  fitting  of  the  impression  tray  differs  in  no  respect 
from  the  fitting  of  a  tray  where  plaster  is  used,  except  that 
the  distal  extension  of  the  vault  portion,  so  commonly  re- 
quired for  plaster,  is  unnecessary  when  compound  is  used. 
Narrow  flange,  close-fitting  trays  of  the  Kerr-Greene  type 
are  especially  indicated,  although  other  forms  of  trays  can 
often  be  used  to  advantage.  The  compoiuid  selected  should 
become  plastic  "at  a  low  temperature,  and  liarden  quickly. 

The  Perfection  C'Ompound  made  by  the  Kerrs  of  Detroit 
fulfills  the  requirements  better,  perhaps,  than  any  other  mate- 
rial on  the  market.  It  is  furnished  in  the  form  of  cakes  for 
impressions,  and  also  of  tracing  sticks  for  making  additions 


82  TECIINIC    OF    TAKING    IMPRKSSIOXS 

when  necessary  lo  the  iieripliery,  or  any  ;irea  nf  the  iiiiiires- 
sion. 

'I'lie  aniouiit  tif  compouiHl  i-e(|uire(l  I'or  an  impression, 
when  tlie  tray  is  chise  tittiiiM',  is  very  slii^'ht,  nsually  h'ss  than 
(irie  hair  a  eak'e. 

SOFTENING  THE  COMPOUND 

The  modeling  compound  is  tlioronghly  warmed,  prefer 
ably  in  hot  water,  removed,  and  the  moisture  taken  up  with 
a  towel  or  napkin.  With  the  lingers  it  is  formed  into  a  ball, 
working  the  wrinkles  from  above,  underneatli.  Tliis  ball  is  then 


I.INdlAL     MEW     OF 


set  in  the  center  of  the  vault  portion  of  the  tray,  and  with 
the  fingers  the  compound  is  disposed  against  the  fiange  so  as 
to  assume  the  general  form  of  the  impression.  Or  the  com- 
pound may  be  worked  out  in  a  sheet  of  more  or  less  uniform 
thickness,  and  disposed  evenly  in  the  interior  of  the  tray. 
The  former  method  is  to  be  preferred,  as  a  perfectly  smooth 
imjiression  surface  is  readily  secured,  while  with  the  latter 
method,  creases  are  apt  to  form  while  adjusting  the  material. 
The  tray  is  heated  around  the  flange  and  maxillary  por- 
tion, over  a  small  frame,  to  cause  the  compound  to  adhere 
to  it  slightly.  The  tray  is  inverted  and  the  sus-face  to  be  im- 
in-essed  is  reheated  over  the  flame,  to  render  it  soft  and  plas- 
tic.   It  should  then  be  quickly  dii^ped  in  warm  water  to  prevent 


TUCIINIC    OF    TAKING     IMPRESSIONS  SI! 

the  eouipoiniil  stickiiiii'  to  the  tissues  while  ])assiii,n'  tiiruiii;li 
the  lips. 

INTRODUCING  THE  FILLED  TRAY 
The  tray  is  then  introchiced  in  the  montli  hy  the  same 
method  of  procedure  as  outlined  under  the  head  of  "Full 
Cases  in  Plaster."  In  fact,  almost  the  same  technie  is  fol 
lowed  with  comjwund  as  with  plaster,  viz. :  centering  the  tray ; 
partial  seating  of  the  impression  on  the  ridge;  drawing  out 
the  lip  and  cheeks  from  the  flange  margin;  carrying  the  im- 
pression to  place  under  pressure;  forcing  the  periyjheral  sur- 
plus in  close  adaptation  to  the  tissues,  particularly  along 
the  distal  vault  portion.  The  index  and  middle  fingers  ot 
both  hands  can  be  applied  to  the  compound  which  extends 
distally  beyond  the  tray  margin,  to  lift  up  and  hold  it  in  con- 
tact with  the  palatine  tissues.  These  fingers  can  alternately 
support  the  tray,  and  develop  adaptation  of  the  compound  to 
the  tissues  from  one  tuberosity  to  the  other. 

When  the  adaptation  is  completed,  moderate  pressure  is 
maintained  on  the  central  portion  of  the  tray,  and  the  im- 
pression chilled  with  cold  water,  applied  with  syringe  or  small 
sponge  or  najikin. 

On  removal,  the  imi^ression  is  inspected  closely  to  see 
that  all  essential  areas  have  been  copied.  The  excessive 
peripheral  surplus  is  then  trimmed  away  and  the  sharp 
angles  caused  by  the  cutting  smoothed  off.  Should  there  be 
any  slight  deficiency  at  any  point,  a  little  heated  compound 
applied  with  the  tracing  stick  and  the  impression  returned 
to  place  and  firmly  seated  will  correct  the  error. 

PERIPHERAL  READAPTATION 

The  impression,  as  it  now  stands,  even  if  the  steps  have 
been  accurately  carried  out,  is  no  better,  and  (juite  likely  not 
as  good,  as  an  ordinary  plaster  impression. 

The  efficiency  of  modp''"^;  /.oi>^ppn.i.^  lies  in  the  fact  that 
with  proper  technie  the  soft  areas  of  the  mouth  mav  be  com- 
l)resse(J,  and  a  corresponding  relief  from  ]>ressure  on  the 
hard  area  be  secured.  As  a  result,  the  denture,  when  con- 
structed, will. bear  uniformly  on  the  hard  and  soft  areas  alike, 
and  in  those  cases  of  prominent,  hard  raphae,  practically  en- 
tire relief  from  pressure  may  be  afforded. 

To  secure  the  compressive  effect  of  the  comjiound,  the 
impression,  on  removal,  is  thoroughly  chilled,  the  surplus 
trimmed  away,  and  the  entire  impressed  areas  heated  quite 


84  TKCHNIC    OF    TAKING     IMl'KKSaiONS 

hot  over  a  small  Buiiscn  or  alcoliol  flame,  to  the  depth  of 
about  one-sixteenth  of  an  inch.  In  this  condition  it  is  again 
returned  to  the  mouth,  properly  seated,  the  muscles  drawn 
outward,  and  steady  pressure  applied  for  two  or  three  min- 
utes. The  amount  of  force  necessary  to  apply  varies  from 
three  to  ten,  or  even  fifteen  pounds,  according  to  conditions. 
Extremely  soft,  spongy,  but  not  resilient,  tissiies  are  copied 
better  with  moderate,  while  harder  areas  require  a  greater 
amount  of  pressure. 

DISTRIBUTION    OF   THE    PLASTIC    COMPOUND    UNDER 
MAINTAINED   PRESSURE 

When  the  layer  of  softened  compound  is  of  uniform  thick- 
ness and  is  sufficiently  plastic,  under  continued  pressure  the 
material  gradually  flows  from  the  hard  to  the  soft  areas,  com- 
pressing the  latter  and  relieving  the  pressure  on  the  former, 
until  a  sort  of  equilibrium  is  established.  If  care  is  taken 
in  carrying  out  the  technical  details,  the  finished  denture  will 
have  a  similarly  uniform  bearing  on  the  tissues,  which  will 
add  greatly  to  its  stability. 

At  the  time  of  forcing  the  impression  up  against  the  tis- 
sues, the  excess  compound  is  naturally  moved  from  the  in- 
terior of  the  tray,  externally  and  over  the  flange  margin.  The 
tendency  is  for  the  compound  to  curl  outward,  away  from  the 
process.  It  therefore  becomes  necessary  to  readapt  the 
periphery  of  the  impression  to  the  border,  to  seal  against  the 
ingress  of  air.    This  step  is  accomplished  as  follows : 

PERIPHERAL   READAPTATION 

On  removal  of  the  impression  the  second  time,  it  is 
chilled  and  the  peripheral  margins,  buccally,  labially,  and 
lingually,  are  reheated.  It  is  again  returned  to  the  mouth  and 
seated.  With  the  index  finger  the  softened  margins  are  firmly 
pressed  into  close  contact  with  the  border,  buccally  and  labiallj^ 
first,  correcting  the  vault  portion  last.  Sometimes,  however, 
the  adaptation  of  this  margin  is  carried  out  as  a  separate, 
final  step.  Only  the  periphery  is  softened  in  this  rim  adjust- 
ment, since  if  the  whole  impression  is  reheated,  the  effect  of 
the  previous  compressive  steps  would  be  lost  and  adaptation 
would  be  impaired. 

The  inqiression  can  be  tested  as  to  adaptation  by  having 
the  patient  make  muscular  effort  to  displace  it  or  by  biting 
on  something  to  see  if  it  can  be  tipped.    The  removable  handle 


TECHNIC    OP    TAKING    IMPRESSIONS  85 

trays  of  the  Greeue  type  are  very  conveuient  for  testing' 
tlie  stal)ility  of  the  impression.  They  are  also,  on  account  of 
their  small  size  and  g-enerally  correct  form,  especially  adapted 
to  work  in  edentulous  mouths  with  compound,  eitlier  alone, 
or  eonibined  witli  phister. 


AN    T  TI'EIl     IMI-IIKSSIOX     SIIOWIN'G     ■■MrSCLE     TRIMMEl 


If  the  impression  is  readily  displaced  by  the  patient's 
efforts — can  be  thrown  down  in  laughing,  speaking,  biting,  or 
even  coughing — the  adaptation  is  not  perfect,  and  an  effort 
should  be  made  to  determine  the  weak  ]ioint  and  correct  it. 

A    SUMMARY    OF    STEPS    IN    MODELING    COMPOUND 
IMPRESSION  WORK 

To  summarize,  the  steps  for  compound  impression  work 
are  as  follows : 

Examination  of  the  mouth. 

Selection  and  adaptation  of  tray. 

Heating  and  adapting  modeling  compound  to  tray. 

Introduction  into  mouth,  and  centering  tray. 

Partial  seating  of  the  impression. 

Steadying  tray  while  lip  and  cheek  muscles  are  pulled 
outward  from  tray  margin. 

Carrying  tray  to  place  under  medium  pressure. 

General  adaptation  of  peripheral  surplus. 

Muscular  exertion  by  patient  to  indicate  location  and 
extent  of  muscular  attachment. 

All  of  these  manipulative  details  should  1)e  quickly  cai'- 
ried  out,  so  that  the  last  step  mentioned  may  1)e  accomplished 
while  the  compound,  is  still  capable  of  yielding  under  the 
stress  of,  and  being  indented  by,  the  lip  and  cheek  muscles. 

On  removal  the  impression  is  chilled,  the  surplus  mois- 
ture al)sorl)ed,  the  impressed  areas  heated  to  a  depth  of  one 
to  one  and  one-half  millimeters,  and  the  tray  returned  to  the 
mouth.  It  is  correctly  seated,  and  steady  pressure  applied 
for  two  or  three  minutes,  or  mitil  fairly  well  hardened. 


S()  TIOCIINIC    OF    TAKING     IMPRESSIONS 

Kl'Iuovc,  chill,  sol'tcii  the  iici'i|)lieral  iiiai'giii  lo  (he  dcplli 
of  ubout  two  millimeters,  and  return  to  the  mouth. 

Adapt  labial  and  buccal  periphery  to  the  process,  and  the 
distal  margin  of  the  vault  portion  to  tissues,  using  finger 
pressure,  applied  directly  to  the  compound  rim. 

Test  stability;  if  satisfactory,  remove,  heat  the  periphery 
to  a  slight  depth,  and  quickly  return  to  the  mouth  for  final 
muscular  adaptation  by  the  patient. 

Now  remove  the  impression,  again  examine  tlie  vault  por- 
lion  of  the  mouth  to  detei'mine  the  extent  of  the  hard  area, 
and  with  a  scraper  relieve  that  portion  impressed  by  tlie 
r.-ililic  to  the  depth  of  one-fourth  to  one  millimeter,  depending 
OH  the  condition  of  soft  tissues. 

Return  to  tlie  mouth  for  final  trial.  As  before  inti- 
mated, the  best  way  to  test  an  impression  is  for  the  patient 
to  subject  it  to  every  muscular  action  the  denture  will  be 
subjected  to,  as  well  as  its  resistance  to  tipping  stress.  In  no 
case  will  the  cast  derived  from  an  impression  be  more  ac- 
curate than  the  impression  itself.  It  therefore  follows  that 
if  an  impression  is  easily  dislodged,  the  resultant  denture 
will  be  even  more  readily  dislodged  than  the  impression. 

IMPRESSIONS  OF  LOWER  EDENTULOUS  CASES  IN  MODELING 
COMPOUND 

The  general  details  of  handling  modeling  compound,  as 
just  described  for  upper,  applies  in  man\'  respects  to  the  lower 
cases  as  well. 

The  fitting  of  the  tray;  heating  and  placing  the  com- 
pound; introduction  into  the  mouth;  centering;  partial  seat- 
ing; drawing  the  tissue  folds  out  from  under  the  tray  margin ; 
forcing  the  impression  to  place ;  steadying  tray  while  gen- 
eral adaptation  to  the  border  is  secured  liy  pressure  on  lips 
and  cheeks,  are  similar  in  detail  to  upper  cases. 

The  adaptation  of  the  compound  against  the  lingual  sur- 
faces should  be  carefully  wrought  out.  When  the  steps  have 
been  carried  out  as  just  mentioned,  the  tray  should  be  held 
firmly  in  ])lace  and  the  compound  adapted  to  the  lingual  border 
with  the  fingers,  l)eing  especially  careful  to  secure  as  perfect 
ada])lation  against  the  lower  disto-lingual  tissues  as  possible. 
The  final  test  for  the  depth  of  impression  is  obtained  by 
contraction  of  the  mylo-hyrid  muscles. 

On  first  introducing  the  impression,  the  ]iaiient  should 
elevate  the  tongue  while  the  operator  directs  the  compound 
into  correct  position  with  finger  pressure.    Wlien  adapted,  the 


TECHNIC    OF    TAKING    IMPRESSIONS  87 

compound  is  cliilled,  tlie  impression  is  removed,  and  the  ex- 
cessive surplus  is  trimmed  awaj'.  The  impressed  areas  are 
then  reheated  and  the  impression  again  returned  to  the 
moutli.  After  drawing-  the  muscles  from  under  the  tray  mar 
gins,  pressure  is  applied  to  force  the  compound  from  liard  to 
soft  areas,  as  outlined  ])reviously,  peripheral  adaptation  with 
linger  pressure  is  secured,  and  the  impression  is  chilled  and 
removed. 

A  method  for  securing  close  peripheral  adaptation  of 
lower  dentures  to  the  process,  with  relief  from  pressure  on 
the  crest  of  the  border,  is  suggested  by  Dr.  J.  W.  Greene.    A 


stream  of  hot  water  from  a  small-s})outed  vessel  is  allowed 
to  run  through  the  deepest  part  of  the  impression  until  the 
compound  in  this  location  is  thoroughly  softened,  care  being- 
taken  not  to  heat  the  edges.  The  entire  impression  is  then 
quickly  dipped  in  hot  water  so  as  to  soften  all  of  the  im- 
pressed areas  to  a  slight  extent.  The  impression  is  then 
quickly  returned  to  the  mouth,  and  with  a  springy  or  "wave 
like"  motion,  it  is  lightly  pressed  down  upon  the  border, 
chilled  and  removed. 


PARTIAL  IMPRESSIONS   IN   MODELING  COMPOUND 

There  are  few  partial  cases,  indeed,  where  modeling  com- 
pound will  meet  the  requirements  as  well  as  plaster.  Almost 
without  exception  in  the  class  of  cases  under  consideration. 


88  TECHNIC    OF    TAKING    IMPRESSIONS 

undercut  surfaces  are  present,  which  cau  only  be  copied  by 
an  unyielding  material  that  will  break  on  removal,  or  by  tak- 
ing a  sectional  impression  which  can  be  separated  along  pre- 
determined lines. 

Modeling  compound  can  l)e  used  to  advantage  in  sec- 
tional work,  the  character  and  extent  of  the  undercut 
surfaces  determining  the  form  and  number  of  the  sections. 
The  manner  of  procedure  is  as  follows : 


The  form  of  the  first  section  is  decided  upon.  Compound 
is  applied  slightly  in  excess  of  what  is  needed  to  form  this 
part.  When  cool,  it  is  properly  shaped  and  those  surfaces  of 
the  first  section  which  form  contact  areas  with  the  second 
section,  are  varnished  with  sliellac,  and  before  it  has  become 
dry  thin  tin-foil  is  spread  evenly  over  them  and  laid  down 
smoothly.  When  this  first  section  is  chilled  and  the  tin-foil 
slightly  oiled,  the  next  section  can  be  adapted  to  it,  and  by 
quickly  chilling  the  latter  no  change  of  form  will  occur  in  the 
first  section. 


TECHNIC    OF    TAKING    IMPRESSIONS  89 

The  two  or  more  sections  necessary  to  inclose  teeth  with 
constricted  necks,  fill  nndercnt  spaces,  or  open  embrasures, 
should  be  so  trimmed  as  to  permit  the  impression  proper,  in 
which  they  are  finally  inclosed,  to  separate  from  them  witli- 
out  distortion.  On  removal  of  the  im^jression,  the  sections  are 
separated  and  placed  in  their  respective  locations  in  the  ma- 
trix formed  by  them  in  the  impression.  They  may  be  held 
firmly  in  position  by  Inting  a  little  wax  along  the  joints. 
Either  compound  or  plaster  may  be  used  for  the  general 
impression  material  in  these  cases  of  "coring."  If  the  for- 
mer is  used,  the  entire  core  should  be  covered  with  foil  and 
■oiled,  and  the  manipulative  procedures  carried  out  rapidly,  so 
that  the  inherent  heat  in  the  sectional  material  may  not 
isoften,  and  the  pressure  in  placing  it  distort  the  impression. 
With  plaster,  as  an  impression  material,  the  oiling  of  the 
cores  is  sufficient. 


(MI  AFTER     VTTI 
TREATMENT  AND  FILLING  OF  IMPRESSIONS 

PRODUCTION  OF  CASTS 

As  previously  stated,  tlie  degree  of  success  attained  in 
denture  construction  depends  on  the  development  of  three 
essential  requisites,  viz:  xtse.fulness,  good  looks  and  comfort. 

The  realization  of  two  of  these,  usefulness  and  comfort; 
dejieuds  primarily  upon  the  impression  and  the  cast  derived 
therefrom,  since  the  latter  gives  the  reverse  form  to  the 
denture.  The  necessity,  therefore,  for  accuracy  in  impression 
taking  and  cast  construction  is  imperative,  for,  if  the  founda- 
tion is  faulty,  the  superstimcture  will  fail.  A  defective  im- 
pression invariahly  yields  an  imperfect  cast.  It  does  not 
follow,  however,  that  a  satisfactory  impression  will  always 
yield  a  perfect  cast.  The  accuracy  of  the  cast  depends  upon 
the  care  and  precision  exercised  in  its  production. 

The  technique  of  cast  construction  is  similar,  whether 
the  impression  is  of  plaster  or  of  modeling  compound.  The 
details  differ  slightly.  Each  class  will  be  taken  up  separately, 
and  the  important  details  noted. 

TREATMENT  OF   PLASTER  IMPRESSIONS   IN  EDENTULOUS 
CASES 

Certain  preparatory  steps  must  be  carefully  carried  out 
in  the  impression  before  the  cast  is  produced : 

First — The  impression  should  be  examined  closely  to  see 
that  it  is  intact.  If  broken,  the  pieces  should  be  placed  in 
correct  position,  firmly  luted  with  wax,  and  the  impression 
itself  secured  in  the  tray. 

Second — The  scraping  of  those  parts  impressed  by  the 
hard  areas  of  the  mouth,  as  detailed  in  a  previous  chapter, 
should  be  carefully  execvited,  and  the  impression  freed  from 
debris  with  a  clean  sable  brush. 

Third — A  staining  medium  which  will  ])euetrate  to  the 
depth  of  1  to  2  mm  should  be  applied  to  the  exposed  surfaces, 
so  that  in  cutting  the  impression  to  weaken  it,  in  removal  from 
the  cast,  the  stained  portion  will  indicate  the  near  approach 
to  the  line  of  demarkation  between  the  two,  and  thus  prevent 
injury  from  the  knife. 

Fourth — A  separating  medium  must  be  applied  to  the 

9Q 


TREATMENT    AND    FILLINC    OF    IMPKESSIOXS  91 

iini)r('ssi()ii  to  i)rev('iit  the  plaster  coiistitntiiii;'  I  lie  cast  from 
heeomiiig  so  firmly  adherent  to  it  that  the  two  cannot  be 
separated  without  defacing  the  cast. 

The  reason  wliy  a  second  addition  of  plaster  adheres  to 
one  previously  hardened,  unless  steps  are  taken  to  prevent, 
is  due  to  the  fact  that  plaster  crystallizes  in  setting  and  the 
crystals  are  grouped  so  as  to  leave  many  spaces  between, 
as  has  been  i^reviously  shown.  The  face  of  an  impression 
presents  just  such  a  formation.  It  has  also  been  shown  that 
in  a  fresh  mix  of  plaster,  the  granules  of  the  half  hydrate 
are  actually  dissolved  in  the  water,  and  that  in  and  from  this 
solution  the  crystals  of  di-hydrate  form. 

Where  such  a  mixture  is  applied  to  a  surface  of  plaster 
previously  set,  the  solution,  to  a  certain,  extent,  is  taken  up 
by,  and  tills  some  of  the  interspaces  in  the  hardened  plaster, 
and  there  crystallizes.  These  crystals  are  in  reality  so  many 
irregular  points  projecting  from  the  freshly  set  plaster,  ex- 
tending in  various  directions  into  the  face  of  the  previously 
set  mass,  thus  anchoring  the  two  bodies  of  plaster  together. 

In  separating  the  two,  many  of  these  projecting  crystals 
are  necessarily  broken,  and  in  breaking,  the  faces  of  both 
masses  are  more  or  less  injured.  Sometimes  the  two  masses 
adhere  so  closely  as  to  render  separation  impossible  with- 
out destroying  the  cast  and  impression  as  well.  The  remedy 
lies  in  literally  waterproofing  the  surface  of  plaster  against 
which  the  fresh  mix  is  to  be  cast,  which  prevents  the  plaster 
in  solution  from  entering  the  spaces  referred  to. 

The  selection  and  proper  application  of  suitable  staining 
and  separating  mediums  is  therefore  of  the  greatest  impor- 
tance where  the  production  of  accurate  casts  is  desired. 

STAINING  FLUIDS 

A  staining  fluid  should  be  capable  of  penetrating  either 
moist  or  dry  plaster  to  a  depth  of  1  or  2  mm  for  reasons 
before  stated.  Since  its  purpose  is  to  stain  only,  it  should 
l)e  absorbed  by  the  plaster  to  which  applied,  without  form- 
ing a  film  on  the  surface. 

A  thin  alcoholic  solution  of  orange  shellac  is  a  most  ex- 
cellent medium  for  staining.  If  used  thin,  quite  a  dark  tinge 
may  be  imparted  to  the  impression  by  applying  two  or  three 
coats  without  glazing  the  applied  surfaces.  Each  application 
should  be  allowed  to  dry  before  the  next  is  laid  on. 

An  aqueous  solution  of  some  of  the  analine  colors  is 
frequently  used,  hut,  unless  carefully  handled,  will  stain  the 


92  TKKATMKNT    AM)    I'lhlJNC    OK    IMPKKSSJOiNS 

fingers,  and  is  difficult  to  roniove.  Coloring  matter  is  some- 
times added  to  the  separating  medium,  the  idea  heing  to  con- 
vert it  into  a  staining  medium  as  weU. 

Most  separating  mediums,  however,  do  not  penetrate  tlie 
plaster  to  any  appreciable  dei)th,  and  therefore  tlie  stain  is 
(!onfined  very  closely  to  the  line  of  demarkation  between  the 
impression  and  the  cast.  The  stain  applied  to  an  impression 
in  this  manner  will  not  give  sufficient  warning  when  cutting 
the  impression  away,  and  in  partial  cases  especially,  the  cast 
is  very  liable  to  be  injured.  The  aqueous  solutions  to  be 
described  later  may,  by  adding  a  suitable  pigment,  be  ef- 
fective both  as  a  separating  and  staining  medium. 

SEPARATING  MEDIUMS 

The  preparations  used  for  separating  purposes  are  known 
under  various  names,  as  separating  or  parting  mediums, 
fluids,  varnishes,  etc.  They  may  be  procured  of  the  supply 
houses,  or  compounded  in  the  laboratory  with  very  little 
effort. 

REQUIREMENTS 

To  accomplish  the  desired  result,  a  separating  medium 
to  be  used  in  cast  production  particuarly,  should  possess  cer- 
tain requisite  qualities : 

First — It  should  be  impervious  to  moisture,  after  being 
applied  to  j^laster  and  allowed  to  dry. 

Second — It  should  not  modify  the  areas  covered  to  any 
aj^preciable  extent,  and  hence,  should  be  effective  when  ap- 
plied in  an  extremely  thin  film. 

Third — It  should  present  a  smooth,  glazed  surface  when 
dry,  so  as  to  produce  a  correspondingly  smooth  surface  to 
the  cast. 

Fourth — It  should  have  sufficient  cohesiveness  to  stick 
to  the  applied  surface,  and  not  become  adherent  to  the  cast. 

Fifth — It  should  dry  or  harden  quickly,  and  not  combine 
chemically  with  the  plaster,  or  be  subject  to  deleterious  change 
itself. 

CLASSIFICATION   OF   SEPARATING   MEDIUMS 

A  simple  classification  of  the  separating  mediums  in  com 
mon  use  are  here  presented : 

Alcoholic  solutions 
Ethereal  solutions 
Aqueous  solutions 
Oils 


TREATMENT    AND    KILLING    OF    LMPKESSIONS  93 

ALCOHOLIC  SOLUTIONS 
SANDARAC   VARNISH 

Sandarac  is  a  resinous  exudate  from  the  Thyia  Articulata 
of  the  pine  family,  wliich  grows  in  northern  Africa.  The 
gum  exudes  from  the  tree  in  the  form  of  small  globules, 
called  tears,  ranging  in  color  from  pale  yellow  to  brown.  The 
light  variety  is  considered  the  best,  and  selected  tears  of  this 
color  should  be  used  in  making  the  varnish  for  separating 
purposes.  It  comliines  in  various  proportions  with  alcohol, 
but  if  too  small  a  percentage  of  the  latter  is  used  in  its  com- 
position, or  if  the  alcohol  is  allowed  to  evaporate,  the  varnish 
becomes  too  thick  for  use  in  accurate  cast  production.  If 
from  any  cause  it  is  too  thick,  the  addition  of  a  little  alcohol 
will,  after  standing  a  time,  reduce  it  to  proper  consistency. 

Sandarac  and  alcohol  in  the  following  proportions  make 
a  satisfactory  varnish  for  separating  purposes : 

Selected  light  sandarac 6  oz. 

Grain  alcohol 24  oz. 

Digesting  in  a  water  bath  of  moderate  temperature  will 
aid  in  dissolving  the  gum. 

It  is  not  advisable  to  add  a  pigment  to  this  varnish  in 
order  that  it  may  serve  as  a  staining  medium  also.  Sandarac 
varnish  does  not  penetrate  the  surface  of  plaster  to  any  ap- 
preciable depth,  and  the  stain  will  not  extend  beyond  the 
depth  penetrated. 

The  best  plan  is  to  stain  the  impression,  as  before  sug- 
gested, with  thin  shellac,  which  readily  i^enetrates,  and  after 
it  is  dry,  apply  the  sandarac.  If  of  proper  fluid  consistency, 
one  coat  of  sandarac  is  sufficient.  If  rather  thin,  two  coats 
should  be  applied,  allowing  the  first  to  dry  before  making 
the  second  application,  and  the  second  should  be  dry  before 
making  the  cast. 

ETHEREAL  SOLUTIONS 

Under  this  division  two  substances  will  be  described 
which  are  dissolved  in  ether,  viz:  collodion  and  soap. 

COLLODION 

Collodion  may  be  procured  at  any  drug  store,  or  it  can 
be  compounded  in  the  dental  laboratory.    It  is  made  by  dis- 
solving gun  cotton  in  ether,  using  enough  of  the  latter  to  ' 
make  a  thin,  syrupy  liquid.     Since  gun  cotton  is  highly  in- 


(»4  TREATMKNT    AND    FII.UNG    OF    IMPHKSSIONS 

ll;niiiii;ilil('  and  ctlicT  also,  to  a  lesser  extent,  care  must  be 
exercised  in  making  the  solution  to  keep  it  away  from  a 
tlamc.  The  impression  should  be  stained,  as  previously 
described,  before  using  collodion  as  a  seijaraling  medium. 

ETHEREAL    SOAP 

I'Jthereal  soap  is  frequently  used  in  tlie  class  of  work 
under  consideration.  A  fine  quality  can  be  procured  from 
drug  houses,  and  if  used  properly  on  a  previously  stained 
impression,  will  serve  as  a  good  separating  material. 

AQUEOUS    SOLUTIONS 
BORAX   AND   SHELLAC 

A  saturated  solution  of  borax  in  water  will  dissolve 
shellac,  producing  a  fluid  capaljle  of  staining  the  impression. 
This  is  really  the  only  separating  medium  that  combines  both 
staining  and  separating  qualities  so  as  to  get  the  desired  re- 
sults. It  can  be  compounded  in  the  dental  lalioratory  as 
follows : 

Water  in  large-mouth  bottle  1  gal. 

Borax    lA  lb. 

By  applying  heat  (water  bath)  and  stirring  occasionally, 
the  water  becomes  saturated.  A  little  excess  of  borax  re- 
maining in  the  bottom  of  the  vessel  will  do  no  harm,  and  in- 
sures full  saturation  of  the  water. 

To  this  solution  add  X^  lb.  of  ordinary  brown  shellac 
in  flakes,  and  let  stand  a  few  days.  It  will  be  gradually  dis- 
solved, and  the  liquid  will  assume  a  purplish  tinge,  due  to 
the  action  of  the  borax  on  the  shellac.  The  solution  of  the 
shellac  may  be  hastened  by  the  application  of  moderate  heat, 
and  also  by  stirring  occasionally.  A  white  scimi  arises  to 
the  surface  of  the  fluid,  which  should  be  removed  before 
bottling.  By  siphoning  the  liquid  out  of  the  bottle,  neither 
the  scum  on  top  nor  the  excess  of  borax  and  shellac  in  the 
bottom  will  be  disturbed.  The  best  quality  of  medium  is 
produced  by  allowing  the  solution  to  stand  a  week  or  more, 
stirring  occasionally,  before  siphoning  into  bottles.  It  should 
be  kept  tightly  corked  when  not  in  use,  to  prevent  evaporation 
of  the  water. 

In  using  this  as  a  separating  medium,  it  should  be  ap- 
plied freely  and  quickly  with  a  fair-sized  brush,  bathing  the 
entire  impression  surfaces  with  the  liquid.  The  brush  should 
be  used  to  distribute  it  evenly  at  first,  and  before  it  begins 


TREATMENT    AND    FILUNG    OF    IMPRESSIONS  95 

to  thiokeu,  to  take  up  the  suri^his.  Tlie  tirst  application  is 
absorbed  by  the  plaster  without  leaving  a  decided  tilni,  and 
in  this  manner  the  impression  is  stained.  When  dry,  a  second 
coat  is  a])plied  and  also  allowed  to  dry  before  producing  a 
cast.  The  tinal  coat  should,  and  if  properly  applied  will,  pre- 
sent a  smooth,  glazed,  thin,  uniform  layer  on  all  surfaces  cov- 
ered, and  enable  the  impression  to  be  readily  removed  from 
the  cast.  The  tirst  mention  of  this  solution  that  the  writer 
is  aware  of  appeared  in  Gorgas,  Ed.  1895. 

SOAP  SOLUTION— AQUEOUS 

Soap  lather  serves  as  a  good  separating  medium  when 
applied  to  a  shellac  stained  impression.  The  soap  should  be 
worked  well  into  the  surfaces  so  as  to  till  the  interspaces  be- 
tween the  crystals,  after  which  practically  all  excess  should 
be  removed  with  clear  water  and  a  clean  brush.  In  partial 
cases,  special  care  must  be  taken  to  free  the  impressions  of 
the  teeth  from  the  lather,  or  the  air  contained  therein  will 
prevent  the  settling  of  the  cast  plaster  into  the  matrices,  or 
impressions  of  the  teeth. 

WATER  AS  A  SEPARATING  MEDIUM 

By  thoroughly  saturating  a  plaster  impression  with 
water,  no  other  separating  medium  need  be  applied.  The 
impression  must  be  filled  while  saturated,  and  separated  from 
the  cast  as  soon  as  the  latter  has  set.  Very  good  results  can 
be  secured  in  this  manner,  if  the  precautions  mentioned  are 
observed.  If,  however,  the  impression  and  cast  are  not  sep- 
arated very  soon  after  the  latter  has  set,  a  union  of  the  two 
occui's  which  will  inhibit  separation  without  injuring  one  or 
both. 

OILS 

Oils  are  not  good  separating  mediums  luider  any  circum- 
stances, although  commonly  used  for  flask  sei)aration,  and 
sometimes  in  impression  work.  The  surface  of  the  cast 
plaster  contains  many  minute  air  bubbles  not  present  when 
some  of  the  other  mediums  mentioned  are  used.  Lard,  sperm 
and  the  paraffin  oils  are  usually  used  for  this  purpose.  When 
employed  as  f.  separating  medium,  the  impression  should  be 
previously  stained  with  shellac. 

GENERAL  REMARKS 

A  thorough  understanding  of  the  ])hysical  nature  of 
]ilaster  and  of  the  separating  mediums  in  use  is  essential 


96  TREATMENT    AND    PILIjING    OP    IMPRESSIONS 

in  securing  accurate  results.  Carelessness  in  applying  a  mo 
dium  to  an  impression  usually  results  in  an  imperfect  cast. 

Care  and  attention  to  details  is  just  as  necessary  in  th;; 
class  of  work  being  considered,  as  in  any  of  the  other  essential 
details  of  denture  construction. 

A  chain  is  only  as  strong  as  its  weakest  link,  and  therefore 
an  imi3erfect  cast,  regardless  of  how  accurately  all  other  de- 
tails are  carried  out,  will  result  in  the  finished  denture  prov- 
ing more  or  less  disappointing  to  both  patient  and  pros- 
thetist. 

FORMS  FOR  CASTS  AND  MODELS 

All  casts,  whether  full  or  partial,  u]iper  or  lower,  should 
have  flat  bases  with  sides  either  i)arallel  or  slightly  converging 
from  the  base  to  the  peripheral  face  outline.  The  flaring 
form  is  essential  when  the  cast  is  to  be  used  as  a  model. 


The  central  palatine  portion  of  upper  and  floor  of  lower 
casts  should  be  about  one-half  an  inch  thick  to  give  stability 
throughout  the  various  steps  to  which  they  are  subjected  in 
denture  and  die  construction.  In  general  the  peripheral  out- 
line of  casts  should  conform  to  those  of  the  alveolar  arches. 
In  trimming,  the  peripheral  surplus  of  plaster  should  be  re- 
duced, so  as  to  bring  the  sides  close  to  the  reflection  of  the 
labial  and  buccal  tissues,  so  that  later  on,  in  waxing  and 
flasking,  there  will  be  no  excessive  surplus  to  interfere  with 
these  steps.  The  crescent  shape  so  frequently  given  lower 
cases  is  not  recommended  because  of  the  liability  of  the  cast 
to  break  in  removal  of  the  impression,  and  later  on,  when 
detaching  the  cast  from  the  occluding  frame.  This  form  may 
l)e  adopted  when  the  Kerr  metal  forms  are  used  in  conjunc- 
tion with  plaster. 


TREATMENT    AND    PILLING    OF    IMPRESSIONS  97 

CASTS  FOR  CELLULOID  CASES 

In  constructing  casts  for  celluloid  cases,  they  should  be 
made  sufficiently  thick  and  of  a  coarse  variety  of  plaster,  or 
of  Spence's  Compound,  so  as  to  withstand  heavy  stress. 
Spence's  Plaster  Compound  makes  a  very  resistant  and  satis- 
factory cast  for  celluloid  cases  much  better  than  any  grade 
of  plaster  procurable.  Casts  for  this  class  of  work  are  made 
of  the  same  general  form  as  previously  described. 

Magnesium  oxy-chloride  is  also  an  excellent  material  for 
casts  for  celluloid  work,  but  is  extremely  difficult  to  remove 
from  the  dentiire. 

CASTS  FOR  PLASTIC  METAL  BASES 

Cast  metal  base  plates  are  formed  by  casting  aluminum, 
tin,  tin  alloys,  or  gold  into  matrices  composed  of  some  re- 
fractory investment  compound.  The  usual  materials  used 
are  finely  ground  silex,  asbestos,  pumice  stone,  marble  dust, 
soapstone.  etc.,  combined  in  varying  proportions  with  suffi- 
cient plaster  to  till  the  voids  between  the  granules,  and  thus 
act  as  a  cementing  medium.  The  refractory  material  is  in- 
corporated to  prevent  cracking  of  the  investment  when  heated, 
and  because  less  change  in  form  will  occur  when  and  while 
heated,  than  with  plaster  alone.  Casts  for  this  class  of  work 
are  of  the  same  general  form  as  those  pre\'iously  described. 

CASTS  DESIGNED   FOR  MODELS   IN  THE   PRODUCTION   OF 
METAL  DIES 

In  shajting  a  cast  for  a  model  it  should  possess  certain 
characteristics: 

First — Its  sides  should  flare  outward  from  face  to  base. 
at  an  angle  ranging  from  75  to  80  degrees  from  the  hori- 
zontal, to  facilitate  its  easy  removal  from  the  sand  matrix. 

Second — It  should  be  as  thin  as  ]iossible  to  be  consistent 
with  strength,  since,  according  to  brass  and  iron  molders. 
thin  patterns  or  models  are  less  apt  to  distort  the  matrix  in 
removal  than  when  thick  and  bulky  ones  are  employed. 

Third — The  base  should  be  flat,  to  accord  a  firm  founda- 
tion for  the  model  in  packing  the  sand  matrix. 

Foiirtli — Tha  base  should  bear  such  relation  to  the  vault 
portion  that  the  inclination  of  the  latter  upward  from  the 
deeper  or  alveolar  iiortions  of  the  matrix  shall  be  uniform 
and  highest  at  the  distal  margin.  If  the  central  vault  portion 
is  higher  than  the  distal  margin  of  the  matrix,  a  dome-shaped 
space  in  the  die  results,  in  which  gases  accumulate  and  find 


98 


TREATMBNT    AMI    FILIJNC    Op"    IMPIt?:SS10NS 


vent  tlirons'li  the  partially  solidiiicd  metal.  This  fretiuently 
causes  so  serious  a  defect  as  to  render  the  die  worthless.  This 
danger  is  obviated  by  so  forming  the  base  of  the  model  as  to 
raise  the  anterior  higher  than  the  posterior  portion.  It  may 
also  be  obviated  by  packing  sand  mider  the  anterior  portion  of 


PLASTER   MODEL    SHOWING    PKOJECTIONS    OF    TBIilllED    TEETH 

tlie  model  and  elevating  it  in  this  manner,  before  placing  the 
molding  ring.  The  better  plan  is  to  develop  the  correct  form 
of  the  model  in  plaster. 

CASTS  DESIGNED  FOR  MODELS  FOR  PARTIAL   DENTURES 

Models  for  partial  cases  are  given  the  same  general 
flaring  form  as  those  for  full  cases.  In  addition,  the  teeth 
must  be  cut  off  squarely  about  one-sixteenth  of  an  incli  from 


DIAGRAMSLVTIC    VIEW    OF    TIllMilED    MODEL 


the  gingival  line.  This  is  necessary,  first,  because  the  gen- 
eral contour  of  the  teeth  will  not  permit  of  their  withdrawal 
from  the  sand  matrix  without  distorting  the  latter.  Second, 
it  permits  the  plate  to  be  reflected  against  their  surface,  there- 
by strengthening  it.    If  reduced  to  the  length  suggested,  the 


TREATMENT    AXD    FILLING    OP    IMPRESSIONS  99 

removal  of  the  model  from  the  sand  can  in  most  oases  be 
accomplished  readily. 

In  lower  partial  cases  when  the  anterior  teeth  are  pres- 
ent, these  teeth  on  the  model  should  have  only  their  incisal 
thirds  removed.  When  the  die  is  secured  and  the  base  is 
swaged,  the  latter  should  be  allowed  to  extend  up  over  the 
cingulaj,  to  afford  stability  to  the  denture  and  protect  the 
gums  from  stress,  as  well  as  to  guard  against  the  ingress  of 
food  between  the  teeth  and  substitute  in  this  location. 

UNDERCUTS   AREAS 

Any  depressions  or  decided  undercuts  on  the  laliial  or 
buccal  surfaces  of  the  model,  not  involving  areas  covered  by 
the  denture,  can  be  eliminated  by  filling  in  with  plaster  or 
hard  wax  and  giving  such  surfaces  the  proper  flare  for  with- 
drawal from  the  matrix. 

The  outer  surfaces,  as  well  as  the  bases  of  models,  should 
be  finished  with  fine  sandpaper  to  render  them  smooth,  and 
the  entire  model  varnished  with  two  or  three  coats  of  shellac 
evenly  applied. 

CORES 

A  core  is  an  addition  of  investment  compound,  or  some 
refractory  material,  which,  when  built  against  an  undercut 
surface  on  a  model  and  properly  trimmed,  is  used  for  develop- 


ing the  negative  of  that  surface  in  the  sand  matrix,  and  fur- 
nishing a  form  against  which  the  die  may  be  cast.  The  con- 
structive steps  are  as-  follows : 

The  varnished  model  is  oiled  over  the  area  to  be  covered 
by  the  core.  The  investment  compound  is  mixed  to  a  thick 
consistency  and  applied  to  the  undercut  surface  of  the  model, 
extending  it  from  the  base  to  near  the  crest  of  the  l)order,  and 
slightly  beyond  the  undercut  area  at  either  end.  It  should  be 
from  6  to  8  mm  thick.    If  too  tiiin,  it  is  lialile  to  warp  in  dry- 


mo  TREATMENT    AND    KILLING    OP    LMPRESSlOXS 

iug,  or  break  wlieu  iu  use.  If  too  thick,  it  will  interfere  with 
the  centering  of  the  model  in  the  molding  ring.  When  set,  it 
is  trimmed  so  that  its  outer  surface  is  parallel  with  the  side 
of  the  model  it  covers.  The  ends,  as  well  as  the  sides,  should 
converge  slightly,  from  base  to  crest.  The  upper  portion  of 
the  core,  where  it  finishes  against  the  border,  should  present 
a  right  angle  to  this  surface,  and  tlius  give  the  core  a  flat 


MODEL    WITH    CORE    IN     POSITION 

seat  in  the  sand  matrix.  When  trimmed  and  sandpapered  it 
is  removed  from  the  model  and  the  moisture  driven  off  at 
moderate  temperature  to  prevent  warping.  The  surface  is 
rendered  smooth  by  rubbing  soapstone  into  it.  When  fin- 
ished as  described,  it  is  returned  to  the  model  and  is  ready 
for  use. 

CONSTRUCTION  OF  CASTS— GENERAL  REMARKS 

The  construction  of  the  cast  is  ordinarily  spoken  of  as 
"pouring  the  impression."  The  term  is  incorrect  and  mis- 
leading as  well,  for  the  reason  that  plaster  intended  for 
casts  and  in  the  fiasking  of  cases  should  never  be  so  thin 
as  to  be  readily  "i>oured"  from  the  bowl. 

Plaster  of  such  consistency,  when  set,  is  inherently  weak, 
low  in  density,  and  less  resistant  to  stress  than  is  the  case 
when  the  mix  is  thicker.  This  is  due  to  the  fact  that  when 
thin,  an  excess  of  water  is  present  and  occupying  space  that 
should  contain  calcium  half  hydrate.  When  crystallization 
sets  in,  the  plaster  in  solution  in  the  water  is  gradually  taken 
up  to  complete  the  crystals  partly  formed,  and  to  form  the 
nuclei  for  other  crystals. 

The  half  hydrate  solution  is  thus  constantly  being  de- 
pleted of  its  calcium  sulphate  in  the  building  up  of  new 
crystals,  with  no  corresponding  diminution  in  the  bulk  of 
water.  In  other  words,  when  set  and  the  excess  water  has 
evaporated,  the  mass  will  contain  fewer  crystals  and  more 


TREATMENT    AND    FILLlNfJ    OP    IMPRESSIONS  101 

spaces  thau  will  a  mass  of  similar   hulk  mixed  to  proper 
consistency. 

A  cast  produced  from  a  thin  mix  of  plaster,  as  before 
stated,  will  be  less  resistant  to  stress  thau  a  denser  one,  and 
when  subjected  to  heavy  pressure,  as  in  the  closure  of  an  over- 
packed  flask,  will  yield,  the  crystals  l)reaking  under  the  load. 

DELETERIOUS  PROPERTIES  OF  PLASTER 

Special  care  should  be  exercised  in  the  mixing  of  plaster 
for  any  purpose  to  have  it  of  proper  consistency ;  also  in 
avoiding  excessive  stirring,  which  induces  needless  expansion. 
It  should  be  sufficiently  plastic  to  conform  to  all  irregular  sur- 
faces by  slight  jarring,  but  not  so  thin  as  to  pour  readily. 
Disregard  of  the  peculiar  properties  of  this  most  sensitive 
material,  viz :  its  tendency  to  expand,  its  susceptibility  to 
compression  imder  load,  and  the  deleterious  action  of  heat 
and  moisture  upon  it,  results  in  manifold  errors  and  mishaps 
that  lead  to  impaired  adaptation  and  frequent  failures  in 
denture  construction. 

The  recognition  of  these  deleterious  properties  has  re- 
sulted in  greater  care  being  exercised  by  many  in  manipulative 
procedures  with  plaster  than  was  formerlj'  displayed,  as  well 
as  in  the  introduction  of  more  stable  and  resistant  materials 
for  casts.  Among  these  may  be  mentioned  Spence's  Plaster 
Compound — a  mixture  of  plaster,  Portland  cement,  and  other 
substances  for  controlling  expansion.  This  compound  is  much 
less  compressible,  while  its  expansive  index  is  lower,  than  the 
best  grades  of  plaster. 

MATERIALS  USED  FOR  CASTS 

The  materials  commonly  used  for  casts  for  both  vul- 
canite and  other  cases  are  here  presented  in  order,  ranging 
from  those  having  the  greatest  to  those  showing  the  least 
resistance  to  stress: 

a.     Magnesiiim  Oxy-chloride. 

1.  Spence's  Plaster  Compound.  " 

2.  Coarse  Building  Plaster, 
o.     French's  Regular  Plaster. 

4.  French'*;  Impression  Plaster. 

5.  Ordinary  Commercial  Plaster. 

DELETERIOUS  EFFECT  OF  ACCELERATORS  ON  CASTS 

Plaster  easts  containing  accelerators  such  as  common 
salt  or  potassium  sulphate  have  a  greater  affinity  for  mois- 


102  TREATMENT    AND    FILLING    OF    IMPRESSIONS 

ture  and  soften  nioro  quickly  in  the  vulcanizer  in  tlie  presence 
of  heat  and  steam,  than  do  those  from  wliich  these  substances 
have  been  omitted.  Therefore,  to  avoid  danger  of  distortion 
of  easts  in  vulcanizing,  Impression  Plasters  should  not  be 
used  for  casts,  as  they  contain  accelerators — usually  potas- 
sium sulphate.  The  fourth  class,  therefore,  for  causes  de- 
tailed, is  unsuited  for  cast  production. 

The  fifth  class  mentioned  is  usually  a  plaster  of  uncer- 
tain quality,  sometimes  over  or  imder  burned,  containing  im- 
l)urities  which  render  it  more  or  less  granular,  and  of  uncer- 
tain density  when  set. 

FINAL  TREATMENT  OF  THE  IMPRESSION 

The  impression  having  l)een  ])roperly  prepared  by  reliev- 
ing, staining  and  varnishing,  as  jireviously  described,  should 
be  immersed  and  allowed  to  remain  in  water  for  a  minute 
or  two,  while  a  camel's  hair  brush  is  passed  over  its  surface 
to  dislodge  the  air  bubbles  present.  It  is  then  removed  and 
freed  from  the  excess  water  by  throwing  it  out  or  passing 
a  good  sized  pellet  of  absorbent  cotton  lightly  over  the  sur- 
faces. The  idea  is  to  moisten  the  surfaces  of  the  impression 
immediately  before  filling,  so  that  the  cast  material  will 
flow  freely  over  all  areas,  and  that  the  face  of  tlie  cast,  when 
set,  will  be  smooth  and  free  from  air  spaces. 

MANIPULATION  OF  SPENCE'S  PLASTER  COMPOUND 

Tliis  material  is  slow  setting  and  therefore  can  be  mixed 
very  thick.  The  instructions  are  to  use  four  oimces  of  tlie 
compound  to  one  of  water.  The  first  step  is  to  place  three 
ounces  of  the  compound  in  the  bowl  and  add  the  full  amount 
of  water  (one  ounce)  to  it.  Thoroughly  mix  until  it  be- 
comes soft  and  uniformly  plastic  throughout,  then  add  the 
other  ounce,  a  little  at  a  time,  working  each  portion  in  well 
before  making  the  next  addition.  The  essential  point  in 
mixing  this  material,  as  in  plaster,  is  to  distribute  the  water 
evenly  through  the  mass,  so  that  each  particle  and  granule 
may  have  an  equal  proportion  to  any  other. 

FILLING  THE  IMPRESSION 

Since  the  mass  is  thick  and  plastic — much  like  putty — 
only  a  small  quantity  should  be  placed  in  the  impression  at 
a  time,  and  by  jarring  and  finger  pressure,  forced  to  place. 
The  entire  impression  is  filled  in  this  manner,,  a  little  at  a 


TREATMENT    AND    FILLING    OF    IMPRESSIONS  UK! 

time,  and  tlie  form  of  the  cast  developed  with  the  spatula, 
squaring  u\)  the  sides  and  making  the  base  flat.  The  cast 
should  be  about  one-half  inch  thick  in  the  central  portion 
for  necessary  strength. 

In  lower  cases  the  space  between  the  lingual  portions  of 
the  impression  should  be  bridged  across  with  the  compound. 
■This  may  be  accomplished  with  the  spatula,  or  ])y  placing  the 
impression  on  the  bench  after  the  deeper  portions  have  been 
filled,  and  packing  the  lingual  space  with  a  compact  mass  of 
moist  paper;  a  temporary  support  will  thus  be  afforded  the 
material  while  being  bridged  over  and  in  setting. 

Another  method  often  resorted  to  is  to  bridge  over  the 
lingual  space  with  a  sheet  of  wax  before  filling  the  impression. 
This  should  be  fitted  neatly  and  luted  firmly  to  the  lingual 
margins  of  the  impression,  so  as  not  to  interfere  with  the 
develoiunent  of  the  areas  on  which  tlie  denture  is  to  rest. 

MANIPULATION   OF  PLASTER   IN   CAST  CONSTRUCTION 

Fill  the  bowl  about  one-third  full  of  water,  and  into  this 
sift  French's  regular  dental  jilaster  until  the  free  water  is 
all  taken  up.  By  adding  the  plaster  slowly,  as  it  settles  into 
the  water,  solution  takes  place  quickly,  and  but  little  stirring 
will  be  required  to  render  the  mix  homogeneous.  It  should 
be  stirred  slightly,  but  not  to  excess.  The  plastic  mass  should 
be  stiff  enough  to  require  jarring  to  settle  it  to  place. 

FILLING  THE  IMPRESSION  WITH  PLASTER 

A  portion  is  placed  near  the  central  part  of  the  im- 
pression and  the  tray  grasped  in  the  fingers  and  tapped  on 
the  edge  of  the  bench  to  settle  the  plaster  in  the  deepest  por- 
tions. If  the  impression  has  been  broken  in  a  number  of 
pieces  and  luted,  it  is  sometimes  best  to  use  the  fingers  which 
grasp  the  tray  as  a  cushion  in  jarring  the  plaster  to  place, 
to  prevent  the  impression  or  the  pieces  from  becoming  de- 
tached— a  mishap  which  sometimes  occurs  if  the  vibration  is 
sharp  and  rapid.  Additions  of  plaster  are  made  and  the 
\ibration  continued  until  the  entire  impression  is  filled  and 
the  cast  given  its'  proper  outline  with  the  spatula.  Care 
should  be  taken  in  forming  the  cast  to  avoid  excessive  bulk, 
either  in  thickness  or  peripheral  outline,  as  the  surplus  periph 
erally  inqtedes  the  removal  of  the  inqiression  and  must  even- 
tually lie  cut  away,  while  a  thick  base  interferes  with  proper 
mounting  of  the  cast  on  the  frame,  and  later  on  in  flasking,  it 


104  TREATMENT    AND    FILLING    OF    IMPRESSIONS 

must  be  reduced  to  centralize  the  case  in  tlie  flask.  Lower 
casts  are  produced  in  the  same  manner  described  in  tlie  use  of 
the  Spence  compound. 

CASTS  OF  PARTIAL  CASES— SPENCE'S  COMPOUND 

In  filling  partial  impressions  with  Speuce's  compound, 
the  material  should  be  forced  into  each  tooth  matrix  with  a 
suitable  square  end  instrument,  but  care  must  be  taken  to 
avoid  marring  the  impression  in  doing  so.  Each  matrix  is 
filled,  and  the  compound  as  it  is  placed  in  the  impression  is 
jarred  and  pressed  to  place,  to  make  a  compact  union  with 
that  already  packed.  The  general  form  of  the  cast  should  be 
the  same  as  for  full  cases. 

CASTS  OF  PARTIAL  CASES— PLASTER 

The  plaster  mix  for  partial  should  be  of  al)out  the  same 
consistency  as  for  full  impressions.     If  too  thick,  it  will  be 


difficult,  if  not  impossible,  to  fill  the  matrices  of  the  teeth, 
while  if  too  thin,  the  teeth  on  the  cast  will  be  frail  and  easily 
broken,  because  of  the  imperfect  density  of  the  plaster. 

In  introducing  the  plaster  into  the  impression,  the  first 
portion  should  be  placed  near,  but  not  over,  one  of  the  tootli 
matrices,  and  liy  inclining  the  impression  somewhat  and  jar- 
ring, the  plaster  will  flow  down  one  side  of  the  matrix,  spread 
out  and  settle  over  the  bottom,  and  then  rise  up  the  opposite 
side  until  the  opening  is  filled.  Each  matrix  should  receive 
individual  attention  in  order  that  a  perfect  cast  of  each  tooth 
may  be  obtained.  If  an  attempt  is  made  to  fill  several  mat- 
rices at  once,  the  plaster  is  liable  to  flow  too  freely  into  some 
of  the  openings,  confining  the  air  in  the  deeper  portions,  and 
thus  result  in  an  imperfectly  filled  impression. 


TREATMENT    AND    FILLING    OF    IMPRESSIONS  105 

STRENGTHENING  ISOLATED  PLASTER  TEETH  ON  CASTS 

Ofteutimes  wbeii  the  uatural  teeth  are  long  and  isolated, 
the  plaster  teeth  can  be  materially  strengthened  by  inserting 
a  small  piece  of  orange  wood  in  each  matrix,  while  the  plaster 
is  yet  plastic,  and  before  the  impression  is  entirely  filled.  The 
small  round  Japanese  toothpicks  of  orangewood  are  well 
adapted  for  this  purpose,  being  of  suitable  size  and  especially 
tough.  The  sharp  point  should  be  cut  off,  the  stick  cut  to 
suitable  length,  usually  an  inch,  and  placed  conveniently  at 
hand  before  filling  the  impression.  The  advantage  of  wood 
over  metal  pins  is  that  in  ci;tting  off  the  ends  of  the  plaster 
teeth  in  flasking,  the  wood  will  cut  as  readily  as  the  plaster, 
while  metal  pins  must  be  cut  very  carefully,  or  the  plaster 
teeth  enclosing  them  will  be  fractured. 

CASTS  FROM  MODELING  COMPOUND  IMPRESSIONS 

Preliminary  Treatment  for  Cast  Production 

EQUALIZING  DENTURE  BEARING  BY  SCRAPING  HARD  AREAS 
OF  THE  IMPRESSION 

Since  the  character  of  the  material  used,  and  the  manner 
of  manipulation  followed  in  taking  impressions  in  modeling 
compound,  tend  to  relieve  pressure  of  the  denture  on  the 
hard,  and  increase  its  bearing  on  the  soft,  areas  of  the  mouth, 
it  is  not  necessary  to  scrape  the  areas  impressed  by  the  hard 
tissues  to  the  same  extent  in  modeling  compoimd  as  in  plaster 
impressions.  Some  slight  relief,  however,  in  most  cases  will 
prove  beneficial,  and  with  the  variation  just  stated,  the  in- 
structions given  in  reference  to  the  treatment  by  scraping 
of  plaster  impressions,  apply  to  the  class  under  consideration. 

TREATMENT  OF  THE  SURFACE  OF  THE  IMPRESSION 

Modeling  compound  impressions  are  waterproof,  and 
therefore  no  separating  or  staining  mediums  are  needed,  as 
in  plaster  work.  The  impression,  however,  should  be  dipped 
in  water,  the  air  bubbles  dislodged  with  a  brush,  and  the 
excess  moisture  removed  with  absorbent  cotton.  No  free 
water  should  be  allowed  to  remain  in  the  deeper  portions, 
for  if  present  it  will  reduce  the  density  of  the  plaster  in  the 
cast  in  that  area,  and  weaken  it,  as  previously  explained. 
While  the  impression  can  be  filled  without  moistening,  a 
smoother  surface  to  the  cast  can  be  produced  if  this  precaution 
is  taken. 


106  TREATMENT    AND    KlLLlNi;    OF    IMPRESSIONS 

Exception  to  tlii.s  inctliud  of  treatuiciit  miiist  l)o  made 
when  magnesium  oxy-cliloride  is  used.  The  impression  should 
bo  given  a  tliin  film  of  sandarae  varnish,  the  latter  allowed 
to  dry,  and  the  surfaces  not  moistened  previous  to  filling. 

FILLING  THE  IMPRESSION— FULL  CASES 

The  mix  of  plaster  should  be  made  in  the  same  manner, 
and  of  similar  consistency  to  that  used  in  plaster  work. 
If  any  variation  is  made,  the  mass  should  be  thicker,  since 
the  impression  can  be  tapped  sharply  in  settling  the  contents 
to  place,  without  danger  of  dislodging  it  from  the  tray,  and 
a  comparatively  thick  mix  can  be  readily  adapted  to  full 
u])ppr  or  lowei'  impressions  with  ease. 

FILLING  THE  IMPRESSION  IN  PARTIAL  CASES 

As  previously  stated,  modeling  compound  is  not  a  suit- 
able material  for  partial  cases  unless  the  sectional  method  is 
employed,  but  if  used  for  impression  purjooses,  the  casts  are 
produced  in  the  same  manner  as  from  partial  impressions  in 
plaster.  Isolated  plaster  teeth  should  also  be  strengthened 
in  the  same  manner  as  outlined. 

TIME    REQUIRED    FOR   PLASTER   CASTS   TO    SET    BEFORE   RE- 
MOVING THE  IMPRESSION 

From  fifteen  to  twenty  minutes'  time  should  be  given  the 
plaster  cast  to  harden  before  removing  the  impression.  If 
this  step  is  carried  out  too  soon,  the  face  of  the  cast  is  liable 
to  be  marred  by  handling,  since  it  takes  some  time  for  the 
plaster  to  develop  a  reasonable  degree  of  hardness.  On  the 
other  hand,  the  separation  should  not  be  delayed  too  long, 
since  at  the  beginning  of  crystallization  expansion  sets  in 
rapidly,  and  continues  in  a  gradually  decreasing  ratio  for 
twenty-four  liours  or  more. 

WARPING  OF  THE  IMPRESSION  AND  CAST 

As  previously  stated  in  the  consideration  of  plaster,  when 
an  impression  is  allowed  to  remain  in  the  tray  and  the  cast 
in  the  imjiression  for  some  time,  both  will  be  more  or  less 
warped.  To  obviate  this  difficulty  as  much  as  possible,  the 
tray  and  impression  should  be  removed  as  soon  as  the  ]»laster 
constituting  the  cast  has  hardened  sufficiently  to  permit. 

REMOVAL  OF  THE  TRAY 

The  first  step  in  separating  the  impression  and  cast  is 
the  removal  of  all  excess  of  the  impression  material  extend- 


TREATMENT    AND    FILLING    OF    LMPRESSIONS  107 

hig  over  tlic  outer  surfaces  of  the  labio-lmeeal  flange  of  tlie 
tray.  This  is  easily  accomplished  1)y  i)aring  it  off  with  a 
suitable  plaster  knife. 

The  cast  and  margins  of  the  impression  are  then  grasped 
with  one  hand,  avoiding  contact  with  the  tray  flange,  when, 
by  tapping  the  handle,  and  if  necessary  the  flange,  the  tray 
and  impression  will  readily  separate. 

REMOVAL   OF  IMPRESSIONS— FULL  CASES 

With  a  sharii  knife  carefully  ]iare  away  the  impression 
opi)osite  the  alveolar  crest  until  the  staining  medium  indi- 
cates the  near  approach  to  the  cast.  The  paring  should  ex- 
tend from  one  tuberosity  around  the  crest  of  the  border  to 
the  opposite  side. 

A  few  light  taps  on  the  Ijuccal  and  labial  portions  of  the 
impression,  followed  by  inserting  the  point  of  tlie  knife  be- 
tween the  latter  and  the  cast  at  the  peripheral  line  of  junc- 
tion, will  break  away  the  outer  portions  of  the  impression. 

By  tapping  the  vault  portion  and  inserting  the  point  of 
the  knife  at  the  line  of  demarkation  distally,  the  remainder 
can  be  removed  without  difificulty.  If,  however,  the  rugae  are 
prominent,  and  the  vault  is  deep  and  narrow,  it  will  be  best 
to  cut  a  ^^-shaped  groove  mesio-distally  through  the  central 
vault  portion  and  practically  divide  it.  The  groove  should 
be  carried  deep  enough  to  disclose  the  stained  area.  A  slight 
prying  movement  on  either  half  will  cause  fracture,  when  they 
will  come  away  readily. 

REMOVAL  OF  THE  IMPRESSION— PARTIAL  CASES 

The  same  steps  as  to  removal  of  the  surplus  of  the  im- 
pression from  the  tray,  and  the  tray  itself,  as  previously  de- 
scribed in  full,  apply  to  partial  cases  as  well.  The  removal 
of  the  impression  from  the  cast,  however,  re(|uires  more  care 
and  necessitates  the  fracturing  of  the  impression  into  smaller 
pieces,  to  oliviate  the  breaking  of  the  teeth  from  the  cast. 

First — The  impression  opposite  the  occlusal  and  incisal 
l)ortions  of  the  teeth  should  be  carefully  pared  away  until 
the  stained  area  .opposite  each  tooth  and  <'usp  as  well,  is 
l)lainly  visible.-  If  the  cusps  of  the  teeth  are  particularly  sharp 
and  well  defined,  to  avoid  breaking  them,  the  paring  may 
be  carried  along  the  mesial  and  distal  slopes  of  the  cusj)s 
until  the  stain(>d  areas  present  two  nearly  unbroken  lines, 
indicating  the  position  of  the  buccal  and  lingual  marginal 


108  TREATMENT    AND    FILI.INC    OE    IMPRESSIONS 

ridges.     This  ]iractically  separates  tlie  labio-ljuecal   portion 
from  the  body  of  tlie  impression. 

CUTTING  V-SHAPED  GROOVES  TO  WEAKEN  THE  IMPRESSION 

Second — A  V-shaped  j^roove  is  usually  cut  opposite  each 
cuspid  tooth  and  eminence  perpendicularly,  if  not  already  cut 
in  removing  the  im]iression  from  the  month,  extending  from 
incisal  to  peripheral  margin.  The  plaster  which  fills  the 
voids  occasioned  by  missing  teeth  should  be  carefully  di- 
vided with  the  knife  mesio-distally  at  the  points  of  shortest 
diameter  of  the  spaces.  This  permits  the  labial  or  l)uccal  sec- 
tions of  plaster  to  be  removed  in  an  outward  direction,  and 
the  lingual  portions  to  be  removed  inwardly  later  on,  without 
engaging  with,  or  marring  the  adjacent  teeth. 

If  sheets  of  wax  have  been  attached  to  the  floor  of  the 
tray  in  fitting,  so  as  to  enter  the  spaces,  these  of  themselves 


I'ARTIAl,     IMI'IIKSSKIX     l'Ain'1,1     c;Hii(i\i;|i     Fill!    RF;M0VAI. 


partially  divide  the  impression  where  placed,  and  facilitate 
the  cutting  with  the  knife.  The  sections  should  be  tapped 
lightly  to  start  them,  or  the  point  of  the  knife  may  be  applied 
and  slightly  pressed  into  the  peripheral  line  of  junction  of 
the  cast  and  impression.  By  prying  outward,  the  sections 
will  come  away  readily,  thus  exposing  the  labial  and  buccal 
surfaces  of  the  teeth. 

Third — A  V-shaped  groove  is  cut  around  the  lingual 
surface  of  the  impression,  near  the  occlusal  third  of  the  teeth, 
and  divided  perpendicularly  opposite  each  tooth.  These  sec- 
tions are  then  removed  one  at  a  time,  which,  when  completed, 
exposes  the  occlusal  and  a  portion  of  the  lingual  surfaces  of 
the  teeth. 

Still  another  groove  is  cut  entirely  around  the  lingual 
surface  of  the  impression,  the  apex  of  which  is  directed  toward 
the  gingival  area,  and  the  plaster  divided  in  sections  as  just 


TREATMENT    AND    FILLING    OP    IMPRESSIONS  109 

described,  wliicli  when  removed  will  leave  the  teeth  entirely 
exposed. 

Fouiih — The  central  or  vault  portion  still  requires  re- 
moval. If  the  vault  is  flat  and  no  undercuts  are  pi'esent,  a 
few  light  taps  with  a  slight  prying  movement  at  the  line  of 
junction  of  the  impression  with  the  cast  posteriorly,  will  dis- 
lodge it.  When  the  vault  is  deep,  the  better  plan  will  be  to 
divide  the  remaining  portion  into  two  or  three  sections  and 
remove  them  separately.  If  the  point  of  the  knife  has  been 
well  under  control,  the  removal  of  the  impression,  when  car- 
ried out  in  detail  as  described,  will  result  in  a  cast  with  un- 
broken teeth  or  cusps,  and  r;nmarred  surfaces. 

REMOVAL    OF    MODELING    COMPOUND    IMPRESSIONS    FROM 
CASTS 

Modeling  comi^ound  impressions,  both  full  and  partial. 
can  be  removed  from  casts  l)y  the  application  of  either  dry  or 
moist  heat,  preferably  by  softening  in  hot  water.  The  tray, 
impression  and  cast  are  placed  in  a  pan  of  water,  and  the 
latter  heated  sufficiently  to  render  the  compound  plastic,  but 
not  excessively  soft.  The  tray  is  iirst  removed  and  the  com- 
pound at  the  peripheral  margins  peeled  away  from  the  buccal 
and  labial  surfaces  of  the  border,  drawing  it  occlusally  and 
incisally  and  away  from  the  cast.  But  little  difficulty  will 
occur  in  removal  in  full  cases,  unless  the  compound  has  been 
overheated,  in  which  case  it  will  adhere  to  the  cast.  In  re- 
moving the  impression  in  partial  cases,  time  should  be  given 
for  the  heat  to  penetrate  through  the  compound  and  render 
it  plastic  throughout.  If  this  precaution  is  not  observed  and 
an  attempt  is  made  to  remove  the  compound  from  the  voids 
or  spaces,  fracture  of  some  of  the  teeth,  in  most  instances, 
will  occur. 

Should  any  of  the  comjiound  adhere  to  the  cast  in  various 
places,  as  it  frequently  does,  it  may  be  readily  removed  by 
heating  some  dry  compound  in  the  Bunsen  flame  until  quite 
sticky,  then  dip  the  cast  in  warm  water,  first  to  slightly  soften 
the  undetached  compound,  and  second,  to  prevent  the  heated 
mass  from  adhering  to  the  cast.  The  dry,  heated  compound 
is  firmly  pressed  against  the  adliereut  pieces  and  quickly 
withdrawn,  reheating  it  in  the  flame  each  time,  if  necessary, 
to  keep  it  adhesive,  until  all  of  the  remaining  portions  are 
removed. 


110  TKKATMKNT    AND    FILLING    OK    LMI'KKSSIONS 

SPECIAL  MATERIALS  USED  FOR  CASTS  IN  VULCANITE  WORK 

It  is  a  well-establislied  fact  that  when  plaster  is  sub- 
jected to  stress,  or  compressive  force,  the  surface  crystals,  or 
those  first  takin<i;  the  load  crush  and  break  down,  when  the 
stress  passes  the  modulus  of  resistance  of  the  material. 

It  has  also  been  demonstrated,  tliat  the  force  ordinarily 
Hxcrled  in  closin.a;  an  overpaeked  flask  is  far  in  excess  of  that 
which  ]ilaster  can  stand  without  the  crystals  crushing  and 
the  face  of  the  cast  becoming  distorted. 

The  effect  of  such  distortion,  he  it  small  or  great,  on 
casts  against  whicli  vulcanite  or  celluloid  dentures  are 
molded,  is  to  impair,  if  not  altogether  destroy,  the  ada])tati()n 
of  tlie  dentures  to  the  oral  tissues. 

Two  ways  are  possible  for  lessening  if  not  entirely  over- 
coming the  danger  of  distortion  of  dentures,  due  to  yielding 
of  the  plaster  casts  under  the  influence  of  excessive  pres- 
sure, heat,  and  moisture,  during  vulcanization. 

The  first  of  these  does  not  require  the  use  of  any  special 
materials  other  than  those  commonly  employed  in  the  dental 
laboratory.  The  method  of  technic  differs  in  some  respects 
from  that  usually  followed  in  such  procedures,  the  variations 
being  noted  undei'  the  rlosivg  of  flasks,  preparatory  to  vul- 
canizing. 

The  second  plan  recpiires  that  the  cast  be  constructed  of 
a  material  harder  and  more  resistant  to  stress,  and  to  dele- 
terious influences  in  general,  than  is  plaster. 

Several  matei'ials.  capable  of  withstanding  much  greater 
crushing  strain  than  i)laster,  may  be  made  use  of,  the  proper- 
ties of  one  of  the  most  important  of  which  will  now  be  con- 
sidered, since  its  value  when  properly  manii)ulated  is  unques- 
tioned. 

ARTIFICIAL  STONE 

OXYCHLORIDE   OF   MAGNESIUM 

Several  years  ago  the  idea  occurred  to  the  writer  that 
because  of  its  density,  smoothness  of  surface,  and  impervious- 
iiess  to  water,  the  materials  used  in  the  manufacure  of  arti- 
ficial stone  might  l)e  employed  in  cast  construction,  and  the 
])roblem  of  denture  warpage  be  solved,  or  the  difficulties  re- 
sulting therefrom  greatly  reduced. 

From  data  furnished  by  the  late  Prof.  Vernon  J.  Hall 
many  exi)eriments  were  made  with  various  materials,  ])articu- 
larly  with  the  oxide  and  chloride  of  magnesium.  The  first 
experiments,  conducted  with  chemically  pure  products,  were 


TREATMENT    AND    FILLING    OF    IMPRESSION'S  111 

unsuccessful.  Attention  was  then  given  the  commercial  prod- 
ucts, since  these  were  extensively  used  in  various  industrial 
lines.  From  the  first,  difficulties  were  encountered,  due  prin- 
cipally to  fracture  lines  forming  in  the  mass  in  hardening.  In 
some  cases  very  perceptible  contraction  was  noticeable. 

Fracture  was  later  found  to  be  due  to  the  presence  of 
carbon  dioxide  in  the  oxide  of  magnesia.  Its  presence  may  be 
accounted  for  in  two  ways.  Magnesium  oxide  is  produced 
usually  by  burning  magnesium  carbonate,  just  as  calcium 
oxide  or  lime  is  produced  by  burning  calcium  carbonate.  In 
both  cases  the  carbondioxide  is  driven  off  when  the  process 
is  properly  conducted.  Unless  the  calcination  is  thorough 
all  of  the  CO2  will  not  be  eliminated.  Again,  the  oxide  of 
magnesia  may  be  properly  prepared,  but  if  left  exposed  to  the 
air,  it  will  take  up  moisture  and  carbon-dioxide,  and  gradually 
return  to  the  carbonate.  From  whatever  source  it  may  come, 
its  presence  in  the  oxide  of  magnesia  renders  the  latter  worth- 
less for  cast  construction.  The  remedy  consists  in  recalcining 
the  mixed  oxide  and  carbonate  above  a  red  heat,  to  expel  the 
CO2,  or  if  this  is  not  practicable,  discard  it  for  a  better  grade 
of  material. 

Contraction  in  the  hardened  mass,  noticable  in  the  space 
seen  between  the  impres.sion  and  cast  when  the  latter  has 
hardened,  is  the  result  of  using  an  under-saturated  solution  of 
the  chloride,  the  liquid  with  which  the  powdered  oxide  is  com- 
bined. By  increasing  the  strength  of  the  liquid  to  full  satura- 
tion, adding  crystal  chloride  until  there  is  a  slight  excess  in 
the  bottom  of  the  stock  vessel,  contraction  can  be  overcome. 

The  length  of  time  required  for  setting — about  twelve 
hours — is  considered  an  objection  by  some,  but  the  advan- 
tages gained  in  more  perfect  adaptation  of  the  denture  to  the 
oral  tissues  and  in  increased  density  of  the  vulcanite  far 
outweigh  the  disadvantages  mentioned. 

ADVANTAGES   OF  OXYCHLORIDE   OF   MAGNESIUM 

The  jDrincipal  advantages  of  oxychloride  of  magnesium 
for  casts  in  vulcanite  work  are  these :  hardness,  density, 
smoothness  of  surface  and  an  extremely  low  expansive  index, 
less  than  one-fourth  that  of  the  ])est  grades  of  plaster.  It 
is  sufficiently  impervious  to  moisture  and  heat  to  maintain  its 
form  without  crushing,  even  under  heavy  pressure.  The 
writer  has  vulcanized  two  baseplates  on  the  same  cast,  both  of 


112  TREATMENT    AND    EILLINC,    OF    IMPRESSIONS 

which  showed  satisfaftory  achqitatioii  to  the  oral  tissues.  At 
the  end  of  tlie  second  vidcaiiization,  the  cast,  although  per- 
meated with  moisture,  was  quite  hard  and  resistant  to  stress 
and  on  evaporation  of  the  moisture  appeared  much  harder 
than  casts  constructed  from  the  best  grades  of  plaster  before 
vulcanization. 

Rubber  of  any  shade  vulcanized  in  contact  with  oxy- 
chloride  of  magnesium  is  hard,  dense,  elastic,  capable  of  tak- 
ing a  high  polish,  and  on  account  of  the  density  of  the  cast  is 
practically  free  from  nodules. 

Partial  dentures  vulcanized  on  casts  of  this  material  show 
all  the  characteristic  lines  and  fine  surface  markings  of  the 
teeth  and  tissues  against  which  it  is  molded  as  clearly  as 
an  accurate  plaster  impression  can  reproduce  them,  because 
the  cast  is  not  changed  or  defaced  in  the  slightest  degree  by 
manipulative  procedures. 

EXPANSION 

In  tests  made  for  expansion,  the  greatest  movement 
registered,  from  the  buccal  face  of  one  tuberosity  to  the 
corresponding  opposite  surface,  was  15/10,000  of  an  inch, 
against  from  60/10,000  to  100/10,000  of  an  inch  in  casts  made 
from  the  best  grades  of  plaster. 

COMPRESSION 

Comparative  compression  tests  on  blocks  of  plaster  and 
of  magnesium  comiJound,  set  over  night,  showed  the  following 
result :  size  of  blocks  ly^xli/oxi^  inches ;  area  of  plunger,  14 
inch.  In  the  plaster  blocks,  the  plunger  began  sinking  into 
the  block  at  twenty  pounds,  and  under  continued  pressure 
penetrated  about  '^/g  inch,  the  block  breaking  at  100  pounds. 

The  magnesium  blocks  showed  no  ijerceptible  compres- 
sion up  to  1,000  pounds,  at  which  point  they  suddenly  crushed. 
In  one-inch  cubes,  the  oxychloride  of  magnesium  will  stand  a 
crushing  strain  of  nearly  5,000  pounds,  according  to  Major 
Gilmore,  U.  S.  A. 

MATERIALS   USED  FOR  CAST  CONSTRUCTION 

The  following  instruction  in  reference  to  procuring  and 
handling  the  magnesium  materials  for  casts  covers  the  essen- 
tial points  to  be  kept  in  mind. 

MAGNESIUM   OXIDE 

There  are  two  varieties  of  magnesium  oxide,  known  as  the 
light  and  heavy  oxide.    The  difference,  which  is  one  of  specific 


TREATMENT    AND    FILL-ING    OF    IMPRESSIONS  113 

gravity  and  not  of  chemical  constitution,  is  bvonglit  about  by 
tlie  manner  in  wliicli  tlie  magnesite  (MgCOj)  is  burned.  In 
"Cements,  Limes,  and  Plasters,"  E.  C.  Eckel  says:  "If 
MgCOs  be  strongly  heated,  the  effect,  as  with  lime  carbonate, 
is  to  drive  off  the  CO2,  leaving  the  MgO  as  a  white  solid.  A 
curious  and  technologically  important  phenomenon  connected 
with  the  temperature  employed  is  to  be  noted.  If  the  calcina- 
tion is  carried  on  quickly  at  a  red  heat  the  magnesia  resulting 
will  have  a  specific  gravity  of  o.OO  to  3.07,  while  if  the  cal- 
cination is  long  continued  or  carried  on  at  a  higher  tempera- 
ture the  resulting  MgO  will  be  much  denser,  possessing  a 
specific  gravity  of  3.61  to  3.80." 

For  the  construction  of  casts,  the  heavy  oxide  commer- 
cially known  as  porcdered  magnesite,  or  calcined  magnesia, 
should  be  employed.  To  prevent  its  return  to  MgCOa,  by 
absorbing  COo  and  moisture  from  the  air,  as  indicated  by  its 
becoming  granular  and  lumpy,  it  should  be  kept  in  airtight 
containers,  just  as  ]ilaster  must  be  protected  in  damp  climates. 

MAGNESIUM  CHLORIDE 

Magnesium  chloride  is  a  crystalline,  deliquescent  suli- 
stance,  having  much  the  appearance  of  sea  salt.  It  is  obtained 
in  several  ways,  a  common  source  being  by  heating  mag- 
nesium ammonium  chloride  (MgC'L  NHj  CI)  to  about  460  C. 
The  ammonium  chloride  volatilizes,  leaving  anhydrous  MgCL. 

The  ordinary  commercial  product,  instead  of  the  chem- 
ically pure  chloride,  is  suitable  for  use  in  cast  construction ; 
some  of  the  commercial  products  occasionally  contain  HSO4 
as  an  impurity.  When  present,  in  the  chloride  solution,  it  will 
in  time  render  the  hardened  mass  of  oxychloride  somewhat 
soluble  in  water.  The  sulphuric  acid  can  be  eliminated  by 
adding  barium  hydrate  to  the  chloride  solution.  When  the  re- 
sulting precipitate,  bariimi  sulphate  ceases  to  form,  it  indi- 
cates that  the  acid  has  been  neutralized.  From  6  per  cent  to 
10  per  cent  liy  weight  of  the  reagent  compared  with  the 
chloride  is  required.  This  method  of  neutralizing  the  acidity 
of  the  magnesium  chloride  solution  is  more  strongly  indicated 
when  the  oxychloride  material  is  to  be  wrought  into  work  of  a 
])ermanent  character  and  is  not  as  essential  for  vulcanite  casts, 
since  the  latter  are  destroyed  after  vulcanization,  in  removal 
from  the  dentures.  After  two  years  almost  constant  use  of 
magnesium  oxychloride,  the  writer  has  not  found  it  neces- 
sary to  purify  any  commercial  chloride  solution,  but  has  fre- 


114  TREATMENT    AND    FIT.LIN(;    OP    IMPRESSIONS 

queiitly  been  obliged  to  re-ealcine  the  oxide  to  drive  off  tlie 
COo,  as  previously  mentioned. 

PREPARING  THE  MAGNESIUM  CHLORIDE  SOLUTION 

In  the  average  dental  practice  but  a  comparatively  small 
amount  of  magnesium  oxychloride  will  be  used  in  the  course 
of  a  month,  so  the  preparation  of  a  large  quantity  is  not  ad- 
visable. It  is  a  better  plan  to  make  up  one  or  two  quarts  of 
the  licjuid  chloride,  renewing  the  solution  from  time  to  time 
as  needed.  In  this  way  the  quality  of  the  liquid  can  easily  be 
kept  ui^  to  standard. 

To  make  the  solution,  put  2  pints  of  water  in  a  clean 
2  quart  glass  bottle,  and  add  the  crystal  chloride  until  com- 
plete saturation  of  the  water  is  effected.  The  visible  test  of 
full  saturation  of  the  water  appears  in  the  presence  of  undis- 
solved crystals  of  chloride  in  the  bottom  of  the  vessel. 

A  half-inch  layer  of  crystals  in  the  bottom  of  the  vessel  at 
all  times  will  do  no  harm  and  will  keep  the  solution  fully  satu- 
rated. If  the  crystals  disappear,  add  more  until  the  usual 
amount  of  excess  is  restored,  and  if  they  increase,  due  to 
evaporation  of  the  water,  add  more  of  the  latter.  After  full 
saturation  of  the  water  has  occurred,  the  liquid  should  not  be 
shaken  up  nor  the  crystals  disturbed  in  decanting  off  a  por- 
tion for  use. 

MANNER     OF     MIXING     THE     OXIDE     WITH     THE    CHLORIDE 
SOLUTION 

Place  a  sufficient  amount  of  the  chloride  solution  to  form 
a  cast  in  the  plaster  bowl  and  sift  in  the  oxide  just  as  plaster 
is  manipulated,  stirring  much  more  vigorously  and  for  a 
longer  time  than  when  plaster  is  used.  Additions  of  the  oxide 
are  made  from  time  to  time  and  the  stirring  continued  until 
the  mass  is  sufficiently  thick  to  stand  alone.  This  is  an  ex- 
tremely important  requirement,  for  when  too  thin  the  oxy- 
chloride overflows  the  bounds  of  the  impression  and  the  cast 
cannot  be  built  up  to  proper  form. 

The  object  in  vigorous  stirring  is  to  eliminate  all  air 
that  may  be  in  the  powdered  magnesite  and  to  coat  every 
granule  with  a  film  of  the  liquid.  The  tendency  of  all  begin- 
ners in  using  this  material  is  to  slight  the  stirring,  and  econo- 
mize on  the  powder,  with  the  result  that  although  the  mass 
hardens  well  and  is  smooth,  there  is  an  excess  of  the  chloride 
present  and  the  cast  will  more  readily  fracture  under  stress 


TREATMENT    AND    PRILLING    OF    IMPRESSIONS  115 

than  when  tlie  material  is  thickly  mixed.     It  is  also  inclined 
to  soften  more  readily  during  vulcanization. 

TREATMENT   OF  IMPRESSIONS 

To  get  an  al)solutely  smooth  surface  (o  a  cast  of  this 
material  it  is  necessary  to  have  a  smooth  surface  to  the  im- 
pression. This  can  best  lie  secured  by  treating  either  plaster 
or  modeling  compound  impressions  with  a  varnish  hav- 
ing a  sandarac  base.  Gilbert's  Imperial  Varnish  fulfills  the 
requirements  well. 

In  filling  modeling  compound  imjiressions  with  plaster 
the  surfaces  are  merely  moistened  with  water  to  accellerate 
the  flow  of  plaster  over  the  impressed  areas.  With  oxy- 
chloride,  although  moisture  on  the  surface  of  the  impression 
would  insure  ease  of  introduction,  its  in'esence  would  eventu- 
ally deteriorate  the  surface  of  the  cast,  rendering  it  softer  and 
less  resistant  to  stress. 

Modeling  compound  impressions  are  varnished  because 
unless  so  treat''d  tlie  compound  is  at  times  extremely  dif- 
ficult to  remove  from  the  oxychloride  cast. 

FILLING  THE   IMPRESSIONS 

The  impression  is  tilled  with  oxychloride  mixture  in  much 
the  same  manner  as  with  plaster,  with  this  exception:  Since 
the  face  of  the  impression  is  dry,  for  reasons  previously 
stated,  to  prevent  the  formation  of  creases  in  the  east  where 
two  or  more  additions  of  the  mixture  may  meet,  it  is  best  to 
a])]ily  each  subsequent  addition  to  an  area  already  covered, 
and  l)y  vibration  let  the  mass  last  added  settle  down  and  push 
the  margins  of  tliat  already  adapted  over  the  uncovered  areas 
of  the  impression. 

In  partial  cases,  impressions  of  teeth  sliould  be  tilled 
with  a  small  tamper  to  avoid  the  confinement  of  air  in  the 
matrix. 

The  mass  of  oxychloride  should  be  built  to  the  proper 
form  of  the  cast,  being  careful  to  avoid  any  excess,  since  when 
set,  it  is  very  difficult  to  cut  with  a  knife.  By  adjusting  a 
bead  of  wax  on  the  periphery  of  the  impression  to  outline 
th(>  extreme  margi-ns  of  the  cast,  and  by  Imilding  the  iruitei'ial 
to  this  head  much  amioyance  will  be  averted  later  on. 

GENERAL   REMARKS 

By  mixing  from  50  to  SO  ])er  cent  of  clean  sand  with  50 
to  20  per  cent  of  the  oxide  of  magnesum  a  harder  and  much 


116  TREATMENT    AND    FILLINCJ    OF    IMPRESSIONS 

more  resistant  mass  M'ill  result  than  if  the  oxide  and  i-IMoride 
alone  are  used. 

By  tilling  the  impression  partially  with  oxy('hh)ride  jnix- 
ture  and  inserting  a  previously  selected  metal  model  form 
(Kerr's),  an  extremely  small  amount  of  the  material  will  be 
required  and  the  jteripheral  outline,  as  well  as  the  depth  of  the 
cast,  will  be  kept  within  minimum  limits,  since  the  oxy- 
chloride  need  not  cover  the  metal  form  on  these  surfaces. 

Tlie  material  should  not  be  disturbed  by  attempting  to 
remove  the  im]iression  until  thoroughly  Jiardened.  It  usually 
reciuires  about  12  hours  to  set.  Should  the  mass  have  spread 
out  over  the  sides  of  the  impression  much  more  than  is  desir- 
able it  may  be  trimmed  peripherally  in  four  or  five  hours 
after  mixing  without  endangering  the  cast. 

Thorp's  applied  Chemistry  has  this  to  say  in  reference 
to  the  chemical  reaction  which  occurs  in  combining  the  oxide 
and  chloride  of  magnesium. 

"When  highly  claimed  magnesia  is  treated  with  a  strong 
solution  of  magnesium  chloride  it  dries  in  a  few  hours  to  a 
hard  mass  of  oxychloride,  capable  of  receiving  a  high  polish. 
A  sample  prepared  in  this  manner  and  hardened  by  six 
months'  exposure  to  the  air  was  found  to  consist  of  a  mixture 
of  Mg  C  O,  with  a  compound  of  Mg  CL  5  Mg  0  17  H,  O.  On 
heating  to  180°  C.  it  was  converted  into  Mg  CL  5  Mg  O  6  H,  0. 
By  prolonged  treatment  with  water  the  whole  of  the  mag- 
nesium chloride  was  extracted  and  the  compound  2  Mg  0  3  H. 
O  left. 

"This  residual  hydrate  is  a  compact  solid  as  hard  as 
sandstone  and  possessing  a  brilliant  sui'face. 

"Magnesia  cement  is  used  very  extensively  as  a  binder 
in  connection  with  briquetting  in  the  manufacture  of  artificial 
building  stones,  tiles,  grindstones,  and  emery  and  polishing 
wheels.  Its  binding  quality  is  very  considerable  and  it  is  very 
plastic  and  cheap. 

"A  good  mixture  for  this  use  consists  of: 

"25  parts  magnesia  (!):■!  Mg  O). 

"25  parts  magnesium  chloride  (45  per  cent  solution). 

"50  parts  water. 

"About  5  pounds  of  this  mixture  will  serve  to  cement 
95  parts  of  stone,  emery,  etc.  The  resulting  blocks  are  very 
solid  and  harden  thoroughlj^  in  a  few  hours." 

(Eckel.    Cements,  Limes,  and  Plasters.) 


TREATMENT    AND    FILUNG    OF    IMPRESSIONS  117 

HISTORY 

In  1853  M.  Sorel,  an  eminent  French  chemist,  discovered 
that  zinc  chloride  when  mixed  with  zinc  oxide  formed  a 
cement.  This  is  essentially  the  hasis  of  our  oxychloride  of 
zinc  cements  today,  bnt  it  was  not  introduced  to  nor  used  by 
the  dental  profession  until  many  years  after  its  discovery. 

Shortly  after  this  discovery  Sorel  found  that  the 
chlorides  and  oxides  of  several  other  metals  possessed  similar 
properties. 

TJie  most  imjiortant  and  valuable  combination  he  discov- 
ered was  that  the  oxide  and  chloride  of  magnesium  united  to 
form  a  substance  as  hard  as  stone.  Further,  that  by  com- 
bining coarsely  crushed  rock,  as  marble,  granite,  limestone, 
etc.,  with  a  small  percentage  of  the  oxychloride  of  mag- 
nesium the  resulting  mass  would  stand  an  enormous  strain  be- 
fore crushing. 

The  value  of  this  discovery  was  immediately  recoguized 
and  made  use  of  in  the  industrial  field  in  the  production  of 
artificial  stone  known  as  Sorel 's  stone. 

(Bibliography.) 

A  practical  treatise  on  Coignet-Beton  and  other  artificial 
stone.    Q.  A.  Gillmore,  1871. 

Cements,  Limes,  aucl  Plasters.    E.  C.  Eckel,  1909. 


('  II  A  I'T  K  \l     1  X 

BASES  FOR  ARTIFICIAL  DENTURES 

ill  pi-(islli('tic  iiroctMlurcs,  that  pdi-lioii  ol' a  (Iciiturc  wliicli 
rests  upon  the  oral  tissues,  and  to  which  tlie  teeth  are  attached 
by  various  means,  is  called  a  base. 

REQUISITE  PROPERTIES  OF  A   DENTURE  BASE 

'i'he  material  selected  for  a  base  for  an  artilicial  dentui'e 
should  i)ossess  certain  requisite  i)roperties : 

First — It  should  be  rigid,  in  order  to  retain  its  form  under 
stress. 

Second — It  should  be  dense  and  ndn-jx irons. 

Third — It  should  be  free  from  action  by  oral  secretions 
or  food  piroducts. 

Fourth — It  should  l)e  odorless  and  tasteless. 

Fifth — It  should  be  a  reasonably  good  conductor  of  ther- 
mal changes. 

Sixth — It  should  be  readily  adapted  to  the  die  or  cast 
of  the  mouth. 

Seventh — It  should  be  ca})able  of  takirg  and  retaining  a 
high  polish. 

Two  general  classes  of  materials  are  utilized  as  bases 
for  artificial  dentures.  The  first  consists  of  metals,  as  gold 
and  its  alloys,  platinum,  aluminum,  and  various  alloys  of  tin. 
The  second  class  consists  of  plastic  vegetable  substances,  as 
vulcanite,  gutta  ])ercha.  and  celluloid. 

GOLD  BASES 

Pure  gold,  because  of  its  softness  and  lack  of  rigidity, 
is  not  used  as  a  base  for  artificial  dentures,  except  in  special 
cases,  and  then  only  when  combined  with  gold  of  a  lower 
carat.  Twenty  Karat  gold  is  most  commonly  employed  in 
denture  construction,  although  18K  gold  is  frequently  used. 
The  objections  to  the  latter  are  on  accov;nt  of  its  greater 
rigidity,  which  renders  it  more  difficult  to  conform  to  the  die, 
and  its  tendency  to  discolor  in  some  mouths. 

Twenty  Karat  gold  plate  more  nearly  fulfills  the  re- 
quirements mentioned  as  a  base  than  any  of  the  other  mate- 

118 


BASES    FOR    ARTIFICIAI.    DENTURES  119 

rials  employed  for  this  piir]iose,  except  jilatiuiim.  Its  beau- 
tiful, rich  yellow  color,  freedom  from  taste,  odor  or  oxidation, 
or  tendency  to  discolor,  its  rigidity  in  comparatively  thin 
sheets,  its  high  conductivity  and  the  ease  with  which  it  can 
be  polished,  place  it  in  the  front  rank  for  materials  used  for 
dentures.  The  principal  objections  to  its  universal  use  are 
due  principally  to  the  difficulty  in  securing  close  adaptation 
to  the  oral  tissues,  as  a  result  of  the  sequent  steps  of  con- 
struction, and  to  the  expense  involved  in  the  production  of 
such  substitutes.  It  could  and  should  be  used  in  many  cases 
where  dentures  of  the  less  expensive  class  are  now  consiructed, 
particuarly  in  partial  cases. 

In  addition  to  the  advantages  mentioned,  gold  combines 
the  greatest  strength  with  the  least  bulk,  of  any  other  base. 

PLATINUM  BASES 

The  oral  tissues  under  a  well  adapted  platinum  base  re- 
tain their  normal  tone,  while  but  little  change  occurs  in  the 
bony  processes.  It  has  been  noticed  in  porcelain  crown  and 
bridge  work,  the  frame  work  of  which  is  composed  of  i3lat- 
inum,  that  the  tendency  for  food  to  accumulate  or  plaques  to 
form  on  exposed  or  partially  protected  platinum  surfaces,  is 
decidedly  negative  as  compared  with  alloyed  or  pure  gold  in 
similar  situations.  This  is  supposed  to  be  due  to  some  un- 
known, inherent  quality  in  the  platinum  itself,  not  possessed 
by  other  metals,  which  tends  to  preserve  hygienic  conditions, 
even  under  adverse  circumstances.  Whether  this  view  is 
correct  or  not,  the  fact  remains  that  when  platinum  base  den- 
tures are  well  adapted  and  free  from  mechanical  causes  of 
irritation,  the  tissues  remain  remarkalily  healtliy  and  normal 
under  such  substitutes. 

In  addition  to  the  peculiarly  benign  effect  of  platinum  on 
the  oral  tissues,  this  metal  possess  practically  all  of  the  good 
(jualities  ascribed  to  gold.  In  color  it  is  bluish-white.  It  is 
practically  infusible  under  the  ordinary  blowpipe  flame.  It 
may  be  used  as  a  base  plate  in  the  same  manner  as  gold  is 
employed,  the  teeth  being  attached  either  by  soldering,  or 
with  vulcanite,-  An  alloy  of  platinum  and  iridium,  which  is 
harder  and  more  resistant  than  platinum  itself,  would  be 
jireferable,  however,  since  pure  platinum  is  slightly  softer  and 
more  easily  bent  than  20K,  gold  of  equal  thickness. 

The  usual  method  followed  in  making  use  of  platinum  in 
denture  construction  is  in  conjunction  with  porcelain.     The 


120  BASES    FOR    ARTIFICIAL    DEMTtJRES 

teeth  are  first  attached  b.y  soldering,  the  porcelain,  which 
gives  the  denture  its  contour,  being  subsequently  fused  around 
them  and  over  the  base,  blending  with  teeth  and  base  to  form 
a  homogeneous  mass.  The  advantages  and  disadvantages  of 
continuous  gum  dentures  will  be  discussed  when  dentures  of 
tliis  class  are  described. 

ALUMINUM   BASES 

Aluminum  is  frequently  used  as  a  base  for  artificial  den- 
tures in  both  cast  and  swaged  form.  It  is  the  lightest  of  all 
of  the  metals,  is  a  good  conductor  of  thermal  changes,  and  is 
non-irritating  to  the  tissues  when  properly  constructed. 

Since  this  metal  cannot  be  soldered  successfully,  it  re- 
quires considerable  care  to  develop  the  means  for  attaching 
the  teeth  to  the  base  with  vulcanite  in  swaged  base  dentures. 
When  the  base  is  produced  by  casting,  this  difficulty  is  easily 
overcome,  the  necessary  anchorage  for  the  vulcanite  being 
formed  in  the  wax  model  and  reproduced  in  the  casting- 
process. 

Cast  base  aluminum  dentures  are  inclined  to  disintegrate 
in  some  mouths,  due  largely  to  castings  of  this  metal  being 
of  more  or  less  imperfect  density.  When  examined  under  a 
magnifying  glass,  many  minute  spaces  are  disclosed.  When 
broken,  and  the  fractured  surfaces  are  examined,  these  spaces 
are  present  and  can  be  seen  in  the  body  of  the  casting,  as 
well  as  on  the  outer  surfaces.  The  use  of  a  pure  aluminum, 
with  proper  technic  in  casting,  will  largely  overcome  this 
difficulty. 

For  various  reasons,  however,  a  swaged  base  is  usually 
more  satisfactory  and  less  inclined  to  irritate  the  tissues  than 
a  east  base. 

TIN  ALLOY  BASES 

Alloys  of  tin  and  cadmium,  tin  and  bismuth,  and  other 
similar  combinations,  are  frequentlj^  used  in  the  production 
of  bases  for  lower  substitutes,  to  give  weight  to  the  finished 
denture,  and  by  gravity  assist  in  its  retention.  When  prop- 
erly constructed,  they  are  non-irritating  to  the  tissues  and 
serve  well  the  purpose  for  which  they  are  intended.  Care 
should  be  taken,  however,  in  the  construction  of  dentures  of 
this  class  to  avoid  excessive  weight,  on  account  of  the  tendency 
of  the  substitute  to  tire  the  mandibular  muscles  and  produce 
irritation  of  the  soft  tissues. 


BASES    FOR    AilTIFICIAL    DENTURES  121 

VULCANITE  BASES 

Because  of  the  slight  expense  involved  and  the  com- 
paratively simple  technical  details  attending  its  manipulation, 
vulcanite  is  very  extensively  used  as  a  base  for  artificial  den 
tures.  When  pro])er  care  is  exercised,  most  efficient  and  serv- 
iceable substitutes  for  the  natural  teeth  can  be  produced 
when  this  material  is  used  as  a  base. 

ADVANTAGES 

First — Better  adaptation  can  be  secured  with  vulcanite 
than  with  any  other  basic  material. 

Second — Ease  of  manipulation  in  the  constructive  steps. 

Third — Inexpensive,  first,  as  to  cost  of  material,  and  sec- 
ond, as  to  production ;  consequently  dentures  of  this  type  are 
possible  for  persons  of  moderate  means. 

DISADVANTAGES 

First — Vulcanite  is  a  poor  conductor  of  thermal  changes. 

Second — In  order  to  have  the  inherent  strength  to  resist 
stress,  vulcanite  bases  are  necessarily  more  bulky  than  metal 
bases. 

Third — Vulcanite  decreases  the  acoustic  properties  of 
the  palatine  vault  to  a  greater  extent  than  do  metal  bases. 

Fourth — Unless  special  care  is  exercised  in  finishing  the 
palatine,  as  well  as  all  surfaces  of  vulcanite  dentures,  inflam- 
matory conditions  of  the  mucous  tissues  frequently  ensue. 
Such  conditions  have  been  erroneously  ascribed  to  other 
causes,  some  of  which  will  be  discussed  later. 

THERMAL  CONDUCTIVITY  OF  VARIOUS  DENTURE 
BASE  MATERIALS 

Vegetable  substances,  as  compared  with  the  metals,  are 
poor  conductors  of  thermal  changes.  The  following  table 
by  Prof.  R.  von  Wardroff  (slightly  modified)  on  the  conduc- 
tivity of  various  substances,  gives  the  conductivity  of  vulcan- 
ite, as  well  as  of  the  metals  used  in  denture  construction.  "The 
coefficient  of  thermal  conductivity  of  a  substance  indicates  the 
amount  of  heat  energy,  measured  in  calories,  conducted  from 
one  face  to  the  op]iosite  face  of  a  centimeter  cube  of  the  sub- 
stance, when  one  of  the  faces  is  maintained  one  degree  hotter 
than  the  other.    The  amount  of  heat  energy  conducted  is  pro- 


122  BASICS    FOR    ARTIFICIAL    DENTURES 

portional  to  the  difference  in  temperature  l)etween  the  op- 
posite faces." 

"A  calorie  is  the  amount  of  heat  energy  required  to  raise 
the  temperature  of  a  gram  of  water  one  degree  Centigrade." 

Silver  at  zero  C 1.00000=1 

Copper  at  zero  C 1.00000=1 

(lold  at  zero  C TS200=%  (Approx.) 

Aluminum  at  zero  C 34300=1/3  " 

Platinum  at  zero  C 11500=1/9  " 

Paraffin  at  zero  C 00061=1/166 

Vulcanite  at  zero  C 00040=1/250 

Beeswax  at  zero  C 00009=1/1111 

Silver  being  rated  as  1,  gold  transmits  only  %,  aluminum 
1/3,  platinum  1/9  and  vulcanite  1/250  calories  in  the  same 
length  of  time. 

CAUSE  OF  ORAL  INFLAMMATORY  CONDITIONS  UNDER 
VULCANITE  BASES 

Several  tlieories  have  been  advanced  as  to  the  cause  of 
inflanmiatory  conditions  frequently  arising  from  the  wearing 
of  vulcanite  dentures,  the  principal  ones  of  which  are  as 
follows : 

(1)  Lack  of  proper  conduction  of  thermal  changes  to, 
and  radiation  of  heat  from,  the  oral  tissues. 

(2)  Deleterious  effects  of  coloring  matter  in  vegetable 
bases. 

(3)  Mechanical  irritation. 

(4)  Unhygienic  conditions. 

CONDUCTIVITY   OF  THERMAL   CHANGES 

While  there  is  a  marked  difference  in  the  rate  of  con- 
ductivity of  the  metals  and  the  vegetable  bases,  there  is  no 
evidence  to  prove  that  the  noticeable  deficiency  of  vulcanite 
in  tills  respect  is  directly  responsible  for  the  troubles  some- 
times ascribed  to  it. 

Possibly  in  rare  cases,  particularly  wlien  other  active 
causes  are  present,  the  oral  mucoids  membrane  may  be  in- 
fluenced by,  and  its  general  tonicity  impaired  through,  the  non- 
responsive  medium  of  a  vulcanite  base.  However,  the  fact 
that  many  hundreds  of  thousands  of  vulcanite  dentures 
are  l)eing  worn  with  comfort,  under  which  no  inflammatory 
conditions  of  the  mucous  membranes  have  developed,  is  evi- 


BASES    FOR    ARTIFICIAL    DENTURES  123 

dence  in  itself  that  the  pereentaiic  of  eases  due  solely  to  poor 
coudnctivity  is  extremely  small. 

Many  cases  of  so-called  rubber  sore  mouths  have  come 
under  the  observation  of  the  writer.  Some  of  these  were 
corrected  by  the  substitution  of  metal  base  dentures  of  con- 
tinuous gums,  gold  or  aluminum,  and  others  with  gold-lined 
vulcanite  dentures.  The  largest  percentage  of  cases  presented 
were  satisfactorily  relieved  on  the  introduction  of  properly 
fitted  and  finished  vulcanite  cases.  In  no  instance  that  can 
now  be  recalled  was  there  a  recurrence  of  the  inflammatory 
conditions,  which  would  undoulitedly  have  occurred  had  the 
primal  cause  been  due  to  non-conductivity. 

DELETERIOUS    EFFECT    OF    COLORING    MATTER    IN 
VEGETABLE  BASES 

The  red,  ])iuk,  brown  and  maroon  rubliers,  as  well  as 
celluloid  and  zylouite,  are  usually  given  their  tints  by  the 
addition  of  ^■arying•  i^roportions  of  vermilion  or  the  sulphuret 
of  mercury  Hg.S.  The  idea  has  been  advanced  that  during 
tlic  process  of  vulcanization  some  of  the  sulphuret  may  fail 
to  unite  closel}^  with,  or  it  may  be  expelled  from,  the  rubber, 
thus  leaving  the  pigment  comparatively  free  or  only  weakly 
combined  with  the  base.  After  introduction  and  use  of  the 
denture,  the  vermilion  becomes  an  irritant  to  the  tissues  and 
the  inflammatory  conditions  mentioned  follow.  Again,  it 
has  been  thought  possible  that  the  comparatively  free  sul- 
phuret b}"  the  action  of  the  fluids  of  the  mouth,  which  are 
sometimes  slightly  acid,  may  be  converted  into  mercuric  chlor- 
ide or  corrosive  su.blimate,  a  decided  irritant,  and  the  con- 
ditions mentioned  be  thus  produced.  These  ideas,  however, 
are  unproven  theories  and  cannot  account  for  the  fact  that 
inflammatory  conditions  sometimes  develop  under  dentures 
of  black  vulcanite  which  contain  no  mercury  or  other  irritat- 
ing pigment  of  any  character,  and  sometimes  under  metal  base 
dentures  as  well. 

The  more  logical  explanation  of  the  conditions  under  con- 
sideration is  that  they  are  due  to  rough  or  defective  surfaces 
of  the  denture,  as  well  as  to  lack  of  hygienic  attention  to  the 
mouth  and  denture  on  the  part  of  the  patient. 

MECHANICAL  IRRITATION 

The  negative  form  of  the  mouth  is  given  to  a  vulcanite 
denture  by  molding  the  rubber  while  in  a  plastic  state  over  a 
cast  of  plaster,  or  some  similar  material,  and  holding  it  in 
contact  with  the  cast,  under  pressure,  while  hardening. 


124  BASES    FOR    ARTIFU'IAl.    DENTURES 

As  lias  been  mentioned  beloie,  tlie  manner  ol'  erystal- 
lization  of  plaster  results  in  the  formation  of  minute  spaces 
between  the  crystals.  When  examined  under  a  magnifying 
glass,  the  sui'face  of  a  plaster  cast  presents  many  minute  ir- 
regularities. In  addition  to  the  spaces  between  the  crystals, 
there  are  other  and  larger  spherical  spaces,  due  to  the  pres- 
ence of  air  in  the  plastic  mass  itself,  and  also  to  air  heing 
caught  between  the  latter  and  the  impression  surface  in  tilling. 
These  spherical  spaces  are  sometimes  quite  numerous,  some 
visible,  and  others  lying  just  under  the  surface  of  the  cast, 
obscured  by  a  thin  film  of  plaster. 

Under  the  pressure  exerted  in  closing  the  packed  flask, 
tlie  rubber  is  forced  into  the  visible  as  well  as  some  of  the 
obscured  irregularities  and  spherical  spaces,  and  in  vulcan- 
izing, hardens  in  the  irregular  form  thus  assumed. 

When  the  case  is  vulcanized,  removed  from  the  flask, 
thoroughly  cleaned  with  a  scrub  l)rush,  and  examined,  that 
portion  moiilded  against  the  surfaces  of  the  cast  will  be  found 
irregular  and  nodular,  as  a  result  of  the  conditions  mentioned. 
Unless  thoroughly  removed  and  the  surfaces  highly  polished, 
these  nodules  and  irregularities  become  mechanical  sources 
of  irritation,  frequently  sufficient  to  set  up  inflammatory  con- 
ditions. 

Hyiiersemic  conditions  and  oftentimes  traumatic  injury 
frequently  develop  at  local  points,  imder  a  vulcanite  denture. 
The  cause  may  nearly  always  be  traced  to  soiue  defect  in  the 
denture  at  that  point,  either  from  roughness,  ruidue  pres- 
sure, or  imperfect  adaptation.  Sometimes  obscure  spiculse 
are  present  in  the  palatine  vault,  and  the  pressure  of  the  den- 
ture on  the  mucous  tissues  overlying  these  points  causes  dis- 
comfort, and  frequently  marked  inflammation  develops. 
Sharp,  uneven  points  in  the  process,  resulting  from  recent 
extraction,  are  also  sources  of  irritation.  Such  conditions  de- 
velop under  metal  base,  as  well  as  vulcanite  dentures. 

UNHYGIENIC   CONDITIONS 

Lack  of  care  of  the  denture  on  the  part  of  the  patient  is  a 
most  common  source  of  inflammatory  conditions  of  the  oral 
mucous  membrane.  Mucous  plaques  seem  to  form  on,  and 
particles  of  food  to  become  attached  more  readily  to,  vulcanite 
than  to  metal  base  dentures.  Tlie  reason  for  this  is  ob- 
vious. A  metal  base  as  a  rule  is  usually  smoothly  finished, 
while  vulcanite  is  seldom  given  the  high  polish  it  is  capable 
of  taking  on. 


Bases  for  artificiai.  dentures  125 

The  rough  surfaces  on  the  palatine  portion  of  a  denture, 
previously  referred  to,  furnish  a  favorable  location  for  the 
formation  of  plaques  in  whieh  micro-organisms  flourish.  Dr. 
G-.  V.  Black  called  attention  to  this  fact  many  years  ago,  and 
stated  his  belief  that  the  by-products  of  the  bacteria  were 
largely  responsible  for  many  cases  of  rubber  sore  mouths. 
These  plaques  often  form  in  protected  locations  on  reasonably 
well-polished  vulcanite,  and  occasionaly  on  metal,  base  den- 
tures, if  the  patient  does  not  cleanse  them  thoroughly  and 
regularly. 

Most  of  the  disadvantages  ascribed  to  vulcanite  can  be 
greatly  reduced,  or  practically  eliminated,  if  proper  care  is 
observed  in  the  construction  of  dentures  of  this  material,  and 
they  are  given  proper  care  by  the  patient. 

CELLULOID  BASES 

Celluloid  is  a  mixture  of  gun  cotton,  camphor  gum,  oxide 
of  zinc,  and  vermilion.  As  prepared  for  dental  purposes  it 
comes  moulded  in  blanks  of  various  sizes.  A  blank  is  placed 
in  the  flask  matrix,  subjected  to  heat,  and  the  flask  closed 
under  heavy  pressure.  If  imperfections  are  present  in  the 
cast,  the  negative  of  these  will  be  reproduced  in  the  denture. 
The  avoidance  of  such  imijerfeclions  is  the  first  consideration; 
the  second,  equally  as  important,  is  their  removal  from  the 
denture,  if  any  are  present.  Otherwise,  similar  irritation  of 
the  oral  mucous  membrane  is  liable  to  occur,  as  in  vulcanite 
cases. 

Celluloid  is  not  as  resistant  to  wear  nor  to  the  action  of 
the  oral  fluids  as  vulcanite.  Alcohol  acts  on  it  somewhat,  and 
in  some  mouths  it  discolors  badly.  It  is  of  a  beautiful  pink 
shade  and  occupies  a  place  between  porcelain  and  the  best 
quality  of  pink  vulcanite,  in  its  resemblance  to  the  natural 
gum  tissues.  When  carefully  manipulated  and  properly  fin- 
ished, it  is  an  excellent  base  for  temporary  dentures,  and  in 
some  mouths  will  prove  satisfactory  for  permanent  substi- 
tutes. It  is  capable  of  taking  an  extremely  high  polish,  which, 
however,  is  soon  lost  if  abrasive  powders  are  used  in  cleans- 
ing it. 

When  properly  finished,  the  tissues  retain  their  tonicity 
under  celluloid  fully  as  well  as  under  metal  base  dentures.  As 
a  matter  of  fact,  if  reasonable  skill  is  exercised  in  the  technical 
details,  good  substitutes  can  be  produced  with  any  of  the  mate- 
rials here  described ;  while  on  the  other  hand,  poor  teclmic 
with  the  best  materials  is  productive  of  indifferent  results,  if 
not  positive  failure. 


0  li  A  P  T  E  R    X 

SWAGED  METAL  BASE  DENTURES 

Swaging  is  the  process  of  adapting  or  conforming  metal, 
usually  in  sheet  form,  to  a  carved,  cast,  or  prepared  harder 
object  called  a  die,  by  means  of  blows  or  pressure. 

Swaged  metal  bases  of  gold,  ]ilatinum  or  aluminum,  such 
as  are  used  in  denture  construction,  are  given  the  reverse  or 
negative  form  of  the  mouth  by  swaging  a  plate  of  suitable 
thickness  between  a  metallic  die,  and  a  counterdie  of  metal 
or  some  other  luaterial  which  fulfills  the  purpose  of  a  metal 
counterdie,  as  rubber,  soap,  clay,  etc.  In  case  any  of  the  latter 
named  substances  are  employed,  they  must  be  confined  within 
a  suitable  receptacle. 

In  the  production  of  a  swaged,  metallic  l)ase  denture, 
therefore,  a  die  fulfills  a  similar  ])urpose  to  that  of  a  plaster 
cast  in  the  production  of  a  plastic  base  denture. 

COMPARATIVE  RESULTS  IN  ADAPTATION  OF 
SWAGED,  AND   VULCANITE  BASES 

As  a  general  proposition  it  is  more  difficult  to  secure  as 
close  an  adaptation  of  a  swaged  metal  base  to  the  oral  tissues, 
as  can  be  secured  when  vulcanite  is  employed.  This  statement 
is  based  on  the  fact  that  in  the  production  of  dentures  with 
metal  bases,  a  greater  numlier  of  constructive  steps  must  be 
carried  out  than  are  required  in  the  production  of  vulcanite 
dentures. 

SEQUENT    STEPS    IN    SWAGED    BASE    DENTURE 
CONSTRUCTION 

a.  An  impression  of  the  moutli  is  secured. 

b.  From  the  impression  a  cast  of  the  mouth  is  obtained, 
which,  by  proper  trimming,  with  additions  if  necessary,  and 
final  varnishing,  is  converted  into  a  model. 

c.  By  imbedding  the  model  in  molding  sand  and  with 
drawing  it,  a  sand  matrix  is  formed. 

d.  A  die  is  produced  by  casting  molten  metal  in  the  sand 
matrix. 

e.  By  imbedding  all  but  the  face  of  the  die  in  sand,  and 
casting  a  lower  fiising  metal  over  the  exposed  portion,  a 
counterdie  is  obtained. 


SWAGED    METAL    BASE    DENTURES  127 

f.  A  baseplate  is  produced  by  swaging  a  sheet  of  metal 
of  the  required  character  and  thickness  l)etween  the  counter- 
die  and  die,  until  the  plate  metal  closely  conforms  to  all  sur- 
faces of  the  latter. 

g.  Wiring  the  periphery  and  lingual  surface  of  the  base 
and  attaching  anchoi'ages  for  the  vulcanite. 

h.  Includes  the  general  steps  of  occluding  the  teeth,  wax- 
ing, flasking,  packing,  closing  the  flask,  vulcanizing  and  finish- 
ing the  case. 

In  carrying  out  each  one  of  the  sequent  steps  mentioned, 
except  (e),  some  loss  of  detail  or  departure  from  the  true  con- 
tour of  the  oral  tissues  to  be  covered  by  the  denture,  is  liable 
to  occur,  which  may  impair  the  adaptation  of  the  finished 
product.  If  more  than  one  error  occurs,  the  tendency  is  to 
increase,  rather  than  diminish,  any  previous  defect,  while 
in  the  end  any  one,  or  the  several  errors  combined,  may  seri- 
ously impair  or  entirely  destroy  the  adaptation  of  the  denture. 

SEQUENT    STEPS    IN    VULCANITE    DENTURE    CONSTRUCTION 

In  the  sequent  steps  of  vulcanite  denture  construction,  it 
is  necessary  to  carry  out  (a),  the  first  part  of  (b),  and  (h), 
as  detailed;  (c),  (d),  (e),  (f)  and  (g)  are  neither  necessary 
nor  applicable.  Thus  it  is  seen  that  of  the  eight  general  steps 
carried  out  in  the  production  of  swaged  metal  base  dentures, 
but  three  are  required  to  produce  vulcanite  substitutes. 

The  intermediate  steps,  unnecessary  in  vulcanite  work, 
but  essential  in  the  swaging  process,  require  the  greatest  care 
in  execution,  to  avoid  errors.  The  principal  mishaps  liable 
to  occur  in  these  intermediate  steps  are  as  follows : 

(c)  Distortion  of  the  sand  matrix  in  removal  of  the 
model. 

(d)  (1)     Distortion  of  the  sand  matrix  in  pouring  the 

molten  die  metal. 

(2)  Accumulation  of  steam  or  gas  in  the  matrix, 

causing  roughness  and  imperfections  in  the 
die. 

(3)  Warpage   of   the   die,   due   to   contraction   in 

cooling. 
(f)     (1)    .Marring  the  high  ])oints  on  the  face  of  the 
die  in  adapting  the  plate  with  the  horn  mal 
let,  and  subsequently  in  swaging. 

(2)  Spreading  or  sjilitting  of  tlie  die  under  hammer 

lilows  or  i^ressure. 

(3)  Failure   to   secure   perfect   adaptation   of  the 

baseplate  to  the  face  of  the  die. 


128  SWAGED    METAL    BASE    DENTURES 

(g)  Distortion  of  the  plate  in  soldering,  in  attaching 
the  rim  wires  and  anchorages  for  the  vulcanite. 

All  of  these  steps,  if  carefully  carried  out,  may  be  com- 
]ileted  without  ]iercei)tible  errors  occurring,  and  the  adapta- 
tion of  the  baseplate  to  the  oral  tissues  may,  on  trial,  be  found 
satisfactory,  yet  under  (h),  in  the  final  closing  of  the  flask, 
when  overpacked  and  subjected  to  undue  pressure,  the  adapta- 
tion of  the  denture  is  frequently  impaired  or  destroyed. 

The  excess  rubber  in  the  overpacked  matrix,  in  closure 
of  the  flask,  forces  the  baseplate  against  the  supporting  plas- 
ter, and  if  excessive  stress  is  applied,  causes  distortion  not 
only  of  the  foundation  on  which  it  rests,  but  bends  the  base- 
plate as  well.  The  warped  condition  the  denture  thus  assumes 
becomes  permanent  after  vulcanization. 

This  brief  summary  of  the  commonly  occurring  errors 
which  tend  to  impair  the  adaptation  of  swaged  base  dentures 
is  not  intended  to  disparage  the  utility  of  substitutes  of  this 
type,  nor  to  discourage  their  more  general  production,  but 
rather  to  emphasize  the  need  of  accuracy  in  technical  proced 
ures.  "When  properly  constructed,  the  usefulness,  beauty  and 
comfort  of  swaged  metal  base  dentures — their  general  ex- 
cellence, in  fact,  is  thoroughly  established  and  unquestioned. 

APPLIANCES  AND  ACCESSORIES  USED  IN  DIE  AND 
COUNTERDIE  CONSTRUCTION 

The  necessary  appliances  used  in  the  production  of  dies 
and  counterdies  are  as  follows: 


1. 

Molding  flasks. 

o 

Molding  sand. 

3. 

Sieve. 

4. 

Talcum  powder. 

5. 

Straight  edge. 

6. 

Laboratory  knife. 

7. 

TTeating  ajijiliances. 

s. 

Melting  ladles. 

9. 

Die  metal. 

10. 

Counterdie  metal. 

n. 

Wliiting  and  alcohol, 

12. 

Sable  brush. 

MOLDING    FLASKS 


The  ordinary  molding  flasks  are  l>and-likc,  slightly  taper 
ing  rings  of  cast  iron,  open  at  both  ends.    Peripherally,  they 


SWAGED    METAL    BASE    DENTURES  129 

conform  to  the  outline  of  the  alveolar  arches.  They  vary  in 
size,  the  usual  set  consisting  of  a  nest  of  four  rings,  ranging 
from  -i  to  21 2  inches  in  diameter,  and  214  inches  in  depth.  The 
smallest  flask,  which  corresponds  in  size  and  general  outline 
form  to  the  base  of  the  average  model,  is  used  for  confining 
the  metal  within  the  base  outline  of  the  die,  and  thus  increas- 
ing its  depth,  to  avoid  spreading  or  splitting  during  swaging 
Various  forms  of  special  flasks,  such  as  the  Bailey,  Lewis, 
and  Hawes  flasks,  are  also  in  common  use.  The  two  former 
are  designed  to  increase  the  depth  of  the  die  over  that  of  the 
model,  while  the  latter  is  intended  to  obviate  the  use  of  cores, 
when  imdercuts  are  present  on  the  labial  or  buccal  surfaces 
of  the  model. 

MOLDING  SAND 

Sand  of  the  finer  vai'iety,  such  as  is  used  by  brass  or  iron 
molders  mav  be  iised  to  advantage  in  the  laljoratorv.     It  is 


NEST   OF   lIOLDrNG   RINGS 


rendered  moist  and  workable  by  spraying  occasionally  with 
water,  just  enough  being  incorporated  to  render  it  cohesive. 
An  excessive  amount  of  moisture  present  would  develop  an 
excessive  quantity  of  steam  in  casting,  and  result  in  imper- 
fections in  the  die.  The  sand  should  be  sifted,  thoroughly 
worked  with  the  hands,  and  allowed  to  stand  a  short  time 
before  use,  to  develop  uniform  density  and  cohesiveness,  or 
temper,  as  it  is  called. 

The  supply  houses  furnish  prepared  molding  sand,  such 
as  "Chase's,"  a  combination  of  fine  sand  with  oil,  and  "Cal- 
ear,"  a  combiuatioii  of  marble  dust  with  glycerin  or  oil.  With 
moderate  use,  these  prepared  sands  give  good  service,  last  a 
considerable  length  of  time,  and  are  more  convenient  to  use 
than  the  common  sand.  Used  frequently,  they  soon  deteri- 
orate and  lose  the  cohesive  property,  because  of  the  burning 
out  of  the  oil  or  glycerin.     The  addition  of  a  small  quantity 


1311  SWAGED     MKTAL    BASE    DENTURES 

of  the  latter,  and  the  thorough  sifting  and  working  of  the 
mass  will  restore  cohesiveness. 

THE  SIEVE 

It  is  essential  that  sand  of  any  variety  should  be  kept 
free  from  lumps,  foreign  substances  and  particles  of  metal 
that  may  become  detached  from  the  die  and  counterdie  in 
casting.  For  this  purpose  a  No.  20  mesh  sieve  should  be  kept 
at  hand,  and  before  forming  the  matrix,  the  sand  should  be 
run  through  it  once  or  twice.  This  treatment  not  only  re- 
moves debris,  but  renders  the  sand  more  workable  by  dis- 
seminating the  drier  particles  among  the  damper  portions, 
and  develops  cohesive  property  as  well. 

TALCUM  POWDER 

The  model,  which  should  be  flaring,  smooth,  varnished  and 
perfectly  dry,  is  dusted  and  thoroughly  rubbed  with  soapstone 
to  i^revent  the  sand  from  adhering  to  it.  The  excess  should 
be  removed  with  a  soft  brush  before  imbedding  the  model  in 
sand. 

THE   STRAIGHT   EDGE 

A  straight  edge  of  metal  or  wood  is  used  for  striking  off 
the  excess  sand  that  extends  above  the  molding  flask  after 
packing.  Since  this  surface  of  the  sand  becomes  the  base 
of  the  matrix  and  must  support  the  weight  of  the  molten 
metal  in  casting,  it  should  set  flat  at  all  points  upon  the  bench 
on  which  it  rests,  so  that  it  will  not  yield  or  break  under  the 
weight  of  the  molten  die  metal. 

THE   LABORATORY   KNIFE 

A  straight  blade  knife  is  used  for  removing  a  tapering 
section  of  sand,  beginning  at  the  ring  margin  and  slightly 
increasing  in  depth  to  the  periphery  of  the  model.  This 
trimming  is  necessary  to  free  the  model  at  its  periphery  and 
allow  it  to  drop  from  the  sand  without  fracturing  the  matrix 
margins. 

HEATING  APPLIANCES 

A  burner  capable  of  developing  a  considerable  amount 
of  heat  is  an  essential  factor  in  laboratory  procedures.  It 
is  a  time  and  money  saver  as  well.  The  very  common  method 
of  placing  the  ladle  over  an  ordinary  Bnnsen  burner  and 
applying  the  blow-pipe  flame  directly  on  the  die  metal  to  more 
rapidly  fuse  it,  is  to  be  discouraged,  since  this  procedure  in- 


SWAGED    MKTAL    BASK     IIKXTHRKS  131 

duces  oxidation  and  deterioration  of  the  nietai  in  a  very 
short  time.  The  application  of  the  hU)w-pipe  tlame  underneatli 
the  ladle  is  not  objectionable,  further  than  that  it  is  usually 
unnecessary,  if  sufficient  heat  is  developed  by  the  burner. 

MELTING   LADLES 

Toadies  used  for  melting  the  die  metal  should  be  of  cast 
iron  or  stamped  from  heavy  iron  of  not  less  than  one-eighth 
inch  in  thickness.  Ladles  of  this  tyi)e  are  preferable  to  those 
made  of  thin  sheet  metal,  first,  because,  being  thicker,  they 
absorb  and  retain  more  heat,  thereby  accelerating  the  fusing 
of  the  metal,  and  second,  because  of  their  greater  rigidity. 
There  should  be  a  lip  or  spout  on  the  side,  through  which  the 
molten  metal  may  be  directed  in  a  small  stream  while  pouring 


jrELTISG    LADLES 


it  into  the  matrix.  Ladles  used  for  melting  zinc  should  be 
coated  inside  with  whiting  until  the  iron  is  thoroughly  oxi- 
dized, to  prevent  the  zinc  from  alloying  with  it.  The  alloy 
of  zinc  and  iron,  if  it  is  allowed  to  form,  is  taken  up  by  the 
molten  zinc,  which  is  thus  rendered  harder,  while  the  ladle 
sides  are  gradually  reduced  in  thickness  by  the  constant  alloy- 
ing process,  and  are  eventually  perforated. 


DIE  METAL 

A  metal  used  for  die  purposes  should  possess  certain 
requisite  properties. 

First — It  should  neither  expand  nor  contract  in  assuming 
a  solid  state. 

Second — It  should  fuse  at  a  moderately  low  temperature. 


132  SWACJED    MKTAL    BASK     DKNTURKS 

Third — It  should  be  sufficiently  hard  and  resistant  to 
stress  so  that  the  high  points  and  general  surface  markings 
of  the  die  will  not  be  defaced  or  battered  down  in  swaging  the 
plate. 

Fourth — It  should  be  cohesive,  so  as  to  maintain  its 
form  without  splitting  or  spreading  under  pressure  or  hammer 
blows. 

Zinc,  Babbitt's  metal,  Melotte's  metal  and  a  variety  of 
alloys  similar  in  composition  to  the  latter,  are  used  for  die 
pm-poses. 

ZINC 

Zinc  has  long  been  used  and  is  still  very  extensively  em- 
ployed in  the  making  of  dies  for  dental  purposes.  It  fuses 
at  the  highest  temperature  and  is  the  hardest  of  any  of  the 
metals  or  alloys  commonly  used  for  dies  for  prosthetic  pur- 
poses. Its  fusing  point  is  about  433  deg.  C.  In  cooling,  it 
contracts  perceptibly  and  oftentimes  warps  to  a  marked  de- 
gree, depending  on  the  form  of  the  matrix  in  which  it  is 
cast. 

For  years  it  has  been  known  that  plaster  expands  in 
setting  and  zinc  contracts  in  cooling.  From  these  facts,  the 
axiom  was  deduced  that  the  expansion  of  the  plaster  model 
compensates  for  the  contraction  of  the  zinc  die.  This  cer- 
tainly would  be  a  simple  solution  of  the  problem  if  the  amount 
of  contraction  in  the  die  equaled  the  expansion  of  the  plaster 
model,  and  if  the  factor  of  warpage  could  be  eliminated.  Since 
there  is  no  correlation  of  the  movements,  however,  the  ab- 
surdit.y  of  the  axiom  is  apparent. 

SHRINKAGE  OF  METALS  IN  PASSING  FROM  LIQUID  TO 
SOLID  STATE 

The  following  table  from  Kent's  "Engineers'  Pocket 
Book"  on  the  shrinkage  of  castings  is  as  follows: 

Cast  Iron %  inch  per  linear  foot — 1  inch  sectional  area 

Brass 3/16    "      "       "       "       "    "  "  " 

Steel  %    "      "       "       "       "    " 

Malleable  Iron.     %    "      "       "       "       "    "  "  " 

Zinc    .5/16    "      "       "       "       "    " 

Tin    1/12    "      "       "       "       "    " 

Aluminum    ....  3/16    "      "       "       "       "    "  "  " 

Britannia    1/32    "      "       "       "       "    " 

Larger  or  bulkier  castings  shrink  slightly  less  propor- 
tionately, while  smaller  ones  shrink  more  than  the  amounts 
indicated  in  the  table. 


SWAGED    METAL    BASE    DENTURES  133 

A  die  of  zinc  derived  from  a  sand  matrix  21/2  inches 
across  from  one  bnccal  surface  to  the  other  shrinks  about 
1/16  of  an  inch,  while  a  plaster  model,  in  which  the  expansive 
movement  is  high,  expands  less  than  1/64  of  an  inch.  In 
cooling,  the  tendency  of  the  metal  is  to  rest  on  the  dome,  or 
that  portion  of  the  matrix  which  gives  form  to  the  palatal 
vault  of  the  die,  and  for  the  borders  to  draw  inward  from  the 
sides  and  upward  from  the  base  of  the  mold.  The  warpage 
thus  resulting  decreases  the  height  of  the  palatine  vault  and 
reduces  the  buccal  diameter,  in  many  cases,  to  such  an  extent 
as  to  require  the  construction  of  a  more  accurate  die  on  which 
to  finish  the  base. 

When  zinc  dies  are  used,  it  is  the  common  practice  to 
cast  two,  and  frequently  three,  as  a  preliminary  step  in  swag- 
ing a  denture.  It  also  frequently  occurs  that  a  baseplate, 
when  adapted  to  one,  will  fit  neither  the  other  dies  nor  the 
plaster  model  from  which  they  were  derived.  It  is  then  a 
problem  as  to  which  die  most  nearly  represents  the  true  oral 
contour.  This  can  only  be  determined  by  trial  of  the  base  in 
the  mouth,  after  swaging  on  each  die  sei^arately. 

To  partially  overcome  the  errors  occurring  in  the  use  of 
zinc,  as  well  as  other  dies,  the  following  steps  are  recom- 
mended : 

TREATMENT  OF  PLASTER  MODELS  TO  ARREST 
EXPANSION 

First — As  soon  as  the  plaster  cast  from  which  the  model 
is  to  be  formed  has  set  sufficiently  hard  to  permit,  the  im- 
pression should  be  removed  and  the  cast  converted  into  model 
form  by  trimming  and  additions,  as  required.  The  moisture 
present  sliould  then  be  expelled  by  applying  moderate  heat. 
Overheating  tends  to  both  warp  the  model  and  disintegrate 
the  plaster.  The  varnish  should  lie  applied  last,  since,  if  ap- 
plied before  heating,  it  prevents  the  ready  evaporation  of  the 
moisture.  Drying  the  model  in  tliis  manner  stops  the  chemical 
action,  and  hence  expansion  in  the  plaster,  which  otherwise 
woiild  continue  for  twenty-four  hours  or  more. 

Second — When  the  sand  mold  is  secured,  the  molten  die 
metal  is  cast  into  it  at  as  low  a  temperature  and  in  as  thickly 
liquid  a  condition  as  may  be,  and  yet  be  plastic  enough  to 
insure  its  becoming  adapted  to  all  portions  of  the  matrix.  In 
other  words,  thorough  evaporation  of  moisture  from  the 
model,  if  driven  off  soon  after  the  cast  is  constructed,  lessens 
its  expansion,  and  filling  the  matrix  with  the  die  metal,  poured 


1H4  SWAUKD    METAL    BASK    1>KNTUKKS 

at  HS  low  a  tempei'ature  as  possible,  reduct^s  contraction  and 
lessens  warpage.  If  cast  while  overheated,  the  metal  assumes 
a  decidedlj^  crystalline  strncture,  is  very  brittle  on  hardening, 
and  contracts  perceptibly. 

Zinc  dies,  after  cooling,  may  be  annealed  and  rendered 
much  tougher  and  more  cohesive  if  heated  to  a  temperature 
of  between  100  to  150  deg.  ('.  If  heated  nnicli  above  150  deg. 
C.  they  again  become  very  brittle.  This  process  of  annealing 
is  resorted  to  in  the  production  of  sheet  zinc,  the  cast  ingot 
being  heated  as  above  indicated  and  passed  through  rolls 
until  reduced  to  the  required  thickness.  The  malleability  im- 
parted to  it  by  annealing  is  retained  on  cooling. 

BABBITT   METAL 

Babbitt  metal  is  an  alloy  of  copper,  tin  and  antimony  in 
varying  proportions.  It  was  designed  by  the  man  whose  name 
it  bears — Isaac  Babbitt — as  an  anti-friction  metal  for  bear- 
ings. As  commonly  compounded  it  is  too  soft  for  die  purposes, 
but  when  combined  in  the  proportions  suggested  by  Dr.  L.  P. 
Haskell,  the  alloy  is  non-shrinking,  resistant  to  stress,  nearly 
equal  to  zinc  as  to  hardness,  fuses  at  a  lower  temperature,  and 
is  superior  in  other  respects.  Dr.  Haskell's  formula  is  as 
follows: 

Copper  1  part 

Antimony    2  parts 

Tin    8  parts 

This  Babbitt  metal  fuses  at  260  deg.  C,  casts  well,  and 
copies  accurately  the  surfaces  against  which  it  is  poured,  if 
of  proper  fluid  consistency.  The  antimony  present,  which 
imder  ordinary  conditions  expands  in  cooling,  eliminates  to 
a  great  extent,  if  not  altogether,  any  tendency  of  the  alloy  to 
contract  in  passing  from  the  fused  to  the  solid  state.  A  die 
made  of  Babbitt  metal  therefore  more  nearly  represents 
the  form  and  proportion  of  the  plaster  model  than  does  one 
made  of  zinc.  Its  comparatively  low  fusibility  is  also  a  de- 
cided advantage.  For  these  reasons,  principally,  the  use  of 
Babbitt  metal  for  dies  is  gradually  increasing. 

Haskell's  Babbitt  metal,  properly  compoimded,  can  be 
procured  of  the  supply  houses.  If  it  is  deemed  advisable  to 
make  it  in  the  laboratory,  the  following  directions  by  Hall  will 
aid  in  producing  a  well-alloyed  product :  "Melt  the  copper  and 
half  of  the  tin,  then  add  the  antimony  and  the  remainder  of 
the  tin.  Stir  vigorously  and  keep  the  surface  of  the  alloy 
covered  with  powdered  charcoal." 


SWAGED    METAL    BASE    DENTURES  135 

When  melted  repeatedly,  and  especially  at  high  temper- 
atures, Babbitt  metal  deteriorates,  owing  to  the  formation 
and  retention  within  the  alloy  of  some  of  the  oxides  of  the 
component  metals.  These  oxides  may  be  partially  removed 
and  the  metal  restored  to  working  condition  by  heating  to  a 
a  high  temperature,  adding  scrap  beeswax,  stirring  thor- 
oughly, and  skimming  off  the  dross  as  it  accumulates  on  the 
surface.  Covering  the  surface  of  the  molten  metal  with  fine 
charcoal  and  stirring  well  also  removes  soiue  of  the  oxides 
present. 

Dr.  Haskell  recommends  the  addition  from  time  to  time 
of  a  little  tin  for  restoring  the  fluidity  of  the  alloy,  since  by 
repeated  fusing  some  of  the  latter  metal  is  lost  by  oxidation 
and  volatilization. 

As  previously  intimated,  all  die  metals  and  alloys,  if  over- 
heated, deteriorate  rapidly.  Care  should  therefore  be  observed 
to  remove  the  metal  from  the  fire  before  the  entire  mass  is  in 
a  molten  condition.  The  heat  absorl^ed  by  the  already  melted 
metal  is  usually  sufficient  to  melt  one-fourth,  and  frequently 
one-half,  its  Imlk  of  the  still  unfused  portion  after  removal 
from  the  fire.  This  plan  obviates  overheating,  and  consequent 
excessive  oxidation.  It  also  insures  smoother  castings,  since 
the  metal  being  poured  at  low  temperature  generates  less  gas 
or  steam  on  coming  in  contact  with  the  sand  matrix,  than  when 
overheated. 

MELOTTE'S  METAL  AND  OTHER  FUSIBLE  ALLOYS 

A  class  of  metallic  compounds  known  as  fusible  alloys  or 
triple  alloys  are  much  used  for  die  purposes  in  crown  and 
bridge  construction,  and  occasionally  as  dies  for  dentures. 
These  alloys  are  not  as  hard  as  zinc  or  Babbitt  metal,  but  on 
account  of  their  low  fusiliility  and  the  sharpness  of  castings 
produced,  the.v  are  very  serviceable  and  much  used. 

The  triple  alloys  contain  three  metals,  usually  tin,  lead 
and  bismuth,  in  varying  proportions.  Bismuth  has  the  prop- 
erty of  expanding,  imparting  hardness,  and  reducing  the  fus- 
ing point  of  the  alloy  considerably  below  the  mean  fusing 
point  of  the  three  metals,  which  is  272  deg.  C.  When  alloyed, 
the  metals  melt  at  about  100  deg.  C. 

Another  class  of  alloys  similar  in  character  to  the  triple 
alloys,  but  composed  usually  of  four  metals,  are  also  in  com- 
mon use.  These,  in  addition  to  the  metals  mentioned,  contain 
antimony  or  cadmii>m,  both  of  which,  like  bismuth,  have  the 
property  of  reducing  the  fusing  point  of  the  alloy  of  which 


13«  SWAGED    METAL    BASE    DENTURES 

they  are  a  part.  They  also  expand  in  cooling,  and  when  in- 
corporated, impart  this  property  to  alloys,  resulting  in  the 
production  of  sliarj)  castings.  The  low  fusibility  of  this  type 
of  compounds  jiermits  of  their  being  poured  into  fresh  plaster 
impressions  direct,  without  the  necessity  for  drying  out  the 
latter.  Such  castings  as  a  rule  are  very  shai'p,  well  defined, 
and  of  reasonable  hardness. 

COMPOSITION   OF  FUSIBLE  ALLOYS 

Melting 

Name.  Tin.  Lead.  Bismuth.  Antimony.  Cadmium.     Point. 

Melotte's    5                 3  8  lOO'C. 

Newton's    3                 5  8  95°C. 

D'Arcet's    1                1  2  93°C. 

Dalton's   3                .5  lOVa  92°C. 

Onion's 2                 3  5  92°C. 

Rose's   3                 8  8  79°C. 

Wood's    1                 2  4  1  71°C. 

CUnch6    48  32,.5  9              IOV2 

Richmond's   20  19      <  48                                13  65.5°C. 

Hodgen's   3                 5  8  2                                106.6°C. 

The  fusible  alloys,  being  hard  and  more  or  less  crystalline, 
lack  the  coliesiveness  of  zinc  or  Babbitt's  metal.  Dies  for 
full  dentures,  composed  of  such  alloys,  should,  tlierefore,  be 
made  sufficiently  thick  to  ])revent  fracturing  under  hammer 
blows.  When  used  under  hydraulic  or  screw  ])res.sure,  a  die 
of  moderate  thickness  will  resist  stress  without  change,  if  its 
base  and  that  surface  of  the  iiress  on  which  it  rests  are  fiat. 

COUNTERDIE  METAL 

A  counterdie  should  be  composed  of  a  softer  metal  than 
the  die  of  which  it  is  the  complement.  This  is  essential  for 
three  reasons : 

First — If  the  die  and  counterdie  were  of  e(iual  hardness, 
both  must  yield  in  swaging,  the  die  becoming  slightly  smaller 
and  the  counterdie  slightly  larger,  in  order  to  make  room  for 
the  interposed  plate.  Such  change  in  the  die  and  its  conse- 
quent effect  on  the  baseplate  would  impair,  if  not  altogether 
destroy,  the  adaptation  of  the  latter  to  the  oral  tissues. 

Second — The  tendencies  of  a  die  and  counterdie  of  equal 
hardness  to  shear,  or  at  least  reduce  in  thickness,  the  plate 
being  swaged  over  o])posite  parallel  surfaces,  as  on  the  buccal 
surfaces  of  prominent  tuberosities,  is  very  marked.  This 
tendency  is  not  apparent  when  the  counterdie  is  composed  of 
a  softer  metal  than  the  die. 

Third — A  somewhat  yielding  counterdie  opposed  to  an 
unyielding  die  carries  the  plate  into  the  inequalities  of  the 


SWAGED    METAL    BASE    DENTURES  137 

die,  with  its  irregularly  disposed  surfaces,  better  than  if  the 
two  were  of  equal  hardness. 

A  eouuterdie  is  usually  made  by  pouring  molten  metal 
over  the  face  of  a  die.  To  prevent  fusion  of  the  face  of  the 
die,  and  consequent  union  of  the  two  masses  of  metal  while 
casting,  the  counterdie  metal  should,  as  a  rule,  melt  at  a  lower 
temperature  than  that  of  the  die;  the  die  should  be  cold,  and 
the  counterdie  metal  should  be  poured  at  as  low  a  temperature 
as  possible. 

When  melted,  the  casting  of  the  counterdie  metal  should 
be  deferred  until  it  begins  to  thicken  around  the  sides  of  the 
ladle,  when  it  may  be  cast  against  the  face  of  the  die  in  a 
semi-liquid  condition. 

Lead  is  used  for  counterdies  with  zinc  dies,  the  difference 
in  the  fusing  points  of  the  two  metals  being  124  deg.  C.  An 
alloy  of  7  parts  lead  and  1  part  tin  is  used  for  counterdies 
with  Babbitt  metal  dies,  the  difference  in  the  fusing  points  of 
the  alloys  being  about  50  deg.  C. 

Both  die  and  counterdie  can  be  made  from  the  same  alloy 
in  the  bismntii  compounds,  the  only  precautions  necessary  to 
observe  to  prevent  union  being  to  have  the  die  cold,  and  to 
allow  the  metal  for  the  counterdie  to  assume  a  pasty  condition 
before  casting.  A  square-end  tamper  pressed  against  the 
plastic  mass  immediately  after  casting  will  force  it  against 
the  face  of  the  die.  and  insure  close  adaptation  of  the  former 
to  the  latter. 

Usually,  however,  tiie  fusible  alloys  are  used  in  con- 
junction with  some  swaging  device  or  press.  In  such  cases, 
only  the  die  or  the  counterdie  is  formed  of  the  fiisible  alloy, 
the  plate  to  be  swaged  being  adapted  between  the  metallic 
form  on  one  side,  and  some  yielding  material  on  the  opposite 
side,  such  as  soft  rubber,  moldine,  damp  tissue  paper,  or 
modeling  compound.  Si;ch  methods,  however,  are  only 
adapted  to  the  swaging  of  the  purer  and  thinner  forms  of 
gold  plate,  or  of  pure  platinum. 

WHITING  AND   ALCOHOL   SOLUTION 

A  solution  of  whiting  (preciintatcd  chalk)  and  alcohol  is 
essential  for  coatifig  the  surface  of  a  die  previous  to  casting 
the  counterdie."  A  solution  of  whiting  in  water  will  fulfiill 
the  same  purpose,  but  alcohol  is  much  better,  as  this  solution, 
when  applied,  dries  immediately,  while  the  aqueous  solution 
does  not.  A  little  gum  arabic  added  to  the  solution  will  im- 
part adhesiveness  to  the  film  when  applied,  and  dry  and  pre- 


l.'iS  SWAGED    MKTAL    BASE    DENTURES 

veut  exposure  of  the  juetal  surfaces  by  tlie  Tul)biug  off  of  the 
film,  should  anything  come  in  contact  with  the  die  face.  Car- 
bonizing the  die  is  also  recommended,  Imt  the  process,  although 
effective,  is  a  filthy  one  and  soils  the  hands  imnecessarily. 

BRUSHES 

A  medium-sized  sable  or  soft  bristle  brush  is  very  useful 
for  removing  soa]istone  or  sand  from  the  model,  and  for 
cleaning  up  the  outer  surfaces  of  the  matrix  generally  before 
removing  the  model. 


CHAPTER     XI 

TECHNIC  OF  DIE  AND  COUNTER  DIE 
CONSTRUCTION 

FORMING  THE  SAND  MATRIX 

The  table  or  laboratory  beiieli  should  be  covered  with  a 
large  sheet  of  clean  paper,  to  assist  in  recovering  the  sand 
after  the  die  is  cast. 


The  model,  having  been  prepared  as  previously  de- 
scribed, is  placed  on  the  paper  face  up,  the  largest  molding 
flask  of  the  iiest  of  four  placed  over  it,  the  large  ead 
down,  and  so  adjusted  that  the  model  will  occupy  a  central 
position  within. 


140        TECHNIC    OF    DIB    AND    COUNTER    DIE    CONSTRUCTION 

Sifted  sand  is  now  filled  in  the  molding-  flask  until  even 
with  the  face  of  the  model,  and  packed  into  the  space  between 
the  latter  and  the  flask  periphery.  The  pressure  on  the  sand 
should  be  light  at  first,  so  as  not  to  move  the  model  from  its 
central  position.  As  soon  as  the  model  is  firmly  fixed  in 
place,  the  sand  should  be  still  further  compressed,  until  firm 
and  compact,  special  stress  l)eing  exerted  to  force  it  outward 
against  the  flask  walls.  More  sand  is  added,  and  with  the 
fingers  pressed  compactly  against  the  flask  walls  imtil  the 
packed  portion  stands  slightly  above  the  crest  of  the  model. 
The  sand  in  the  vault  or  central  portion  of  the  model,  which 
is  not  yet  compressed,  should  cover  this  area  at  this  stage  to 
a  depth  of  about  one-half  an  inch. 

Careful,  uniform  pressure  with  the  fingers  should  be 
made  on  the  sand  over  the  central  area  of  the  model,  sufficient 


SKCTIONAI-    VIEW    ()]''    CAST    AND    MdT.DIXG    RING 

to  bring  the  granules  in  fairly  close  contact,  without  render- 
ing the  surface  too  dense  or  compact,  or  wedging  the  sand 
too  tightly  between  the  lingually  inclined  walls  of  the  model. 
If  too  loosel}^  packed,  the  sand  will  lack  cohesion  and  be  dis- 
turbed in  pouring  the  molten  metal  into  the  matrix.  If  too 
densely  compressed,  the  gases  or  steam  generated  by  the  hot 
metal  coming  in  contact  with  the  moisture  or  oil  in  the  sand 
cannot  escape  through  the  densely  packed  matrix  as  rapidly 
as  formed.  It  then  finds  its  way  out  lietween  the  matrix  walls 
and  the  die,  or  forms  vent  holes  through  the  die  itself,  in 
either  case  causing  roughness  and  imperfections  of  the  latter. 

When  the  sand  is  wedged  too  tightly  in  the  vault  portion 
of  the  model,  it  frequently  fractures  and  parts  from  the  matrix 
when  the  model  is  withdrawn. 

The  remaining  space  in  the  flask  is  filled  and  compressed 
until  the  sand  stands  above  the  margin.  The  straight  edge 
is  now  passed  over  the  top  of  the  flask  and  the  surplus  sand 
struck  off.    The  flask  is  inverted  and  that  surface  from  which 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION        141 

the  excess  sand  was   struck  now  becomes  the  base  of  the 
matrix. 

The  surface  of  the  packed  tiask  pointing  upwards  shows 
the  base  of  the  model  surrounded  by  the  sand.  A  thin 
V-shaped  section  l)eginning  at  the  flask  periphery  and  ex- 
tending to  that  of  the  model  is  sliced  oft"  with  the  knife,  so 
as  to  expose  the  angle  of  the  model  base,  and  thus  clear  it 
from  the  matrix  margins.  By  lifting  and  tipping  the  flask, 
the  detached  sand  will  fall  off.     The  finer  particles  can  lie 


nEMO\IXG     EXCKSS    OF    SAND    FKOM     PACKED    RINf! 

removed  with  the  lirush,  and  by  gently  blowing  them  from  the 
surface. 

REMOVAL  OF  THE   MODEL   FROM  THE   MATRIX 

When  iiroperly  flared,  dried,  varnished  and  rubbed  witli 
talcum  powder,  the  model  can  usually  be  removed  from  the 
matrix  without  difiSculty.  Unfavorable  conditions,  principally 
due  to  some  peculiar  form  of  the  model  itself,  are  sometimes 
present.  In  such  cases,  the  exercise  of  extreme  care  is  neces- 
sary to  avoid  distortion  of  the  essential  surfaces  of  the  matrix 
in  removing  the  model.  The  adhesion  of  the  sand  to  the 
surfaces  of  the  model,  as  the  result  of  compression  in  pack- 


Ha        TECHNIC    OK    DUO     AND    COUNTER     DIE    CONSTRUCTION 

ing,  must  be  overcome  or  broken,  when,  it'  no  undercuts  are 
present,  the  model  will  come  away  readily. 

The  following  is  the  usual  order  of  removal  of  the  model 
from  the  matrix,  ranging  from  the  simi^lest  metliods  to  those 
requiring  careful  attention : 

1.  Gravity — Weight  of  model  si;fficient  to  dislodge  it. 

2.  Vibration — Tapping  the  side  of  tlie  flask. 


HEMOVINC  Till> 


3.  Removal  of  model  by  rotation. 

4.  Tapping  base  of  model  to  break  sand  adhesion  and 
rotating. 

5.  Prying  to  break  adhesion  and  rotating. 

6.  Tapping  and  lifting  outward. 

7.  Removal  of  models  with  undercuts — cores. 

8.  Removal   of  models  with  undercuts   overcome   with 
Hawes  flask. 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTIOX         143 
REMOVAL    OF    THE    MODEL    IN    LIFTING    THE    FLASK 

When  the  form  of  tlie  model  is  correct,  the  condition  of 
the  sand  suitable,  and  the  packing  of  the  flask  is  of  the  proper 
density,  the  model  will  occasionally  drop  from  the  matrix  in 
lifting  tlie  flask  to  invert  it.  This,  however,  occurs  more  often 
when  tlie  sand  has  been  but  loosely  packed  in  the  flask,  or  when 
tlie  sides  of  the  model  are  excessivelv  flared.     It  niav  occur. 


r.i!i;.\KiN(;  ai'hesiox  hktwf.kx  sand  axd  MonEi>  v.\  TAri'iNo  base  of  latteh 

as  before  stated,  under  proper  conditions.  When  the  model 
drops  out  by  its  own  weight,  a  close  inspection  of  the  matrix 
should  be  made  to  see  that  its  several  surfaces  are  smooth 
and  the  sand  sufficiently  compact  to  insure  smooth  surfaces  to 
the  die  when  cast. 

TAPPING  THE  MODEL  BASE  TO  BREAK   ADHESION 

A  few  light  taps  on  the  base  of  the  model,  near  the  center, 
with  a  small  hammer  or  light  instrument,  will  usually  l)reak 


144        TECHNIC    OF    DIB    AND    COUNTER    DIE    CONSTIUICTION 

the  adhesion  of  the  «aud  to  tlie  several  surfaces.  The  tapping 
should  not  be  sufficiently  heavy  to  produce  perceptible  move- 
ment of  the  model  in  the  matrix.  Heavy  or  unequal  tapping 
is  liable  to  distort  the  sand  and  result  in  an  imperfect  matrix. 
By  rotating  the  flask  as  before  described,  the  model  can  usually 
be  dislodged. 

REMOVAL   OF  THE   MODEL   BY    ROTATION 

The  flask  is  lifted  from  the  bench,  the  base  resting  in  the 
palm  of  tlie  hand,  tlie  tlmmb  against  tlie  flat  side,  when,  with  a 


ROTATING    MODEI-.    OUT    OF    POSITION 


quick  pronatiiJg  nlo^■emont,  the  model  may  be  rotated  outward. 
If  it  is  not  dislodged  in  this  manner,  the  flask  should  be  set 
on  a  clear  surface  of  the  bench,  so  that  the  sand  base  may  be 
lirmh'  supported  over  its  entire  area. 


REMOVAL  OF  THE  MODEL  BY  VIBRATION 

A  simple  method  of  removal,  frequently  successful,  con- 
sists in  inverting  the  flask  and  tapping  the  sides  lightly  with 
a  small  instrument.  The  vibration  thus  produced  will  often 
be  sufficient  to  dislodge  the  model.     Vibration  produced  in 


TECHNIC    OF    DIB    AND    COUNTER    DIE    CONSTRUCTION        145 

this  manner  may  also  be  applied  in  difficult  cases  after  other 
means  have  been  resorted  to,  for  breaking  the  adhesion  be- 
tween sand  and  model. 

BREAKING  ADHESION  BY   PRYING  THE  MODEL 

If  the  preceding  steps  fail  to  break  the  adhesion  of  the 
sand  and  free  the  model,  it  can  be  overcome  by  inserting  the 
point  of  a  knife  against  the  back  of  the  model,  the  blade  rest- 
ing on  the  flask  margin,  which  will  serve  as  a  fiilcrnm,  and 
with  a  slight  prying  movement  lift  the  back  of  the  model  the 
least  perceptible  amount.  Rotation  of  the  flask  should  again 
be  made,  when  the  model  will  readily  come  away. 

REMOVAL  OF  THE   MODEL  BY   GRAVITY 

Occasionally,  wlien  the  vault  portion  of  the  model  is  deep 
and  the  labial,  buccal  and  lingual  surfaces  of  the  border  at 
various  jjoints,  particularly  in  the  anterior  portion,  are  nearly 
parallel  with  each  other,  it  may  not  be  possible  to  rotate  the 
model  out,  as  described,  without  distorting  the  matrix.  In 
other  words,  the  relationship  of  the  several  surfaces  men- 
tioned, to  each  other,  requires  that  the  model  be  removed  in  a 
line  of  direction  approximately  parallel  to  these  surfaces,  in- 
stead of  attempting  to  rotate  it  out.  Removal  in  such  cases 
may  be  accomplished  in  two  ways : 

First — Tap  the  model  base  to  break  adhesion.  Invert  the 
flask,  maintaining  the  model  in  position  with  finger  pressure 
while  doing  so;  place  the  inverted  flask  over  the  edge  of  the 
bench,  holding  it  flat  and  moving  forward  until  the  model  is 
well  supi>orted  before  releasing  finger  pressure,  until  finally 
the  entire  flask  base  rests  on  the  bench ;  lift  the  flask,  and  if  the 
model  is  still  retained  in  the  matrix,  with  a  small  instrument 
tap  the  outer  side  of  the  flask  lightly.  The  vibration  thus 
produced  is  usually  sufficient  to  dislodge  the  model. 

Second — Should  the  preceding  steps  fail  to  free  the  model 
from  the  matrix,  it  may  be  removed  by  direct  traction.  The 
projection  of  the  model  margins  above  the  sand  is  so  slight 
that  it  cannot  be  accurately  and  carefull.y  lifted  from  the  mat- 
rix by  grasping-  its  periphery.  So  other  means  for  grasping- 
it  must  be  provided.  A  small  hole  may  be  drilled  in  the  center 
of  the  base,  into  which  a  taper  instrument  can  be  driven  to 
serve  as  a  handle,  or  two  grooves  may  be  cut  on  either  side  of 
the  center,  about  one-fourth  of  an  inch  apart.  The  sides  of 
the  intervening  section  of  plaster  should  be  parallel  to  each 


14«        TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION 

other,  thus  affording  means  for  grasping  the  base  of  llic  model 
centrally  with  a  pair  of  tweezers. 

While  this  method  of  removal  is  positive  and  can  be 
applied  to  any  model  without  undercuts,  unless  care  is  ob- 
served the  matrix  mav  be  marred.    To  avoid  error,  the  instru- 


RELEASINC    iMODEI.     I'.Y    TArTIXG     SIDE    OF     PM.ASK 

ment  or  tweezers  must  not  be  gras^jed  too  rigidly,  while  the 
line  of  traction  must  coincide  with  and  be  approximately  par- 
allel to  the  several  surfaces  to  be  released.  Holders  follow  a 
similar  method  in  removing  patterns  from  the  sand.  To  break 
adliesion  and  free  the  pattern,  they  usually  tap  the  instriunent 
which  serves  as  a  handle,  sideways  in  various  directions, 
while  traction  is  at  the  same  time  applied  for  the  removal  of 
the  pattern. 

In  prosthetic  j^rocedures,  the  instrument  which  serves 
as  a  handle  in  removing  the  model  should  not  be  tapped  lat- 
erally, as  the  tendency  would  be  to  enlarge  the  matrix 

With  a  properly  flared  model  having  no  undercuts,  and 
the   sand  packed   to  proper  density,   the   prj-ing  or  lifting 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION         147 

process  for  breaking  the  adhesion  of  the  sand  and  dislodging 
the  model,  need  seldom  be  resorted  to.  It  shonld  be  borne  in 
mind  that  the  least  possible  manipulation  of  the  model  in 
effecting  its  removal  will  yield  the  most  accurate  matrix. 

NECESSITY   FOR  THE   USE  OF   CORES 

Models  having  undercuts  cannot  be  removed  from  the 
sand  without  distorting  the  matrix,  unless  means  are  taken  to 
overcome  the  difficultv.     The  usual  method  resorted  to  is  bv 


MFTINU    MDIiEl.    H(OM 


means  of  cores,  the  construction  of  which  has  been  previously 
described. 

A  model  having  a  core  addition  to  its  outer  surface 
usuallj'  presents  an  unsymmeti'ical  peripheral  outline.  In 
placing  the  molding  flask  over  such  a  model,  the  former  should 


148       TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION 

be  SO  adjusted  that  the  model  will  occupy  a  central  position, 
regardless  of  the  form  or  position  of  the  core. 

Sand  is  packed  around  and  over  tlie  model  and  core, 
care  being  taken  to  wedge  the  latter  firmly  against  the  model 
in  the  condensing  process.  Removal  of  the  model  and  core 
from  the  matrix  is  effected  by  some  of  the  methods  described, 
usually  by  tapping  and  rotation. 

After  removal,  the  core  is  separated  from  the  model, 
dried,  and  returned  to  its  position  in  the  matrix,  where  its 
inner  surface  completes  the  matrix  wall  and  reproduces  the 
reverse  form  of  the  undercut  surface  of  the  model. 

Sufficient  pressure  should  be  made  on  the  core  in  seating- 
it  in  the  matrix  to  wedge  it  slightly  in  the  sand,  so  as  to 


THE     HAW  I' 


prevent  displacement,  since,  if  not  firmly  attached,  the  molten 
metal,  when  introduced,  on  account  of  its  greater  specific 
gravity,  will  raise  the  core  out  of  its  position. 


CONSTRUCTION  OF  THE  MATRIX  IN  THE  HAWE'S 
FLASK 

An  accurate  sand  matrix  may  be  secured  from  a  model 
having  external  undercut  areas,  without  the  use  of  cores,  by 
means  of  the  Hawe's  Molding  Flask. 

This  appliance  is  cylindrical  in  form,  five  inches  in  di- 
ameter and  three  inches  deep.  It  is  divided  into  an  upper  and 
a  lower  section,  held  in  proper  relation  by  means  of  guide 
pins.  The  lower  half  consists  of  three  sections  hinged  to  open 
outward.  Each  section  has  a  flange  at  either  end,  directed 
radially  inward.  When  pinned  together,  the  end  flange  of 
each  section  approximates  the  flange  of  the  adjoining  section, 
thus  dividing  the  interior  space  of  the  flask  into  three  partial 
sectors. 

The  model  is  placed  between  the  three  flanges  of  the  lower 
section,  its  median  line  opposite  one  and  its  tuberosities  op- 
posite the  two  other  points,  respectively.  The  crest  of  the 
border  should  rise  slightly  above  the  level  of  the  ring. 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION         149 

Sand  is  packed  around  the  outer  sides,  into  and  above  all 
undercut  surfaces  of  the  border,  but  not  over  the  face  of  the 
model.  Particular  care  should  be  taken  to  condense  the  sand 
firmly  in  each  sector  of  the  flask  and  against  the  model,  so 


LOWER    SECTION'    OP    HAWE'S    EI.ASK    SHOWINYi    MOPET.    IX    I'OSITION 


FIKST   SECTION  WITH   SAND  PACKED   AROUND   5I0DEL 

that  it  will  not-  be  displaced  in  the  subsequent  steps  of  free- 
ing the  model. 

Powdered  charcoal  is  sifted  over  the  packed  sand  and 
model  face  to  prevent  adhesion  of  the  sand  now  to  be  added, 
the  surplus  blown  off,  the  second  section  of  the  ring  adjusted. 
In  this  the  sand  is  packed  and  the  surplus  struck  off  in  the 


160       TKCHNIC    OF    DIK    AND    COUNTER    UlE    CONSTRUCTION 

usual  manner.  The  upper  half  of  the  flask  is  now  lifted  off, 
inverted,  and  set  aside  so  as  not  to  disturb  the  sand  surface 
which  has  copied  the  model  face. 


SKCOXIl     SHCTIUX     OK     KI.ASK     SET     I.N     I'OSITI 


SECOND   SECTION   r. 


The  model  is  removed  by  drawing  the  pin  from  one 
of  the  disto-buccal  flange  joints  and  carefully  opening  the 
ring.  As  the  sectors  separate,  the  sand  between  the  flange 
ends  and  the  model  breaks  with  a  clean  fracture,  and,  on  ac- 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION        151 

count  of  the  flask  form,  the  matrix  is  thus  divided  into  three 
sections.     The  model  is  drawn  out  through  the  open  side  of 


Li'l'EIt    Sm'TIlIN    1U;M(I\EIi.     l.dWKU    SECTION    SEI'ARATKl),     KOI!    RELEASE    OK    MODEL 

the  ring.  When  tlie  model  is  removed  and  the  flask  sections 
are  brought  together  again,  the  fractured  surfaces  of  sand 
are  again  readapted  to  each  other  as  before,  and  form  the  con- 
tinuous outer  wall  of  the  matrix. 


MODEL    REMOVED.     SECTIONAL     PART    OF     FLASN     CLliSED 

Special  care  should  be  taken  to  remove  any  sand  that 
mav  have  become  lodged  between  the  flask  joints  and  flanges. 


152       TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION 

for  if  allowed  to  remain,  the  sections  cannot  be  closed  pi'op- 
erly. 

The  pin  removed  in  opening  the  flask  is  now  slipped  into 
its  joint,  and  the  inverted  top  half  of  the  flask  is  lifted  and 
oarefnlly  set  in  place  on  the  sectional  portion,  the  projecting 
pins  guiding  it  to  position.  The  entire  flask  is  turned  over, 
and  if  the  ste])s  have  been  properly  carried  out,  the  matrix 
will  be  found  to  be  satisfactory. 

Should  a  margin  of  sand  along  any  of  the  sectional  lines 
be  broken  lightly,  it  will  seldom  be  found  necessary  to  at- 
tempt restoration  of  the  matrix,  as  the  metal  which  will  fill 
the  opening  can  easily  be  removed  from  the  die  when  cast. 


UI'I'EK    HALF   IIF  FLASK  SET   AND    CASK   INAESTED    FOR    RECEI'TIOX   OF   THE   METAL 

The  utility  of  this  special  flask,  both  for  accuracy  of  re- 
sults and  the  saving  of  time,  is  keenly  appreciated  by  those 
who  have  used  it.  Unfortunately,  its  good  points  are  unknown 
to  many,  and  the  core  method,  although  less  accurate  and  re- 
quiring longer  time,  is  most  frequently  resorted  to  in  cases 
of  external  undercut  models. 

EXAMINATION    OF   THE    MATRIX 

When,  by  whatever  method,  the  sand  matrix  is  formed, 
it  should  be  closely  examined  to  see  that  none  of  the  essential 
surfaces  have  been  disturbed;  to  see  that  the  sand  is  suffi- 
ciently compact  to  insure  smooth  surfaces  to  the  die  when 
cast,  and  before  pouring  the  molten  metal,  to  see  that  no 
loose  sand  is  present. 


TKCHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION        153 

FORMING  THE  DIE 
MELTING  THE  DIE   METAL 

A  satisfactory  saud  mold  or  matrix  liaving  been  secured 
from  the  model,  it  is  ready  to  receive  the  molten  die  metal. 
To  conserve  time,  the  ladle  containing  the  latter  is  usually 
placed  on  the  fire  before  making  the  matrix,  since  the  pro- 
duction of  the  latter  usually  requires  less  time  than  is  con- 
sumed in  fusing  the  metal.  The  progress  of  fusion  should  be 
noted,  however,  and  when  about  three-fourths  melted,  the 
ladle  should  be  removed  from  the  fire.  The  excess  of  heat 
absorbed  by  the  metal  up  to  this  point  is  usually  sufficient  to 


COMPLETED    MATIilX    IX    SAND 


effect  the  fusion  of  the  unmelted  portion  after  removal  from 
the  fire.  This  plan  also  lowers  the  temperature  of  the  mass 
to  somewhere  near  the  proper  degree  for  casting. 

A  thin  spatula  of  soft  wood  should  be  used  for  stirring 
the  metal  and  removing  the  oxides  and  impurities.  If  the  wood 
burns  or  chars,  it  indicates  that  the  metal  is  too  hot  to  cast. 
The  lower  the  temperature  at  which  the  metal  can  be  intro- 
duced into  the  matrix  and  yet  be  sufficiently  fluid  to  conform 
accurately  to  all  irregularities,  the  less  shrinkage  of  the  die 
will  occur.  Also  a  less  quantity  of  gas  or  steam  will  be  gen- 
erated in  the  matrix,  and  as  a  result  a  smoother  die  will  be 
produced. 

CASTING  THE  DIE 

When  the  metal  is  melted,  the  oxides  removed,  and  the 
proper  degree  of  fluidity  attained,  the  ladle  is  carried  to  one 


154        TECHNIC    OK    UIB    AND    COUNTER    DIE    CONSTRUCTION 

of  the  disto-bnecal  angles  of  the  flask,  and  as  close  to  the 
sand  as  possible  without  disturbing  the  latter  by  contact  of 
the  ladle  lip. 

The  object  in  bringing  the  ladle  close  to  the  matrix  is 
to  prevent  displacement  of  the  sand  which  occurs  when,  in 
pouring,  the  metal  falls  from  a  considerable  distance  upon  it. 

Through  the  ladle  spout  a  small  stream  of  metal  is  di- 
rected into  the  back  of  the  mold  and  the  entire  matrix  is 
filled  in  this  manner,  even  with  the  sand  margins.    The  ladle 


should  be  returned  to  the  tire  immediately  in  order  to  keep 
the  remainder  of  the  metal  in  a  molten  condition  while  ad- 
justing the  ring  for  increasing  the  depth  of  the  die  with  addi- 
tional metal.  A  flask  ring,  usually  the  smallest  of  the  set. 
the  periphery  of  which  should  be  slightly  greater  than  that  of 
the  matrix  margin,  is  i^laced,  large  end  down,  and  pressed 
slightly  into  the  sand.  Some  sand  should  be  quickly  packed 
around  its  outer  base  to  prevent  the  escape  of  the  metal  now 
to  be  added  to  the  die. 


TECHNIC    OF    DIK    ANU    COUNTER    DIE    CONSTKUCTJON         155 

Tlif  ladle  (iontainin^  tlie  reuiaimler  of  tlie  molten  metal 
is  brought  close  to  the  edge  of  the  small  ring  jiist  placed 
and  a  sufficient  amount  of  metal  added  to  tliat  first  cast  to 
give  the  die  a  depth  of  about  2  inches  in  its  central  part. 
This  step  can  and  should  be  carried  out  so  rapidly  tlmt  miion 
between  the  first  and  second  casts  of  metal  will  be  effected 
and  a  solid  one-piece  die  result. 

When  hardened,  the  die  is  removed  b>'  tipping  the  flask 
rings  over  and  tai)]nug  to  free  the  i)acked  sand  from  the 
interior,  while  that  on  the  outer  surface  of  the  die  is  scraped 
and  brushed  awav.    Tlie  die  and  flasks  are  usuallv  cooled  im- 


SECTIOXAL    VIEW   OF    SMALL    RING    ADJUSTED   TO    SAND    MATRIX 

mediately  in  water  and  wiped  dry,  preparatory  to  casting  the 
counterdie.  The  die,  however,  will  be  more  tenacious  and  less 
inclined  to  crack  under  the  hammer  blows  if  allowed  to  cool 
slowly. 

INSPECTION  AND  CORRECTION  OF  THE  DIE 

Any  projecting  imperfection  on  the  die  due  to  holes  in  the 
sand  matrix  should  be  removed  with  scrapers,  chisels  or  burs, 
if  necessarj',  and  tlie  surfaces,  where  such  defects  exist,  made 
to  correspond  with  those  of  the  model.  Any  serious  defects 
in  the  die,  when  cast,  either  as  accretions,  holes  or  pits  are 
liable  to  result  in  imperfect  adaptation  of  the  plate  when 
swaged.  8uch  a  die  should  be  discarded  and  a  perfect  one 
secured. 


156       TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION 


r.AII.EV  FLASK 


DIE  AND  COUNTERDIE  PHODUCED  LX  BAILEY  FLASK 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION        157 


DIE    AXD    (  iHNTEIililB    SEPARATED 


LEWIS    FLASIC 


ir>S        TKCHNK'    OK    DUO    AND    COHNTKK     DUO    CONSTRUCTION 


DIE     AN"I>     I'dr.NTKltDIK     I'lKllHrKU     IN      I.KU  IS     l-I.ASK 


DIE    AND    f'OTINTERDIE    SEPABATEH 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION        159 

CONSTRUCTION  OF  THE  COUNTERDIE 
PREPARATORY  STEPS 

The  large  flask  iu  which  the  matrix  for  the  die  was  formed 
is  now  inverted  or  placed  small  end  down  on  the  hench  and 
partially  filled  with  sand.  In  this  the  die  is  set  and  evenly 
centered  to  the  ring.  The  depth  of  sand  under  the  die  base 
should  be  sufficient  to  raise  the  entire  labial  and  buccal  sur- 
faces of  the  die  border  slightly  above  the  upper  margin  of 
the  flask. 

Tlie  space  between  the  flask  walls  and  the  die  is  now 
filled  in  with  sand  which  should  be  firmly  condensed  and 
finished  off  evenly  with  the  top  margin  of  the  flask,  the 
inner  margin  of  the  sand  terminating  against  the  peripheral 
plate  line  on  the  die.  This  leaves  only  the  essential  surfaces 
of  the  die  ^asible  and  standing  above  the  general  level  of 
the  sand  and  flask  margin. 

The  exposed  surfaces  of  the  die  are  now  carefully  brushed 
to  remove  any  adhering  sand.  In  case  of  decided  undercuts, 
sand  is  tightly  packed  into  them  at  this  time  so  as  to  preclude 
the  counterdie  metal,  when  cast,  from  entering  such  areas 
and  later  preventing  the  ready  separation  of  the  die  and 
counterdie.  Subsequently,  when  swaging,  this  defect  of  the 
counterdie  is  overcome  by  placing  strips  of  lead  or  tin  against 
the  plate  opposite  the  deficient  area,  the  strips  being  of  suf- 
ficient thickness  to  make  up  for  the  lack  of  contour  in  the 
counterdie. 

The  die  is  now  coated  with  a  solution  of  whiting  and  al- 
cohol, to  which  a  little  gum  Arabic  is  added  to  render  it  ad- 
hesive after  the  alcoliol  evaporates.  The  film  of  whiting 
practically  obviates  the  tendency  of  the  counterdie  metal  to 
imite  with  the  die  in  casting. 

A  flask  ring,  corresponding  in  size  with  the  one  in  which 
the  die  is  imbedded,  is  adjusted  peripherally  to  the  latter, 
large  end  down,  to  form  the  matrix  in  which  to  cast  the 
counterdie.  A  smaller  ring,  however,  may  be  used  for  form- 
ing the  matrix  walls  for  the  counterdie,  when  the  die  is  of 
medium  or  small"  size.  Such  a  ring  reduces  the  counterdie 
peripherally  and  adds  to  convenience  in  handling.  Wlien 
the  small  ring  is  used,  it  is  set  on  the  sand  surrounding  the 
die  and  its  lower  margin  l)anked  up  with  sand  to  prevent 
the  escape  of  the  molten  metal  while  casting. 


160       TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION 
MELTING  THE  COUNTERDIE  METAL 

The  fusing  of  the  counterdie  metal  is  accomplished  in 
essentially  the  same  manner  as  is  employed  for  the  die 
metal.  It  should  be  removed  from  the  fire  before  the  entire 
mass  is  melted  and  stirred  to  lower  the  temperature  and  col- 
lect the  oxides  and  impurities  present.  These  should  be 
skimmed  off  and  the  stirring  continued  until  the  metal  be- 
gins to  assume  a  pasty  condition. 

The  object  in  allowing  the  metal  to  cool  somewhat  and 
thicken  slightly  before  casting,  is  to  avoid  danger  of  fusion 
of  the  die  and  its  consequent  union  with  the  counterdie,  a  mis- 


hap which  frequently  occurs  when  the  latter  metal  is  cast 
while  overheated. 


CASTING  THE  COUNTERDIE 

When  the  metal  begins  to  congeal  around  the  ladle,  it  is 
quickl}^  emptied  into  the  ring  and  over  the  face  of  the  die. 
Should  the  metal  be  in  such  a  thickly  plastic  state  that  it  fails 
to  assume  a  level  position  in  the  ring  when  cast,  it  should  be 
pressed  down,  while  yet  soft,  with  a  square-end  tamper,  to 
give  a  flat  base  to  the  counterdie. 

As  a  matter  of  fact,  the  counterdie  metal  can  be  cast 
while  in  a  liquid  condition  if  proper  precautions  are  taken, 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION        161 

viz:  the  die  must  be  cold,  its  exposed  surfaces  coated  with 
whiting,  the  metal  allowed  to  cool  to  about  the  point  of  con- 
gealing, or  so  that  it  will  not  char  soft  wood,  and  in  easting, 
directing  the  stream  of  metal  on  the  sand  surrounding  the  die, 
and  not  on  the  die  face. 

When  poured  in  a  liquid  condition,  the  metal  should  be 
cast  slowly.  In  this  manner  it  rises  gradually  up  over  the 
surfaces  of  the  die,  and  at  the  same  time,  from  exposure  to 
the  air  and  through  contact  with  the  cold  die,  sand,  and 
ring,  the  metal,  if  at  or  slightly  above  the  point  of  fusion,  is 
reduced  in  temperature  so  that  union  of  the  two  will  not 
occur. 

CONSTRUCTION    OF   THE   COUNTERDIE    BY    DIPPING 

A  method  sometimes  followed  for  securing  a  counterdie 
consists  in  pouring  the  metal  into  a  ring  of  suitable  size  and 
immersing  the  face  of  the  chilled  die  in  it  the  necessary  depth 
to  cover  the  surfaces  involved  by  the  base  plate.  The  die  is 
held  with  the  fingers  or  a  pair  of  tongs  until  the  counterdie 
metal  has  hardened  sufficiently  to  sustain  its  weight. 

THICKNESS    OF   THE    COUNTERDIE 

In  the  swaging  process  the  die  and  plate  are  driven  more 
or  less  deeply  into  the  counterdie,  the  latter  yielding  under 
the  hammer  blows.  To  prevent  the  defacement  of  the  prom- 
inent points  on  the  die,  the  counterdie  should  have  a  depth  of 
at  least  one-half  inch  in  its  shallowest  part,  or  that  portion 
between  the  high  points  of  the  die  face  and  the  base  of  the 
counterdie,  which  rests  on  the  anvil.  A  good  die  may  be 
readily  distorted  when  the  counterdie  is  too  shallow  and 
much  stress  is  applied  in  swaging. 

SEPARATION   OF  THE   DIE   AND   COUNTERDIE 

When  the  counterdie  metal  has  solidified,  the  rings  are 
tipped  over  and  disengaged,  the  sand  brushed  off,  and  the 
die  and  counterdie  chilled  in  cold  water. 

The  two  are  loosened  by  placing  on  the  swaging  block 
and  striking  the  die  base  sharplv  with  the  hammer,  when  they 
may  readily  be  separated.  If  this  procedure  fails  to  break 
adhesion  between  the  two,  the  die  should  be  struck  sideways 
in  various  directions.  Should  this  effort  prove  futile,  the 
source  of  adhesion  will  be  the  result  of  mechanical  anchor- 
age, due  to  undercut  surfaces  on  the  die  into  which  the  coun- 


162        TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION 

terdie  metal  has  flowed  in  easting,  or  to  fusion  of  the  two 
masses  of  metal  at  some  point.  If  due  to  undercuts  on  the 
die,  properly  directed  hammer  blows  against  its  sides  will 
enlarge  'the  eounterdie  sufficiently  to  release  the  die.  Ad- 
hesion from  this  source  is  the  result  of  carelessness,  and  will 
not  occur  if  the  undercut  surfaces  of  the  die  are  corrected 
with  sand  before  casting  the  coimterdie. 

When  adhesion  is  di;e  to  fusion  and  luiion  of  the  two 
masses  of  metal,  the  die  and  eounterdie  are  separated  by 
hammering,  prying,  wedging  or  chiseling,  as  is  found  most 
convenient.  Such  means  result  in  the  defacement  of  both 
die  and  eounterdie  and  usually  necessitates  the  reconstruction 
of  each. 

Special  care  should  be  exercised  in  such  cases  where 
fusion  of  the  two  occurs,  to  entirely  remove  and  cast  aside 
that  portion  of  the  die  and  eounterdie  that  have  become 
united,  before  melting  either  one. 

If  the  alloy  thus  formed  is  allowed  to  remain  adherent 
to  the  die  metal,  the  harness  and  fusibility  of  the  latter,  if 
used  again,  will  be  reduced,  and  if  with  the  eounterdie,  it  will 
render  that  alloy  harder  and  higher  fusing. 

PARTIAL  COUNTERDIES 

A  method  of  using  several  eounterdies  of  gradually  in- 
creasing area  has  been  in  vogue  for  many  years.  The  object 
in  using  these  progressive  eounterdies  is  to  insure  the  close 
and  uniform  adaptation  of  the  base  plate  to  the  central  vault 
portion  first,  before  the  labial  and  buccal  surfaces  have  been 
lapped  over  and  conformed  to  the  border. 

Such  eounterdies  are  very  efTeetive  in  those  cases  where 
the  arch  is  narrow  and  the  palatine  vault  is  deep,  as  by  their 
use  the  tearing  of  the  plate  is  obviated. 

Usually  in  this  method,  three  eounterdies  are  required; 
the  first  covering  the  palatine  vault  and  terminating  some- 
what inside  of  the  border  crest ;  the  second  should  cover  the 
vault  and  extend  somewhat  outside  of  the  border  crest;  the 
third  consists  of  a  eounterdie  of  the  regular  form,  made  in 
the  manner  previously  described. 

CONSTRUCTION  OF  PARTIAL  COUNTERDIES 

To  construct  a  partial  eounterdie,  the  die  is  set,  base 
down,  on  the  table,  a  large  molding  flask  set  evenly  over  it 
and  sand  packed  around  it  and  even  with  the  top  of  the  flask, 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION         l«:j 

leaving  the  central  portion  of  the  die  exposed.  With  a  suit- 
able instrument  the  sand  is  cleared  away  so  as  to  make  a 
slightly  flaring  matrix  in  the  sand,  the  floor  of  which  con- 
sists of  that  portion  of  the  die  to  be  covered  by  the  partial 
counterdie.  The  exposed  face  of  the  die  is  coated  with  whit- 
ing and  the  partial  counterdie  cast  in  the  matrix  in  the  ordi- 
nary manner. 

Partial  counterdies  should  be  of  sufficient  depth  or  ex- 
tend far  enough  above  the  die,  when  in  position,  to  enable 
them  to  be  grasped  firmly  with  the  fingers  and  thumb  while 
swaging.  The  metal  used  for  partial  counterdies  may  be  of 
lead,  the  regular  counterdie  metal  of  lead  and  tin,  or  com- 
posed of  one  of  the  triple  alloys,  such  as  Melottes  metal. 

MATRIX  COUNTERDIES 

A^arious  substances,  such  as  soap,  clay,  modeling  com- 
pound, shot,  etc.,  as  previously  mentioned,  may  be  used  in- 
stead of  the  ordinary  cast  coimterdie,  when  the  material  is 
confined  a  suitable  receptacle,  or  matrix. 

The  Parker  shot  s wager  is  one  type  of  appliance  used 
for  such  purpose.  This  device,  however,  is  intended  more 
particularly  for  seciiring  the  final  adaptation  of  a  base  plate 
to  the  die  or  plaster  model  itself,  if  such  step  is  deemed  ad- 
visable. 

The  device  in  which  the  other  materials  mentioned  are 
used  consists  of  a  heavy  cast  iron  base,  in  the  center  of  which 
is  a  deep  recess  corresponding  peripherally  with  the  inner 
walls  of  the  small  casting  ring  used  for  increasing  the  depth 
of  the  die.  The  soap  or  other  material  is  placed  in  the  re- 
cess and  covered  with  a  sheet  of  soft,  pliable  leather,  to  pre- 
vent adhesion  of  the  swaging  material  to  tlie  plate. 

When  the  adaptation  of  the  plate  has  been  fairly  de- 
veloped with  the  horn  mallet,  it  is  placed  on  the  die  and  the 
latter  introduced  into  the  recess. 

Since  the  periphery  of  the  die  coincides  with  and  closely 
fits  the  opening  in  the  ring,  escape  of  the  plastic  material  is 
prevented.  Under  hammer  blows  or  screw  power,  the  force 
tlius  delivered  distributes  the  material  and  equalizes  the  pres- 
sure so  as  to  drive  the  plate  into  all  inequalities  and  against 
all  surface  of  the  die. 

This  device  obviates  tlie  making  of  counterdies  in  many 
instances,  since  it  is  applical)le  to  the  swaging  of  base  plates 
of  almost  any  form  when  the  dies  are  properlj'  constructed. 


Ui-!        TKCHNIC    OF    DUO    AND    COUNTKIt    Dll!:    CONSTRUCTION 

The  leatlu'i-  should  ))e  vciuovcd,  (he  plastic  material  built 
liigli  in  the  center,  and  the  leather  again  returned  to  place,  for 
each  new  case  swaged.  This  step  is  necessary  to  insure  pal- 
atine adaptation  of  the  ])late  liefore  the  pressure  is  brought 
on  the  buccal  surfaces. 


TOP  OP  PAHKEU  SHOT  SWAGBR 


The  method  here  outlined  is  especially  useful  in  the 
swaging  of  aluminum  base  plates.  On  account  of  its  stiffness 
and  elasticity,  18K  gold  cannot  be  readily  adapted  by  this 
means.  The  device,  however,  as  a  time  saver,  is  a  valuable 
adjunct  to  tlie  laboratory  e(|uipment. 


S34  I'eiiii  ^\^ 


BASE   OF   PARKER   SHOT   SWAGER 


COUNTERDIES  FOR  PARTIAL  CASES 

In  constructing  counterdies  for  partial  dentures,  the 
die  is  imbedded  in  the  sand,  so  as  to  leave  exposed  the  area 
to  be  covered  by  the  baseplate,  the  surfaces  of  the  teeth  re- 
moved by  cutting  and  possibly  a  slight  amount  of  the  labial 


TECHNIC    OF    DIE    AND    COUNTER    DIE    CONSTRUCTION        165 

and  buccal  surfaces  of  the  die  to  ouide  and  liold  it  iu  position 
in  the  couuterdie  while  swaging. 

Nothing  is  gained  by  having  tlio  die  deeply  depressed  in 


the  counterdie.  In  fact,  such  a  condition  is  a  disadvantage, 
rendering  the  removal  of  the  plate  more  difficult,  as  from  time 
to  time  it  is  taken  out  for  inspection  and  trimming. 


C  TT  A  P  T  K  R     X  I  T 

CONSTRUCTION    OF    SWAGED    DENTURE    BASES 
OF  GOLD 

SECURING  PATTERN  FOR  THE  GOLD  PLATE 

Suitable  dies  and  counter  dies  having  been  constructed, 
the  next  step  is  to  secure  a  pattern  for  cutting  the  gold  plate. 
By  the  use  of  a  pattern  two  important  objects  are  attained, 
viz.: 

First.  Unnecessary  loss  of  gold  will  be  obviated.  The 
trimmings  and  tilings  that  accumulate  in  adapting  a  gold  plate 
to  a  die  are  classed  as  "scrap,"  which  must  either  be  refined 
before  using  again,  or  be  returned  to  the  refiners  at  a  loss  of 
about  1-5  the  original  cost.  When  care  is  taken  in  keeping  the 
scraps  assorted  and  free  from  solder,  filings  and  impurities, 
they  can  be  remelted,  rolled  into  plate,  and  used  again  without 
loss. 

Second.  A  piece  of  gold,  cut  to  the  required  outline  of 
the  denture,  is  more  easily  adapted  to  the  die  than  an  exces- 
sively large  piece.  The  tendency  of  the  plate  to  shift  slightly 
in  the  preliminary  ste^Ds  of  swaging  necessitates  a  surplus  of 
about  1-16  of  an  inch  peripherally  in  tlie  gold  for  full  as 
well  as  partial  cases. 

Tin  foil,  sheet  lead  or  paper  may  l)e  used  as  a  pattern. 
A  sheet  of  No.  60  tin  or  lead  foil  is  conformed  to  the  die  with 
finger  pressure  or  a  large  pellet  of  compact  cotton,  and  the 
excessive  surplus  trimmed  off.  It  is  again  returned  to  the  die, 
readapted  and  finally  swaged  in  tlie  counterdie.  One  or  two 
light  lilows  with  the  hammer,  or  the  weight  of  the  die  itself, 
will  secure  close  adaptation.  Wlien  removed,  the  excess  is 
trimmed  away,  allowing  for  the  l-Ki-inch  surplus  previously 
mentioned. 

With  the  fingers  the  ])attern  is  carefully  bent  aiad  reduced 
to  nearly  a  flat  condition,  care  being  taken  not  to  strain  or 
draw  it  more  in  one  area  than  another.  It  is  now  laid  on  the 
flat  joalm  of  one  hand  and  struck  a  sharp  blow  with  the  open 
palm  of  the  other.  This  reduces  the  foil  to  flat  sheet  form, 
slightly  wrinkled  in  some  places  and  possibly  torn  in  others 
from  the  swaging,  yet  representing  reasonably  well  the  re- 
quired perijiheral  outline  of  the  denture. 

166 


CONSTRUCTION   OF   SWAGED  DENTURE   BASES  OF  GOLD        167 

The  foil  itself  may  be  used  as  a  pattern  or  its  outline 
may  be  traced  on  a  sheet  of  thin  cardboard,  which,  when  cut, 
facilitates  the  marking  of  the  gold  plate  because  of  its  greater 
thickness  and  stiffness.  The  tracing  of  the  pattern  on  the  gold 
is  most  easily  aecomijlished  with  a  round  shauk,  sharp  pointed 
instrument,  held  perpendicularly.  If  neither  tin  or  lead  foil 
is  at  hand,  ordinary  tough  writing  paper,  although  not  as  sat- 
isfactory, will  serve  for  the  pattern. 

"When  trimmed  to  pro])er  outline,  the  pattern  is  laid  on 
the  sheet  of  gold  plate,  so  that  when  the  latter  is  cut  the  grain 
or  lamina  developed  in  rolling  rims  crosswise  or  from  buccal 
to  buccal,  this  being  the  line  of  direction  of  greatest  stress  on 
the  baseplate,  in  swaging  as  well  as  in  masticatory  effort. 

CARAT  OF  GOLD  USED  FOR  DENTURE  BASES 

Twenty  carat  gold  is  the  standard  tineness  of  plate 
used  for  denture  bases.  The  advantages  of  this  grade  of  gold 
are:  excellent  color,  but  little  tendency  to  discolor  in  the 
mouth,  no  metallic  taste,  comparatively  easy  to  adapt  to  dies, 
good  resiliency  when  medium  to  thick  gauges  are  used. 

The  only  disadvantage  noticeable  is  the  tendency  of  the 
lighter  gauges  to  become  distorted  under  heavy  stress.  Obvi- 
ated by  using  gauges  of  i)late  appropriate  to  the  stress  the 
denture  will  be  subjected  to  in  masticatory  effort. 

Eighteen  carat  gold  is  frequently  employed  for  both  full 
and  partial  denture  bases.  The  only  decided  advantage  it  has 
over  twenty  carat  gold  is  in  having  greater  resiliency  than  the 
latter  in  plates  of  equal  thickness,  and,  therefore,  lighter 
gauges  can  be  employed  to  advantage  in  some  cases  than  when 
higher  carats  of  plate  are  used. 

The  disadvantages  of  eighteen  carat  jilate  are :  color  not 
so  good  as  the  twenty  carat,  decided  tendency  to  discolor  in 
the  mouth,  and  in  some  cases  to  exhibit  a  metallic  taste. 

Pure,  twenty-two  and  coin  gold  are  deficient  in 
resiliency  and  are  not  adapted  for  denture  bases  unless  com- 
bined with  gold  of  lower  carat.  In  difficult  cases,  where  the 
maxillary  surfaces  are  very  rough  and  irregular,  and  the 
rugae  are  well  defined,  a  thin  sheet  of,  22  carat  or  24  carat 
gold  is  sometimes  adapted  to  the  die  and  a  second  piece  of  18 
or  20  carat  swaged  over  and  attached  to  the  maxillary  plate 
with  solder.  The  use  of  the  finer  and  softer  grade  of  gold 
next  the  die  permits  all  of  the  irregularities  to  be  accurately 
copied,  while  the  second  plate,  being  harder  and  more  resili- 


168       CONSTRUCTION   OF  SWAGED  DENTURE  BASES  OF  GOLD 

ent,  furnishes  the  necessary  rigidity.  This  method  of  forming 
a  double  base  is  frequently  followed  in  partial  cases,  but  is 
seldom  required  in  full  dentures. 

GAUGES  OF  GOLD  USED  FOR  DENTURE  BASES 

For  full  upper  dentures,  28,  27,  and  26  gauges  of  gold 
are  used  as  conditions  require.  Twenty-eight-gauge,  20-carat 
plate  is  sufficiently  rigid  for  narrow  arclies  where  the  stress 
of  mastication  is  light  to  medium  heavy.  Twenty-seven-gauge, 
20-carat  is  indicated  for  arches  of  medium  width,  medium 
stress,  and  in  narrow  arches  when  stress  is  heavy.  Twenty- 
six-gauge  is  indicated  for  wide  arches  when  the  denture  will 
be  subjected  to  heavy  stress. 

Full  lower  dentures  seldom  require  heavier  than  28-gauge 
plate,  since  the  vulcanite  which  furnishes  attachment  for  the 
teeth  usually  covers  the  entire  base,  and  this,  together  with 
the  peripheral  wiring,  sujoplies  the  needed  rigidity.  Frequent- 
ly 29-gauge  will  prove  satisfactory. 

That  one  may  form  a  just  estimate  of  the  relative  thick- 
ness of  the  gauges  mentioned,  their  value  according  to  the 
Brown  &  Sharp  micrometer  scale  is  here  given.  This  mi- 
crometer scale  is  given  entire  in  the  section  on  metallurgy. 

26  gauge  equals  .01594  of  an  inch 

27  "  "  .01419  "  "  Difference  between  26  and  27  gauge  equals  .00175 

28  "  "  .01264  '■  "                 "  "  27     "     28       "  "         .00155 

29  "  "  .0112(1  •'  "                 "  "  28     "     29       "  "         .00138 

30  "  "  .01002  "  ••                 ■'  '■  29     "     30       "  "         .00123 

To  gain  rigidity  within  restricted  areas,  partial  denture 
bases  are  frequently  formed  of  two  pieces  of  plate,  swaged 
separately,  then  together,  and  finally  soldered.  Usually  two 
pieces  of  30-gauge  or  one  of  .30  and  one  of  29  gauge  are  com- 
bined in  this  manner.  The  two  pieces  of  30-gauge  equal 
.0200,  or  approximately  24-gauge,  which  is  .0201.  The  other 
combination  equals  .0212,  or  about  23y2  gauge.  Various  other 
combinations  of  gauges  can  be  utilized,  as  the  conditions  of 
individual  cases  demand,  broad  bases  requiring  thin,  while 
narrow  bases  call  for  thicker  gauges  of  plate. 

ANNEALING   THE    PLATE 

Gold  plate,  as  usually  furnished  by  the  supply  houses,  is 
not  in  its  softest  possible  condition,  and  therefore  should  be 
annealed  before  attempting  to  adapt  it  to  the  die,  as  well  as 
at  various  times  during  the  swaging  process. 

Hammering,  rolling,  bending,  liurnishing  and  polishing 
tend  to  stiffen  and  render  the  gold,  as  well  as  other  metals, 


CONSTRUCTION    OF   SWAGED   DENTURE    BASES   OF   GOLD        169 

hard,  more  oi*  less  spring}'  and  elastic,  and  reduces  their  pli- 
ability. 

Molecular  tension  is  also  developed  by  working  the  plate, 
a  property  which  tends  to  bring  the  molecules  back  to  the 
original  relation  they  sustained  to  each  other  before  the  plate 
was  subjected  to  working  stress. 

The  hardness,  tension  and  loss  of  pliability  increase  in 
proportion  to  the  stress  to  which  the  molecules  are  subjected. 
Hardness  and  reduction  of  pliability  render  the  securing  of 
perfect  adaptation  of  the  base  plate  to  the  die  difficult.  Mol- 
ecular tension  tends  to  destroy  adaptation  by  warping  the 
plate  when  swaged  to  correct  form,  particularly  when  sub- 
jected to  high  temperatures,  as  in  soldering  on  the  peripheral 
wires  and  the  attachments  for  the  vulcanite. 

Gold  plate  is  annealed  by  laying  it  on  a  clean  charcoal 
or  asbestos  soldering  block  and  applying  the  soft  brush  flame 
of  the  blowpipe  until  the  plate  assumes  a  cherry  red  color, 
when  it  should  be  thrown  quickly  into  clean,  cold  water  or 
alcohol.  Care  should  be  taken  not  to  overheat  or  fuse  the 
gold  at  any  point,  or  its  toughness  and  cohesiveness  will  be 
impaired. 

OILING  THE  DIE  AND  COUNTERDIE 

Before  beginning  to  adapt  the  plate,  the  surfaces  of  both 
die  and  couuterdie  should  be  coated  with  a  thin  film  of  thick, 
viscid  oil,  such  as  vaseline  or  heavy  lubricating  oil.  This  is 
done  for  two  reasons :  First,  to  prevent,  as  much  as  possible, 
the  adhesion  of  the  base  metals  to  the  gold  under  the  heavy 
sliding  friction  induced  by  swaging  the  plate  l^etween  the  die 
and  the  counterdie.  Second,  the  oil  acts  as  a  lubricant  and 
permits  the  gold  to  slide  over  surfaces  which,  if  not  oiled, 
would  result  in  tearing  or  shearing  the  plate.  The  oiling  of 
the  die  and  the  counterdie  is  extremely  important,  and  under 
no  circumstances  should  it  bo  neglected.  Dies  and  counterdies 
composed  of  the  triple  alloys,  such  as  are  used  in  crown  and 
bridge  work,  should  receive  the  same  treatment  for  similar 
reasons  as  stated. 

The  old  method  of  interposing  a  thin  sheet  of  rubber  dam 
between  the  plate  and  couuterdie  to  prevent  contamination  by 
the  base  metal  is.  not  to  be  commended,  as  the  rubber  acts  as 
a  cushion  and  reduces  the  positive  action  of  the  metal  matrix 
against  the  gold. 

CLEANSING  THE  PLATE— PICKLING 

When  gold  plate  becomes  contaminated  by  any  of  the  base 
metals  such  as  are  employed  for  die  and  counterdie  purposes, 


17(1        CONSTRUCriON    OK    SVV.V(iKI)    DKNTrHK    HASKS    OK   VAHJ) 

and  i.s  subjected  to  the  blow  pi pc  or  l')iiiis("ii  flame  in  the  an 
iiealing  process,  an  alloy  is  formed  at  the  points  affected,  which 
is  brittle  and  low  fusing  in  character.  When  this  occurs,  the 
strength  and  fusibility  of  the  plate  is  reduced.  Subsequently, 
in  soldering  operations,  the  areas  so  contaminated  are  very 
liable  to  fuse  and  result  in  the  formation  of  pits  or  holes, 
sometimes  called  "burning  the  plate."  This  is  an  incorrect 
term,  as  the  alloy  is  merely  fused  and  its  tendency  to  spheroid 
causes  it  to  draw  back  to  the  more  infusible  portions  of  the 
plate  not  so  affected. 

To  remove  the  base  metal  that  adheres  to  the  plate  as 
a  result  of  hanmiering  and  friction  between  the  die  and 
counterdie,  it  should  be  boiled  in  dilute  sulphuric  acid  from 
ten  to  tifty  per  cent  strength.  Even  the  action  of  the  acid  fails 
at  times  to  remove  all  of  the  base  metal,  particularly  the  lead 
and  tin,  in  reasonable  time.  Sulphuric  acid,  either  full 
strength  or  diluted,  does  not  act  readily  on  these  metals,  as 
is  apparent  by  the  fact  that  it  is  often  kept  in  lead  containers 
for  a  long  period  without  injury  to  the  vessel.  This,  how- 
ever, is  partly  due  to  the  fact  that  after  a  time  a  film  of  lead 
sulphate  is  gradually  formed,  which  limits  further  action  of 
the  acid  on  the  unaffected  lead. 

A  positive  and  final  method  of  removing  particles  of 
base  metal  from  the  gold  is  by  the  application  of  pumice  stone 
to  the  i)late  with  a  stiff  brush  wheel  on  the  lathe.  This  should 
be  resorted  to  after  boiling  in  acid  and  rinsing  in  water. 

CONFORMING  THE  PLATE  TO  THE  DIE 
STEPS   OF   ADAPTING   THE    GOLD,   IN   FULL    UPPER   CASES 

The  gold  plate  having  been  cut  according  to  i)attern,  is 
now  evenly  centered  over  the  die,  and  with  finger  or  thumb 
pressure  forced  down  into  the  vault  ])ortions  as  closely  as 
possible  in  this  manner.  Tlie  adaptation  is  carried  further 
with  a  horn  mallet,  being  careful  not  to  mar  the  plate  un- 
necessarily with  the  pointed  end.  Two  or  three  forms  of 
mallet,  with  ends  of  different  shapes  and  sizes,  should  be  at 
hand  to  meet  the  varying  conditions  which  present.  The  small 
end  of  the  average  new  horn  mallet  is  usually  too  sharp  and 
too  pointed  to  be  serviceable  and  should  be  cut  ot¥  and  some- 
what rounded  with  a  rasp. 

From  the  very  beginning,  and  until  thoroughly  close 
adaptation  is  secured,  wrinkles  or  folds  in  the  plate  are  very 
liable  to  develop.     Such  mishaps  usually  occur  when  an  at- 


CONSTRUCTION  OF  SWAGED  DENTURE  BASES  OF  GOLD       171 


tempt  is  made  to  closely  conform  a  considerable  area  of  plate 
to  an  irregular  or  constantly  varying  surface  of  the  die,  as 
for  instance  a  deep  palatine  vault,  the  labial  surfaces  of  a 
prominent  or  V-shaped  arch,  or  prominent  tuberosities. 

The  physical  conditions  bearing  upon  the  changing  of  a 
flat  plate  to  the  irregular  form,  assumed  by  a  well-adapted 
base  plate  should  be  borne  in  mind.  Certain  areas  must  be 
raised,  others  depressed,  and  still  others  will  require  but 
little  general  modification.  Molecular  changes  must  be 
brought  about  uniformly.  In  some  locations  the  molecules 
will  be  stretched  and  pulled — occasionally  to  the  point  of  de- 
stroying their  cohesion,  which  will  result  in  thinning  and  tear- 
ing the  plate. 


THE    HORN    M.VLLET 


In  other  areas,  the  molecules  must  be  comi^ressed  upon 
themselves,  the  first  noticeable  effect  of  which  is  in  the  forma- 
tion of  wrinkles,  with  a  slight  tendency  to  thicken  the  plate. 
The  folds  and  wrinkles  must  be  obliterated  as  soon  as  they 
are  formed  and  before  they  are  januned  too  closely  together 
for  correction.  Flat  and  round-nosed  pliers  and  the  plate 
benders  are  used  to  advantage  for  this  purpose.  The  judicious 
use  of  the  horn  mallet  or  a  small  riveting  hammer  will  also 
correct  the  difficulty  by  striking  the  fold  with  a  sliding  blow 
peripherally,  at  the  point  on  the  adfii)t('d  surface  where  it  first 
appears. 

The  vault  portion  having  been  fairly  well  adajited,  cither 
by  the  aid  of  the  partial  counterdie  or  with  the  horn  mallet 
alone,  the  next  step  is  to  conform  the  plate  to  and  over  the 


172       CONSTRUCTION   OF  SWAGED  DENTURE  BASES  OF  GOLD 

crest  of  the  maxillary  borders.  The  die  can  conveniently  be 
held  in  the  hand,  the  thumb  pressing  the  plate  and  keeping  it 
closely  in  contact  with  the  vault  portion,  while  adapting  the 
metal  to  the  border  crest. 

USE  OF  PARTIAL  COUNTERDIES 

The  large  end  of  the  horn  mallet  is  applied  here,  using 
moderate  blows  to  prevent  thinning  the  plate  unnecessarily 
— usually  a  few  well-directed  blows  will  accomplish  the  de- 
sired end.  When  partial  counterdies  have  been  constructed, 
the  second  or  largest  of  the  two  partials  is  applied  to  advan- 
tage following  the  use  of  the  horn  mallet,  for  setting  the  plate 
against  the  maxillary  border. 

In  difficult  cases,  where  much  irregularity  of  the  border 
surface  is  present,  a  clamp  may  be  used  to  advantage  for 
holding  the  adapted  vault  portion  of  the  plate  firmly  in  con- 
tact with  the  die.  A  wad  of  compact,  damp  paper  is  placed 
against  the  vault  portion  of  tlie  plate  to  give  bearing  to  the 
clamp  screw,  prevent  the  latter. from  marring  the  plate,  and 
by  its  tendency  to  spread  slightly  under  screw  pressure,  force 
and  hold  a  considerable  area  of  the  adapted  portion  against 
the  die.  When  partial  counterdies  have  been  constructed,  the 
smallest  of  these  can  be  used  in  lieu  of  the  paper. 

The  die,  with  the  plate  in  position,  can  be  clamped  to  the 
bench,  when  necessary,  to  give  the  prosthetist  the  free  use  of 
lioth  hands,  but  usually  it  will  he  found  best  to  clamp  the  die 
and  plate  together  so  that  they  may  be  held  in  the  hand  and 
turned  in  any  convenient  position  for  the  application  of  the 
mallet  blows. 

Tlie  plate  is  adapted  to  tlie  Jal)ial  and  liueeal  surfaces  of 
the  die  by  striking  a  sliding  blow  from  the  border  crest  to 
the  periphery.  The  adaptation  should  begin  at  the  median 
line  on  the  lalnal  surface  and  be  gradually  developed  distally, 
about  equally  on  both  sides.  In  other  words,  secure  reason- 
ably close  adaptation  from  the  median  line  to  the  cuspid 
eminence  on  one  side,  then  direct  the  effort  to  the  opposite 
side  in  like  manner,  continuing  the  adaptation  similarly  on  the 
buccal  surfaces  and  finishing  at  the  tuberosities. 

Another  method  in  common  practice  is  to  slit  the  plate 
in  the  median  line,  on  the  labial  surface,  from  the  periphery 
to  the  crest  of  the  border.  The  buccal  surfaces  are  then 
adapted  and  the  surplus  plate  worked  forward,  allowing  it 
to  lap  at  the  median  line.  The  excessive  surplus  of  plate  at 
the  lap  joint  is  removed  with  the  shears  and  the  joint  soldered 


CONSTRUCTION  OF  SWAGED  DENTURE  BASES  OF  GOLD       173 

before  the  final  swaging.  The  method  first  described  is  usually 
to  be  preferred,  although  at  times,  when  the  general  form  of 
the  arch  is  narrow  and  the  labial  and  buccal  surfaces  are  deep 
from  the  border  crest  periplierally,  slitting  and  soldering  the 
plate  as  outlined  will  be  convenient  and  satisfactory,  and  will 
enable  the  prosthetist  to  economize  on  time. 

It  is  not  expected  that  the  adaptation  of  the  base  plate 
to  the  die  with  the  horn  mallet  will  be  very  close,  but  it  should 
be  reasonably  well  developed  to  i)revent  folds  from  foi-ming 
in  the  final  swaging  in  the  counterdie. 

The  peripheral  excess  of  the  base  plate  is  trimmed  away 
to  the  required  outline  of  the  finished  denture,  the  plate 
pickled  in  dilute  acid,  polished  on  the  lathe  with  a  stiff  brush 
wheel  and  pumice  stone,  to  remove  any  adherent  particles  of 
base  metal  which  the  acid  does  not  remove,  washed  clean,  and 
thoroughly  annealed,  before  the  final  swaging. 

SWAGING   IN    THE    COUNTERDIE 

The  base  plate  being  clean  and  soft  from  annealing,  and 
the  counterdie  freshly  oiled,  the  final  adaptation  is  quickly 
secured.  The  base  plate  is  placed  on  the  die  and  settled  evenly 
into  the  counterdie,  as  far  as  the  latter  will  receive  it.  Place 
the  counterdie  on  the  swaging  block,  and  with  a  four  to  six 
pound  hammer,  strike  the  base  of  the  die  squarely,  one  rea- 
sonably sharp  blow,  separate,  remove  the  plate,  and  note 
whether  any  folds  or  wrinkles  have  develo]ied,  and  if  so,  re- 
move them.  Beturn  the  plate  and  strike  the  die  two  or  three 
heavy  blows  and  again  inspect,  first  for  folds,  and  finally  for 
adaptation.  Bepeat  as  often  as  may  be  necessary  to  secure 
perfect  approximation  of  the  plate  to  the  die  surfaces  and 
especially  around  the  periphery. 

Finally,  when  the  adaptation  is  satisfactory,  pickle,  polish, 
anneal  and  I'eturn  to  the  countei'die  and  strike  a  final  blow  to 
correct  the  warpage  occasioned  by  the  last  annealing,  and 
which  almost  invariably  occurs.  A  single  well-delivered, 
heavy  blow  following  this  final  annealing  corrects  warpage  and 
does  not  develop  any  further  appreciable  molecular  tension. 

This  latter  step  is  very  important,  for  if  not  cari'ied  out 
as  described  and' the  wiring  of  the  base  plate  is  undertaken 
while  any  molecular  strain  is  present,  warpage  is  most  certain 
to  occur. 

The  periphery  of  the  baseplate  sliould  be  trimmed  with 
shears  and  files,  as  accurately  as  possible,  to  the  required  out- 
line of  the  finished  denture  before  the  final  swaging,  for  if 


174       CONSTRUCTION   OF  SWAGED  DENTURE  BASES  OP  GOLD 

after  trial  in  the  moutli  the  shears  arc  used,  distortion  of  the 
base  plate  is  liable  to  follow  from  the  strain.  Should  this 
occur,  correction  must  be  made  by  reswaging. 

PRELIMINARY   STEPS   IN   SECURING   ANCHORAGE   FOR 
TEETH  TO  BASEPLATE 

lu  full  gold  base  denture  eases,  the  teeth  are  usually  at- 
tached to  the  gold  base  by  means  o¥  vulcanite.  This  method 
of  attachment  obviates  the  many  angles  and  spaces  which 
result  from  backing  plate  teeth  and  joining  them  to  the  base 
with  solder.  Again,  when  more  or  less  absorption  of  the 
border  has  occurred,  and  for  esthetic  reasons  restoration  of 
such  loss  is  necessary,  it  can  be  most  easily  accomplished  in 
vulcanite.  Therefore,  for  hygienic  and  esthetic  reasons,  this 
method  is  resorted  to  in  practically  all  full  denture  cases. 

When  rubber  is  molded  and  vulcanized  against  a  smooth 
surface  of  gold  plate,  the  two  materials  adhere  quite  firmly, 
but  unless  some  positive  mechanical  anchorage  is  provided, 
the  vulcanite  will  part  from  the  baseplate  sooner  or  later, 
under  the  constant  vibratory  stress  of  mastication. 

VARIOUS    MEANS    EMPLOYED    FOR    VULCANITE    ANCHORAGE 

Several  methods  of  anchorage  can  be  utilized  for  in- 
creasing the  bond  of  union  between  the  gold  and  vulcanite, 
none  of  which  alone  will  prove  sufficient,  but  by  combining 
usually  three,  a  permanent  and  lasting  attachment  can  be 
effected. 

USE  OF  WIRE  LOOPS 

First,  in  full  cases,  from  three  to  five  loops  of  wire  or 
narrow  corrugated  strips  of  plate  should  be  soldered  to  the 
maxillary  surface  of  the  gold  base,  at  various  points  along 
the  border,  in  such  manner  as  subsequently  not  to  interfere 
with  the  arrangement  of  the  teeth.  In  closing  the  packed 
flask,  the  rubber  is  molded  around  and  imder  these  anchor 
loops,  where  it  hardens  during  vulcanization.  This  is  the  best 
and  most  positive  form  of  mechanical  anchorage  possible  to 
develop. 

SPURRING  THE  BORDER   SURFACES 

Second,  with  a  diamond  point  engraver,  many  opposing 
spurs  should  be  raised  over  the  entire  area  covered  by  the 
vulcanite.  The  spurs  should  extend  to  the  extreme  margins 
to  prevent  the  thin  edges  of  vulcanite  from  eventually  warp- 
ing and  curling  away  from  the  baseplate. 


CONSTRUCTION   OF  SWAGED  DENTURE  BASES  OF  GOLD       175 
APPLICATION    OF   RUBBER   CEMENT 

Third,  by  applyiug  a  thin  fihn  of  ehloro-rubber  to  the 
surface  of  gold  involved,  just  before  closing  the  packed  flask, 
it  will  act  as  a  cementing  medium  and  aid  the  mechanical  re- 
tention otherwise  provided. 

FORMING   THE    PERIPHERAL    SHOULDER 

In  order  that  the  line  of  junction  of  the  vulcanite  with 
the  gold  base  may  be  symmetrical,  and  to  further  guard 
against  tlie  extreme  margins  of  the  vulcanite  from  curling 


SOLDERING    THE    SIKIll.nEr.    WIRES    TO   AX    VPI'ER  EASE 

away  from  the  baseplate,  a  fine  wire,  usually  19  gauge,  and 
L'O  carat,  is  soldered  to  the  labial  and  buccal  surfaces  and 
continued  around  the  tuberosities  along  the  lingual  aspect  of 
the  border.  The  surface  included  within  this  wire  loop  repre- 
sents the  area  to  be  covered  by  the  vulcanite.  When  soldered, 
the  inner  periphery  of  the  wire  is  scjuared  out  with  small 
stones  and  burs  so  as  to  present  a  square  shoulder  against 
which  the  vulcanite  finishes.  In  attaching  the  wire,  care 
sliould  be  taken  to  avoid  filling  with  solder  the  angle  formed 
by  the  junction  of  the  baseplate  with  the  inner  periphery  of 
the  wire.     The  application  of  an  anti-flux  will  prevent  the 


176       CONSTRUCTION   OK  SWAGED   DENTURE  BASES  OF  GOLD 

solder  from  tilling  angles  and  ooveriug  surfaces  fi-om  which 
it  should  be  excluded. 

The  outer  side  of  the  wire,  or  that  surface  presenting 
toward  the  periphery  of  the  base  and  to  the  central  vault 
portion,  is  filled  in  with  solder  and  afterward  ground  to  meet 
the  baseplate,  merging  it  into  a  symmetrical  curve,  thus 
obviating  the  formation  of  an  angle  into  which  food  might 
find  its  way. 

LOCATING  THE  POSITION  OF  THE  WIRE  ON  THE  BASEPLATE 

The  location!  of  this  wire  which  marks  the  boundaries  of 
the  vulcanite  is  determined  by  occluding  and  waxing  the  teeth 
to  the  base  in  the  position  they  will  occupy  in  the  finished 
denture.  On  the  lingual  side  the  wax  is  contoured  to  repre- 
sent the  normal  curvature  of  the  palatine  vault,  terminating 
it  as  soon  as  possible  without  forming  an  angle  at  its  junction 


SECTIONAL  VIEW  OK  BASE  SHOWING  FINISHED 
SHOULDERS  WITH  VULCANITE  IN  POSITION 

with  the  base  or  alveolar  border.  On  the  other  hand,  it  should 
not  be  extended  too  far  toward  the  center  of  the  vault,  or  the 
contour  of  the  finished  case  will  be  imnecessarily  bulky. 

The  wire  is  attached  to  the  labial  and  buccal  surfaces  of 
the  baseplate  about  one-eighth  of  an  inch  from  the  peripheral 
margin.  It  is  placed  in  from  the  margins  to  this  extent  so  that 
after  the  denture  is  instroduced,  should  perijjheral  trimming 
of  the  base  become  necessary,  it  may  be  accomplished  with- 
out cutting  into  the  vulcanite. 

The  exact  position  of  the  wire  is  determined  by  scratching 
a  line  on  the  gold  base  with  a  sharp  instrument,  just  within 
the  peripheral  margin  of  the  contoured  wax  rim.  The  posi- 
tion of  the  anchor  loops  can  also  be  determined  at  this  time 
by  thrusting  a  sharp  pointed  instrument  through  the  wax 
rim  to  the  basepalte  and  scratching  it  in  the  lingual  embra- 
sures between  the  first  and  second  molars,  the  first  and  second 
biscuspids,  and  as  close  in  to  the  mesio-lingual  angles  of  the 
central  incisors  as  possible,  so  that  this  loop  will  not  inter- 


CONSTRUCTION   OK   SWAGED   DENTL^KE   BASKS   OK   GOLD        177 

fere  with  the  proper  lingual  contour  of  tlie  vulcanite,  hack  of 
the  incisor  teeth. 

The  denture  is  now  removed  from  the  occluding  frame 
on  which  it  has  previously  been  mounted,  the  teeth  and  wax 
rims  are  detached,  and  the  baseplate  thoroughly  cleansed.  A 
piece  of  wire  about  9  inches  long  is  required  for  forming  the 
peripheral  shoulder.  One  end  of  this  is  conformed  and 
clamped  to  the  wire  line,  beginning  usually  at  one  of  the 
tuberosities,  where  it  is  fluxed  and  tacked  with  a  small  piece 
of  solder.  The  baseplate  is  chilled,  the  wire  is  further  con- 
formed along  the  line  for  a  distance  of  one-half  to  one  inch 
and  again  clamped  and  soldered.  This  is  repeated  until  the 
wire  is  attached  to  the  entire  peripheral  outline  on  the  base- 


plate marked.  The  application  of  an  anti-tlux  to  the  inner 
margin  of  the  wire,  before  each  section  is  soldered,  will  pre- 
vent the  filling  in  of  the  angle  with  solder. 

ATTACHING  THE  WIRE   LOOPS 

A  convenient  method  of  applying  the  wire  anchorage 
loops  is  as  follows :  Make  a  right  angle  bend  near  the  end 
of  a  piece  of  19  or  20  gauge  wire  and  touch  the  angle  with 
flux ;  i^lace  a  small  piece  of  solder  on  the  baseplate  at  a  point 
indicated  for  a  loop ;  apply  the  blowpipe  and  when  the  solder 
is  fused  touch  the  bent  wire  to  the  solder,  remove  the  flame 
holding  wire  until  solder  congeals;  clip  oiT  the  long  end  of 
the  wire  near  the  baseplate,  leaving  two  short  spurs  projecting 
for  anchorage.  By  using  a  iwire  6  or  8  inches  long  it  will 
serve  as  a  handle  for  holding  the  loop  while  soldering.  In 
arranging  the  teeih,  if  the  ends  of  the  wire  interfere  they  may 
be  bent  out  of  the  way.  The  teeth  are  now  returned  to  the 
baseplate  and  their  position  and  occlusion  verified  by  trial  in 
the  mouth.  The  steps  of  flaskiug,  packing,  ^mlcanizing  and 
finishing  differ  in  no  essential  particulars  from  those  em- 
ployed in  vulcanite  work  to  which  the  reader  is  referred. 


ITS        CONSTRIK'TION   OK   SWAOKD   nKNTURIO   liASl<:S   OK   COLD 

SWAGING    FULL   LOWER   BASEPLATES  OF  GOLD 
CUTTING   THE    PATTERN    AND    PLATE 

The  pattern  for  a  full  lower  base  is  obtained  in  the  same 
manner  as  for  a  full  upper  denture.  Special  care  should 
be  observed  in  flattening  out  the  foil  or  tea  lead  not  to  dis- 
tort it  by  undue  stretching  of  either  the  labial  or  lingual 
surfaces.  When  the  labial  surface  is  stretched  more  than 
the  lingual,  the  pattern  will  l)e  too  narrow  around  the  curve 
of  the  arch,  or  from  buccal  to  buccal,  while  if  the  lingual 
surface  is  distorted  the  reverse  conditions  prevail. 

The  lamina  of  the  gold  plate  should  run  from  buccal  to 
buccal,  as  in  full  cases,  to  give  strength  in  the  median  line  to 
the  finished  denture. 

CONFORMING  THE  PLATE  TO  THE  DIE  ^ 

It  is  somewhat  more  difficult,  at  the  outset,  to  adapt  the 
metal  plate  to  a  lower  than  to  an  upper  die,  because  its  nar- 
row, curved  foi'm,  as  well  as  the  peculiar  shape  of  the  die, 
renders  it  a  difficult  task  to  prevent  the  plate  from  sliding. 

The  base  should  be  evenly  centered  over  the  oiled  die, 
and  with  the  fingers  and  thumb  held  as  firmly  as  possible  by 
its  outer  periphery.  The  lingual  surfaces  are  bent  down- 
ward and  outward  against  the  lingual  surfaces  of  the  die 
with  liglit  blows  of  the  horn  mallet. 

No  attempt  need  be  made  to  secure  close  adaptation  at 
the  start ;  the  lingual  surfaces,  however,  should  be  conformed 
sufficiently  to  prevent  the  plate  from  sliding  while  bending 
the  labio-buccal  flange  downward  in  contact  with  the  outer 
surfaces  of  the  ridge.  The  plate  benders  are  very  convenient 
for  starting  the  plate  over  the  border.     (See  page  189.) 

Usually  far  too  much  time  is  devoted  to  tlie  use  of  the 
liorn  mallet  in  conforming  the  plate  to  the  die. 

The  beating  of  the  metal  with  the  mallet  develops  undue 
molecular  strain,  thins  the  plate  itself  and  reduces  the  high 
points  on  the  die,  all  of  which  unfavorable  features  can  be 
obviated,  or  at  least  greatly  lessened,  by  the  early  use  of 
the  die  and  counterdie. 

Except  in  cases  of  marked  irregularity  of  the  alveolar 
ridge,  the  swaging  may  begin  as  soon  as  the  plate  is  con- 
formed sufficiently  to  retain  its  position  on  the  die. 

SWAGING   IN    THE   COUNTERDIE 

A  method  applicable  to  all  classes  of  cases  for  prelim- 
inary conformation  of  the  plate  to  the  die,  with  the  minimum 
malleting,  is  as  follows: 


CONSTRUCTION   OF  SWAGED  DENTURE  BASES  OF  GOLD       179 

Place  the  partially-conformed  plate  in  the  counterdie 
and  set  the  die  in  position  upon  it.  Place  the  palm  of  the 
hand  over  the  die,  the  fingers  and  thumb  grasping  the  peri- 
phery of  the  counterdie.  Lift  the  die  and  counterdie,  the 
plate  being  interposed,  and  strike  the  anvil  once  only  with 
the  base  of  the  counterdie.  The  resulting  impact  will  drive 
the  die  partially  into  the  counterdie,  the  plate  being  carried 
with  it.  Remove  the  die  and  plate  and  examine  the  latter 
for  folds  or  wrinkles.  Should  any  have  developed,  correct 
with  pliers  or  mallet  and  repeat  the  step  until  all  tendency 
of  the  plate  to  buckle  is  overcome. 

General  adaptation  of  the  plate  to  the  die  can  be  secured 
in  this  manner  in  a  very  short  time.  Final  swaging  is  accom- 
plished and  close  adaptation  is  developed  with  a  heavy  ham- 
mer on  the  swaging  block,  the  same  as  in  upper  cases,  pre- 
viously described. 

When  extreme  irregularity  of  the  maxillary  ridge  and 
border  surfaces  in  general  exists,  it  is  sometimes  advisable. 
in  order  to  insure  close  adaptation  of  the  baseplate  to  the 
tissues,  to  swage  two  thin  plates  of  30  or  31  gauge  separately, 
then  together,  pickle,  polish  and  unite  with  solder.  After 
soldering,  reswage  to  correct  warpage.  This  method  of 
doubling  the  plate  in  difficult  cases  of  any  class  is  productive 
of  excellent  results. 

SWAGING   THE    PL.'^TE    AGAINST   UNDERCUT    SURFACES 

In  case  undercut  surfaces  are  present  on  the  die,  and 
these  areas  have  been  filled  with  sand  in  the  production  of 
the  counterdie,  as  previously  described,  the  latter  will  be 
deficient  opposite  such  filled-in  areas  of  the  die.  To  conform 
the  plate  to  the  die  and  against  these  surfaces,  strips  of 
lead  of  approximately  the  thickness  of  the  depth  of  under- 
cut are  laid  between  the  plate  and  deficient  counterdie  area, 
and  the  die  and  plate  driven  deeply  into  the  counterdie. 

It  is  usually  useless,  however,  to  force  the  baseplate  into 
deep  undercuts,  because  it  must  necessarily  be  distorted  in 
removal  from  the  die.  The  better  plan  is  to  allow  the  plate 
to  enter  the  undercut  to  a  slight  extent  only,  so  that  in  re- 
moval, although  requiring  to  be  sprung  in  passing  over  the 
bulge  of  the  die,  its  inherent  elasticity  will  return  it  to  origi- 
nal form.  The  deficiency  of  the  base,  in  such  cases,  can 
usually  be  corrected  with  the  vulcanite  by  means  of  which 
the  teeth  are  attached. 

The  same  general  steps  of  trimming:  to  as  nearly  cor- 


180        CONSTRUCTION   OK  SWAGED  DENTURE   BASES  OF  GOLD 

rect  peripheral  outline  as  possible,  before  trial  in  the  mouth, 
pickling,  polishing  and  annealing  to  relieve  molecular  strain, 
followed  by  the  final  blow  to  correct  warpage,  applies  to 
lower  as  well  as  all  classes  of  swaged  base  dentures  which 
must  subsequently  be  subjected  to  soldering  operations. 

PARTIAL  BASEPLATES  OF  GOLD 

The  construction  of  gold  base  i)artial  dentures  requires 
the  exercise  of  as  mucli,  and  in  many  instances  more  care,  than 
is  involved  in  the  production  of  full  gold  bases. 

The  forms  of  dentures  for  partial  eases  vary  widely, 
depending  on  the  number  of  teeth  to  be  replaced,  the  rela- 
tion to  each  other  of  the  spaces  to  be  filled,  the  stress  liable 
to  be  exerted  in  masticatory  effort  and  the  means  of  retention 
to  be  employed. 

In  a  full-gold  base  denture  the  baseplate  continues  with- 
out a  break,  from  the  palatine  vault,  over  the  maxillary  sur- 
faces, to  the  labial  and  buccal  areas,  against  which  its  peri- 
pheral margins  terminate.  The  constantly  varying,  continu- 
ous surfaces  of  such  a  baseplate,  when  adaptation  has  been 
secured  and  molecular  strain  relieved,  together  with  the  at- 
tachment of  the  teeth  to  the  base  by  means  of  vulcanite,  tend 
to  impart  rigidity  to  the  entire  denture  base. 

In  partial  cases,  however,  the  presence  of  some  of  the 
natural  teeth,  against  the  lingual  surfaces  of  which  the  peri- 
phery of  the  baseplate  must  terminate,  necessitates  cutting 
or  notching  the  outer  margin  of  the  denture  to  receive  them. 
This  step  materially  weakens  the  base  wherever  such  notch- 
ing occurs. 

REINFORCING   PARTIAL    BASEPLATES    OF   GOLD 

To  develop  the  required  rigidity,  so  that  under  stress 
of  mastication,  or  in  handling,  the  denture  may  not  become 
permanently  distorted,  one  of  the  several  methods  in  vogue 
for  reinforcing  baseplates  may  be  adopted. 

REINFORCING  THE  BASEPLATE  BY  DOUBLING 

First:  Develop  the  base  from  two  pieces  of  comparatively 
thin  gold  plate,  swage  each  piece  separately,  then  together, 
and  finally  unite  them  with  solder. 

Advantages:    Ease  of  adaptation,  high  degree  of  rigid 
ity,  uniform  thickness  of  baseplate. 

Objections :  None,  aside  from  the  extra  work  of  solder- 
ing. 


CONSTRUCTION  OF  SWAGED  DENTURE  BASES  OF  GOLD       181 

REINFORCING    THE    BASEPLATE    BY    REFLECTION    OF 
MARGINS   AND   WITH   SOLDER 

Second:     Construct  the  base  of  a  single  sheet  of  gold  plate, 
27  or  28  gauge,  reflect  the  margins  against  the  lingiial  sur- 
faces of  the  teeth  involved  and  fill  the  resulting  lingual 
angle  with  high-grade  solder. 
Advantages :    Rigidity  combined  with  comparatively  thin 
base. 

Objections:  Possible  tendency  of  the  solder  to  discolor 
with  use  in  the  mouth. 

REINFORCING   WITH    WIRE   AND    SOLDER 

Third:  Adapt  plate  or  wire  to  the  baseplate  over  the  weak 
areas  onlj',  and  attach  with  solder. 

Advantages :  Rigiditj'  over  weak  areas,  where  specially 
needed,  witli  use  of  minimum  amount  of  material. 

Objections:  Unequal  thickness  of  the  baseplate  because 
the  reinforcement  is  not  uniform. 

SECURING  NEEDED  RIGIDITY  BY  USE  OF  THICK  PLATE 

Fourth :  Use  a  single  piece  of  thicker  gauge  than  that  men- 
tioned in  the  second  method,  No.  25  or  26  gauge  being 
usually  employed. 

Advantages :    Rigidity. 

Objections :    Difficult  to  adapt. 

DEVELOPING  RIGIDITY   BY   USE   OF  SOLDER 

Fifth:  Flow  solder  alone  over  the  weak  areas  of  the  base- 
plate. 

Advantages :    Rigidity. 

Objections:  Tendency  of  the  solder  to  discolor;  unequal 
thickening  of  the  baseplate,  due  to  solder  filling  the  inequali- 
ties and  seeking  its  level. 

The  first  and  second  methods  are  most  frequently  fol- 
lowed and  have  proven  most  successful.  In  certain  cases, 
however,  some  of  the  other  methods  mentioned  may  be  used 
to  advantage. 

The  first-mentioned  method  of  doubling  the  baseplate  is 
specially  applicable  to  those  cases  where  the  teeth  and  spaces 
alternate  with  considerable  regularity,  where  the  rugae  are 
pronounced  and  well  defined,  and  where  the  surface  markings 
of  the  oral  tissues  in  general  are  prominent.  In  such  cases 
a  baseplate  consisting  of  a  single  piece,  sufficiently  rigid  to 


lS:i   CONSTRUCTION  OF  SWAGED  DENTURE  BASES  OF  GOLD 

withstand  stress,  cannot,  because  of  its  inlierent  rigidity,  be 
driven  into  all  of  the  irregularities  of  the  die. 

By  substituting  two  thin  pieces  for  the  single,  thicker 
plate,  and  conforming  and  uniting  them  as  mentioned,  the 
necessary  rigidity  and  required  adaptation  are  readily  se- 
cured. 

HOW    TO    ESTIMATE    THE    APPROXIMATE    THICKNESS    OF    A 
DOUBLED  BASEPLATE 

Experience  has  shown  that  in  partial  dentures,  where 
the  baseplate  is  narrow,  it  should  range  in  thickness  from  27 
to  22  gauge,  depending  on  its  width,  in  order  that  it  may  have 
the  necessary  rigidity  to  withstand  stress. 

The  best  method  for  determining  the  thickness  of  the 
comi^onent  plates,  where  two  are  used,  so  that  they  may  have 
approximately  the  same  rigidity  as  the  single,  thicker  plate, 
is  by  means  of  the  table  of  gauges. 

By  reference  to  this  table  it  will  be  seen  that  24  gauge, 
for  example,  the  probable  required  thickness  of  the  base,  is 
.0201  of  an  inch  thick.  Now  by  combining  two  thicknesses  of 
plate  of  lighter  gauge  as  follows,  the  doubled  plate  will  be 
approximately  equivalent  to  No.  24  gauge : 

27  g.  =  .0149 
34  g.  =  .0063 

.0212 

28  g.  =  .0126 
31  g.  =  .0089 

.0215 

29  g.  =  .0112 

30  g.  =  .0100 

.0212 
These  three  possible  combinations  range  about  midway 
between  No.  24  and  No.  23  gauge,  any  one  of  which  can  be 
used  when  deemed  advisable.  Other  combinations,  varying 
in  thickness,  are  made  in  a  similar  manner,  depending  on  the 
requirements  of  the  case. 

SWAGING    PARTIAL    GOLD    BASES 

When  the  base  is  to  be  of  a  single  thickness  of  plate,  re- 
inforced by  reflection  of  the  margins  and  with  solder  as  out- 
lined in  the  second  method,  the  construction  steps  are  as  fol- 
lows: 


CONSTRUCTION  OF  SWAGED  DKNTl'RE  BASES  UF  GOLD       is:^ 

Oil  the  die  and  oouuterdie;  seom-e  tin  or  lead  foil  pat- 
terns and  trim  to  the  desired  form ;  cnt  the  base  from  plate 
gold,  27  or  28  gauge,  and  20  carat,  according  to  pattern;  an- 
neal and  adapt  to  the  die,  first  with  the  fingers,  then  with  horn 
mallet  sufficiently  to  retain  its  ]iosition  between  the  die  and 


TIXFCIII,    I'ATTKItN    Flllt    I'AHTIAJ, 


counter  die  in  the  initial  stages  of  swaging;  swage  between 
die  and  counter  die,  using  weight  of  die  as  previously  sug- 
gested; with  pliers  correct  any  folds  or  wrinkles  that  form; 
return  to  counter  die  and  strike  one  or  two  heavy,  square 
blows  with  hammer;  correct  wrinkles,  trim  off  excess  and 
again  swage. 


APPLICATION    IW    THE    CHASER    OK    BURNISHER 

To  drive  the  gold  into  the  linguo-gingival  angles  and  em- 
brasures, and  reflect  it  against  the  lingual  surfaces  of  the 
teeth,  a  small  instrument,  shaped  somewhat  like  a  cold  chisel, 
is  used.  Although  in  general  form  its  end  is  chisel-shaped, 
its  edge  is  rounded  to  prevent  cutting  the  gold. 

This  instrument  is  held  firmly  with  the  pen  grasp,  against 
the  gold,  opposite  the  depressions  on  the  die  into  which  it  is 


184       CONSTRUCTION   OF  SWAGED  DENTURE  BASES  OF  GOLD 

to  be  carried.  Under  light,  rapid  mallet  or  light  hammer 
blows,  the  chaser  is  gradually  moved  over  the  plate,  along 
the  lingno-gingival  angles  until  finally  the  gold  is  foroed  into 
all  of  the  depressions  and  inequalities  of  the  die  without  the 
chaser  perceptibly  marring  the  plate  or  die. 

From  time  to  time  the  plate  is  pickled,  polished  and  an- 
nealed, and  the  surplus  trimmed  away  with  the  shears,  plate 
nippers  and  files.  The  plate  nippers  are  very  useful  for  cut- 
ting out  or  notching  the  plate  where  the  teeth  pass  through, 
or  for  cutting  any  short-curved  margin,  where  the  use  of  the 
shears  would  distort  the  plate.     (See  page  186.) 

The  reflected  plate  margin,  which  extends  from  the 
linguo-gingival  angle,  of  tissues  with  teeth,  occlusally  or  in- 
cisally,  against  the  lingual  surfaces  of  such  teeth  as  are  in- 
volved, should  be  about  1/16  of  an  inch  wide.  This  margin 
serves  two  purposes,  first,  being  bent  at  a  decided  angle  to 
the  baseplate  proper,  it  imparts  marked  rigidity  to  the 
periphery  of  the  denture  in  decidedly  weak  areas ;  second,  the 
increased  frictional  bearing  afforded  by  reflecting  the  plate 
against  the  teeth,  adds  stability  to  the  denture.  By  flowing 
solder  into  the  lingual  angle  of  the  plate  and  reflected  portion 
the  rigidity  can  be  still  further  increased. 

SWAGING  DOUBLED   UPPER   BASES 

To  develop  the  required  degree  of  rigidity,  together  with 
the  closest  possible  adaptation  of  the  denture  to  the  oral  tis- 
sues, and,  by  the  simplest  means,  the  baseplate  should  be 
swaged  from  two  pieces  of  plate  and  united  by  soldering  as 
previously  suggested.     The  steps  are  as  follows: 

Cut  two  pieces  9^  20  carat  gold  plate,  according  to  pat- 
tern, selecting  from  the  gauge  table  two  gauges  of  plate  of 
suitable  thickness,  which  when  comlnned  will  afford  the  neces- 
sary^ strength.    No.  29  and  31  gauge  are  commonly  used. 

Adapt  and  swage  the  thinnest  piece  to  the  die.  Trim  it 
peripherally  to  the  required  outline  of  the  baseplate,  reflect- 
ing it  against  the  lingual  surfaces  of  the  teeth  as  previously 
described.  By  using  care  in  trimming  to  the  exact  outline 
at  this  time,  the  loss,  both  of  material  and  time,  will  be 
avoided.  When  swaged,  trimmed,  annealed  and  finally  re- 
swaged  to  the  die  to  correct  warpage  it  is  laid  aside. 

Now  swage  the  second  or  thicker  piece  of  plate.  The 
adaptation  of  this  piece  of  gold  will  not  be  qiaite  so  sharp  as 
that  of  the  first  piece,  first,  because  the  plate  is  thicker,  and 


CONSTRUCTION  OF  SWAGED  DENTURE  BASES  OF  GOLD       185 

second,  because  some  loss  of  detail  of  the  die  must  naturally 
occur  during  the  swaging  of  the  first  plate. 

When  much  loss  of  detail  occurs  to  the  die,  a  new  one 
should  be  run  up,  but  not  necessarily  a  new  counter  die,  as 
one  or  two  hammer  blows  will  force  the  old  counter  die  sur- 
faces into  all  the  inequalities  of  the  new  die. 

The  two  plates  are  now  swaged  together,  the  first,  or 
thinnest,  being  jilaced  next  the  die,  since  being  sharpest,  and 
showing  the  finest  details,  it  should  lie  next  the  tissues. 

The  peripheral  surplus  of  the  second  base  swaged  is 
usuallj^  allowed  to  extend  beyond  the  margins  of  the  first 
base,  to  afford  a  shoulder  on  which  to  lay  the  solder  while 
uniting  them. 


SHOWING  TWO  METHODS  OF  APPLYING  THE  DOUBLER 

In  some  cases,  however,  it  is  advisable  to  reduce  the  sec- 
ond base  periphery  until  it  lies  entirely  within  that  of  the 
first  base.  This  method  obviates  the  use  of  an  excessive 
amomit  of  gold,  but  is  not  always  so  convenient  in  soldering. 

SOLDERING  THE  DOUBLED   BASE 

After  swaging,  the  bases  are  pickled^- polislied  and  washed 
in  clean  water.  A  film  of  clean  borax  paste  is  spread  on  their 
contact  surfaces  and  three  or  four  small  steel  soldering 
clamps  are  applied  to  hold  them  in  contact.  The  clamped 
bases  are  now  laid  on  the  solder  block,  and  small  pieces  of 
solder  placed  peripherally  on  the  marginal  shelf,  and  in  close 
contact  with  the  edge  of  the  first  plate. 

The  brush  flame  of  the  blowpipe,  properly  applied,  will 
fuse  and  draw  the  solder  between  the  two  plates  until  the 
space  is  perfeetl,v  filled  and  the  two  are  united.  Merely  unit- 
ing the  two  bases  at  the  peripheral  margins  will  not  be  suffi- 
cient nor  will  the  needed  strength  be  developed;  the  solder 
must  be  drawn  through  from  one  margin  to  the  other,  and  the 
base  plates  imited  into  one  solid  mass.  A  good  plan  to  insure 
complete  union  between  the  two  plates  is  to  set  the  clamped 


186       CONSTRUCTION   OF  SWAGED  DENTURE  BASES  OF  GOLD 

piece  on  tlie  block  so  tliat  the  shelf  on  which  the  solder  is 
placed  is  higher  than  the  opposite  margin  on  which  no  solder 
is  laid.  Heating  the  piece  uniformly,  until  the  solder  fuses, 
will  result  in  its  being  drawn  down  until  it  shows  continuously 


VARlUlS    FdFiMS 


along  the  lower  margin  of  the  now  united  base.  A  break  in 
the  line  of  solder  on  either  margin  indicates  that  some  of  the 
area  between  the  plates  is  not  filled. 

The   peripheral    surplus   is   now    removed   with    shears, 
plate  nippers,  files  and  stones,  and  the  plate  reswaged  to  cor- 


PLATE  NIPI'ERb    FOR    t  I  TTING    PI  VTE    AROUND    TEETH 

rect  warpage  due  to  soldering  and  from  cutting.    It  is  again 
pickled,  polished,  washed  and  is  ready  for  trial  in  the  mouth. 


DOUBLING   PARTIAL  LOWER  BASES 

Frequently  a  lower  partial  denture  of  single  thickness 
may  be  rendered  sufficiently  rigid  by  burnishing  or  swaging 


CONSTRUCTION   OF  SWAGED  DENTITRE  BASES  OF  GOLD        187 

and  soldering  to  it  a  piece  of  plate  hut  little  larj^er  than  the 
weak  areas. 

Lower  partial  dentures,  involving  the  replacement  of  tlie 
posterior  teeth  only,  are  frequently  reinforced  anteriorly  by 
a  second  piece  of  plate  overlaying  the  iirst,  the  ends  of  which 
pass  backward  and  terminate  about  %  inch  back  of  the  last 
natural  teeth,  or  so  as  to  extend  well  onto  the  saddle  portion 
of  the  base  and  outward  to  or  beyond  the  crest  of  the  border. 

In  dentures  of  this  type  the  baseplate  should  extend  well 
up  over  the  cingulse  of  all  of  the  anterior  teeth  present,  to  af- 
ford support  to  the  denture  in  tliis  region;  prevent  it  set- 
tling down  when  subjected  to  stress,  and  thus  avoid  injury 
to  the  soft  tissues  underlying  it. 

DEVELOPING    RIGIDITY    BY    USE    OF    WIRE    AND    SOLDER 

When  teeth  are  to  be  attached  to  the  gold  base  plate  by 
means  of  a  plastic  base,  the  wire  which  is  soldered  on  to  form 
a  shoulder  against  which  to  finish  the  vulcanite  can  fre 
quently  be  placed  in  such  position  or  extended  onto  weak 
areas  so  that  when  soldered  the  required  rigidity  is  devel- 
oped without  the  necessity  of  doubling  tlie  entire  baseplate, 
the  wire  and  the  solder  used  for  the  shoulder  thus  fulfilling 
two  purposes. 

One  of  the  most  important  considerations  in  the  plan- 
ning and  construction  of  partial  dentures  is  to  determine  the 
means  of  retention  that  will  render  the  appliance  most  effi- 
cient. At  the  time  of  planning  the  denture  retention  means 
must  be  decided  upon,  as  these,  to  a  certain  extent,  determine 
the  form  of  the  baseplate. 

APPLICATION  OF  FRICTIONAL  APPLIANCES 

When  specialized  frietional  appliances,  as  the  Roach  or 
Grilmore  attachments,  are  to  be  used,  the  crowns  or  inlays  to 
which  the  stationary  parts  of  the  appliances  are  fixed  are 
usually  constructed  before  the  impression  is  secured,  from 
whicli  in  sequence  the  die  will  eventually  be  formed.  In  case 
crowns  are  used  for  the  attachment  of  retention  appliances, 
these  are  set  in  position  on  their  respective  roots,  afterward 
reproduced  in  the  die,  wholly  or  in  part,  and  the  baseplate 
swaged  to  conform  to  them  just  as  to  the  natural  teeth.  The 
application  of  the  attachments  under  consideration  will  be 
given  in  another  section. 


188       CONSTRUCTION   OF  SWAGED  DENTURE  BASES  OF  GOLD 

When  any  of  tlie  ordinary  foi'ins  of  clasps  aro  to  he  em- 
ployed the  order  of  procedure  is  as  follows : 

The  clasps  and  baseplate  having  heen  constructed,  the 
clasps  are  placed  in  position  on  the  teeth  thej^  are  to  embrace. 
The  baseplate  is  introduced,  the  points  of  interference  with 
the  clasps  noted  and  filed  away  until  it  can  be  firmly  and 
evenly  seated  on  the  tissues,  without  displacing  the  clasps  or 
itself  becoming  dislodged  by  them. 

An  impression  in  plaster  is  now  taken  of  the  clasps, 
teeth  and  baseplate;  when  removed  the  clasps  are  returned 
to  position  in  the  im})re,ssion,  wedged  apart,  luted  to  place  and 
a  east  secured,  by  means  of  which  the  clasps  and  baseplate  are 
held  in  correct  relation;  they  are  then  attached  to  the 
baseplate  by  soldering  in  such  manner  as  to  interfere  the 
least  possible  extent  with  the  resiliency  of  the  clasp. 

TAKING  THE  BITE 

In  partial  cases,  when  a  number  of  natural  teeth  are 
present  and  in  normal  occlusion,  a  mash  bite,  sufficiently  bulky 
to  receive  and  hold  firmly  the  bite  stem  of  the  face  bow  in 
front  of  the  anterior  teeth  and  without  interference  with  oc- 
clusion, will  usually  fulfil  all  requirements  for  occluding  the 
teeth,  after  the  casts  have  been  secured  and  mounted  on  the 
occluding  frame  by  means  of  the  face  bow. 

When  any  complications  are  present,  or  when  a  consid- 
erable number  of  teeth  are  being  replaced,  the  best  plan  is  to 
occlude  the  teeth,  attach  them  to  the  baseplate  with  sticky 
wax  and  try  the  model  denture  in  the  mouth.  This  method 
proves  the  occlusion,  the  degree  of  esthetic  success  attained 
as  to  form,  color  and  arrangement  of  the  teeth,  the  position 
for  the  lingual  shoulder  wire  against  which  the  vulcanite  will 
finish,  when  such  means  of  attachment  of  teeth  to  base  is 
employed,  and  enables  the  prosthetist  to  judge  the  value  of 
his  work  at  a  time  when  corrections  can  readily  be  made, 
should  occasion  require. 

ATTACHING  TEETH  TO  BASEPLATE  BY  SOLDERING 

When  but  little  absorption  of  the  process  has  occurred, 
in  spaces  occasioned  by  loss  of  the  natural  teeth,  the  best 
means  of  attaching  the  porcelain  substitutes  to  the  gold  base 
is  usually  by  backing  a  plate  tooth  with  gold,  in  the  usual 
manner,  grinding  it  to  position  on  the  cast,  attaching  it  to  the 
base  with  sticky  wax,  investing  the  case  in  some  good  invest- 


CONSTRUCTION   OF  SWAGED  DKNTURE  BASES  OF  GOLD       189 

iiieiit  iiiaterial,  and  liually  tlowiiig  .solder  ovpr  the  entire  back- 
ing and  against  the  baseplate  at  its  jnnction  with  the  latter. 

Frequently,  in  order  to  render  the  repairing  of  the  case 
simple,  in  case  of  accident,  some  of  the  replaceable  types  of 
crowns  or  facings  in  common  use,  as  the  Steele,  Groslee,  Davis, 
etc.,  can  be  used  to  advantage. 

AVlien  the  bite  is  extremely  close,  so  close,  in  fact,  that 
porcelain  cannot  stand  the  stress  of  mastication  without  frac- 
turing, a  wax  tooth  of  the  dimensions  refjuired  may  lie  formed 
and  cast,  or  a  cusp  may  be  swaged.  IiIKmI  in  solidly  and 
attached  to  the  base  with  solder. 


PLATE  BENDEKS.  VKRY   ISEFUI^   FOR   CON- 
FORMING   A    BASEPLATE    ALONG    THE    BOR- 
DER     IX      PRELIMINARY      SWAGING       (SEE 
PAGE    1-.S) 


CHAPTER    XIII 

ALUMINUM  BASE    DENTURES 

Aluminum  is  used  to  a  considerable  extent,  in  both 
cast  and  swaged  form,  as  a  base  for  dentures.  The  ^ood 
qualities  of  this  metal  may  be  summed  up  as  follows :  It  is 
malleable,  tough,  comparatively  rigid,  good  color,  shows  but 
little  tendency  to  discolor,  odorless,  tasteless,  and  a  good  con- 
ductor of  thermal  changes. 

Some  of  the  objections  and  disadvantages  of  the  metal, 
in  general,  in  its  application  to  denture  construction  are  as 
follows:  It  is  extremely  difficult. to  solder,  and  when  sol- 
dered the  joints,  under  the  influence  of  oral  secretions,  dis- 
color badly ;  in  some  cases  the  solder  itself  is  rapidly  dissolved 
away,  particularly  when  mercury  is  one  of  its  constituents. 

Since  soldering  operations  are  difficult,  the  ordinary 
means  for  forming  finishing  shoulders,  attaching  loop  anchor- 
ages, and,  in  partial  cases,  imiting  one  or  more  isolated  teeth 
to  the  base,  as  carried  out  in  gold  base  denture  construction, 
are  not  practicable.  Other  means,  therefore,  must  be  resorted 
to  for  developing  the  attachment  of  the  vulcanite  to  the  den- 
ture base,  and  while  these  means  are  more  or  less  efficient, 
they  require  more  care  and  involve  greater  effort  than  when 
accomplished  by  soldering. 

Aluminum  is  susceptible  to  the  action  of  dilute  hydro- 
chloric acid,  the  alkalis,  and  salt  solutions  in  general.  Since 
food,  and  consequently  the  oral  secretions  at  times,  contain 
these  substances  more  or  less  diluted,  of  course,  aluminum 
bases  frequently  show  a  decided  tendency  to  disintegration  in 
the  mouth.  These  facts  are  in  accordance  with  observations 
made  by  Figuier  in  his  Year  Book  for  1858.  One  of  the  early 
editions  of  Richardson  quotes  him  as  follows:  "Caustic 
alkalis,  potash  and  soda,  and  even  ammonia,  dissolve  alumi- 
num sensibly."  He  also  states  that  common  salt  and  acetic 
acid  (vinegar),  especially  when  mixed,  attack  and  dissolve 
aluminum.  He  adds  that  the  mixture  of  salt  and  vinegar  for 
seasoning  a  salad,  made  in  a  spoon  of  aluminum,  feebly  but 
inevitably  attacks  it. 

The  same  edition  further  says :  ' '  Calvert  states  that  when 
aluminum  is  immersed  in  water  for  anv  considerable  length 


ALUMINUM    BASE    DENTURES  191 

of  time,  oxidation  takes  place  slowly. ' '  It  is  therefore  plainly 
apparent  why  the  snrfaces  of  dentures  of  this  type,  both  cast 
and  swaged,  become  etclied  and  roughened  with  use,  and  in 
time  so  reduced  in  thickness  as  to  be  useless. 

Pure  aluminum  is  more  resistent  to  the  action  of  the  sol- 
vents mentioned  than  the  more  or  less  impure  commercial 
varieties,  and,  therefore,  in  both  cast  and  swaged  work,  only 
the  purest  jiroducts  obtainable  should  be  employed. 

Aside  from  the  general  disadvantages  just  cited  of  the  use 
of  aluminum  for  denture  bases,  there  are  certain  deleterious 
properties  which  arise  in  casting  the  material  and  whicli  will 
need  special  mention. 

CAST    BASES   OF   ALUMINUM 

The  principal  advantage  of  a  cast  aluminum  hase  lies  in 
the  fact  that  the  vulcanite  anchorage  can  be  more  readily 
developed  on  a  cast  than  on  a  swaged  base.  Loops  and 
spurs  of  wax,  in  addition  to  the  usual  periplieral  rims,  can  be 
arranged  on  the  model,  and  all  reproduced  at  the  time  of  cast- 
ing. Peripheral  rims  are  of  decided  advantage,  as  when  iiro])- 
erly  formed  tliey  will  effectually  prevent  the  thin  margins  of 
vulcanite  from  curling  away  from  the  base,  a  defect  which 
is  specially  noticeable  in  both  cast  and  swaged  aluminum 
bases. 

Another  decided  advantage  of  a  cast  over  a  swaged  base, 
from  an  esthetic  point  of  view,  is  that  in  case  absorption  of 
the  border  has  ]irogressed  irregularly,  the  greater  j^ortion  of 
the  required  restoration  can  be  accomplished  in  metal  instead 
of  vulcanite,  as  is  necessary  with  swaged  bases.  Tlie  distribu- 
tion of  the  vulcanite  can  therefore  be  made  symmetrical  in 
cast  bases,  while  in  swaged  bases  it  can  seldom  be  accom- 
plished, the  finished  case  often  presenting  a  very  unsightly 
and  unbalanced  appearance  after  the  necessary  contour  has 
been  developed. 

Cast  aluminum  base  dentures,  although  promising  much 
from  an  esthetic  standpoint,  usually  fall  very  mueli  short 
of  perfection  from  the  practical  point  of  view.  Two  very 
serious  drawbacks  are  manifest  in  dentures  of  this  type ;  first, 
the  tendency  of  castings  to  warp  in  the  making,  thus  impair- 
ing, if  not  entirely  inhibiting,  successful  adaptation  and  reten- 
tion of  the  denture;  second,  imperfect  density  of  the  casting 
when  produced. 


192  ALUMINUM    BASE    DKNTURES 

WARPAGE    OF    CAST    BASES 

"Warpage  of  a  cast  base  is  due  to  two  causes;  tirst,  the 
inherent  tendency  of  most  metals  to  contract  in  passing 
from  a  fused  to  a  solid  state  is  very  marked  in  aluminum; 
second,  the  heat  necessary  to  volatilize  the  wax  and  prepare 
the  matrix  to  receive  the  molten  metal  causes  contraction  and 
warpage  in  the  investment  itself,  so  that  when  east  the  fused 
metal  is  forced  against  a  distorted  form.  In  addition  to  this, 
warpage  in  the  metal,  due  to  contraction,  also  occurs  to  fur- 
ther complicate  the  difficulty.  Warpage  is  a  most  serious 
fault,  and  because  of  the  resulting  misfits  it  occasions  has 
retarded  the  use  of  the  cast  base  more  than  all  other  causes 
combined.  The  method  for  correcting  warpage  will  be  de- 
tailed later. 

IMPERFECT  DENSITY  OF  CAST  ALUMINUM  BASES 

Imperfect  density  in  a  casting  is  due  to  contraction  of 
the  metal  toward  many  centers  as  it  assumes  a  crystalline,  or 
rather  granular,  form  in  cooling,  each  granule  or  crystal  be- 
coming a  center  toward  which  the  cooling  metal  contracts. 
As  a  result  of  this  contractile  tendency,  many  spaces  neces- 
sarily result  throughout  the  substance  of  the  casting.  Very 
often  they  are  invisible  to  the  eye,  and  in  a  newly  finished 
case,  the  metal  appears  dense  and  homogeneous,  but  with  use 
in  the  mouth  the  porosity  becomes  apparent.  A  low  power 
magnifying  glass  discloses  many  open  spaces  on  the  surface 
of  any  aluminum  casting.  If  broken,  the  spaces  will  be  found 
more  or  less  generally  disseminated  throughout  the  fractured 
sections. 

ACTION    OF    ORAL    FLUIDS    ON    ALUMINUM 

Fluids  of  the  mouth  find  their  way  into  these  pits 
and  open  spaces,  and  in  those  mouths  where  solution  of  the 
metal  does  occur  the  action  is  much  more  rapid  than  when 
the  metal  is  free  from  such  imperfections. 

The  oral  fluids  contain  during  and  for  some  time  after 
each  meal  attenuated  particles  of  food;  these  find  their  way 
into  the  pits,  are  retained,  and  after  a  time  deconi])ose,  often 
giving  rise  to  very  disagreeable  odors.  Bicarbonate  of  soda 
solution  and  sometimes,  in  extreme  cases,  dilute  caustic  soda 
are  used  for  cleansing  and  removing  odors  from  vulcanite  and 
gold  base  dentures.  These  solutions  should  not  be  used  for 
cleansing  aluminum  base  dentures  because  of  their  solvent 
action  on  the  metal.    Dilute  nitric  or  sulphuric  acids,  neither 


ALUMINUM    BASK    DENTUKKS  193 

of  which  liave  any  perce])tibh^  action  on  alnniinum,  may  lie 
used  instead  of  the  alkalis  for  removing  odors.  The  acid 
should  be  neutralized  with  weak  aqua  ammonia  and  the  den- 
ture washed  thoroughly  in  water  to  remove  all  traces  of  the 
latter. 

GRANULAR    STRUCTURE    OF    CAST    ALUMINUM 

As  before  stated,  in  passing  from  a  fused  to  solid  con- 
dition aluminum  assumes  a  granular  form.  The  metal  con- 
tracts toward  the  granular  centers  and  thus  produces  the 
open  spaces  referred  to.  In  addition  to  this  change  there  is 
a  molecular  rearrangement  distinctly  noticeable  by  the  slight 
crackling  sound  on  removal  of  the  case  from  the  flask,  appar- 
ently regardless  of  the  length  of  time  it  remains  in  the  flask. 
This  is  no  doubt  due  to  the  release  of  tension  on  the  already 
contracted  and  warped  base,  by  the  removal  of  the  cast  and 
matrix,  the  presence  of  which,  at  the  time  of  solidifying  of 
the  metal,  partially  restricted  full  contractile  movement. 

For  these  and  various  other  reasons  not  here  detailed  the 
casting  of  dense,  well  fitting  baseplates  of  aluminum  is  prac- 
tically an  impossible  task.  Summarized,  the  advantages  and 
objectionable  features  of  cast  aluminum  bases  may  be  stated 
as  follows : 

Advantages :  Convenience  in  developing  required  vul- 
canite anchorage ;  great  esthetic  possibilities. 

Disadvantages :  Warpage  of  the  base  during  and  after 
casting;  imperfect  density  of  the  casting  when  produced; 
susceptibility  of  cast  bases  to  solution  by  the  oral  fluids. 

There  are  many  methods  of  technic  in  vogue,  also  many 
kinds  of  casting  devices  in  use  at  the  ]iresent  time  for  the 
production  of  cast  bases  of  aluminum.  Lack  of  time  and 
space  as  well  will  preclude  more  than  an  outline  of  the  essen- 
tial steps  common  to  most  systems  of  casting.  Two  general 
methods  will  be  described,  known  as  the  indirect  and  direct 
methods.  Dr.  Hart  J.  Goslee  has  recently  described  in  detail 
an  indirect  system  of  casting  he  has  formulated,  and  which 
promises  to  correct  some  of  the  disadvantages  of  the  cast 
base  (Dental  Eeview,  August,  1914).  The  following  is  a 
brief  outline  of  the  indirect  methods  referred  to. 

CASTING    BASES    BY    THE    INDIRECT    METHOD 

The  advantages  of  the  indirect  over  the  direct  method  of 
casting  depends  upon  the  preservation  of  the  original  cast 
(model)  of  the  mouth  until  after  the  base  has  been  produced. 


194  AX,UMINUM    BASE    DKNTURES 

and  of  the  correction  by  swaging  of  this  usually  warped 
base  on  the  original  cast  of  the  mouth.  The  technic  of 
the  system  is  as  follows : 

TECHNIC   OF   FORMING  THE   WAX    MODEL 

An  accurate  impression  of  the  arch  is  secured  in  the  im- 
pression material  most  strongly  indicated. 

This  impression  is  filled  with  either  a  hard  cast  jolaster, 
or,  better  still,  a  mixture  of  oxy-chloride  of  magnesia,  be- 
cause of  its  much  greater  hardness. 

The  cast,  of  whatever  material  composed,  should  have  a 
fiat  base,  and  be  of  good  depth,  to  prevent  fracture  under  the 
stress  of  subsequent  swaging. 

To  this  cast  of  the  mouth  a  sheet  of  pink  wax  slightly 
thicker  than  the  base  is  to  be,  is  conformed,  and  trimmed  to 
correct  outline  of  the  baseplate. 

Small  rolls  of  wax,  about  one-eighth  of  an  inch  in  diame- 
ter, are  adjusted  peripherally,  and  burnished  smoothly  to  the 
required  form  to  afford  finishing  shoulders  for  the  vulcanite. 

Anchorage  loops  for  the  vulcanite  are  attached  at  several 
points,  in  such  manner  as  not  to  interfere  with  the  correct 
arrangement  of  the  teeth. 

Three  rolls  of  wax,  also  an  eighth  of  an  inch  in  diameter 
or  slightly  larger,  are  attached,  one  to  the  most  distal  point 
of  each  tuberosity  and  the  other  to  the  extreme  median, 
labial,  surface  of  the  baseplate.  These  are  brought  into  a 
common  jjoint  opposite  the  center  of  the  palate  and  there 
united  with  a  slightly  larger  roll  standing  at  right  angles, 
which  serves  as  a  sprue  former.  This  arrangement  of  the 
wax  rolls  which  form  the  smaller  sprues  is  applicable  to  cases 
when  invested  in  the  open  end  ring  flask.  This  type  of 
flask  is  usually  shallow.  In  such  ease  the  three  sprue  formers 
should  be  placed  nearly  horizontal  and  as  close  to  the  base- 
plates as  possible,  to  conserve  perpendicular  space  and  make 
room  for  ample  depth  to  the  crucible  in  the  toj)  of  the  flask. 

When  the  deep  box  flask  is  used,  the  rolls  of  wax  are  at- 
tached to  the  baseplate  in  the  same  location  as  above  de- 
scribed, but  are  all  brought  back  of  the  distal  margin  of  the 
cast  and  there  united  to  a  slightly  larger  sprue  former,  or 
they  may  be  attached  separately  but  close  to  each  other  to  the 
crucible  former.  The  flasked  case  in  this  instance  will  then 
present  three  separate  openings  leading  from  the  base  of 
the  crucible  to  the  matrix,  while  in  the  former  instance  there 


ALUMINUM  HASK  UKNTUKKS  19r. 

is  ouly  one  exit,  the  divergeuce  of  tlie  small  sprues  occurring 
in  the  investment. 

In  both  cases,  regardless  of  whether  the  molten  metal 
leaves  the  crucible  by  one  or  three  exits,  it  enters  the  matrix 
at  three  widely  divergent  points.  The  three  streams  of  metal 
which  issue  from  the  several  entrances  must  spread  out,  till 
the  entire  matrix,  meet,  and  coalesce  without  forming  seams. 
The  pressiire  exerted  on  the  molten  metal  must  be  sufficient  to 
force  the  contained  air  within  the  matrix  into  the  invest- 


WAX  FORMETl  FOR  MAIilNG   SPRDE  RODS 


ment,  or  out  through  sprue  vents,  otherwise  it  will  be  caught 
and  confined  somewhere  between  the  margins  of  the  inflowing 
portions  and  result  in  holes. 

Still  another  method  of  attaching  the  wax  sprue  formers, 
applicable  when. the  case  is  to  be  cast  by  centrifugal  force,  is 
as  follows:  A  roll  of  wax  three-sixteenths  of  an  inch  in 
diameter  is  attached  to  the  extreme  labial  surface  of  the  base- 
plate and  extends  up  to  the  crucible  to  form  the  feed  sprue. 

Two  smaller  vent  sprue  formers  extend  from  the  highest 
point  of  each  tuberosity  to  the  outer  margin  of  the  crucible, 


i:i(i  ALUMINUM     BASK     ]  )IO.\TI'KKS 

al)()\'(^  tlic  l('\('l  of  tile  iMiiilaiiicil  nict.'il  w  licii  I'liscd.  In  rasting, 
the  metal  eiitcsrs  llic  iiiatiix  IVdin  tlif  crucible  at  the  lowest 
point,  and  on  the  priiici]ilc  that  a  liiinid  will  seek  its  level  it 
rises  njjward  in  the  matrix,  the  air  escaping  through  the  vent 
sprues.  Since  the  exits  of  these  sprues  are  higher  than  the 
level  of  the  metal  in  the  crucible  the  latter  will  rise  nearly 
to  the  top  of  the  ojienings  of  the  vent  sprues,  but  cannot 
escape. 

INVESTMENT  OF  THE  WAX   MODEL 

Tlie  baseplate  having  been  given  its  required  form,  and 
the  anchorage  lugs  attached,  it  is  ready  for  flasking. 

A  fine  grained,  slight  porous  investment  material, 
which  is  hard  when  set,  should  be  selected  for  flasking  the 
wax  model.  A  small  amount  of  this  is  mixed  moderately 
thin,  and  with  a  brush  is  spread  carefully  and  evenly  over 
the  entire  surface  of  the  baseplate  to  eliminate  all  air  bubbles. 
With  a  spatula  more  is  now  added,  care  being  taken  to  work  it 
under  and  aroimd  the  sprue  formers  so  as  to  entirely  enclose 
them ;  the  labial  and  buccal  surfaces  should  also  be  fully  cov- 
ered with  a  layer  sufficiently  thick  to  withstand  handling  when 
the  cast  is  removed.  Altogether  the  investment  should  cover 
the  baseplate  from  one-fourth  to  three-eighths  of  an  inch 
thick. 

When  hardened,  the  half  invested  wax  l)aseplate  is  care- 
fully removed  from  the  cast  of  the  mouth  on  which  it  has  been 
formed,  another  mix  of  investment  made,  and  with  a  brush 
the  entire  interior  of  the  baseplate  is  covered  with  it,  care 
being  taken  here  as  before  to  eliminate  all  air  bubbles.  More 
investment  is  added  to  this,  to  take  the  place  of  the  original 
cast,  extending  it  labially,  distally,  and  buccally,  to  overlap 
and  unite  firmly  with  that  on  the  reverse  side. 

The  wax  model  and  most  of  the  sprue  formers  are  now 
encased  in  a  comparatively  rigid  shell  of  hardened  invest- 
ment, which  should  be  trimmed  so  as  to  enter  the  flask  with- 
out encroaching  on  the  sides  at  any  point.  Completion  of  the 
investment  in  a  ring  flask  is  carried  out  as  follows : 

Sufficient  investment  material  to  surround  the  ease  and 
till  the  ring  is  mixed  somewhat  thicker  than  that  used  in  first 
covering  the  wax  model.  This  is  filled  in  the  ring,  the  hard- 
ened core  containing  the  wax  model  is  soaked  in  water  for 
a  moment  to  exclude  the  air  and  insure  perfect  union  between 
it  and  the  freshly  mixed  mass,  and  is  then  pressed  well  down 
to  the  bottom  of  the  ring  to  give  ample  space  for  the  crucible 


ALUMINUM    BASK    DENTURES  197 

ill  the  Upper  end.  A  slight  vihiatorv  iiioveiiient  of  tiie  spatiihi 
in  tlie  plastic  mass  will  cause  it  to  settle  around  and  over 
the  core  and  permit  the  air  to  escape. 

The  investment  is  smoothed  up  level  with  the  top  of  the 
flask  and  around  the  wax  sprue  former  which  should  occupy 
a  central  ]iosition  in  the  upper  surface  and  extend  above  the 
upper  margin  of  the  flask. 

When  hardened,  the  investment  is  trimmed  out  to  form 
a  crucible  for  containing  the  metal  while  fusing  and  prepara- 
tory to  casting.  This  should  be  deep  and  wide  enough  to  hold 
considerably  more  metal  than  the  matrix  will  contain.  In 
some  forms  of  flasks  the  wax  sjDrue  formers  before  the  case  is 
invested  are  united  with  a  crucible  former,  which,  by  means 
of  guides,  is  carried  to  correct  position  in  the  flask  and  the 
investment  is  molded  arormd  it,  thus  obviating  the  necessity 
of  cutting  the  crucible. 

PREPARING   THE   CASE   FOR   CASTING   THE   METAL 

The  flask  should  lie  placed  above  a  low  flame  and  gradu- 
all.y  heated  to  dissipate  the  wax.  The  heat  may  be  increased 
from  time  to  time  to  aecellerate  the  volatilizing  of  the  wax, 
but  at  no  time  should  it  exceed  370  degrees  F.,  as  that  is  the 
temi^erature  at  which  iilaster  is  readily  and  quickly  disinte- 
grated. By  heating  the  case  for  a  long  time  at  low  tempera- 
ture the  wax  can  be  removed,  the  matrix  cleared  of  residue, 
and  the  integrity  of  the  investment  maintained  far  better 
than  with  the  I'apid  application  of  intense  heat. 

As  in  inlay  work,  smoother  castings  will  result  if,  after 
clearing  the  matrix,  the  invested  case  is  allowed  to  cool  some- 
what before  introducing  the  molten  metal.  The  temperature 
should  not  be  allowed  to  drop  too  low  or  the  metal,  wliich  even 
when  well  fused  is  slightly  sluggish,  will  lose  some  of  its 
heat  by  radiation  and  contact  with  cooler  media,  become 
chilled,  and  clog  in  the  matrix,  or  in  some  cases  in  the  sprues 
and  result  in  an  imperfect  casting. 

CASTING  THE  FUSED   METAL 

Aluminum  may  be  cast  by  vai'ious  means,  compressed 
gas  or  air,  by  ]%artial  vacuum,  by  a  combination  of  the  two 
means  just  mentioned,  by  steam,  centrifugal  force,  and  liy 
actual  mechanical  pressure. 

In  any  case  and  by  whatever  means  the  casting  is  accom- 
plished, the  object  in  utilizing  one  or  more  of  the  forces  men- 


I'.'S  ALUMINUM     IIASK     I  IION'l'l  I  ItKS. 

tioned  is  ti)  lid  the  niiilri\  nl'  I  he  coiitaiiiud  air,  eilluu-  at  the 
instant  of  easting,  as  in  tlic  case  ol'  the  vacnnm  appliance, 
or  force  the  molten  metal  into  the  matrix  with  sufficient  pres- 
sure to  drive  the  air  into  tlic  jiorous  investment  or  through 
vent  sprues,  and  fill  the  entire  space  with  fused  metal  under 
compression. 

Although  more  difficult  to  cast  shar^jly  than  some  of  its 
alloys,  pure  aluminum  should  he  used  hecause  of  its  greater 
resistance  to  chemical  action. 

A  thin,  slightly  tough  film  of  oxide  quickly  forms  on  the 
surface  of  molten  aluminum,  which  limits  further  oxidation. 
Because  of  the  lightness  of  the  metal  and  the  slight  tenacious- 
ness  of  the  surrounding  film  of  oxide  the  molten  metal  does 
not  fall  into  or  fill  even  a  large  sprue,  as  would  be  the  case 
with  any  of  the  metals  of  greater  specific  gravity,  but  requires 
vibration  or  some  applied  force  to  drive  it  into  the  matrix. 

When  first  fused,  aluminum,  although  plastic,  is  sluggish, 
and  if  cast  in  this  condition  will  not  copy  fine  lines  sharply. 
The  blowpipe  flame  should,  therefore,  be  continued  on  the  mol- 
ten mass  a  sufficient  time  to  bring  it  to  a  thinly  liquid  condi- 
tion, yet  without  overfusing,  before  forcing  it  into  the  matrix. 

A  new,  clean  ingot  (not  scraps  nor  previously  used  pieces) 
containing  nearly  twice  as  much  metal  as  the  case  requires  is 
placed  in  the  crucible  and  the  blowpipe  flame  applied.  The 
flame  should  be  large  and  the  heat  forced  as  rapidly  as  pos- 
sible, to  melt  the  metal  before  any  great  degree  of  heat  is 
transmitted  to  the  matrix,  and  thereby  cause  unnecessary 
dimensional  changes  in  its  walls. 

When  brought  to  a  thoroughly  liquid  condition,  the  film  of 
oxide  is  cleared  away,  the  casting  force,  of  whatever  character 
employed,  is  applied  and  the  metal  is  driven  into  the  matrix. 

Since  metals  having  much  greater  specific  gravity  than 
aluminum  require  pressure  of  7  poimds  or  more  to  cast 
densely,  it  naturally  follows  that  to  produce  sharp,  well  defined 
and  dense  castings  of  this  much  lighter  metal  more  force 
should  be  applied  in  injecting  it  into  the  matrix.  From  8  to  12 
pounds  direct  pressure,  or  14.7  pounds,  full  vacuum  pressure, 
which,  however,  even  though  the  gauge  records  it  is  never 
realized,  is  none  too  much.  Pressure  should  be  maintained 
until  the  metal  congeals,  the  idea  being  to  condense  upon 
themselves  the  granules  or  crystals  as  long  as  the  harden- 
ing nu^ss  will  yielcl  under  the  applied  pressure. 

When  cast,  the  case  should  be  allowed  to  cool  down  gradu- 


ALUMINUM    BASE    DENTURES  199 

ally;  suddeu  cliilling  will  induce  more  warpage  and  greater 
molecular  change  in  the  casting  than  will  occur  when  the  tem- 
perature is  gradually  lowered. 

FINISHING  AND  SWAGING 

On  removal  of  the  casting  from  the  flask  the  waste  gates 
are  removed  witli  a  saw,  the  surfaces  and  margins  smoothed 


up  with  files,  stones,  and  fine  emery  cloth  on  the  lathe  mandrel. 
All  nodules  and  irregular  areas  are  removed  from  the  palatine 
and  border  surfaces.  The  baseplate  should,  in  fact,  be  prac- 
tically finished,  except  the  freshening  of  the  margins  of  the 
viilcanite  shoulder,  which  on  account  of  danger  of  marring 
should  be  deferred  until  after  the  final  swaging. 


PARTIALLY  FINISHED  CASTING,   NOT  Sl'URKED 

The  baseplate  is  now  set  on  the  original  cast  of  the  mouth, 
placed  in  the  swaging  device,  and  subjected  to  screw  or 
hydraulic  pressure  sufficiently  heavy  to  adapt  it  to  all  parts  of 
the  cast  face.  The  final  finishing  is  now  given  the  shoulder 
against  wliich  the  vulcanite  is  to  nliut,  witli  square  edge  stones. 


200  ALUMINUM     HASK    UKNTUKKS 

Any  other  areas  that  may  need  attention  are  smoothed,  and 
the  baseplate  is  ready  for  the  application  of  the  wax  rims. 
The  constrnctive  steps  from  this  i^oint  on  are  the  same  as  in 
vulcanite  work. 

ATTACHING  THE  TEETH  TO  BASE  WITH  VULCANITE 

In  addition  to  the  anchorage  loops  nsually  provided  in  the 
waxing  of  the  case  before  flasking,  a  graver  is  used  to  raise 
heavy  spurs  in  various  directions  around  and  under  which  the 
vulcanite  will  be  molded.  A  film  of  chloro-rubber  ]iainted  on 
the  surfaces  to  be  covered  by  the  vulcanite  acts  as  a  cement- 
ing medium  and  increases  the  efficiency  and  permanency  of 
the  joint  between  the  latter  and  the  metal  base. 

DIRECT    METHOD    OF    PRODUCING   A    CAST    BASE    OF 
ALUMINUM 

The  direct  method  of  producing  a  cast  base  of  aluminum 
is  identical  to  that  followed  in  indirect  casting,  up  to  the  point 
of  removal  of  the  wax  model  from  the  cast,  previous  to  invest- 
ing the  case.  In  this  method,  the  wax  model  baseplate  remains 
with  the  cast,  the  two  are  invested  together,  the  cast  becomes 
a  ]»art  of  the  matrix,  and  is  destroyed  in  the  production  of  the 
easting.  To  correct  a  misfit  due  to  warpage  by  this  method  a 
new  impression  and  another  cast  must  be  produced,  on  which 
the  wai'ped  casting  can  be  readapted  by  swaging  or  the  entire 
case  must  be  reconstructed,  beginning  with  the  impression. 

Since  the  average  cast  baseplate,  made  by  the  direct 
method,  lacks  that  positive  adhesion  to  the  tissues  so  desir- 
able, and,  in  fact,  essential  to  usefulness  and  comfort,  and 
since  a  casting  of  this  type  can  be  readily  corrected  by  swaging 
on  an  accurate  cast  of  the  mouth,  it  is  obvious  that  the  so- 
called  indirect  method  is  literally  the  most  direct,  because  one 
impression  and  one  oast  of  the  mouth  fulfills  all  requirements 
while  the  direct  method  usually  requires  two,  since  to  secure 
the  desired  adaptation  it  must  be  reswaged. 

Until  the  dimensional  changes  in  both  investment  mate- 
rials and  aluminum  due  to  thermal  variations  can  be  over- 
come to  a  greater  extent  than  is  possible  by  present  methods, 
the  adaptation  and  general  usefulness  of  cast  aluminum  bases 
can  be  greatly  inqircncd  liy  swaging. 

CENTRIFUGAL  CASTING  OF  ALUMINUM 

Another  mctliod  of  casting  aluminum  bases  with  centri- 
fugal force  l).\  tlic  Dr.  "W.  W.  Wood's  ai)|)liances  will  now  be 


ALUMINUM     r.ASh:     lHON'I'rUKS  201 

brieliy  describt'd.  These  appliances  consist  ol'  a  sjiecial  llask, 
au  adjustable  cover,  a  crncibie  roinier,  a  base  Wn  attacliiiig  tlie 
wax  model  to  the  sin'ue  I'oi-nier,  a  hi,i;li  ,i;'ear<Ml  cenli'ifnual 
machine  for  forcing  the  molten  metal  into  the  matrix,  dou 
ble-burner  stove  for  heatin.u'  the  invested  case  and  for  mell- 
uvj;  the  alnminmn,  a  small  ifon  crncibie  I'or  holdinn  llie  metal 
while  heating,  and  from  whicli  it  is  ponred  into  the  crncibie 
of  the  flask,  and,  tinally,  two  sheet-iron  hoods  for  <'onfining 
the  heat  aronnd  both  tiask  and  crncibie  in  the  preliminary 
steins. 

TECHNIC 

The  crucible  former  has  thi-ee  openings  in  its  apex,  and 
in  these,  three  rods  of  wax  al)ont  one  inch  long  are  luted. 


CHIICIBLE  FORMER    ANn    WAX    MODEL   READY    FOR   ATTACHMENT 

The  crucible  former  is  adjusted  to  the  cast-iron  base.  The 
wax  rods  bent  to  unite  with  the  baseplate  at  each  tuberosity 
and  in  the  central  vault  portion. 

The  cast  should  not  extend  beyond  the  round  end  of  the 
base,  otherwise,  in  forcing  the  crucible  to  place  the  wax 
sprues  are  liable  to  be  disconnected. 


MIXING  AND  APPLYING  THE   INVESTMENT  TO  THE  WAX 
MODEL   BASE   AND   CAST 

A  mix  of  some  good  quality  of  investment  is  applied  to 
the  wax  base  with  a  brush,  jiainting  it  against  all  surfaces 
so  as  to  eliminate  the  air.    A  mix  of  coarser  investment  can 


ALUMINUM     BAS1<;    DKNTURKS 


ATTACHING    WAX  MODEL   TO   CRDCIBLE   FORMER 


WAX   MODEI,  ATTACHED  BEADY   FOB   imTISTMENT 


ALUMINUM    BASE    DENTUHKS  203 

be  made  and  extended  not  only  over  the  wax,  but  carried 
up  around  the  exposed  sides  of  the  crucible  former  in  a  layer 
sufficiently  thick,  when  hardened,  to  rigidly  unite  the  cast, 
wax  base  and  crucible  former. 

When  hardened,  the  attached  cast  and  crucible  former 
are  removed  from  the  cast-iron  base  and  investment  applied 
to  the  opposite  side  in  a  similar  manner  as  described. 

INVESTING   THE    CASE    IN    THE    FLASK 

The  tiask  is  now  tilled  about  two-thirds  full  of  coarse 
iii\('stiiu'nt  mixed  modoratclv  tliin. 


'••t*-^ 


INTEODUCING   THE  PARTIALLY    INVESTED   WAX   MODEL   IN   FLASK 

The  invested  wax  model  and  crucible  former  are  dipped 
in  water  and  introduced  in  the  partially-filled  flask,  with  a 
churning  motion  to  eliminate  air  and  cause  the  investment 
to  settle  closely  around  that  already  hardened.  The  cnicible 
former  should  rest  upon  the  margins  of  the  flask. 

When  set.  the  flask  is  inverted  over  the  flame  to  slightly 
warm  the  wax  sprues  and  crucible  former  when  the  latter, 
by  tapping  slightly,  will  readily  come  away.     By  oiling  the 


ALUMINUM  BASK  DKNTUUES 


crucible  former  befor( 
easily  from  the  flask. 


apjilyiui;-  tlic 


'stiiieiit  it  will  part 


DRYING  OUT  THE  CASE 

The  flask  is  ])laced  on  its  side  over  a  low  flame  until  wax 
has  melted  and  partially  flowed  out  through  the  sprues. 

It  is  now  inverted  over  the  flame,  the  size  of  which  is  in- 
creased, the  sheet-iron  hood  adjusted,  heat  maintained  until 
investment  is  thoroughly  dry. 

While  the  invested  case  is  drying  out,  which  rcMjuires 
usiuilly  about  an  hour,  the  aluiniiiuiii  should  1)e  ]>lac('(l  in  the 


IIKATINC;    THE 


,\SE    AM)    ALUMINUM 


iron   crucible,    set   over    the    smaller    burner    and   the    hood 
adjusted. 

Since  aluminum  rec(uires  a  higher  temperature  to  fuse 
than  that  developed  by  the  burner,  the  blow  pipe  flame  should 
be  applied,  and  the  metal  brough  to  a  well-fused  liquid  con- 
dition. 

CASTING 

When  the  nu)isture  has  been  driven  from  the  investment, 
and  the  latter  has  attained  ]iractically  a  low,  red  heat 
(900°  F.),  the  flask  is  adjusted  to  the  arm  of  the  casting  ma- 
chine, the  cover  set  in  position  and  firmly  clamped. 


ALUMINUM  BASE  DENTURES 


Ari'l.VlNU    THE    COVER 


2&6 


ALUMINUM    BASK    UENTURKS 


POURING   THE  MOLTEN   ALCMINXTW 


ALUMINUM    BASE    DENTURES  207 

The  melted  metal  is  now  quickly  poured  into  the  cru- 
cible, through  the  small  opening  in  the  cover,  and  the  ma- 
chine set  in  motion  as  rapidly  as  possible. 

To  thoroughly  condense  the  metal  the  centrifugal  force 
should  be  continued  for  at  least  three  minutes  or  until  the 
aluminum  has  solidified. 


APPE.AJIA-NIE     OF     AN     UPPER    A>T1    LOWER    BASE    AS    THEY    COM^    FROII    FLASK 

The  methods  here  outlined  vary  somewhat  from  those 
previously  described,  principally  in  the  manner  and  amount 
of  heat  applied.  The  results,  however,  in  both  density  of  cast- 
ings   and    low    shrinkage    produced,    justify    the    writer    in 


DR.    WOOD'S   METHOD  OF   PP.EPARING    THE    ^TJLCANITE    ATTACHSfENT 

strongly  recommending  the  centrifugal  method  and  processes 
similar  to  those  just  described. 


IMPORTANT  PROPERTIES   OF  ALUMINUM   IN 
REFERENCE   CASTING 

Schnabel  gives  the  following  data  in  reference  to  alumi- 
num. These  facts  are  more  appropriately  placed  here  than 
in  the  section  on  metallurgy. 


208  ALUMINUM     BASK    DENTUUKS 

"The  I'ractuic  of  cast  nluiniiiuiii  shows  a  coarse  fiber 
and  irregular  grain,  while  it  is  sinewy  or  tine  grained,  and 
shows  a  high  silky  iiistic  alter  being  liannnered  and  rolled." 

According  to  l)e\ille,  alnininuni  crystallizes  in  regular 
octaliedra,  if  cooled  slowly.  According  to  Rose,  the  crystals 
/do  not  belong  to  the  regular  system. 

The  specific  gravity  of  aluminum  at  22°  C.  is  2.64  for 
cast,  and  2.70  for  drawn  metal.    Its  specific  beat  is  0.202. 

It  melts  at  red  heat,  between  600  and  700  C.  At  a  higher 
temperature  it  volatilizes,  but  the  exact  boiling  point  has  not 
yet  been  determined. 

As  its  specific  heat  is  high,  it  needs  much  heat  and  some 
time  to  fuse;  and  as  its  latent  heat  is  also  great,  it  takes  a 
long  time  to  cool  and  solidify. 

According  to  Deville,  when  it  is  cast  into  small  bars  it  is 
several  hours  before  these  can  be  held  in  the  hand. 

There  is  a  diminution  of  volume  during  solidifying,  the 
shrinkage  being  1.8  per  cent  of  the  original  volume." 

SWAGED  BASES   OF   ALUMINUM 

Because  of  the  difficulty  in  the  past,  and  even  at  the 
present  time,  attending  the  jiroduction  of  successful  cast 
base  aluminum  dentures,  yet  recognizing  the  need  of  a  metal- 
lic base  less  expensive  than  gold,  many  prosthetists  have 
turned  to  the  swaged  aluminum  liase,  hoping  to  find  in  that 
the  much  desired  substitute. 

Swaged  aluminum  bases  have  been  employed  for  years, 
with  varying  degrees  of  success,  or  what  is  more  literally 
true,  of  disapointment,  for  in  the  larger  percentage  of  cases 
they  have  not  fulfilled  the  hopes  of  the  prosthetist  nor  the 
practical  needs  of  the  patient. 

The  principal  and  valid  objections  to  swaged  bases  of 
aluminum,  as  ordinarily'  constructed,  are  as  follows : 

First,  general  deterioration  of  the  metal  in  the  mouth. 
The  solvent  action  of  the  oral  fluids  and  foodstuffs  on  alumi- 
num is  manifested  in  several  ways,  first,  by  destroying  the 
polish  of  the  base,  followed  by  deeper  etching  of  the  exposed 
surfaces;  this  in  turn  results  in  gradual  thinning  and  eventual 
weakening  of  the  base  jjlate,  distortion  under  stress,  forma- 
tion of  holes,  and  finally  loss  of  adhesion. 

Second,  difficulty  in  securing  effective  and  permanent 
anchorage  between  the  metal  and  vulcanite,  and  of  prevent- 
ing the  lingual  margins  of  vulcanite  from  curling  away  from 


ALUMINUM     BASK    DENTURES  20<l 

the  baseplate,  a  fault  wliicli  often  occurs  c\cn  tliouuli  the  gen- 
eral anchorage  may  he  satisfactory. 

COMPARATIVE    DURABILITY    OF    CAST    AND    SWAGED    BASES 
OF   ALUMINUM 

T]ie  statement  is  frequently  n:ade  that  the  east  is  more 
generally  satisfactory  and  permanent  than  the  swaged  alumi- 
num base.  This  is  undoubtedly  true  of  the  average  swaged 
base  as  made  today,  but  is  not  iu  accordance  with  fact  with 
reference  to  bases  of  heavy  gauge,  constructed  by  the  more 
improved  methods  of  teclmic. 

Let  us,  for  a  moment,  consider  the  difference  in  tiiick- 
ness,  and  bulk  of  metal  in  general,  between  the  aierage  cast, 
and  the  average  swaged  base. 

The  wax  whicli  forms  the  model  l)aseplate  determines 
the  thickness  of  the  cast  base,  since  the  investment  matrix 
is  formed  against  and  around  it.  Those  familiar  with  the 
casting  of  aluminum  know  that  it  cannot  with  certainty  and 
at  all  times  be  east  into  constricted  spaces.  Therefore,  to 
be  certain  of  producing  a  reasonably  perfect  casting,  and, 
further,  to  insure  its  having  the  required  inherent  strength, 
the  wax  of  which  the  model  baseplate  is  formed  must  be  of 
sufficient  thickness  to  meet  the  above  requirements  in  the 
formation  of  the  matrix. 

Usually  the  base  of  the  wax  model  is  formed  by  applying 
a  sheet  of  pink  baseplate  wax  over  the  face  of  the  cast.  This 
is  further  strengthened  by  the  addition  of  the  wax  rolls  which 
form  tlie  vulcanite  finishing  shoulders.  In  nearly  every  case 
a  slight  additional  film  of  wax  will  be  added  to  the  palatine 
area,  the  prostlietist  feeling  that  such  an  addition  will  make 
certain  a  perfect  casting,  while  if  too  thick,  the  baseplate  can 
be  reduced  without  injury. 

Now  the  thickness  of  the  av^erage  pink  baseplate  wax  i 
16  gauge,  or  0.050  of  an  inch  thick.  The  completed  wax  model, 
and  consequently  the  casting,  on  account  of  the  addition  of 
wax  noted,  usually  measures  14  or  13  gauge,  or  0.064  or 
0.072  thousandths.  It  is  true,  some  of  this  thickness  may  be 
lost  in  the  final  finishing  of  the  denture,  but  in  the  many  prac- 
tical cases  observed  and  gauged  by  the  writer  of  work  done 
by  the  best  prosthetists,  all  exceeded  17  gauge  or  0.045  of  an 
inch  in  thickness,  while  a  number  ranged  between  15  and  14 
gauge. 

Most  of  the  swaged  base  dentures  at  the  present  time 
are  constructed  of  26  gauge,  0.016.    It  will  be  observed  that 


210  ALUMINUM    BASE    DENTURES 

'26  gauge  is  aiiproxiuiatcly  only  oiic-tliird  the  thickness  oi'  17 
gauge,  therefore  the  cast  base,  being  three  times  thicker  than 
the  plate  ordinarily  used  in  swaged  work,  besides  being  thick- 
ened and  thereby  gi'eatly  strengthened  by  the  peripheral  rims, 
should  outlast  the  swaged  base  a  proportionate  length  of 
time  under  conditions  most  favorable  to  the  swaged  base, 
while  under  adverse  conditions  to  be  mentioned  later  the  time 
efficiency  of  the  latter  becomes  greatly  reduced. 

The  first  well-written  description  within  the  writer's 
knowledge  of  the  swaged  aluminum  base  appeared  in  the 
American  System  of  Dentistry,  1888.  In  that  article,  20 
gauge  plate  was  recommended  as  being  most  suitable  and 
practical  and,  unfortimately,  many  still  adhere  to  the  use  of 
that  and  even  lighter  gauges. 

The  anchorage  for  the  vulcanite  was  obtained  by 
raising  opposite  spurs  on  the  labial,  buccal  and  lin- 
gual border  surfaces.  Practically,  this  method  of  anchor- 
age proved  insufficient.  Later  someone  suggested  drill- 
ing a  number  of  holes,  one  sixteenth  of  an  inch  or 
larger,,  through  the  baseplate,  at  vaiious  points  along 
the  border  surfaces,  countersinking  the  border  or  palatine 
ends  of  the  holes,  filling  the  holes  with  wax  in  flasking  to  ex- 
clude the  plaster  so  that  the  vulcanite  would  fill  both  holes 
and  countersunk  portions  and  l)ecome  riveted,  as  it  were,  at 
several  points,  to  the  baseplate.  Another  method  of  anchor- 
age consists  in  developing  loops  in  the  Ijorder  surface  of  the 
base  itself  by  means  of  a  special  plier-like  device.  In  a  gen- 
eral way  these  methods  solved  the  question  of  anchorage  and 
obviated  the  frequent  mishap  of  the  body  of  vulcanite  in  which 
the  teeth  were  mounted  from  being  dislodged  from  the  base- 
plate. 

In  this  system  of  technic  as  first  outlined,  no  provision 
was  made  for  a  finishing  shoulder  for  the  vulcanite,  conse- 
quently it  was  found  that  after  being  in  use  a  short  time 
the  thin,  sharp  margins  of  vulcanite  where  they  joined  the 
base,  particularly  on  the  lingual  side,  would  curl  up,  break 
off  or  draw  away  from  the  metal,  leaving  an  unsightly  joint, 
annoying  to  the  tongue,  into  which  food  would  find  its  way. 
To  overcome  this  very  objectionable  feature,  a  groove  in  the 
baseplate  was  cut  at  the  line  of  termination  of  the  vulcanite 
with  the  base,  in  order  to  thicken  and  strengthen  the  margin 
of  the  vulcanite. 

This  method  of  forming  tlie  finishing  shoulder  on  26 
gauge  and  even  somewhat  thicker  bases  is  not  successful,  be- 


ALUMINUM    BASE    DENTURES  211 

cause  if  the  groove  is  cut  deeply  enough  to  give  the  needed 
strength  to  the  vulcanite,  the  baseplate  is  so  weakened  that 
fracture  often  occurs  under  stress  in  a  short  time. 

When  26  or  even  heavier  gauges  of  aluminum  are  swaged 
in  the  ordinary  manner,  the  plate  being  first  adapted  to  the 
die  with  the  horn  mallet,  the  injudicious  application  of  mallet 
force,  particularly  on  high  points  and  in  deep  depressions, 
as  the  central  portion  of  a  high  vault,  will  result  in  thinning 
the  base  over  such  areas.  These  same  high  points  and  de- 
pressed areas  are  subject  to  special  stress  in  waging  between 
the  die  and  counter  die.  They  are  very  liable  to,  and  usually 
do,  become  contaminated  with  die  and  counter  die  metal.  Un- 
less the  base  metal  is  removed  by  thoroughly  polishing  before 
annealing,  an  alloy  is  formed  which  apparently  is  more  readily 
acted  upon  by  the  oral  fluids  than  is  the  iincontaminated 
plate.  The  result  of  such  action  is  seen  in  the  formation  of 
holes  in  the  affected  areas.  The  thinning  of  the  plate  from 
careless  malleting  undoubtedly  aids  in  the  early  formation 
of  these  openings,  probably  through  the  disturbance  of  nor- 
mal molecular  cohesion,  thus  reducing  the  resistance  of  the 
aluminum  to  chemical  action. 

SUMMARY  OF  THE  CAUSES  OF  DETERIORATION  OF  SWAGED 
BASES  OF  ALUMINUM 

Briefly  summed  up,  the  real  causes  of  the  rapid  deteriora- 
tion and  general  failure  of  the  26-gauge  swaged  aluminum 
base  appears  to  be  due  to  the  following: 

First,  contamination  of  the  aluminum  by  the  die  and 
counter  die  metal,  with  possible  formation  of  an  alloy,  easily 
disintegrated  chemically. 

Second,  excessive  thinning  by  mechanical  working,  of  a 
plate,  which  is  conceded  to  be  the  lightest  of  the  series  of 
gauges  used,  suitable  for  denture  bases  of  this  type. 

Third,  molecular  disturbance  of  the  metal  in  certain 
areas,  which  reduces  its  integrity  as  sheet  metal  and  lowers  its 
resistance  to  chemical  action. 

Fourth,  reduction  of  the  inherent  strength  of  the  base- 
plate by  the  cutting  of  a  lingual  groove. 

Fifth,  failure. to  develop  thoroughly,  the  several  means 
of  anchorage  possible,  as  previously  outlined. 

It  is  the  opinion  of  the  writer,  based  on  a  number  of 
years  practical  and  clinical  experience,  that,  comjiared  bulk 
for  bulk,  the  base  swaged  from  sheet  aluminum  will  outlast 
the  cast  base. 


2:2  ALUMINUM  BASK  DKNTURKS 

CONSTRUCTION   OF  SWAGED  ALUMINUM   BASES 

As  has  been  previously  iutimated,  only  the  heavier  gauges 
of  aluminum  should  be  employed  in  the  construction  of  swaged 
bases  for  dentures,  in  order  that  the  basej^late,  when  weak- 
ened as  it  nnist  be  liy  grooving,  to  form  the  vulcanite 
shoulder,  may  still  have  sufficient  inherent  strength  to  resist 
masticatory  stress. 

For  a  number  of  years  past  no  lighter  than  18,  and  fre- 
quently 16,  gauge  has  been  recommended  and  used  in  prac- 
tice by  the  writer,  in  most  instances  with  very  gratifying- 
results.  Aluminum  plate  of  these  gauges  and  even  heavier 
can,  with  proper  technic,  be  conformed  to  a  die  with  com- 
parative ease.  The  plate  should  not  be  annealed  before  be- 
ginning nor  at  any  time  during  or  after  the  swaging  opera- 
tion. Any  base  metal  from  die  or  counterdie  can  l)e  removed 
with  polishing  wheels  and  tlius  the  formation  of  the  low 
fusing  alloy,  due  to  annealing,  either  of  which  apparently 
renders  the  base  more  susceptible  to  oral  fluids  and  food 
chemicals,  can  be  avoided. 

TECHNIC   OF   SWAGING 

The  actual  constructive  steps  are  as  follows: 
A  die  and  counter  die  are  secured  in  the  usual  manner. 
Both  are  oiled  with  a  film  of  heavy,  viscid,  oil.  Vaseline  will 
answer  if  a  thicker  oil  is  not  obtainable.  The  oil  will,  to  a 
great  extent,  prevent  contamination  of  the  aluminum  by  the 
die  and  counter  die  and  lubricate  the  surfaces,  thus  obviating 
the  tearing  of  the  base. 

Several  large  sheets  of  an  ordinary  newspaper  are  sat- 
urated with  water  and  the  excess  expressed  under  heavy 
pressure,  as  one  would  squeeze  the  water  out  of  a  wadded  up 
towel.  The  ball  of  condensed  paper  should  be  about  three 
inches  in  diameter.  This  is  placed  directly  over  the  opening 
of  and  on  the  counter  die,  and  flattened  slightly  by  pressure. 
On  the  paper  a  sheet  of  suitable  size  of  18  or  16  gauge  alumi- 
num, as  the  case  requires,  is  placed,  the  die  set  in  position  on 
the  plate  and  held  firmly  with  the  fingers,  and  its  base  struck 
two  or  three  heavy  blows  with  the  swaging  hammer.  The 
first  effect  of  the  swaging  will  be  to  drive  the  plate  into  the 
palatine  vault  of  the  die,  to  a  greater  or  less  extent,  withoul 
bending  it  over  the  outer  sides  of  the  border,  the  sheet  sliding 
over  the  inclined  surfaces  of  the  oiled  die  without  tearing  or 
becoming  thinned  to  any  appreciable  degree.     The  plate  is 


ALUMINUM  BASE  UENTUKES 


ROLL  OF    DAMP   PAPER    ARTt'STED    TO    fOVXTERDlE 


RESULT    OF    FIRST    SWAGING    ON    I'AFER    MASS 


214  ALUMINUM    BASE    DENTURES 

now  examiued,  and  wrinkles  corrected  if  any  have  formed. 
Tliis  preliminary  swaging  does  not  drive  the  plate  or  die 
into  the  counter  die,  but  into  the  ball  of  paper  which  should 
now  be  reformed  and  the  plate  swaged  again  as  before.  Two 
or  three  swagings  are  usually  sufficient  to  secure  fair  palatine 
and  partial  border  adaptation.  In  case  the  palatine  arch  is 
deep  and  it  is  difficult  to  drive  the  plate  into  the  dee])est  por- 
tion of  it,  the  die  may  he  set,  base  down,  on  the  swaging  block, 
a  ball  of  paper  large  enough  fill  the  vault  space  is  adjusted, 
and  a  piece  of  hardwood  about  an  inch  in  diameter  and  long 
enough  to  serve  as  a  handle,  the  end  of  which  is  rounded,  is 
set  against  the  paper,  and  with  the  hammer  adaptation  is 
quickly  secured.  The  paper  is  now  removed  from  the  counter 
die  and  re-formed  into  a  layer  about  one-fourth  inch  thick. 


ItKSri.T    OF    FIRST    SWAGING    ON    I'lATi: 


This  is  spread  over  the  counterdie  and  into  its  depression, 
the  plate  set  in  i^osition,  and  with  the  die  it  is  driven  partially 
to  place,  with  two  or  three  light  blows  of  the  hammer.  Re- 
move, correct  wrinkles,  trim  oft"  excessive  surplus,  and  repeat 
the  swaging  until  adaptation  is  secured,  always  keeping  a 
considerable  layer  of  paper  between  the  counterdie  and  plate. 
The  time  required  for  swaging  a  base  of  heavy  plate  by 
this  method  is  usuallj*  less  than  ten  minutes,  after  the  die  and 
counterdie  have  been  secured  and  the  paper  ball  prepared. 
The  lingual  surface  of  the  base  does  not  show  an  indentation 
or  scratch,  if  reasonable  care  is  observed.  The  baseplate 
is  not  perceptibly  thinned  at  any  ])oint,  and  an  adaptation  to 
the  die,  equal  to  that  secured  in  the  usual  way  with  thinner 
plate,  can  readily  be  developed.  'I'he  paper  acts  as  a  cushion, 
and  obviates  tearing,  stretching,  and  excessive  thinning  of 
the  plate.  With  a  thick  die,  heavy  smashing  blows  can  be 
delivered  with  a  heavy  hammer,  and  the  plate  quickly  brought 


ALUMINUM    BASH    IJENTUKKS  215 

into  shape,  tlie  ousliioii-like  aetiun  of  the  paper  obviating  to 
a  great  extent  the  marring  of  the  die  face. 

Care  should  be  taken  to  keep  the  anterior  margin  of  die 
back  of  the  corresponding  opening  in:  the  counter  die  while 
swaging  in  the  paper  ball,  otherwise  there  is  danger  of  shear- 
ing the  plate  anteriorly  as  the  die  is  driven  into  the  flattening 
mass  of  paper. 

Practically  the  same  results  can  be  secured  with  the  Ash 
liubber  Cushion  Swager,  or  with  any  good  hydravilic  press  in 
which  a  yielding  or  plastic  material  can  be  interposed  be- 
tween the  plate  and  counterdie  or  which,  by  confining  prop- 
erly, will  answer  for  the  counter  die. 

DEVELOPING    THE    VULCANITE    SHOULDERS    AND 
ANCHORAGES 

In  all  cases,  whenever  possible,  the  location  of  the  finish- 
ing shoulder  for  the  vulcanite  should  be  determined  after 
having  occluded  the  teeth,  waxed  up  the  case  and  tried  the 
denture  in  the  mouth.  This  plan  enables  the  prosthetist  to 
develop  the  correct  lingual  contour  of  the  denture  in  wax,  so 
that  enunciation  may  be  normal,  and  lay  the  shoulder  line  at 
the  margin  of  the  wax  as  determined  by  this  final  test.  The 
groove  is  cut  and  the  shoulder  developed  in  the  aluminum 
base  after  the  case  is  flasked  and  separated.  Or  this  may  be 
the  order  of  jorocedure : 

The  line  may  be  located  and  the  groove  cut,  after  having 
occluded  the  teeth,  before  trial  in  the  mouth.  This  plan  will 
give  approximately  accurate  results,  but  occasionally  it  will 
be  found  necessary  to  restrict  or  extend  the  area  as  first  out- 
lined. In  case  extension  is  necessary  this  can  be  easily  ac- 
complished, but  when  the  area  must  be  restricted,  the  shoulder 
having  already  been  formed  too  far  to  the  lingual,  an  un- 
sightly marring  of  the  baseplate  results  which  is  difificult. 
if  at  all  possible,  to  eliminate.  Finally  this  method  may  be 
adopted. 

It  is  conmion  practice,  but  decidedly  a  wrong  method,  to 
locate  the  position  of  and  form  the  shoulder  by  guesswork 
iiefore  trial  in  the  mouth  or  even  arranging  the  teeth,  because 
in  nearly  every  ipstance  some  modification  will  be  found 
necessary  when  the  teeth  have  been  occluded. 

TECHNIC   OF   FORMING  THE   SHOULDER 

The  shoulder  is  formed  by  first  cutting  a  groove  with  a 
small  wheel  bur  in  the  engine,  following  the  line  scratched  on 


21(i  ALUMINUM     BASK    DIONTCIiKS 

the  ]ilate  wliich  marks  tlio  line  of  jimetioii  of  tlie  wax  with 
tiie  l)aseplate.  This  groove  usually  extends  from  slightly  in- 
side the  center  of  the  tuberosity  on  one  side,  lingually,  around 
to  the  corresponding  point  on  the  opposite  side.  The  outer 
or  buccal  margin  of  the  groove  is  chiseled  or  ground  away, 
cutting  the  plate  freely  and  broadly,  to  give  the  necessary 
depth  to  the  vulcanite  margin  which  will  later  occupy  the 
angle  and  adjacent  area.  The  shoulder  is  not  extended  around 
the  labial  niid  Imccal  surfaces  in  these  cases  as  it  is  in  cast 


bases,  or  in  gold  base  dentures,  since,  if  pi'operly  anchored, 
the  vulcanite  will  not  curl  or  warp  away  from  the  baseplate. 

SPURRING   THE   BASE 

The  general  anchorage  for  the  vulcanite  is  developed  by 
raising  7nany  heavy  opposed  spurs  on  the  area  to  be  covered 
by  it.  These  spurs  can  be  made  heavier  and  longer,  and  are 
therefore  much  more  effective  than  it  is  possible  to  develop 
on  lighter  gauges  of  plate. 

ANCHORAGE    BY     PERFORATING    THE    BASE 

In  addition  to  the  spurs,  five  or  more  holes,  oiie-sixteenth 
■jf  an  inch  in  diameter  or  slightly  larger,  are  drilled  through 
the  base,  one  on  each  tuberosity,  one  opposite  each  cuspid 
eminence,  on  the  labial  surface,  and  one  on  the  border  crest 
opposite  or  between  the  central  incisors.  It  is  essential  that 
holes  be  placed  in  these  locations  for  obvious  reasons ;  there 
is  no  objection  to  increasing  the  number,  when  by  so  doing 
the  efficiency  of  the  anchorage  can  be  improved.    The  palatine 


ALUMINUM     BASE    DENTUKKS  217 

ends  of  the  holes  are  conutersunk,  and  hiter  the  entire  hole 
should  be  filled  witli  wax,  to  exclude  the  plaster  in  flasking, 
thus  insuring  the  rubber  becoming  firmly  anchored  to  tlie 
base  at  several  divergent  points.  The  loop  forming  plier 
may  be  used  to  raise  anchorage  loo])s  instead  of  forming  the 
holes  as  described. 

In  fliese  cases,  as  in  all  other  classes  of  dentures  where 
vulcanite  and  metal  join,  cliloro-rubber  or  ordinary  rubber 


cement  should  be  painted  on  the  metal  ])arts  just  ])efore  clos- 
ing the  packed  matrix,  to  insui'e  a  permanent  and  water 
tight  joint. 


FORMATION   OF   THE   VULCANITE    SHOULDER   BY 
MEANS   OF   A   DOUBLER 

A  method  recently  introduced  fni'  fdrming  tlie  lingual 
shoulder  without  grooving  the  baseplate  is  accomplished  by 
swaging  a  partial  base,  covering  the  palatine  portion  of  the 
base  proper,  its  margins  laid  in  correct  i)osition  to  form  the 
lingual  tinisliing  shoulder.  The  doubler  is  attached  to  the 
base  by  three  or  more  aluminum  rivets,  which  are  invisible  if 
the  holes  on  both  sides  of  the  plate  are  slightly  coiintersunk 


218  ALUMINUM    BASK    DENTURES 

and  tlie  wire  which  serves  as  rivets  fills  the  holes  accurately. 
Since  there  is  no  actual  union  between  tJie  two  pieces  of  plate 
other  than  being  lield  in  contact  with  the  rivets,  fluids  of  the 
mouth  must  sooner  or  later  find  their  way  between,  and  a 
disagreeable  odor  develop.  With  a  successful  solder  for 
uniting  the  two  plates  the  doubler  would  prove  of  great  ad- 
vantage in  many  cases,  particularly  in  badly  absorbed  cases. 
In  such  instances  the  margin  of  the  doubler  in,  the  absorbed 
area  could  be  lifted  away  from  the  base  and  raised  to  a  level 
with  the  plate  at  the  corresponding  point  on  the  opposite 
side.     This  will  permit  the  proper  palatine  contour  to  be 


APPLICATION   OV    A    DOUBLER   HELD   BY  RIVETING 

developed  without  showing  an  unsymmetrical  area  of  vul- 
canite at  any  point. 

SOME   FACTS   ON  THE   HISTORY    OF   ALUMINUM 
CASTING 

The  first  efforts  within  tlie  writer's  knowledge  of  at- 
tempts at  casting  aluminum  were  made  by  Dr.  J.  B.  Bean,  of 
Baltimore,  who,  in  1867,  had  granted  to  liim  Patent  No.  68548, 
for  a  device  for  casting  aluminum,  a  description  of  which  may 
be  found  in  the  patent  records  of  that  year. 

The  essential  points  of  the  apparatus  consisted  of  a  box- 
like flask,  in  which  the  matrix  was  formed  in  an  investment  of 
plaster  and  pumice  stone.  There  were  three  openings  com- 
municating with  the  interior  of  the  flask,  one  for  the  intro- 
duction and  another  for  the  exit  of  liydrogen  gas,  which  was 
forced  into  and  filled  the  matrix  at  the  instant  of  casting. 


VLLIMINLIM     IJASK    UENTLUtKS  21!l 

tbereb}'  excluding  tliL-  atmosphere  and  preventing  oxidation 
of  the  metal. 

The  third  opening  had  litted  to  it  a  long,  tapering,  de- 
tachable conduit  of  soapstoue,  which  served  also  as  a  reser- 
voir for  sustaining  a  standing  column,  of  considerable  height, 
of  excess  molten  aluminum.  The  specific  claim  made  for  the 
conduit  was  that  it  atTorded  means  for  "supplying  fluid  metal 
to  compensate  for  contraction  of  the  metal  in  the  mold,  as 
well  as  to  secure  a  denser  casting  by  means  of  the  detach- 
able reservoir,  D,  heated  previous  to  the  pouring  of  the  metal 
as  described." 

Dr.  Bean's  demise  occurred  in  1870,  and  as  no  one  at  that 
time  seemed  to  have  succeeded  in  mastering  the  technic  of 
his  process,  but  little  progress  was  made  in  aluminum  cast- 
ing until  the  latter  part  of  the  eighties. 

In  June,  1888.  the  Dental  Register,  Dr.  C.  C.  Carroll,  pre- 
sented a  method  of  casting  aluminum  under  pressure,  together 
with  a  description  of  his  apparatus  for  carrying  out  the  steps 
as  detailed.  While  interesting,  time  and  space  are  too  limited 
to  present  his  method  in  full,  and  since  it  has  no  direct  bear- 
ing on  present  day  technic,  for  fuller  details  than  those  which 
follow  the  reader  is  referred  to  the  article  in  the  journal 
mentioned  or  to  Harris',  edition  of  1892. 

The  essential  features  of  the  Carroll  apparatus  consisted 
of  a  flax  in  which  the  matrix  was  formed  of  a  mixture  of 
three  parts  plaster  and  one  of  fine  sand  or  marble  dust. 

The  crucible  was  detachable,  and  served  as  a  receptacle 
for  the  metal  while  fusing.  After  adjusting  the  metal  to  the 
flask,  the  fused  metal  was  cast  directly  into  the  matrix  through 
a  central  sprue,  which  subdivided  within  the  investment  into 
three,  one  leading  to  each  tuberosity,  the  other  to  the  distal 
vault  portion.  At  the  time  Of  easting,  the  top  of  the  crucible 
was  closed  with  a  tightly  fitting  plug.  To  this  a  rubber  hand 
bulb  was  connected,  which  on  compressing  forced  the  molten 
metal  into  the  matrix. 

In  the  hands  of  careful  prosthetists,  the  Carroll  appa- 
ratus was  capable  of  producing  a  fairly  dense  casting,  with 
probably  no  more  warpage  than  occurs  in  the  eastings  of 
today.  The  apparatus  was  easily  thrown  out  of  adjustment, 
while  the  melting  of  the  metal  was  difficult  to  accomplish. 
These  objections  coupled  with  the  frequent  failures,  due  to 
various  causes,  lead  to  its  final  abandonment. 

Between  1892  and  1895,  the  Fenner  and  the  Zeller  ap- 
pliances were  introduced.    These  were  similar  in  this  respect, 


220  ALUMINUM     HASK     DKNTUKKS 

tliat  each  consisted  of  a  l\vo-])iece  tlask  in  wliicli  the  wax  model 
was  invested,  and  to  one  of  the  lialvos  of  the  tlask  was  lixcd  a 
(!i'ncible  in  wliicli  tlie  ahnninuin  was  fnscd. 

In  tlie  Fenner  appliance,  the  top  of  the  crncihle  was  turned 
true  and  a  close  fitting  cap  adjusted  to  it.  A  tube  was  set  in 
the  cap.  through  whicli  was  transmitted  tlie  compressed  air, 
by  means  of  which  the  metal  was  forced  into  the  matrix. 

In  the  Zeller  appliance  a  partial  vacuimi  was  created  in 
the  matrix  and  the  metal  was  drawn  in  by  suction. 

Later  on  Dr.  R.  C.  Brophy  demonstrated  that  by  having 
reasonalily  large  sprues,  the  aluminum  when  sufficiently  fluid, 
could  be  made  to  fill  the  matrix  by  tapping  the  flask.  An  alloy 
of  90  per  cent  of  aluminum  and  to  w^hich  some  other  metals, 
were  added  to  increase  the  specific  gravity,  cast  lietter 
by  this  method  than  the  pure  aluminum. 


( '  n  A  P  T  K  H     X  [  V 

WEIGHTED  LOWER  DENTURES 

Weighted  lower  dentures  are  indicated  in  those  cases  in 
which  the  alveolar  border  is  badly  absorbed,  and  where  a 
denture  of  ordinary  weight  is  liable  to  be  more  or  less  dis- 
turbed by  the  action  of  the  tongue  and  cheek  muscles.  Be- 
cause of  their  greater  specific  gravity,  dentures  of  this  type 
retain  their  position  better  under  masticatory  stress  and  in 
speaking  than  do  those  corai)osed  of  vulcanite  alone.  The 
weight  for  dentures  of  this  class  is  provided  for  in  three 
ways : 

First,  by  using  weighted,  instead  of  ordinary,  rubber  for 
the  base. 

Second,  by  inclosing  a  bar  of  metal  within  an  ordinary 
vulcanite  case. 

Third,  by  casting  a  base  of  metal,  to  whicli  the  teeth  are 
attached,  usually  with  vulcanite. 

DENTURES  OF  WEIGHTED  VULCANITE 

Weighted  rubber  consists  of  ordinary  dental  rubber,  hav- 
ing uniformly  incor])orated  within  it  coarse  filings  of  tin  or 
some  metal  that  does  not  readily  oxidize.  In  the  construction 
of  weighted  dentures,  this  rubber  is  substituted  for  the  ordi- 
nary basic  material,  the  incorporated  metal  furnishing  the 
additional  weight  required.  The  technic  of  construction  dif- 
fers in  no  respect  from  that  of  an  ordinary  vulcanite  case. 

VULCANITE   DENTURES   WEIGHTED    BY    MEANS   OF   A 
METALLIC  CORE 

Additional  weight  may  be  given  a  vulcanite  denture  dur- 
ing the  constructive  steps  as  follows  :  Shape  a  bar  of  tin  or  one 
of  its  alloys,  so  that  it  will  fit  within  the  matrix  walls  of  the 
flasked  case  without  interfering  with  those  walls,  the  border 
crest  of  the  cast,  or  the  ridge  lap  of  the  enclosed  porcelain 
tooth.  The  outer  wall  or  gum  portion  of  the  matrix  is  packed 
with  pink  rubber  first;  the  lingual  portion  is  lined  with  basic 
material,  packing  it  carefully  imder  the  pins  of  the  teeth : 
the  bar  of  metal,  previously  conformed,  and  tested,  is  laid 
in  the  partially  filled  matrix,  the  remainder  of  the  rubber  is 

221 


■Z22  VVKKiHTKU      LUWIOH      UKNTII  KICK 

added,  and  tbo  flask  is  closed  and   viilcaui/.i'd   in   tlie   usual 
manner. 

This  simple  method  of  imparting  varying  degrees  of 
weight  to  a  denture,  as  the  conditions  of  the  case  requires,  is 
oftentimes  very  effective. 

CAST  METAL  BASES 

When  a  denture  of  considerable  weight  is  indicated,  a 
base  is  cast  in  metal  for  supplying  the  required  weiglit,  and  to 
this  the  teeth  are  attached  by  various  means,  the  most  con- 
venient being  vulcanite.  Since  the  metal  which  forms  the 
base  is  cast,  the  entire  matrix  into  which  it  is  cast  must  be 
composed  of  some  refractory  material  that  will  not  change 
form  perceptibly  under  the  heat  to  which  it  will  be  subjected 
in  preparing  it  to  receive  the  molten  metal.  Plaster  is  un- 
suited  for  this  purpose  because  of  its  tendency  to  crack  under 


heat.  A  number  of  good  investment  compounds  are  procur- 
able, those  ordinarily  used  for  crown  and  bridge  purposes 
being  applicable  to  the  casting  of  this  type  of  denture  bases. 

TECHNIC  OF  A  WEIGHTED  CAST  BASE 

The  details  of  construction  of  a  cast  lower  base  is  as 
follows : 

From  a  suitable  impression  of  the  lower  arch,  develop  a 
cast  in  investment  material. 

Soften  a  sheet  of  pink  baseplate  wax,  and  apply  to  the 
face  of  the  cast. 

Trim  it  to  the  approximate  outline  of  the  denture  base. 

Adapt  rolls  of  wax  to  the  labio-buccal  and  lingual  peri- 
pheries of  the  case,  burnishing  them  so  as  to  form  a  con- 
tinuous shoulder  against  which  the  vulcanite  will  rest.  The 
outer  surfaces  of  these  strips,  which  in  reality  form  the  outer 
and  inner  walls  of  the  denture  base,  should  be  squared  up 
practically  parallel  with  each  other,  so  that  the  metal  base 


WEIGHTED     LOWER     DENTURES  223 

and  the  vulcanite  may  form  a  continuous  surface  from  the 
margins  of  the  denture  base  to  the  gingivae  of  the  teeth. 
These  surfaces  may  be,  and  usually  are,  more  or  less  curved, 
but  the  line  of  junction  of  the  vulcanite  with  the  base  should 
be  free  from  angles.  Or  stated  differently,  both  buccal  and 
lingual  surfaces  of  the  metal  base  should  meet  the  corre- 
sponding surfaces  of  the  vulcanite  so  as  to  form  continuous 
surfaces  without  forming  angles. 

Usually  one  thickness  of  baseplate  wax  over  the  general 
surface  of  the  cast,  increased  by  the  rims  around  its  margin, 
will  prove  sufficiently  bulky,  when  reproduced  in  metal,  to 
give  the  necessary  weight  to  the  denture  for  retention 
purposes. 

Excessive  weight  in  lower  base  dentures  should  be  avoid- 
ed, as  they  tire  the  masticatory  muscles,  frequently  to  such  an 
extent  that  the  patient  cannot  wear  a  dentiu'e  of  this  type 
with  comfort,  or  continuously,  but  must  lay  it  aside  from  time 


SHOULDER    SURFACES 


to  time,  to  give  the  muscles  and  oral  tissues  a  rest.  Irritable 
areas  frequently  develop  under  the  denture  base  at  various 
points,  apparently  without  cause,  but  which  are  in  reality 
directly  traceable  to  the  heavy,  shifting  load  to  which  the 
mucous  tissues  overlying  the  hard,  bony  points  are  constantly 
subjected.  Such  cases  are  relieved  by  reducing  the  weight 
of  the  denture,  and  by  scraping  the  base  over  the  irritated 
areas. 

FLASHING    THE    WAX    MODEL    BASEPLATE 

When  the  wax  model  is  formed  and  anchorage  loops  for 
the  vulcanite  are  properly  placed,  the  case  is  invested  in  a 
Watt's  flask.  Or  an  ordinary  vulcanite  flask  will  answer  the 
same  purpose,  by  making  two  half  round  openings  in  each 
side  of  the  flask,  Cpposite  the  tuberosities,  through  which  the 
metal  may  be  poured. 

The  cast  of  the  mouth  on  which  the  wax  model  has  been 
formed  is  now  trimmed  peripherally,  and  reduced  in  depth, 
so  that  when  set  in  the  lower  half  of  the  flask,  the  peripheral 


224  WEIOHTEU     LOWER     U'ENTURES 

or  border  margin  of  wax  is  level  with  the  line  of  sejjaration 
between  the  two  halves  of  the  flask.  The  east,  when  ])roperly 
trimmed,  is  removed,  a  mix  of  investment  is  made  and  spread 
over  the  bottom  and  against  the  sides  of  the  lower  half  flask. 
The  cast  is  dijjped  in  water,  so  that  it  will  not  absorb  the 
moisture  in  the  freshly  mixed  investment,  and  thus  interfere 
with  its  proper  setting,  pressed  into  the  investment,  and  the 
latter  smoothed  evenly  from  the  inner  margin  of  the  flask 
to  the  periphery  of  the  wax  base.  That  portion  of  the  flask 
in  which  the  casting  gates  are  formed  should  also  be  filled 
level  at  this  time.  When  set,  the  exposed  surfaces  of  the 
investment  are  treated  with  soapstone,  rubbing  it  in  thor- 
oughly, to  prevent  adhesion  of  the  investment  in  the  upper 
half  of  the  flask,  when  added.     Slight  grooves,  leading  from 


I'-I.ASK    FOK    !■ 


the  distal  ends  of  the  baseplate  to  the  outer  ends  of  the  gate 
projections,  should  l)e  drawn  on  the  upper  surface  of  the 
investment  of  the  half  flasked  case,  to  indicate  the  width  and 
direction  of  the  sprues  to  be  cut,  through  which  to  pour  the 
molten  metal.  These  groves  on  the  lower  produce  ridges  on 
the  upper  investment,  which  coincide  in  location  and  direction 
with  the  grooves.  When  half  round  grooves  are  scraped  be- 
tween these  lines,  the  latter  of  which  should  diverge  from 
within  outward  to  give  a  funnel  form  to  the  feed  sprue,  and 
the  two  halves  of  the  flask  are  placed  together,  a  full,  free, 
open  gate  is  formed,  leading  from  without  inward  to  each 
distal  end  of  the  matrix. 

The  second  mix  of  investment  is  now  made,  and  the  top 
half  of  the  flask  entirely  filled  with  it.  Before  adjusting  the 
two  halves  of  the  flask  together,  some  of  the  freshly  mixed 


WEIGHTED     LOWER     DENTURES  225 

investment,  of  whk'li  tliere  should  l)e  a  surplus,  is  applied  to 
the  exposed  surface  of  the  wax  base,  care  being  taken  to  work 
it  into  all  of  tlie  irregular  surfaces  and  angles.  By  piling 
the  investment  somewhat  higher  in  tlie  middle  of  the  case 
than  at  the  edges,  adjusting  the  upper  half  of  the  flask,  and 
closing  under  pressure,  the  excess  is  forced  out  around  the 
margins  and  through  the  openings  on  the  top  and  bottom  of 
the  flask,  thus  eliminating  air  spaces. 

When  the  investment  has  set,  the  flask  is  separated,  the 
wax  removed,  the  half  gates  cut  on  each  side  of  the  flask,  all 
delicate  margins  are  removed,  the  matrix  freed  from  all 
debris,  and  its  entire  interior,  togetlier  with  the  cast  face, 
are  brushed  thoroughly  with  No.  1  graphite  to  aid  in  the 
production  of  smooth  surfaces  to  the  casting.  The  flask  is 
closed  and  clamped,  and  the  joint  between  the  two  halves 
luted  with  a  paste  of  equal  parts  soapstone  and  plaster,  which 
should  be  carefully  forced  into  every  crevice,  to  prevent  the 
escape  of  the  molten  metal  when  poured. 

The  flask  is  now  set  over  a  low  flame  to  expel  the  moisture 
from  the  investment.  The  heat  should  not  be  so  intense  as 
to  disintegrate  the  plaster  binder  of  the  investment.  Tests 
for  moisture  should  be  made,  from  time  to  time,  by  holding 
a  piece  of  polished  cold  steel  or  glass  over  the  gate  openings ; 
when  no  steam  condenses,  the  case  is  ready  for  casting. 

CASTING  THE   BASE 

For  weighted  dentures  any  of  the  several  alloys  pre- 
pared and  sold  for  this  purpose  may  be  used,  or  an  alloy 
which  will  serve  equally  as  well  can  be  compounded  in  the 
dental  laboratory.  Kingsley's  alloy  is  composed  of  tin,  16 
parts,  and  bismuth,  1  part.  Another  which  serves  equally  as 
well  is  tin,  16  parts,  cadmium,  1  ])art.  Tin  alone  will  not  cast 
sharply,  nor  is  it  as  hard  as  an  alloy  of  this  type  should  be 
for  the  ]Hirpose  intended,  therefore  one  or  the  other  of  the 
metals  mentioned  is  added  to  correct  the  fault. 

The  flask  is  now  set  upright,  an  ingot  of  alloy  is  fused  in 
a  small  ladle  and  ])oured  in  one  of  the  o]ienings.  If  the  ease 
is  sufficiently  hot,  perfectly  free  from  moisture,  and  no  cracks 
have  develoi3ed  in  drying  out,  the  metal  will  fill  the  matrix 
and  rise  in  the  opposite  gate,  thus  indicating  that  the  space 
is  filled.  Should  crevices  develop  in  the  investment  while  pre- 
paring the  case  for  casting,  the  flask  should  be  entirely  sur- 
rounded with  molding  sand,  well  packed  around  the  sides, 
leaving  only  the  sprues  exposed,   otherwise  the  metal  will 


2i!G  WEIGHTED     LOWER      DENTURES 

escape  through  some  of  the  opeuings,  and  the  niatiix  be  im- 
perfectly filled. 

When  the  metal  has  crystallized,  the  tlask  is  chilled  in 
cold  water,  and  the  casting  removed  and  cleansed.  The  ex- 
cess metal  is  removed  with  saw  and  fies,  and  those  surfaces 
of  the  base  not  to  be  covered  by  the  vulcanite  are  smoothly 
finished. 

With  a  graver  retention  is  secured  by  raising  heavy, 
opposing  spurs  on  the  area  to  be  covered  hy  the  vulcanite. 
These  spurs  are  developed  in  addition  to  tlic  l(i(i]>s  which  are 
formed  in  casting. 

When  ])roj)er]y  triuHiicd  and  iiolished,  a  roll  of  wax  can 


ST    BASE    WITJl    TEETH    WAXED    1-N    I'OSITIOX 


be  mounted  on  the  cast  base  and  a  wax  contour  model  devel- 
oped in  the  usual  manner. 

MODIFICATION  OF  THE  FOREGOING  METHOD 

Since  the  recent  improvements  in  the  technic  of  casting 
and  in  investments,  and  waxes,  it  is  found  that  these  weighted 
base  dentures  can  lie  handled  much  the  same  as  aluminum, 
that  is,  making  a  singh'  investment  and  dissipating  the  wax 
by  heat. 

The  specific  gi'a\'ity  nl'  the  allov  is  sufricient  to  insure  a 
dense  and  usually  perfect  casting  without  the  ajipli cation  of 
pressure,  as  required  in  aluminum  casting. 

In  flasking  a  weighted  base  denture,  preparatory  to  pack- 
ing and  vulcanization,  the  line  of  sejiaration  of  the  flask  should 
occur  at  the  line  of  junction  of  the  vulcanite  with  the  metal, 
thus  leaving  the  base  in  the  lower  half,  while  the  matrix  con- 
taining the  teeth  is  in  the  upper  half  of  the  flask. 

The  surface  of  the  metal  to  be  covered  by  the  vulcanite 
should  be  painted  with  a  film  of  chloro-rubber,  or  rubber 
cement,  just  before  the  final  closure  of  the  flask. 


WEIGHTRn     LOWER     DENTTIRES  227 

HISTORY 

lu  1856,  Di'.  A.  A.  Blniidy  introduced  a  system  oi'  cast- 
ing denture  bases,  similar  to  the  method  just  outlined,  and 
which  he  designated  the  Cheoplastic  Process,  signifying  "the 
making  of  i)lates  hy  i)nii ring  a  metal  nmde  plastic  hy  heat" 
(Harris). 

The  production  of  a  denture  in  those  days,  by  forming  it 
in  a  matrix,  of  a  plastic  material  which  hardened,  was  an  in- 
novation. Vulcanite  and  celluloid  were  not  yet  introduced, 
and,  therefore,  this  was  the  first  plastic  process  of  denture 
construction. 

The  exact  composition  of  Blandy's  alloy  is  not  known, 
but  the  metals  consisted  of  silver,  bismuth  and  antimony. 

The  introduction  of  vulcanite  as  well  as  celluloid  follow- 
ing shortly  after  lessened  the  interest  in  cast  metallic  bases  in 
general,  but  because  of  the  advantages  of  the  weighted  base 
for  lowers,  more  or  less  use  has  been  made  of  it  where 
indicated. 

Weston,  Wood,  Watt,  Rose,  Kingsley  and  others  have 
formulated  alloys  for  denture  bases,  which  are  mentioned 
elsewhere. 

VULCANITE  BASEPLATES 

In  cases  where  it  is  ajjparent  that  good  adaptation  of  a 
denture  to  the  oral  tissues  may  be  difficult  to  secure,  because 
of  peculiarities  in  form  of  the  Itorder  or  some  unusual  con- 
dition of  the  oral  tissues,  a  preliminary  baseplate  of  vulcanite 
can  oftentimes  be  constructed  to  good  advantage.  This  vul- 
canite form,  molded  over  an  accurate  cast  of  the  mouth, 
affords  a  reliable  test  as  to  adaptation  and  stability  of  the 
baseplate,  before  the  bulk  of  technical  details  have  been  car- 
ried out  and  if  successful  becomes  the  permanent  base.  If 
imsuccessful,  another  one  can  be  constructed,  or  a  different 
plan  of  procedure  adopted,  early  in  the  constructive  stages, 
and  without  further  loss  of  time. 

TECHNIC    OF    CONSTRUCTION 

Over  an  accurate  cast  of  the  mouth  sheet  wax  is  adapted 
in  the  usual  manner,  and  trimmed  to  correct  peripheral  out- 
line. The  wax  baseplate  should  be  slightly  thicker  than  the 
permanent  base  is  to  be,  so  as  to  allow  for  loss  of  material 
in  finishing.  A  roll  of  wax  about  one-eighth  inch  in  diameter 
is  laid,  in  a  svmmetrical  curve,  around  the  lingual  surface  of 


WEKIHTKIJ      LOWKK      UENTUKES 


the  border,  beginning-  a  little  t(i  the  buccal  of  one  tuberosity, 
passing  lingually  and  terminating  at  a  corresponding  point 
on  the  opposite  side.  The  margin  of  wax  presenting  toward 
the   border   crest    sliduld    lie   finislied   squarely   and    without 


vri.rAxrTK  iiASi:  ueahv  to  hkckive  wax  oi'ciasion  rims 

undercuts,  for  it  is  against  this  shoulder  of  the  vulcanite  that 
the  rubber  which  encloses  the  teeth  is  molded.  The  shoulder 
should  be  carried  well  u])  toward  the  crest  of  the  boi'der,  but 
must  be  broadened  linguallx'  ti>  furnish  an  amjile  liase  for  the 


I.INCIAL      \Ii:\\       III'       \      I  IMSIII  II      III  \ll  HL      COM- 
POSED   OF    THHEI;    COLORS    OF    M  LCAXITE 

bicuspids  and  molars.    If  l)roader  than  necessary,  it  is  easily 
reduced  in  the  final  finishing  of  the  denture. 

It  is  not  necessary  to  extend  the  strip  around  the  labial 
and  buccal  periphery  of  the  baseplate,  as  the  pink  vulcanite 


WEIGHTED     LOWER     DENTURES  229 

will  present  a  better  appearance  than  a  rim  of  basic  material 
in  this  location.  That  margin  of  the  strip  presenting  toward 
the  central  vault  portion  of  the  liaseplate  should  be  burnished 
down  smoothly  so  as  to  form  a  synunetrical  curve  witli  the 
general  palatal  arcli. 

Having  been  given  its  pro})er  form  and  being  smoothly 
finished,  the  wax  liaseplate,  on  its  cast,  is  flasked  in  the  usual 


IK    Ari'Llr.\Tlll\    OF    IIASEPLATES 


manner,  the  flask  i)acked,  ami  \iilcanized.  The  baseplate  is 
now  only  roughly  finished  on  the  lingual,  but  thoroughly  pol- 
ished on  the  palatine  surface.  In  this  condition  it  is  ready  to 
receive  the  wax  rim,  tlie  formation  and  a]i)>lication  of  which 
will  be  described  later. 

It  is  common  iiractice  to  form  the  baseplate  of  dark  or  jet 
black  rubber,  and  attach  the  teeth  to  it  in  the  second  A'ulcan- 
ization   with   marodu   oi-   sonic  of  the  lighter  shades  of   red 


\ri'i.iKi)   T( 


rubber.  When  this  plan  is  carefully  executed  most  beautiful 
and  artistic  substitutes  can  be  produced.  Such  a  denture, 
finished,  will  present  palatine  and  border  surfaces  entirely 
black,  a  similar  lingual  surface  extending  well  out  to  the 
lingual  surfaces  of  the  teeth,  a  narrow,  symmetrical  band  of 
maroon  or  red  vulcanite  l)etween  the  black  vault  ] portion  and 
the  teeth,  with  full  gum  restoration  of  granular  ]iink  on  the 
labio-buccal  surface. 


2;i0  WEIC.HTICII      LOWKK      DKNTURBS 

CONSTRUCTION    OF   TEMPORARY    BASEPLATES 
USING  "IDEAL  BASEPLATE,  SPECIAL" 

The  following  directions  should  he  ohserved  in  the  con- 
struction of  temporary  haseplates : 

Place  cast  on  bench,  face  up.  Center  a  sheet  of  rigid 
baseplate  material  (preferably  Ideal,  Special)  over  it.  Ap- 
ply tJie  soft  brush  flame  of  the  blowjiipc,  moving  it  quickly 


IDB.VI,    BASEPLATE    KEMOVED    FROM    CAST 


so  as  not  to  overheat  any  particular  area  and  cause  adhesion 
to  the  cast,  bnt  rather  to  soften  the  whole  sheet  uniformly. 
As  soon  as  it  begins  to  settle,  remove  the  flame,  and  with 
the  fingers  apply  light  pressure  to  adapt  it  to  all  surfaces 
of  the  cast.  Avoid  undue  pressure  which  thins  and  weakens 
the  material  unnecessarily.    Apply  the  blowpipe  to  the  labio- 


SECTIONAL   VIEW    OF    CAST    AND    BASEPLATE    UNIFORMLY    AD/VPTED 

buccal  portions  to  soften  somewhat,  remove  the  partially 
adapted  baseplate,  and  with  shears  cut  the  base  to  approx- 
imately its  correct  peripheral  outline.  Eeturn  to  the  cast, 
correct  the  distortion  that  has  occurred  from  the  use  of  the 
shears,  complete  the  adaptation,  chill  and  use  the  vulcanite  file 
for  the  final  finish  of  the  peri]iheral  margins.    The  file  should 


WElGHTEn     LOWER     DENTURElg  231 

be  applied  diagoiitilly  nr  suuiewliat  along  the  line  of  direc- 
tion of  the  margin  rather  than  crosswise,  to  obviate  fractur- 
ing the  baseplate.  A  thin  blade  spatula,  heated  quite  hot,  may 
be  used  instead  of  the  shears  for  cutting  the  baseplate  to 
correct  peripheral  outline,  passing  it  along  the  peripheral 
line  while  the  baseplate  is  on  the  cast. 

The  baseplate  may  be  reinforced  in  several  ways,  one 
of  the  most  common  methods  being  to  melt  some  of  the  sur 
plus  material  against  the  areas  it  is  desired  to  strengthen, 
and  smooth  the  addition  down  with  a  very  hot  spatula. 
Another  method  is  to  bend  a  piece  of  11  or  12  gauge  brass, 
German  silver,  or  iron  wire  to  the  form  of  the  arch,  but  slight- 
ly smaller,  attach  it  by  warming  and  with  melted  wax  to  the 
baseplate  just  inside  the  border  crest,  so  as  neither  to  inter- 
fere with  the  proper  arrangement  of  the  teeth  nor  with  the 
development  of  correct  lingual  contour  in  the  final  waxing  of 
the  dentui-e. 

When  trimmed  to  correct  peri^iheral  outline,  strengthened 
in  the  weak  areas,  and  tinal  close  adaptation  has  been  se- 
cured, the  baseplate  is  ready  for  the  application  and  pre- 
liminary contouring  of  the  wax  rims. 

TEMPORARY  BASEPLATES  OF  METAL 

Sheet  tin  or  lead,  14  to  16  gauge,  when  properly  adapted 
to  the  cast  makes  a  most  excellent  base  for  wax  contour 
models.  The  simplest  method  of  developing  a  base  of  this 
class  is  as  follows :  A  cast  of  the  mouth  having  been  secured 
and  its  l)ase  made  flat,  it  is  placed  on  the  rubber  cushion  of 
the  Ash  Swaging  Machine,  a  sheet  of  metal  of  suitable  size 
is  laid  over  its  face,  the  other  rubber  cushion  laid  on  the 
sheet  and  pressure  api)lied  to  force  the  metal  partially  to 
])lace.  The  surplus  is  trimmed  off  with  shears,  the  wrinkles 
cori'ected,  and  final  swaging  comjileted  on  returning  to  the 
press.  If  care  is  observed  in  these  steps,  no  injury  will  occur 
to  the  cast,  and  it  can  be  used  subsequently  for  the  comple- 
tion of  the  case.  In  work  of  this  class,  the  use  of  oxy-chloride 
of  magnesia  for  casts  is  most  strongly  indicated,  as,  in  fact, 
it  is  in  all  vulcanite  ^lenture  construction. 

Another  method,  whereby  a  metal  baseplate  similar  to  the 
one  just  described  can  be  formed  without  subjecting  the 
permanent  or  final  casts  to  the  ]iressiu'e  of  swaging,  is  car- 
ried out  as  follows: 

A  reasonably  good  impression  of  the  arch,  involving  all 
of  the  areas  to  be  covered  bv  the  finished  denture,  is  secured 


2;!2  WKIGHTEIl      LOWER      DION'TrKBS 

ill  iiiodcliiiy  coiupouiul,  oiuitting-  the  rt'lieutiiig  .stops  pre- 
viously mentioned.  From  this  impression  a  east  is  secured 
and  a.  tin  base  swaged  as  described.  Tliis  base  is  trimmed 
to  correct  periplieral  outline  and  tested  by  trial  in  the  mouth. 
A  thin  layer  of  softened  modeling  compound  not  more  than 
oue-sixteentli  of  an  inch  thick  is  laid  evenly  over  the  interior 
of  the  baseplate,  which  now  is  to  serve  also  as  an  improvised 
impression  tray.  An  impression,  worked  out  by  reheating 
and  the  various  corrective  steps  previously  mentioned,  is 
secured,  and  all  excess  carefully  removed.  This  now  con- 
stitutes an  impression-baseplate,  on  wliicli  rims  of  wax  can 
be  built  to  form  the  wax  contour  model.  When  transferred 
from  the  mouth  to  the  occluding  frame  b,\-  means  of  the  face 
bow,  instead  of  droi:)ping  tlie  original  casts  on  which  the 
metal  bases  were  formed  into  the  wax  contour  model,  freshly 
mixed  plaster  or  the  magnesia  compound  is  filled  in  and  built 
against  the  bows  of  the  occluding  frame.  If  oiled  before 
forming  the  cast  and  no  undercuts  are  i)resent,  the  wax  model 
denture  will  readily  separate,  when  removed  for  final  trial  in 
the  mouth.  The  advantage  of  this  method  consists  almost 
solely  in  the  increased  stability  of  the  wax  model  dentures 
during  trial  in  the  mouth,  over  temporary  baseplates,  of  any 
type,  adapted  to  casts  in  the  ordinary  manner. 


C  HAP  T  K  R     X  A' 

RETENTION  OF  PARTIAL  DENTURES 

A  partial  denture,  to  l)e  successful,  uuist  fulfill  certain 
requirements : 

First:  It  should  restore  as  fully  as  possible  the  function 
of  mastication  so  far  as  the  latter  may  have  been  impaired 
by  the  loss  of  the  natural  teeth. 

Second:  It  should  restore  the  esthetic  features  of  the 
dental  arch  by  supplying  substitutes  wliich  harmonize  in  form 
and  color  with  the  remaining,'  natural  organs. 

Third :  It  should  be  so  adapted  to  the  remaining  teeth 
and  tissues  as  to  maintain  its  position  with  oertaint}^  and 
comfort  when  the  masticatory  apparatus  is  in  an  active,  as 
well  as  a  passive,  state  without  causing  immediate  or  gradual 
decay  or  injury  to  the  natural  teeth  present. 

Of  the  several  requirements  mentioned,  that  of  retention 
— is  usuallj'  the  most  difficult  of  accomi)lishment.  Various 
means,  both  physical  and  mechanical,  are  employed  to  attain 
this  end,  the  most  important  of  which  are  atmospheric  pres- 
sure, adhesion,  fricfio)i  and  specialised  fricfional  appliances. 

ATMOSPHERIC  PRESSURE  AND  ADHESION 

The  principles  of  retention  l)y  means  of  atmospheric 
pressure,  and  adhesion  also,  have  previously  been  explained. 
For  various  reasons  these  forces,  although  of  value,  are  not 
as  effective  in  the  retention  of  partial  as  of  full  dentures. 

The  degree  of  force  exerted  by  the  atmosphere  and  ad 
hesion  upon  objects  from  between  the  contact  surface  of  which 
the  air  has  been  exhausted  and  close  ada])tation  secured,  is 
directly  jiroportional  to  the  square  of  the  area  involved. 
Therefore  the  more  limited  the  area  of  oral  tissues  covered 
by  the  baseplate,  the  less  can  these  forces  be  relied  upon  for 
retention  purposes. 

In  partial  cases  the  presence  of  natural  teeth  necessarily 
restricts  the  size  t.f  the  baseplate,  since  the  periphery  of  the 
latter  must  fall  within,  or  terminate  against,  the  lingual  sur- 
faces of  the  teeth  involved.  This  reduction  in  size  of  the 
baseplate  therefore  reduces  the  et¥ectiveness  of  adhesive 
force.     Again,  the  line  of  junction  of  the  dentui'e  with  the 

233 


231  KK'rKNTlOX     OF    PAH'I'IAL    DlONTtTIiKS 

iiaturui  tec'tli  is  m  pcciiliaily  \  ulrHMahlc  ijoiiil  Tor  the  ingress 
of  air,  since  tlie  mueons  tissues  of  the  eheeks,  lips  and  palate 
cannot  be  utilized  for  sealing  up  and  i)rotecting  the  margins 
against  the  return  of  air  when  once  withdrawn  from  between 
baseplate  and  tissues,  as  is  the  case  in  full  dentures,  and  this 
also  is  a  further  cause  for  reducing  the  force  of  adhesion. 

FRICTIONAL  RETENTION   OF  PARTIAL  DENTURES 

The  simplest  form  of  frictional  retention  available  for 
partial  dentures  consists  in  abutting  tlie  sides  of  the  latter 
against  the  lingual  surfaces  of,  and  in  the  embrasures  be- 
tween, teeth  situated  on  opposite  sides  of  the  arch,  or  suf- 
ficiently far  apart  to  present  opposing  surfaces,  which,  when 
the  denture  is  in  position,  tend  to  resist  displacement.  The 
alignment  of  the  teeth  must  be  favoralile  for  such  retention. 


CUT    SHOWING    INCM.NATIIIN  TOWARD   EACH   OTHER   OF   TEETH    OX    OI'I'OSITE   SIDES 
OF   THE   AKCH 

viz.,  the  distance  between  the  cervices  of  the  teeth  opposite 
each  other  in  the  same  arch  must  be  greater  than  at  the  points 
of  greatest  lingual  convexities,  or  points  of  their  nearest 
ai^proach. 

A  denture  moulded  over  the  cast  of  a  mouth  with  teeth 
bearing  the  relation  to  each  otlier  as  stated,  will  spring  as 
it  passes  over  the  points  of  nearest  approach  of  the  teeth 
involved,  and  resume  its  normal  width  without  undue  lateral 
pressure  when  firmly  seated  on  the  oral  tissues.  Such  an 
appliance  is  called  a  spring  plate  or  denture,  and  yet  it  does 
not  exert  lateral  pressure  against  the  teeth  except  on  intro 
duction  and  removal. 

When  the  lingual  surfaces  of  the  teeth  diverge  from  gin- 
gival to  occlusal  this  means  of  retention  cannot  usually  be 
utilized,  as  the  constantly  diverging  surfaces  are  mechanically 
opposed  to  such  retention.    Frequently,  however,  by  allowing 


RETENTION    OF    PARTIAL    DENTURES  235 

the  denture  margius  to  extend  into  the  embrasures,  when  the 
latter  are  well  defined,  frietional  retention  may  be  developed 
even  in  those  eases  where  the  general  alignment  of  the  teeth 
presents  more  or  less  parallel    relation  of  surfaces. 

In  such  cases,  and  especially  when  the  crowns  of  the  teeth 
are  too  short  for  clasping,  the  writer  has  inserted  inlays  with 
projecting  lugs  in  two  suitably  situated  opjiosiug  teeth  in 
such  manner  that  the  lugs  will  engage  with,  and  offer  frie- 
tional resistance  to,  the  displacement  of  the  denture.  Some- 
times, too,  How  anchor  screws  inserted  in  the  lingual  sur- 
faces of  the  teeth  will  fulfill  the  requirements  of  the  case. 
The  use  of  the  inlays  and  wire  lugs,  as  suggested,  have  proven 
very  useful  in  many  difficult  cases,  while  no  serious  results 
have  followed  this  method  of  practice. 

In  case  either  the  anchor  wires  or  the  lug  inlays  are  used, 
the  projections  should  lie  rounded  so  as  to  permit  the  denture 


KETENTION  OP   BASEPLATE  BY  MEANS  OP  WIRE  LUGS 

to  spring  in  and  out  of  position  without  catching  on  the  lug 
margins  or  straining  the  teetli  to  an  undue  extent. 

SPECIALIZED  FRICTIONAL  APPLIANCES 

Various  forms  of  specialized  frietional  appliances  are 
in  common  use  for  retaining  partial  dentures  in  position  in 
the  mouth.  These  usually  are  attached  to  and  become  a  part 
of  the  denture  itself.  In  other  cases  the  attachment  consists 
of  two  parts,  one  of  which  is  attached  to  the  denture,  the 
other  to  a  natural  tooth,  to  an  inlay,  to  a  crown  set  upon  a 
natural  tooth  or  root,  or  to  a  wire  or  bar  permanently  fixed 
to  crown  or  inlay. 

Among  the  appliances  in  general  use  may  l)e  mentioned 
clasps  of  various  forms,  double  bars  or  stays,  and  special 
attachment,  such  as  the  Roach,  Grilmore,  Morgan,  etc. 


236  RETENTION     OF    PAKTIAL    UBNTURP^S 

CLASPS 

Clasps  arc  partial  Uiiiid-likc  apj)liaiiccs  ailajitcd  to  tlu; 
natural  teeth  for  retaining  in  the  month  tiie  partial  denture 
of  which  they  form  a  i)art.  They  are  usually  constructed 
of  flat  plate  or  half  round  wii-c  of  gold  clasp  inetal,  composed 
of  pure  gold,  platinum,  silver  and  copper.  This  alloy  pos- 
sesses well  defined  elastic  i)roi)erties.  The  proportions  of 
silver  and  copper  may  he  A-aried,  however,  or  the  silver 
omitted  altogether,  as  its  i)resence  imparts  hut  little 
resiliency. 

Considerahle  difference  of  opinion  exists  as  to  the  ulti- 
mate value  and  utility  of  clasps,  the  argument  of  those  op- 
posed to  their  use  being  that  the  injury  to  the  natural  teeth 
far  outweighs  the  good  derived  from  their  use.  Those  who 
favor  the  application  of  these  appliances  are  e(|ually  as  posi- 
tive in  their  conviction  of  the  benefits  of  such  attachments. 
A  statement  of  the  objections  and  advantages  of  clas^JS  will 
be  in  order. 

OBJECTIONS   TO   THE   USE    OF   CLASPS 

The  princi])al  ol)jections  ui'ged  against  the  use  of  clasps 
are  as  follows : 

First — The  accumulation,  retention  and  fermentation  of 
food  in  the  space  between  clasp  and  tooth  will  invite,  and 
in  many  cases  does,  induce  caries. 

Second — Frictional  action  of  the  clasp  against  the  enamel 
will  abrade  the  latter,  induce  hypersensitiveness  in  the  tooth 
structure,  set  up  gingival,  and  in  some  cases,  peridental  ir- 
ritation. As  consequence  the  patient  suffers  more  or  less 
discomfort,  and  in  time  the  crown  or  the  entire  tooth  may  be 
lost. 

The  deleterious  conditions  here  cited  are  fretpiently  ob- 
served and  therefore  these  objections  have  an  apparently 
good  foundation.  They  can,  however,  in  almost  every  in- 
stance be  traced  to  one  or  more  of  several  causes,  most  of 
which  may  be  averted,  as  for  instance,  injudicious  applica- 
tion of  clasps  to  teeth  unsuited  for  the  extra  stress  they  must 
sustain;  imperfect  technic  in  the  construction  of  the  appli- 
ances; or  to  lack  of  habitual  care  of  the  natural  teeth  and 
denture  on  the  part  of  the  patient. 

ADVANTAGES   DERIVED  FROM   THE   USE   OF  CLASPS 

First — Stability  of  the  denture  at  all  times,  in  speak- 
ing, laughing,  and  in  masticatory  effort  is  practically  insured. 


RETENTION    OF    PARTIAL    DENTURES  237 

Second — By  their  u«e  the  basephite  wliich  carries  the 
replaced  teeth  need  cover  but  a  very  small  area  of  the  oral 
tissues,  since  adhesion  and  atmospheric  pressure  as  a  means 
of  retention  are  unimportant  factors  when  clasps  are  used. 

When  judiciously  applied,  properly  constructed,  and  the 
moutli  is  given  reasonal)le  care  and  attention  by  the  patient, 
clasps  are  of  the  itreatest  convenience  and  comfort,  and  will 
cause  but  little  injury  to  the  teeth  or  tissues.  In  the  expe- 
rience of  the  writer,  the  advantages  gained  from  the  use  of 
clasps,  where  indicated,  are  infinitely  greater  and  far  out- 
weigh any  harm  that  may  result  from  their  presence. 

Should  sensitiveness  be  induced,  or  caries  eventually 
develop,  the  tooth  can  be  devitalized  and  crowned  when  oc- 
casion requires,  and  be  made  to  render  still  further  service, 
by  carrying  a  newly  adapted  clasp.  It  is  seldom  advisable  to 
crown  a  tooth  to  be  clasped  in  anticipation  of  subsequent 
caries,  as  such  procedure  may  never  be  required. 

REQUISITES  OF  A  CLASP 

A  clasp,  as  its  name  implies,  is  an  appliance  which 
grasps  or  clings  to  the  tooth  to  which  it  is  adapted.  To  be 
effective  it  should  embrace  more  than  one-half,  usually  about 
two-thirds,  of  the  periphery  of  the  tooth.  A  clasp  should  be 
so  constructed  that  when  in  position  tirm,  frictional  contact 
is  established  between  both  its  gingival  and  occlusal  peri- 
pheries and  the  axial  walls  of  the  tooth  to  which  it  is  adapted. 
In  fact,  the  efficiency  of  a  clasp  depends  on  closeness  of 
adaptation  to  the  tooth,  resUiency,  and  inlwient  strength. 

ADAPTATION 

Closeness  of  adaptation  insures  stability  by  lessening  the 
tendency  of  the  clasp  to  rotate,  cant  or  slide  when  in  posi- 
tion on  the  tooth,  all  of  which  movements  tend  to  unbalance 
the  denture  when  subjected  to  masticatory  stress.  The  nearly 
parallel  relationship  of  the  axial  walls  of  most  teeth  suitable 
for  clasping  renders  the  attainment  of  this  requisite  dif- 
ficult, in  clasps  of  the  ordinary  partial  band  type.  Stability 
may  be  secured,  when  good  ada]itation  has  been  developed, 
by  the  addition  of- a  small  but  rigid  lug  extending  from  the 
occlusal  margin  of  the  clasp,  up  to  and  over  the  mesial  or 
distal  marginal  ridge  of  the  tooth  clasped.  The  lug  should  be 
located  as  centrally  as  })ossible  between  the  two  extremities 
of  the  clasp.  Such  an  addition  converts  an  ordinary  partial 
band  clasp  into  a  stop  clasp. 


238  RETENTION    OF    PARTIAL    DENTURES 

Without  doubt  this  form  of  clasi),  or  some  modification 
of  it,  in  whicli  tlie  stop  principle  is  embodied,  is  the  most 
satisfactory  and  serviceable  of  any  of  the  common  types  of 
partial  band  clasps.  By  the  addition  of  tlie  stop,  frictional 
wear  of  the  enamel  is  practically  overcome,  undue  pressure 
on  tlie  alveolar  ]irocess  covered  by  the  denture  and  on  the 
gingiva  surrounding  the  tooth  clasped  is  obviated,  and  a 
feeling  of  security  and  comfort  to  the  wearer  of  the  denture 
results,  not  possible  to  be  realized  from  the  use  of  the  ordi- 
nary type  of  clasp.  The  credit  of  having  evolved,  demon- 
strated and  described  the  practical  ai^plicability  of  the  stop 
clasp  should  be  ascribed  to  Dr.  Bonwill. 


THKEE    CASES    IIY    BO.NWH.L    SUOWINCI    HIS    ArPl.lr.VTlO.N    UF    THE    STOP    CLASP.    AND    WIBE 
ATTACHMENT   OF  CLASP  TO  BASEPLATE 

The  degree  of  perfection  of  adaptation  of  the  clasp  to 
the  tooth  depends  on  the  skill  displayed  by  the  prosthetist, 
the  technical  steps  employed,  and  to  a  certain  extent  on  the 
character  and  thickness  of  the  metal  used  in  its  construction. 


RESILIENCY   OF   THE   CLASP 

Resiliency  in  a  clasp  is  that  property  which  permits  it 
to  spring  over  the  enlarged  portion  of  the  tooth  it  embraces 
in  introducing  and  removing  the  denture,  without  becoming 
permanently  distorted  when  subjected  to  such  stress.     This 


RETENTION    OP    PARTIAL    DENTURES  239 

quality  depeiids  ou  the  character  of  the  metal  of  which  the 
clasp  is  composed,  as  well  as  on  the  width  and  gauge  of  the 
clasp  itself.  The  gold  alloy  known  as  clasp  metal,  previ- 
ously mentioned,  is  used  almost  exclusively  for  clasp  con- 
struction because  of  its  hardness  and  well  defined  elastic 
property.  The  elasticity  noticeable  in  a  clasp  when  sub- 
jected to  stress  would  be  classified  in  pliysics  under  the  term 
of  elasticity  of  flexure,  in  which  the  molecules  of  the  clasp 
metal  on  the  inner  periphery  are  elongated  when  subjected 
to  stress,  while  those  on  the  outer  side  are  compressed.  Per- 
manent distortion  occurs  when  the  stress  applied  carries  the 
metal  beyond  the  modulus  limit,  in  which  condition  it  is  said 
to  be  strained,  as  when  stress  is  removed,  the  piece,  of  what- 
ever shape,  does  not  return  to  its  original  form. 

THE    INHERENT   STRENGTH    OF    CLASPS 

A  clas})  may  be  well  adaiited  to  a  tooth,  possess  sutificient 
resiliency  to  be  carried  to,  and  removed  from,  position  in  the 
mouth  without  becoming  distorted  under  ordinary  stress,  and 
yet  prove  imsatisfactory  with  use. 

Undue  stress  exerted  on  clasps  in  iDolishing  on  the  lathe, 
in  introducing  and  removing  the  denture,  careless  handling 
in  cleansing,  letting  the  denture  fall,  as  well  as  other  acci- 
dental causes,  frequently  distort  and  oftentimes  destroy  the 
eft'ectiveuess  of  these  a^jpliances.  Many  clasps  otherwise 
suitable  fail  because  of  lack  of  inherent  strength,  and  con- 
sequently the  very  oliject  for  which  they  are  designed  is 
defeated. 

The  remedy  lies  in  correctly  estimating  the  proper  width 
and  thickness  of  the  clasp  in  proportion  to  its  length,  and 
developing  the  appliance  accordingly.  These  two  factors 
are  determined  by  the  length  of  tooth  to  be  clas^jed.  Short 
teeth  require  narrow,  but  rather  thick,  clasps,  the  thicker 
gauge  compensating  for  the  weakuess  resulting  from  re- 
stricted width. 

A  thick,  narrow  clasp,  hoAvever,  is  not  as  resilient  as  a 
thinner,  wider  appliance  of  equal  length  containing  an  equal 
amount  of  metal  as  the  former.  The  truth  of  this  proposition 
is  plainly  apparent -by  noting  the  difference  in  resiliency  of 
steel  springs  of  Varying  widths  and  gauges.  A  spring  should 
be  so  proportioned  as  to  carry  the  extreme  load  to  which  it 
may  be  subjected  without  tlie  occuri'ence  of  permanent  dis- 
tortion. In  fact,  it  should  possess  a  considerable  range  of 
elasticitv  between  the  extreme  load  limit  to  which  it  will  be 


240  RKTKNTION    OK     I'AR'I'IAI,    DIONTURKS 

subjected  and  tlu'  iiiodulus  limit,  or  point  wlicnc  |)ernianeut 
distortion  occurs. 

Inlierent  strength  with  bulk  to  carry  extreme  loads,  while 
a  high  degree  of  resiliency  is  retained,  is  imioarled  to  springs 
in  tlie  mechanical  field  by  dividing  the  necessary  bulk  of 
metal  into  comparatively  thin  layers  called  leaves.  In  other 
words,  the  spring  is  made  u])  of  several  members  consisting 
of  the  principal  spring  reinforced  by  a  series  of  leaves  of 
gradually  decreasing  length,  but  of  approximately  the  same 
thickness,  rigidly  fixed  to  the  main  spring,  usually  at  the  point 
where  stress  is  api)lied.  The  leaves  throughout  the  greater 
])ortion  of  their  length  are  free  to  slide  or  move  freely  against 
each  other  as  the  load  or  stress  varies,  and  thus  the  resilient 
power  of  each  member  of  the  s])ring  is  utilized  in  reducing 
shock  and  avoiding  strain. 

This  i^rinciple  of  reinforcement  of  clasps  for  dental  pur- 
poses cannot  well  be  applied  for  obvious  reasons,  although 


at  times  it  is  necessary  to  vary  the  flexibility  of  a  clasp  at 
different  points  throughout  its  length.  For  instance,  when 
a  clasp  must  of  necessity  be  narrow,  thick  and  almost  devoid 
of  resiliency  where  it  passes  through  the  interijroximate 
space,  the  buccal  and  lingual  flanges  may  be  increased  in 
width  and  decreased  in  thickness  to  develop  greater  elas- 
ticity. In  sucb  cases  extra  thick  plate  is  used  for  the  clasp 
to  give  strength  in  its  narrowest  part,  and  the  necessary  re- 
duction in  thickness  on  the  l)road  areas  is  made  by  filing, 
grinding  and  polishing.  In  a  numl)er  of  cases  the  writer 
has  secured  excellent  results  by  cutting  a  section  from  the 
central  portion  of  the  broad  areas  of  a  clasp  after  adapta- 
tion has  been  developed,  without  reducing  the  thickness  of 
the  appliance. 

Various  modifications  of  the  ordinary  flat  band  clasp, 
specially  of  the  broad  type,  are  employed  to  decrease  rigidity 


RETENTION    OF    PARTIAL    DENTURES  241 

and  increase  resiliency.  In  addition  to  removing  a  central 
section  from  the  flange  as  detailed,  it  may  be  divided 
throughout  a  portion  of  its  length,  as  suggested  by  Dr.  G.  H. 
Gushing,  or  the  central  area  may  be  removed,  and  the  gin- 
gival portion  severed. 

While  a  clasp  must  possess  inherent  strengtli  sufficient 
to  withstand  unusual  stress,  it  should  not  be  too  unyielding. 
When  deficient  in  elasticity  because  of  its  bulk,  and  at  the 
same  time  possessing  excessive  inherent  strength,  the  tooth 


A   CASE  CONSTRUCTED   BY   DB.    G.    H.    CrSHIXG   IN   ISCO 

which  it  embraces  will  be  subjected  to  unnecessary  strain  in 
removal  of  the  denture  if  the  adaptation  of  the  clasp  to  the 
tooth  is  reasonably  close. 

GAUGES  OF  CLASP  METAL  COMMONLY  EMPLOYED 

Many  clasps  fail  under  stress  of  usage,  as  before  stated, 
because  of  lack  of  inherent  strength.  This  is  usually  the  re- 
sult of  using  too  thin  a  gauge  of  clasp  metal,  or  so  reducing 
their  width  as  to  render  them  weak. 

As  a  rule,  26-gauge  clasp  metal  is  as  thin  as  should  be 


VARIOUS    .METH(III.S    OF     IXrltKA.'^INC     ItF.SI  MKM'I      IX     CLASl'S.     KI  CI'AI,    VIEW 

used.  When  28  gauge  is  employed,  unless  very  wide,  it  should 
be  stiffened  by  flowing  18K  solder  on  the  outer  periphery. 
While  this  method  imparts  rigidity,  it  reduces  resiliency,  and 
therefore  should  seldom  be  adopted. 

Usually  three  gauges  of  clasp  metal  will  answer  for  all 
ordinary  cases  that  may  present :  26  gauge  for  long,  24  gauge 
for  medium  and  22,  or  in  extreme  cases  20  gauge  may  be  re- 
quired, for  short  teeth.  Clasps  of  equal  length  may  vary  in 
width,  thickness  and  resiliency,  and  yet  contain  essentially 


242  RKTENTION    OF    PARTIAL    DRNTURKS 

the  same  auioiint  in  bulk  of  material.  For  example,  a  elasi3 
one-eighth  inch  wide,  composed  of  :20-gange  plate,  which 
equals  .03196  of  an  inch  thick,  will  contain  essentially  the 
same  amount  of  metal  as  one  of  equal  length  and  twice  as 
wide  of  26  gauge,  which  equals  .01594  inch  thick.  Its  re- 
silient index,  however,  will  be  noticeably  less  tlian  that  of  the 
26  gauge  clasp. 

TYPES    OF   CLASPS    MOST    COMMONLY    USED 

Clasps  vary  in  form  according  to  the  requirements  of 
the  case  for  which  they  are  constructed.  These  requirements 
include  the  class  and  forms  of  teeth  to  which  they  are  adapted, 
the  part  they  are  to  fulfill  in  the  retention  of  the  denture,  and 
the  load  they  are  required  to  carry. 

The  ordinary  forms  of  clasps  may  l)e  talnilated  as  fol 
lows: 

1.  Partial  fiat  band  clasp. 

2.  Half-round  wire  clasp. 

3.  Double  wire  or  bow  clasp. 

4.  Stop,  wire  or  band  clasp. 

5.  Double-stay  clasp. 

6.  Stay  clasp. 

THE  PARTIAL  FLAT  BAND  CLASP 

This  form  of  clasp,  as  its  name  indicates,  consists  of  a 
partial  flat  band,  usually  of  clasp  metal,  of  suitable  gauge  and 
width,  which  embraces  about  two-thirds  of  the  tooth  peri- 
phery. The  gingival  and  occlusal  margins  of  the  clasp  should 
be  iDractically  parallel  to  insure  as  nearly  equal  resiliency 
throughout  its  entire  length.  This,  however,  does  not  imply 
that  these  margins  should  be  straight,  but  curved  somewhat 
similar  to,  but  usually  less  pnmounced  than,  the  gingival  gum 
curvature. 

Band  clasps,  should  be  reasonably  broad,  the  average 
width  varying  from  two  to  five  millimeters.  The  broader  the 
clasp,  the  more  stability  will  be  afforded  the  denture. 

On  the  other  hand,  a  clasp  of  this  type  should  not  be  so 
broad  as  to  encroach  upon  the  gum  tissue  and  thereby  induce 
irritation;  neither  should  it  interfere  with  occlusion  of  the 
opposite  teeth.  The  buccal  and  lingual  flanges  can  usually 
be  so  formed  as  to  avoid  impingement  on  the  soft  tissues. 
When  the  tooth  clasped  proximates  with  two  others,  and  the 
gum  septum  in  the  embrasures  through  which  the  appliance 


RETENTION    OP    PARTIAL    DENTURES  243 

passes  is  normal,  or  nearly  so,  it  is  sometimes  difficult  to  en- 
tirely avoid  impingement  on  the  tissues  in  such  locations. 

While  it  is  advisable  in  most  instances  to  avoid  the  use 
of  clasps  where  tissues  fill  the  embrasures,  it  becomes  neces- 
sary to  apply  them  in  other  cases,  especially  where  there  are 
no  other  teeth  of  suitable  form,  or  in  proper  location,  to  be 
utilized. 

When  a  clasp  is  applied  in  such  cases,  extreme  care 
should  be  taken  to  conform  it  closely  to  the  mesial  or  distal 
axial  wall  of  the  tooth  clasped,  to  reduce  it  to  the  minimum 
width  consistent  with  strength,  and  to  smoothly  round  otf  all 
angles  iDresenting  toward  the  gingiva.  The  tissues,  although 
subject  to  compression  for  a  time,  will  usually  adjust  them- 
selves to  the  clasp  without  permanent  injury  resulting. 

THE  HALF-ROUND  WIRE  CLASP 
ADVANTAGES 

Various  gauges  of  half  round  clasp  metal  wire  are  fre- 
fjuently  used  in  clasp  construction.  The  advantages  of  half- 
round  wire  for  this  purpose  are  as  follows: 

First — The  clasp  is  of  uniform  thickness  and  resiliency 
throughout  its  entire  length,  except  where  attached  to  the 
plate,  at  which  point  it  is  rendered  more  ligid  because  of  the 
solder. 

Second — It  can  be  adapted  to  teeth  witli  comparative 
ease. 

Third — Less  tooth  surface  need  be  covered  by  the  clasp, 
and  consequently  there  is  loss  liahiJifji  for  food  to  acmimnlate. 

OBJECTIONS 

First — Wider  space  is  required  between  proximating 
teeth  for  the  accommodation  of  the  clasp. 

Second — Limited  stability  afforded  the  denture  because 
it  does  not  grasj)  the  axial  walls  of  the  tooth  as  firmly  as  a 
broader  clasp. 

THE  DOUBLE  WIRE  CLASP 

This  type  of  cjasp  consists  of  a  wire  of  18  or  19  gauge 
clasp  metal  looped  on  itself  and  the  ends  soldered  so  as  to 
I'orm  an  elongated,  more  or  less  parallel  sided,  endless  band. 
The  distance  between  the  gingival  and  occlusal  wires  varies 
from  one  to  four  m.m.,  depending  on  the  length  and  form  of 
the  tooth  clasped.     To  retain  a  firm  grasp  on  the  tooth,  the 


244  RETENTION    OF    PARTIAL    DENTURES 

gingival  wire  should  lie  to  the  gingival  and  the  other  wire  to 
the  occlusal  of  the  greatest  diameter  of  the  tooth,  thus  tend- 
ing to  resist  displacement  either  gingivally  or  occlusally. 

The  doul)le-wire  clasp  may  he  converted  into  a  stop  clasp 
by  the  addition  of  a  strip  of  heavy  clasp  metal  of  19  or  20 
gauge,  or  square  wire  18  gauge,  bent  so  as  to  form  an  occlusal 
lug,  and  extending  so  as  to  connect  the  two  wires  and  further 
furnish  attachment  of  the  clasp  to  the  gold  liase  or  vulcanite, 
as  the  case  requires. 

Another  modification  of  this  chisiJ,  suggested  by  Dr.  P.  E. 
Roach,  and  by  him  designated  the  "double-bow  clasp,"  con- 
sists in  adapting  the  gingival  wire  closely  to  the  proximate 
surface  of  tlie  tooth,  and  leaving  it  unattached  to  the  lug  bar. 
More  Hexilile  adjustment  is  claimed  for  the  clasp  constructed 
in  this  manner,  particularly  in  those  cases  where  the  substi- 
tute is  designed  to  correct  a  space  between  two  natural  teeth, 
and  where  they  lean  slightly  toward  each  other.  (Dental  Re- 
view, October,  1913.) 

While  lacking  the  strengtli  of  some  of  the  other  forms  of 
clasps  described,  when  well  planned  and  properly  constructed 
the  double-wire  clasp  clings  to  a  tooth  with  wonderful 
tenacity,  and  will  sustain  a  denture  with  firmness  and  com- 
fort to  the  wearer. 

The  principal  advantages  of  the  double-wire  clasp  may 
l)e  summed  up  as  follows : 

First — The  large  extent  of  linear  contact  existing  be- 
tween the  clasp  peripherally  and  the  tooth  surfaces,  with  the 
minimum  amount  of  surfaces  actually  covered. 

Second — Great  resiliency  and  ready  adaptability  of  the 
clasp  to  the  tooth  surfaces. 

Third — Comparatively  simple  to  construct. 

The  principal  disadvantage  lies  in  possible  lack  of  in- 
herent strength,  particularly  in  those  cases  where  the  tooth 
is  large,  requiring  a  long  clasp  peripherally,  and  where  the 
denture  will  be  subjected  to  heavy  sti'ess  or  careless  handling. 

THE  STOP  CLASP 

The  stop  clasp  Juts  been  in'eviously  mentioned  under 
"Requisites  of  a  Clasp."  Clinical  experience  with  this  type 
of  clasp  has  been  so  satisfactory  as  to  lead  to  its  adoption  in 
practically  every  case. 

Any  of  the  forms  of  clasi)s  described  may  be  converted 
into  a  stop  clasp  by  the  addition  of  an  occlusal  lug.  In  case 
of  the  flat-band  clasp  the  lug  may  be  formed  of  the  same  piece 


RETENTION    OF    PARTIAL    DENTURES  245 

of  plate  as  the  clasp  by  allowing  for  the  extra  width  in  cntting 
the  clasp  metal,  or  it  may  be  soldered  on  after  the  appliance 
is  constructed. 

The  lug-  should  be  so  placed  that,  when  the  clasp  is  in 
position,  it  rests  on,  or  hooks  over,  the  mesial  or  distal  mar- 
ginal ridge  of  the  tooth  clasped.  If  the  ridge  is  excessively 
prominent,  it  may  be  reduced  by  grinding  and  polishing  so 
that  the  lug  may  not  interfere  with  the  occlusion  of  the  tooth 


ORDINARY    HAM)    II.ASI'    WITH    STOP.    LINGUAL    VIEW 

in  the  opposite  arch,  or  the  tip  of  the  occluding  cusp  may  be 
ground  and  polished  until  clearance  space  is  gained.  In  case 
the  tooth  clasped  is  carious  and  suitalile  for  the  reception  of 
an  inlay,  it  may  be  restored  in  this  manner  and  a  depression 
made  in  the  occlusal  surface  of  the  inlay,  so  as  to  permit  the 
occlusal  surface  of  the  lug  to  rest  flush  with  that  of  the  re- 
stored part.  It  is  essential  that  the  lug  should  be  slightly 
hook-shaped  and  the  surface  on  which  it  rests  correspondingly 
curved,  to  ])revent  the  tendency  of  the  clasp  to  slide  away 
from  the  tooth  when  the  denture  is  subjected  to  stress. 

THE  DOUBLE,  STAY 

A  method  much  in  vogue  in  Europe,  but  infrequently  ap- 
plied in  this  country,  consists  in  attaching  two  rather  thin 
pieces  of  clasp  metal  of  28  or  29  gauge  to  the  baseplate.  The 
strips  should  be  in  close  apposition  to  each  other,  so  as  to  pass 
through  the  interproximate  space  between  two  suitably  lo- ' 
cated  proximating  teeth.  The  ends  of  the  stays  which  ter- 
minate in  the  buccal  embrasure  are  bent  away  from  each 
other  so  as  to  lie  in  close  apposition  to  the  teeth  they  proxi- 
mate. 

Retention  by  means  of  this  "Doppel  Klammern"  (double 
clasp),  as  the  Germans  term  it,  is  very  effective  in  favorable 
cases.  The  retention  does  not  depend  on  mesial  and  distal 
frictional  contact,  but  on  the  action  of  the  reflected  ends  of 
the  two  flanges  tending  to  draw  the  two  teeth  inward  toward 
the  baseplate.    The  stops  themselves  should  not  exert  spring 


246  RETENTION    OF    PARTIAL    DENTURES 

pressure  on  the  proximating  surfaces  of  the  teeth,  or  in  time 
gradual  and  permanent  separation  of  the  latter  will  occur. 

THE  STAY 

This  appliance  is  commonly  called  a  stay  clasp,  but  the 
term  is  incorrect  since  it  embraces  less  than  one-half  of  the 


THE   DODBI-E    STAY,    SllOWJXf;    EI.EMKXTAL   CONSTRUCTION   DETAILS 


periphery  of  the  tooth  to  which  applied,  and  therefore  does 
not  perform  the  function  nor  fulfill  the  purpose  of  a  clasp. 

AjJijliances  of  this  tyi)e  are  seldom  indicated,  l)eing  usu- 
ally applied  in  those  cases  where  ordinary  frictional  reten- 
tion of  the  denture  is  uncertain  because  of  the  parallel,  or 
slightly  diverging,  relation  of  the  lingual  surfaces  of  the 
teeth  on  opposite  sides  of  the  arch,  and  when  for  any  reason 
clasps  are  contra-indicated.    Two  well  adapted,  opposed  stays. 


THE  STAT  CLASP 


the  ends  of  which  pass  well  into  the  lingual  embrasures,  will 
frequently  give  the  required  stability. 


INDICATIONS  AND  CONTRA-INDICATIONS  GOVERNING 
THE  APPLICATION  OF  CLASPS 

For  the  rdontion  of  partial  dentures,  clasps  may  gen- 
erally Ije  used  to  advantage  in  all  cases  when  the  mouth  is  in 
a  comparatively  healthy  condition  and  the  teeth  are  so  situ- 
ated that  when  the  clasp  denture  is  introduced  it  will  balance 
and  not  become  displaced. 


RETENTION    OF    PARTIAL    DENTURES  247 

Unless  the  teeth  clasped  are  suitably  located,  displace- 
ment of  the  denture  by  gravity,  muscular  strain,  or  the  two 
forces  combined,  will  sooner  or  later  occur,  regardless  of  the 
presence  of  the  clasps.  For  example,  in  an  upper  case  where 
all  of  the  teeth,  except  the  third  molars,  are  missing  and  re- 
tention of  the  denture  depends  solely  on  clasping  these  two 
teeth,  gravity  and  the  action  of  the  lip  and  cheek  muscles  will 
overcome  the  i'esiliency  of  the  clasps  and  result  in  partial,  if 
not  complete,  displacement.  Or  if  the  clasps  are  heavy 
enough  to  resist  these  displacing  foi'ces,  the  teeth  themselves 
will  be  gradually  and  permanently  tipped  liackward,  thus  per- 
mitting the  denture  to  become  unseated  and  the  clasps  will 
then  be  a  detriment  instead  of  an  advantage. 


DIAGR^VJIMATIC    VIEW    Or    CASE    SHOWIXC    •DEXTIRE    liAT.ANCE" 

The  location  for  clasps  best  suited  to  insure  stability  is  at 
a  point  midway  between  the  anterior  and  posterior  terminals 
of  the  denture  on  either  side.  The  tendency  to  tip  anteriorly 
is  thus  instantly  coimteracted  by  pressure  of  the. distal  end  of 
the  denture  against  the  tissues,  and  vice  versa.  Such  bal- 
ancing requirement  really  limits  the  number  of  teeth  that  may 
be  clasped  to  advantage  to  the  second  bicuspid  and  first  molar 
on  either  side,  aKhough  at  times  the  first  bicuspid  and  second 
molar,  if  present  and  on  opposite  sides  of  the  arch,  may  be 
utilized  for  such  purpose.  Although  neither  clasp  would  be 
situated  midway  between  the  mesial  and  distal  terminal,  yet 
a  straight  line  drawn  from  one  clasp  to  the  other  would  dis- 


248  HETRNTION    OF    PARTIAI.    DENTURES 

close  a  diagonal  balance  quite  as  effective  as  when  the  more 
centrally  located  teeth  are  clasped. 

There  is  oftentimes  a  temptation  to  utilize  the  diagonal 
l)alance  by  clasping  the  cuspid  on  one  side — all  of  the  poste- 
rior teeth  on  that  side  having  been  lost — and  the  second  or 
third  molars  on  the  opposite  side.  Usually  such  attempts  re- 
sult in  failure  because  the  conical  form  of  the  cuspid  tooth 
precludes  the  application  of  a  stable,  partial-baud  clasp,  ex- 
cept in  those  cases  where  tissue  absorption  has  progressed 
to  such  an  extent  as  to  expose  the  constricted  jjortion  of  the 
tooth,  tlius  allowing  the  clas]i  to  extend  well  up  over  the 
cingulum. 

When  but  little  absori)tion  of  tissue  has  occurred,  a  modi- 
fied form  of  band  clasp  is  sometimes  constructed  for  cuspids, 
involving  considerable  elTort  in  construction,  but  resulting  in 
marked  stability.     A  cavity  is  formed  on  the  lingual  surface 


LINGUAL,    DISTAL    AND    LABIAL    \IE\V    OP    CUSPID    WITH    LIXOUAI.    LUG    CLASP 

of  the  cuspid  extending  about  two-thirds  of  the  distance  from 
distal  to  mesial,  and  from  near  tlie  gingiva  to  the  incisal  third. 
In  this  cavity  an  inlay  is  placed,  in  which  is  formed  a  round- 
bottomed  groove  extending  from  its  disto-lingual  angle  to 
near  its  mesial  margin.  This  groove  should  be  near  the  gin- 
gival margin  of  the  inlay.  The  distance  between  the  bottom 
of  the  groove  and  the  labio-gingival  surface  of  the  tooth 
should  be  less  than  l)etween  that  point  and  the  diameter  of 
the  tooth  immediately  to  the  incisal  of  it.  A  clasp  is  now 
adajited  to  the  gingival  portion  of  the  tooth  as  closely  as  pos- 
sible, and  embracing  more  than  one-half  of  the  periphery.  A 
piece  of  iridio-platinum  or  clasp  metal  wire  is  fitted  in  the 
groove  and  connected  to  the  clasp  by  interposing  a  piece  of 
plate  or  wire,  and  soldering. 

Usually  some  other  form  of  specialized  frictional  appli- 
ance which  involved  no  display  of  metal  labially  can  be  used 
to  better  advantage  than  the  form  of  clasp  just  described. 


RETENTION    OF    PARTIAL    DENTURES  249 

Sometimes  the  iugemiity  of  tlie  prosthetist  will  be  taxed  to 
the  utmost  to  devise  adequate  means  of  reteution  in  i)artial 
cases.  Frequently,  although  several  teeth  are  present,  they 
may  not  be  suitable  in  form  to  carry  clasps,  or  be  in  correct 
position  to  insure  denture  balance  should  clasps  be  adapted 
to  them.  In  such  cases  specialized  frictional  apj^liances  can 
usually  be  applied  in  some  manner  so  as  to  (leveh)p  the  re- 
quired sta))ility. 

SPECIALIZED  FRICTIONAL  APPLIANCES 

Many  forms  of  specialized  frictional  retention  appliances 
liave  been  devised  in  an  effort  to  overcome  the  disadvantages 
and  weak  points  of  the  various  types  of  clasps  commonly  used. 
Specitically  the  main  objects  sought  in  devising  and  using 
these  special  appliances  are,  to  avoid  danger  of  caries,  as  well 
as  other  injuries  to  the  natural  teeth;  to  secure  greater  stabil- 
ity to  the  dentuite  than  can  be  derived  from  the  use  of  clasps ; 
to  produce  esthetic  restorations  of  the  highest  tyi)e;  and 
finally,  to  develop  a  means  of  reteution  applicable  in  cases 
where  clasps  for  any  reason  are  contra-indicated. 

Most  of  these  appliances  consist  of  two  parts,  and  re((uire 
for  their  api)lication  the  crowning  of,  or  placing  inlays  in,  one 
or  more  of  the  natural  teeth.  One  of  the  parts  is  attached 
either  directly  or  indirectly  to  the  crown  or  inlay,  the  other 
to  the  denture. 


c  H  A  p  ^r  1^".  n   X  \'  1 

TECHNIC  OF  CLASP    CONSTRUCTION 

AXIAL  CONTOUR  FORMS  OF  BICUSPIDS  AND  MOLARS 

The  form  of  the  crown  of  a  bicuspid  or  molar  tooth  usu- 
ally represents  sections  of  two  more  or  less  regular  cones 
reversed,  the  bases  of  which  meet  in  a  common  plane  passing 
through  the  greatest  bucco-liugual  diameter  of  the  tooth,  Cut 
I.     The  gingival  cone  is  quite  regular,  since  the  buccal,  lin- 


CUT   I 
rUOXlMATE    \IE\\    OF    A    lilCUSI'lD    SHOWING    THE    OCCLUSAL    AND    GINGIVAL    CONES 

gual,  mesial  and  distal  axial  surfaces  converge  from  the  in- 
tersecting mid-plane  gingivally.  The  occlusal  cone  is  less 
typical  in  form,  the  buccal  and  lingual  axial  surfaces  converg- 
ing more  or  less  regularly  from  the  mid-plane  (A,  B) 
occlusally,  while  the  mesial  and  distal  surfaces  are  to  a  greater 
or  less  extent  parallel  or  divergent. 

An  elemental  factor  of  great  importance,  relative  to  the 
stability  of  clasps,  should  here  be  mentioned. 

In  Cut  II  let  a  represent  the  buccal  and  h  the  lingual 
flange  of  a  clasp  in  sectional  area.  It  will  readily  be  seen 
that  a  clasp,  so  adjusted  to  the  occlusal  cone,  when  possess- 
ing any  appreciable  grasping  properties,  will  tend  to  lift  or 
unseat  the  denture  from  the  border. 

Again,  a  clasp  without  a  stop,  adjusted  to  the  gingival 
cone  as  represented  by  c,  d,  Cut  III,  would  offer  no  re- 
sistance to  masticatory  stress,  and  if  capable  of  grasping  the 


TKC'HNIC    OK    CLASP    CONSTRUCTION 


tooth,  would  constantly  cause  imduo  pressure  of  the  denture 
against  tlie  border.  As  a  result,  elongation  of  the  tooth  or 
absorption  of  the  border  must  eventually  occur. 

Third,  let  e,  f,  or  g,  h,  Cuts  IV  and  V,  represent 
a  clasp,  one  flange  of  which  embraces  the  occlusal  and  the 
other  the  gingival  cone  of  a  tooth.    In  this  case,  while  passive 


CUT  II 
ADAPTED      TO       OCCLUSAL 
CONE   OF  TOOTH 


CUT  III 
■LASP     ADAPTED     TO    GIN- 
filVAL   CONE   OP   TOOTH 


stability  may  be  developed,  little  or  no  resistance  to  move- 
ment, either  giugivally  or  occlusally,  will  result. 

It  is  therefore  apparent,  that  in  order  to  develop  maxi- 
mum stability  under  all  conditions,  a  clasp  should  embrace  a 
portion  of  each  cone  base,  i.  /,  Cut  VI,  on  both  buccal  and  lin- 
gual surfaces  of  the  tootli.  While  it  is  not  always  possible  to 
secure  this  ideal  I'elationship  between  clasp   and  tooth,   the 


CLASP  jUJAPTED  to 
BUCCOOCCLUSAL  AND 
L  I  N  G  U  O  -  G  INGIVAL 
CONE  OF  TOOTH 


CLASP  ADAPTED  TO  BUCCO 
GINGIVAL  AND  LINGCO-OC 
CLUSAL  CONT;   of  TOOTH 


CLASP  ADAPTED  TO 
EMBRACE  BOTH  OC- 
CLUSAL AND  GIN- 
GIVAL   CON-ES 


principle  should  be  kept  in  mind,  and  an  eti'ort  made  to  utilize 
it  as  fully  as  conditions  permit. 


OUTLINE  OF  THE  VARIOUS  STEPS 

To  encourage  precise  technic  in  the  construction  of 
clasj3s,  and  in  the  application  of  these  appliances  to  denture 
retention,  the  various  steps  which  have  proven  satisfactory 
will  now  be  given  in  se<|uen('e,  witli  more  or  less  detail. 


252  TECHNIC    OF    ChASI'    CONSTRIK'TION 

Assuming  that  tlio  ]jlan  of  the  deiituro  has  been  deter- 
mined, and  that  suitable  teeth  for  clasping  are  present  and 
in  proper  i^osition  to  insure  denture  balance,  the  outline  of 
procedures  is  as  follows. 

First — Securing  an  imi)ression  of  each  tootli  to  be 
clasped. 

Second — Rebuilding  tiie  iin])r('ssion  for  receiving  and 
retaining  the  die  metal. 

Third — Melting  the  die  metal  and  casting  the  die. 

Fourth — Cutting  the  clasp  metal  to  suitable  dimensions. 

Fifth — Consideration  of  the  axial  contour  forms  of  bi- 
cuspids and  molars. 

Sixth — Preliminary  concaving  of  the  strip  to  aid  in  sur- 
face adaptation. 

Seventh — Securing  peripheral  ada]3tation  of  the  strip 
to  the  die  with  pliers. 

Eighth — Securing  surface   adaptation   with   hammer. 

Ninth — Developing  final  surface  and  peri])heral  aday)ta- 
tiou  with  pliers. 

Tenth — Soldering  stops  and  anchorage  lugs. 

Eleventh — Finishing  with  files  and  polishing. 

Twelfth — Securing  the  correct  relation  between  the 
clasps,  the  teeth  they  embrace,  and  the  baseplate. 

Thirteenth — Uniting  the  several  factors  of  the  denture. 

SECURING  AN  IMPRESSION  OF  THE  TOOTH  TO 
BE   CLASPED 

An  impression  of  the  tooth  to  be  clasped,  as  well  as  those 
teeth  which  jiroximate  it,  if  any  are  present,  should  be  taken 
in  plaster.  The  impression  should  include  not  only  the  tooth 
crowns  but  extend  well  onto  the  buccal  and  lingual  alveolar 
borders  as  well. 

By  using  a  small  sectional  or  hinged  tray,  jointed  mesio- 
distally  along  its  occlusal  floor,  the  plaster  may  be  fractured 
and  removed  in  two  principal  sections.  This  manner  of  re- 
moval obviates  the  breaking  of  the  plaster  which  surrounds 
the  crevices  of,  and  fills  the  embrasures  between,  the  teeth. 
An  improvised  cardboard  tray,  when  properly  shaped,  will 
fulfill  the  same  purpose  as  a  divided  metal  tray.  An  ordinary 
metal  tray  may  be  used,  but  should  first  be  oiled  before  in- 
troducing the  plaster,  to  permit  its  ready  removal  from  the 
impression  before  the  removal  of  the  latter  from  the  teeth. 
The  impression  may  then  be  divided  and  removed,  and  re- 
turned to  the  tray,  or  the  parts  may  be  adjusted  and  the 


TECHNIC    OF    CI.ASP    CONSTRUCTION  253 

impression  rebuilt,  as  subsequently  described.  In  such  case, 
the  impression  should  be  grooved  along  its  occlusal  surface, 
when  by  pressure  outward  on  the  buccal,  and  inward  on  the 
lingual  parts,  it  can  be  easily  fractured  and  removed. 


HINGED   TRAV.    WITH    FRAITIREI)    IMI'RESSIOX    I'l.OSED 

To  facilitate  the  ready  fracture  of  the  impression  for 
removal,  on  introduction,  it  should  be  carried  occlusally  until 
the  floor  of  the   tray  touches  the  cusps,  thus   reducing  the 


IMPRESSION,  TAKEN'  WITH  CARDHOARD  TRAY 


depth  of  plaster  in  this  area  so  that  on  pressure  it  will  read- 
ily break 

]\lodehng   conijjound  is  not  a   suitable  material   for  im- 


slclKNll      IHW     SlirKBII     lOR    IMI'UE.SSKIX    OK    AN     ISOLATED    TOOTH 

pressions  in  clasp  work  for  two  reasons ;  first,  because  it 
usually  distorts  in  removal,  and  second,  because  fusible  metal 
will  not  cast  sharply  in  such  an  impression.     It  may.  how- 


254  TIOCHNU;    OK    CLASP    ( 'ONSTUrCTION 

ever,  be  employed  by  the  seetioual  nietliod,  wlieii  the  models 
are  to  be  rnn  in  ('cmciil  or  modelite. 

REBUILDING  THE   IMPRESSION    FOR   RECEIVING   AND 
RETAINING  THE  DIE  METAL,  WHEN  CAST 

An  impression  of  one  or  more  teeth  intended  for  die  con- 
struction in  clasp  work  must  be  rebuilt,  or  prepared  for  the 
reception  of  the  die  metal.    The  steps  are  as  follows : 

The  impression,  having  been  removed  from  the  mouth, 
the  fractured  surfaces  are  freed  from  debris,  the  broken 
parts  replaced  in  proper  relation  to  each  other  and  luted  with 
sticky  wax  sufficiently  to  hold  them  together.  No  wax  should 
occupy  any  portion  of  the  matrix,  as  its  presence,  on  pouring 
the  molten  metal,  would  generate  gas  and  result  in  an  im- 


IMPRESSION  OF  TOOTIt  TO  BE  CLASrED,   TAKEN  WITH  HINGED  TRAT 

perfect  casting.  By  exercising  care  in  handling  the  assembled 
impression  the  use  of  wax  can  frequently  be  dispensed  with. 

To  strengthen  the  assembled  impression  and  hold  it 
firmly  together  a  mix  of  plaster  is  made  and  spread  on  a 
piece  of  paper  on  the  bench.  Into  this  plastic  mass,  the  im- 
pression, and  tray,  if  the  latter  has  been  used  for  holding  the 
fractured  pieces  together,  should  be  sunk  deeply,  and  the  sur- 
plus built  around  the  sides  and  into  the  ends  of  the  impres- 
sion to  form  walls  for  confining  the  metal  in  casting.  It  is 
frequently'  necessary  to  make  additions  to  the  buccal  and 
lingual  margins  of  the  impression  so  as  to  bring  them  up  to 
uniform  height,  and  give  good  depth  to  the  die. 

For  convenience  in  clas])  consti'uction,  the  die  should  be 
from  %  to  1  inch  in  diameter  across  its  base  and  about  1 
inch  in  depth.     These  dimensions  insure  ease  of  handling, 


TECHNIC    OP    CLASP    CONSTRUCTION  255 

and  afford  sufficient  weight  to  the  die  to  render  hammei' 
blows  effective  when  directed  against  the  clasp.  A  die  of 
these  dimensions  will  require  about  l^^  to  2  ingots  of 
Melotte's  metal.    The  use  of  too  light  and  small  a  die  is  re- 


REBriLT     IMPRESSION".       TRAY     AXD 
IMTRESSION   ENCLOSED    IN    SFK- 
ItOUNDINO    PLASTER 


sponsible   for   nuich   of   the   difficulty   encountered   iu    clasp 
construction. 

Since  the  matrix  gives  form  to  the  die,  with  these  di- 
mensions in  mind,  its  formation,  by  imbedding  the  impression 


TOP    MEW   OF   ftEBUILT    IMPRESSION    SHOWING   BINDING 
WIRES   STILL   IN   POSITION 

in  plaster  as  described  and  by  proper  trimming,  is  readily  ac- 
complished. The  usual  method  of  forming  the  matrix  liy  the 
addition  of  mouldiiie  is  more  tedious  and  less  accurate  than 
when  plaster  is  employed.     Unless  firmly  luted,  the  broken 


256  TECHNIC    OP    Cl.ASP    CONSTRUCTION 

parts  are  very  liable  to  hecoiiic  distorted  iind  weds^cd  apart 
in  applying  the  clay. 

When  teeth  proximate  luesially  and  distally  with  the 
tooth  to  be  clasped,  the  impression  of  the  tooth  adjacent  to 
the  interproximate  space  throngh  which  the  clasp  is  to  pass 
shonld  be  tilled  in  with  plaster  or  mouldine,  to  exclude  the 
molten  metal  in  casting.  The  presence  of  a  tooth  in  such  lo- 
cation on  the  die  seriously  interferes  with  clasp  construction. 
The  other  proximating  tooth  should  be  developed  in  the  cast- 
ing, as  it  serves  as  a  guide  in  finishing  the  terminal  ends  of 
the  clasp.  Any  unnecessary  irregularities  such  as  higli  points 
or  depressions,  present  within  the  matrix,  should  be  corrected 
by  trimming  or  additions  as  required.  The  general  form  of 
tJse  die  should  be  cone  shaped,  from  its  base  occlusally. 

The  impression  having  been  converted  into  a  matrix  as 
described  it  should  be  closely  inspected  to  see  that  all  essential 
parts  are  in  place,  that  no  loose  particles  of  debris  are  pres- 


JIELTINO    LADLE    FOR    Ki:SnU.E    JIETAL 


ent,  and  that  no  openings  exist  at  any  jMjint  through  which 
the  molten  metal  can  escape  when  cast. 

Drying  the  plaster  matrix  before  casting  the  die  is  not 
essential,  since  the  fused  metal,  when  poured  at  a  low  tem- 
perature, generates  but  little  steam,  while  that  which  does 
form  finds  ready  exit  outwardly  through  the  matrix  walls.  On 
the  other  hand,  overheated  metal  cast  into  a  damp  or  even 
partially  dried  matrix  will  cause  such  rapid  generation  of 
steam  that  it  cannot  all  escape  before  the  metal  solidities.  Cast- 
ing under  such  conditions  usually  results  in  imi)aired  density 
or  deficient  sharpness  of  the  die. 

CASTING  THE  DIE 

Two  ingots  of  Melotte's  metal  are  placed  in  a  small  melt- 
ing ladle  and  held  over  the  Bun  sen  flame  until  a  little  more 
than  half  of  the  mass  is  fused.  The  ladle  is  then  removed 
and  the  half-melted  metal  stirred  with  a  small  instrument  or 
flat  wooden  spatula,  to  disseminate  the  accumulated  heat 
throughout  the  mass  until  all  is  fused.    Stirring  also  prevents 


TECHNIC  OF  CLASP  CONSTRUCTION  li.",? 

liquatiun  of  tlie  comiioueut  metals,  which,  on  aceouut  of  their 
different  specific  gravities,  gradually  occurs.  The  film  of 
oxide  which  forms  on  the  surface  should  be  skimmed  off  be- 
fore pouring. 

By  watching  the  surface  of  the  fused  metal  at  its  margins, 
it  will  be  seen  that  the  spherical  appearance  noticeable  in  most 
metals  when  fused  gradually  disappears,  and  as  the  tempera- 
ture is  reduced  the  alloy  will  settle  squarely  against  the  ladle 
wall.  This  appearance  denotes  that  the  metal,  although  some- 
what reduced  in  temperature,  is  in  its  most  fluid  condition,  and 
when  cast  will  adapt  itself  to  the  most  irregular  surfaces. 

Usually  in  this  class  of  work  the  casting  is  deferred  until 
the  metal  begins  to  lose  its  fluidity,  or  is  on  the  point  of 
congealing,  in  which  condition  little  or  no  steam  will  be  gen- 
erated, and  a  dense,  sharp  casting  may  be  obtained. 

As  soon  as  the  die  has  hardened  it  can  be  quickly  chilled 
in  cold  water,  although  it  will  be  less  brittle  if  allowed  to  cool 
slowly. 

When  freed  from  the  impression  and  cooled,  the  die  should 
be  inspected  for  defects.  These  usually  appear  as  excres- 
cences, di;e  to  openings  or  spaces  in  the  impression,  caused 
by  loss  of  broken  particles  in  assembling  the  impression  and 
into  which  the  metal  is  cast.  These  defects  are  filed  or  chiseled 
away  so  as  to  restore  the  tooth  to  correct  form.  The  em- 
brasures, when  filled  in,  should  he  burred  or  chiseled  out  and 
the  die  is  ready  for  use. 

CUTTING   THE   CLASP    METAL   TO    SUITABLE 
DIMENSIONS 

A  strip  of  No.  (50  tinfoil,  adapted  to  the  tooth  with  the 
fingers,  and  by  burnishing  if  necessary,  is  cut  to  suitable 
length,  and  slightly  wider  than  the  required  clasp,  to  serve 
as  a  pattern  for  cutting  the  strip  of  clasp  metal.  This  pat- 
tern is  laid  on  a  piece  of  clasp  plate  of  the  required  thickness, 
lengthwise  of  the  lamina  developed  in  rolling  the  ingot  into 
sheet  form,  and  its  outline  marked  with  a  sharp  instrument. 
Failure  to  parallel  the  clasp  with  the  lamina  of  the  plate 
usually  results  in  fracture  of  the  clasp  during  construction  or 
under  slight  stress  when  in  use.  It  also  insures  greater  resil- 
iency in  the  clasp. 

When  a  stop  is  to  he  formed  from  the  same  piece  of  plate 
it  should  be  so  indicated  on  the  ]iatteni  and  the  strip  cut 
wider  at  this  point. 


258  TECHNIC    OK    CLASP    CONSTRUCTION 

Befoi'e  beginning  to  conform  the  strip  of  clasp  metal  to 
the  die  it  should  be  carefullj^  and  imiformly  annealed  at  a 
low,  red  heat.  This  reduces  its  stitTness  but  does  not  deprive 
it  of  all  of  its  resiliency.  The  full  degree  of  elasticity  may  be 
restored  in  the  final  polishing  by  subjecting  the  completed 
clasp,  after  the  final  soldering,  to  the  action  of  a  stiff  brush 
wheel,  on  a  high  speed  lathe,  and  Ity  burnishing. 

PRELIMINARY   CONCAVING   OF  THE   STRIP  OF  CLASP  METAL 

When  the  clasp  strip  has  been  cut  as  described,  the  first 
preliminary  step  in  adaptation  is  to  concave  it  from 
end    to    end    with    the    hawkbill    ])liers,    on    that    side    to 


HAWKBILL    PLIERS    AS    iVTrLIED    l.\    COXCAVIXG    THE    STRIP    OF    CLASP    METAL 

be  applied  to  the  tooth.  This  concave  depression  em 
braces  the  cone  bases  or  greatest  diameter  of  the  tooth, 
and  permits  the  occlusal  and  gingival  margins  of  the 
clasp  to  rest  in  contact  with  the  more  or  less  convex  axial 
walls  of  the  tooth  as  peripheral  adaptation  is  carried  on,  step 
by  step. 

The  terminal  end  of  the  strip,  which  rests  in  the  em- 
brasure and  where  adaptation  is  to  begin,  should  be  rounded 


APri.yiNG    THE    (TRVED     END    OF    CLASP    METAL    STRIP    TO    TOOTH 

on  the  gingival  edge,  curving  it  so  as  to  parallel  the  gum 
margin  as  it  rises  in  the  embrasure,  where  this  end  of  the 
clasp  will  rest. 


TECHNIC    OF    CLASP    CONSTRX'CTION  259 

Frequently  the  convexity  of  the  .slrij)  produeed  by  the 
hawkbill  pliers  is  greater  than  that  of  the  axial  walls  of  the 
tooth.  The  central  portion  of  the  clasp  will  then  stand  away 
from,  while  the  occlusal  and  gingival  margins  will  lie  in  con- 


tact with  the  axial  walls.  This  is  an  advantage  rather  than 
a  detriment,  as  light  hammer  blows,  in  subsequent  steps,  will 
reduce  the  excess  curvature  and  develop  surface  adaptation. 

SECURING  PERIPHERAL  ADAPTATION   OF  THE  STRIP 
TO  THE  DIE  WITH  PLIERS 

The  i)eripheral  ada])tation  of  a  clasp  to  a  die  should  be 
developed  by  steps  rather  than  by  converting  the  strip  at  the 
outset  into  a  partial  baud  of  general  form  by  means  of  the 
clasp  benders.  The  latter  method,  although  most  commonly 
followed,  is  less  accurate  at  the  start  and  in  the  end  will  result 
in  requiring  greater  care  in  securing  adaptation  than  where 
the  former  method  is  employed.  The  following  procedure  is 
practical,  accurate  and  rapid,  when  once  the  technic  is  under- 
stood, and  the  required  skill  for  carrying  it  out  is  developed. 

The  concaved  strip,  its  angle  rounded  as  described,  is  car- 
ried into  the  embrasure  where  it  is  eventually  to  rest,  and  laid 
closely  against  the  axial  surface  of  the  tooth.  By  viewing  it 
oeclusally,  the  areas  not  in  contact  are  readily  noted.  The 
strip  is  then  removed,  held  firmly  with  the  fingers  near  the 
end  being  adapted  and  with  the  hawkbill  pliers  applied  to  an 
area  not  in  contact,  a  positive  bend  is  made  in  a  direction  to 
secure  the  desired  adaptation.  It  should  again  be  returned 
to  the  die  and  the  change  wrought  by  bending  noted.  One 
or  two  additional  beiids  and  trials  may  be  required  to  effect 
reasonably  close  adaptation  of  the  strip  against  an  area  rep- 
resenting about  one-sixth  of  the  tooth  periphery.  In  the  same 
manner  the  strip  is  grasped  somewhat  further  in  from  the 
end  already  conformed,  while  other  bends  are  similarly  made 
until  the  areas  of  the  clasp  not  touching  the  die  are  brought 
into  reasonablv  close  contact. 


260  TKCHNIC    OF    CI.ASl'    CONSTKrCTlON 

When  a  torsional  licnd  in  the  clasp  is  required,  as  iu 
turuing'  the  angles  of  a  bell-erowued  tootli,  it  can  be  accom- 
plished by  substituting  a  pair  of  pliers  for  the  fingers  for 
holding  the  unadapted  strip,  the  hawkbills  being  applied  to 
the  adapted  portion,  while  round  or  flat  beak  or  another  pair 
of  hawkbill  pliers  can  be  used  on  the  unadapted  portion,  as 
the  contour  of  the  surfaces  requires. 

To  illustrate  the  steps  as  outlined,  the  adaptation  of  a 
clasp  to  an  upper  first  bicuspid  will  be  described.  The  two 
ends  of  the  clasp  will  terminate,  mesially. 

The  strip  of  concaved  clasp  metal  is  ai^plied  to  the  mesio- 
buccal  angle  of  the  axial  surface  of  the  tooth  and  the  areas 
not  in  contact  noted.    These  are  connected  to  the  crest  of  the 


buccal  ridge,  usually  representing  a  linear  distance  of  about 
three-sixteenths  of  an  inch.  Adaptation  should  then  be 
secured  between  the  buccal  ridge  and  the  disto-buccal  angle 
in  like  manner.  Then  the  turn  is  made  ai'ound  this  angle 
and  adai)tation  secured  across  the  distal  surface,  to  the  disto- 


lingual  angle.  From  this  point  the  strip  is  bent  against  the 
lingual  surface  to  the  center  of  this  side.  The  final  step  con- 
sists in  turning  the  mesio-lingual  end  of  the  strip  into  place. 
Thus  the  process  of  peripheral  adaptation  of  a  clasp  consists 
of  five,  or,  in  certain  cases,  seven  distinct  steps  where  the 
terminal  ends  of  the  clasp  require  special  adaptation  in  the 
embrasures. 

SECURING  SURFACE  ADAPTATION  OF  THE  CLASP  TO 
DIE  WITH  HAMMER 

Peripheral  adaptation  refers  to  the  bending  of  the  strip 
into  partial  band  form,  so  that  it  eiiibraces  the  ])eriphery  of 


TECHNMC    OF    ('[.AST    ("ONSTRCCTION 


the  tt)otli  closely  tiiroiiniumt  its  ciilirc  li'iigtli.  Peripheral 
eontaet,  however,  does  not  imply  that  the  entire  inner  surface 
of  the  stri])  is  in  close  adaptation  to  the  die  at  all  points  or 
throughout  its  entire  occluso-gingival  width. 

Surface  adajitation  involves  not  only  good  peripheral 
contact,  but  close  approximation,  occluso-gingivally  of  the 
partial  band  to  the  axial  walls  of  the  tooth  or  die  as  well. 
Peripheral  contact  is  comparatively  easy  to  develop  with  suit- 
able pliers,  but  of  itself  does  not  afford  the  required  stability 
in  the  completed  clasp.  Surface  adaptation  is  essential  to 
stability,  Init  is  much  moi-e  difficult  to  secure,  especially  in 
the  thicker  gauges  of  clas])  metal.    The  ]ireliminary  concaving 


KIVETING     HAMMER 


of  the  strij)  with  the  liawkl)ill  pliers  aids  greatly  in  securing 
surface  adaptation. 

Since  the  concavity  of  the  clasp  is  more  or  less  uniform  in 
curvature  from  end  to  end  and  the  axial  walls  of  the  tooth 
constantly  vary  in  curvature,  it  becomes  necessary  to  de- 
crease over  some  and  increase  over  other  areas  the  concavity 
of  the  clasp.  This  is  most  easily  accomplished  with  the  small 
riveting  hammer. 

The  die,  when"  of  the  dinumsions  jireviously  mentioned, 
serves  the  same  purpose  as  an  anvil  and  affords  ample  re- 
sistance to  hammer  blows,  so  that  heavy  gauges  of  clasp  metal 
are  readily  conformed  to  its  surfaces  under  such  stress,  ]u-op- 
erly  applied. 


262  TIOCHNIC    Ol'    CI.ASI'    f'ONSTUt'CTlON 

To  (k'\i'lop  sui'I'acc  iulaiilatidii.  Ilic  siuiic  oihUt  of  pro- 
cedure as  was  followed  with  the  ])liers  is  carried  out  witli 
the  liaimuer,  the  blows  iK^iiif?  first  directed  against  the  mesio- 
buccal  section  of  the  clasj)  and  continued  around  to  the  op- 
posite terminal.  The  ai)plication  of  the  hammer  and  the  horn 
])eni'  mallet  causes  the  clas])  to  ojK'n,  so  that   fi'om  time  to 


llE[.OTTF/S    HORN   PEXE    HAMMER 


time  it  will  be  necessary  to  remove  it  from  the  die  and  reduce 
its  diameter  with  pliers  and  by  finger  jiressure,  until  it  again 
grasps  the  metal  pattern  firmly. 


FINAL  ADAPTATION  OF  THE  CLASP  TO  THE  DIE 

When  general  surface  adaptation  between  clasp  and  die 
has  been  secured  with  the  hammer,  the  final  finishing  touches 


TKCHNIC    OF    CLASP    CONSTRUCTION  263 

are  given  with  tlie  pliers.  The  clasp  should  grasp  the  die 
tooth  so  firmly  as  to  require  considerable  foi'ce  to  dislodge  it. 
Usually  a  clasp,  when  transferred  from  the  die  to  the  natural 
tooth  in  the  mouth,  will  fail  to  grasp  it  closely,  even  though  it 
may  fit  the  die  perfectly.  This  is  due  to  the  fact  that  the  die 
metal  in  cooling  expands  slightly,  and  therefore  the  die  is  in 
reality  a  trifle  larger  than  the  tooth.  Correction  is  easily 
made  in  adjusting  the  clasp  to  the  natural  tooth  in  the  mouth 
by  bending  the  two  flanges  slightly  toward  one  another. 

SOLDERING  THE  STOPS  AND  ANCHORAGE  LUGS  TO 
THE  CLASP 

When  the  clasp  is  constructed  without  a  stop,  and  it  is 
deemed  advisable  to  attach  one,  the  steps  are  as  follows :  Cut 
a  piece  of  22  gauge  clasp  metal  about  1-16  of  an  inch  wide  and 
of  suitable  length  to  form  the  hook  over  the  marginal  ridge, 
extend  gingivally  to  the  ridge  and  furnish  attachment  to  the 
metal  or  vulcanite  liaseplate.  The  clasp  is  placed  in  position 
on  the  die  and  with  a  pair  of  pliers  the  strip  of  metal  is  con- 
formed as  closely  as  may  be  to  the  clasp  and  die,  the  final 
adaptation  being  secured  with  the  hammer. 

The  clasp  and  stop  are  waxed  together  in  proper  relation 
to  each  other  on  the  die,  removed,  invested  and  soldered. 
Final  adjustment  of  the  clasp  to  the  die  is  now  made,  and  the 
position  of  l)oth  the  occlusal  and  gingival  ends  of  the  stop  bar 
corrected  if  necessary.  That  portion  of  the  bar  which  forms 
the  anchorage  lug  should  lie  close  to  the  crest  of  the  border, 
somewhat  to  the  lingual  so  as  not  to  interfere  with  the  placing 
of  the  artificial  teeth.  It  is  frequently  necessary  to  reinforce 
this  iiortion  of  the  bar  so  as  to  render  it  rigid  and  unyielding, 
and  thus  obviate  distortion  of  the  relation  between  the  clasp 
and  denture  when  subjected  to  stress.  Many  clasps,  other- 
wise well  planned  and  serviceable,  fail  because  the  anchorage 
lugs  are  weak,  lack  rigidity  and  bend  under  stress. 

FINISHING  THE  CLASP 

The  ends  and  outer  margins  of  the  clasp  should  be  round- 
ed and  beveled  with  files  and  engine  discs,  and  finally  polished 
with  felt  wheels  and  polishing  powders.  Wlien  properly  fin- 
ished, the  tendency  of  the  clasp  margins  to  irritate  the  soft 
tissues  of  the  cheeks  and  tongue  is  obviated,  and  the  liability 
of  food  to  accumulate  around  the  appliance  is  reduced  to  the 
minimum. 


2til  TPX'HNIC    OK    CLASP    CONSTRUCTION 

Holding  till'  tiiiislied  clasp  i'ur  a  short  tinu'  against  a  stiff 
brush  wheel  running  at  high  speed  will  restore  the  elasticity 
in  the  metal,  which  has  become  reduced  as  a  result  of  solder- 
ing operations.  Eubhing  vigorously  with  a  burnisher  will  also 
have  a  similar  effect. 

VARIOUS    METHODS   OF   CLASP   CONSTRUCTION 

Other  methods  of  clasp  construction  than  those  previ- 
ously described  are  frequently  employed  to  good  advantage, 
some  of  which  will  here  be  briefly  outlined. 

COMBINATION    CLASP   OF    PURE    GOLD    WITH    CLASP   METAL 

Secure  an  impression  of  the  tooth  to  be  clasped.  From 
this  develop  a  model  tooth  in  some  good,  hard  investment  com- 
pound. To  this  model  adapt  a  piece  of  pure  gold  of  the  form 
of  the  clasp  desired,  of  32  or  34  gauge.  The  adaptation  can 
be  readily  secured  first  with  pliers  and  finally  ])y  burnishing 
to  the  model  tooth.  On  this  pure  gold  foundation  apply  a  par- 
tial band  of  clasi>  metal,  slightly  narrower  than  the  clasp  is 
to  be  when  finished,  and  usually  of  2G  gauge.  The  adaptation 
of  the  strip  of  clasp  metal  to  the  i^ure  gold  foundation  clasp 
should  be  reasonably  close,  but  not  necessarily  perfect.  Be- 
tween the  pure  gold  and  the  clasp  metal  strengthener  flow  18 
carat  solder,  contouring  the  outer  surfaces  of  the  clasp  at  the 
same  time,  as  conditions  require.  The  soldering  of  the  two 
pieces  is  accomplished  on  the  model  tooth.  This  is  necessary, 
because  if  removed  from  the  tooth  the  pure  gold  foundation, 
which  is  practically  devoid  of  resiliency,  would  in  all  probabil- 
ity be  permanently  distorted.  Final  adaptation,  which  usually 
consists  in  slighty  reducing  the  diameter  of  the  clasp,  can  be 
accomplished  in  adjusting  to  the  natural  tooth. 

The  objections  to  a  clasp  of  this  type  are,  first,  the  gold 
which  embraces  the  tooth,  because  of  its  softness,  will  in  time 
be  reduced  by  wear,  and  second,  the  resilient  index  of  such  a 
clasp  is  low  in  comparison  to  its  bulk.  Platinum,  or  prefer- 
ably iridio-platinum,  being  slightly  harder,  can  be  used  to  bet- 
ter advantage  for  the  foundation  than  pure  gold. 

CAST    CLASPS 

Clasps  of  any  form  desired,  including  stops  and  ane!ior- 
age  lugs,  can  be  readily  cast  by  the  usual  technic  employed  in 
inlay  work.    Clasps  of  this  type,  however,  are  lacking  in  resil- 


TKCHNIC    OF    CLASP    CO.VSTKIK'TIOX  litif) 

iciK-y,  ami  tui  account  of  the  more  or  less  granular  or  crystal- 
line characti'r  llii'  clas]i  metal  assiiincs  when  cast,  are  very 
liable  to  break  under  stress. 

THE  WIRE  LOOP  CLASP 

The  oonsti'uction  of  a  round  wire  clasj)  is  a  conijiaratively 
simple  operation.  It  is  essential  that  a  Jiard,  resistent  die  be 
formed  of  Melotte's  metal,  amalgam  or  some  of  the  cements, 
to  which  the  wire  may  he  litte<l  with  jiliers  and  by  light  ham- 
mer blows. 

A  plain  wire  loop  clasp,  which  embraces  a  little  more  than 
one-half  of  the  periphery  of  a  tooth,  may  be  readily  and  quick- 
ly conformed  to  the  axial  walls  of  the  die  as  follows: 

As  a  preliminary  requirement  in  such  cases,  the  teeth 
)iroximatiug  the  one  to  be  clasped  should  be  eliminated  in 
forming  the  die  so  that  the  latter  may  stand  alone.  The  wire, 
bent  in  the  form  of  an  elongated  looji,  is  conformed  to  the 
l)eri])hery  of  the  die  tooth  with  pliers.  Through  the  two  ends 
of  the  clasp  a  strii)  of  28-gauge  Gernian  silver  plate  from  1-16 
to  V,s  inch  wide,  depending  on  the  distance  apart  it  is  deemed 
advisable  to  ])lace  the  occlusal  and  gingival  loops,  is  threaded 
and  doubled  back  ou  itself  so  as  to  form  a  loop.  With  the 
flat-n'osed  ])liers  the  two  ends  of  the  strip  are  grasped  and 
twisted  tightly  together.  The  resulting  tension  draws  the 
wire  loop  clasp  tightly  around  the  die.  A  few  light  hammer 
blows  applied  peripherally  to  the  wires  will  permanently  set 
them  to  the  form  of  the  tooth.  Stops  and  anchor  lugs  are 
attached  by  soldering  as  jireviously  described. 

CONTINUOUS  AND  OPEN-LOOP  CLASP 

A  number  of  new  forms  of  continuous  and  open  wire  loop 
clasps  have  been  designed  and  presented  to  the  profession  by 
Dr.  F.  E.  Roach.  In  many  cases  clasi)s  of  the  type  imder  con- 
sideration are  most  useful  and  efficient  and  have  the  advan- 
tage of  extensive  peripheral  contact  with  the  tooth,  while  the 
area  covered  by  the  clasp  is  extremely  limited. 

A  piece  of  18-gauge  clasp  wii'e  for  open  loop,  and  19  or 
20  gauge  for  continuons  loop,  is  bent  in  staple  form.  This  bend 
or  loo]),  forms  an  occlusal  rest  or  stop,  when  a  proximating 
tooth  is  present.  Its  principal  purpose,  however,  is  to  connect 
the  buccal  and  lingual  portions  of  the  clasp,  which,  if  not  so 
joined,  would  lack  inherent  strength.  From  the  occlusal  bend 
both  buccal  and  lingual  wires  drop  into  their  respective  em- 


2t;fi  TECHNIC    OF    CLASP    rONSTRl'CTIOX 

bi'cisures  to  the  gingival  third  of  the  tootii  chisped  when  they 
are  eonfornied  to  the  Iniccal  and  lingnal  surfaces  of  the  tooth, 
joining  on  the  opposite  proximate  surface  to  form  the  anchor- 
age lug.  A  continuous  loop  clasp  of  this  type  can  be  converted 
into  an  open  loop  clasp  by  soldering  the  two  terminals  to- 
gether, which  form  the  anchorage  lug  and  severing  the  lahial 
or  buccal  loop.  The  two  terminals  may  be  doul)led  back  upon 
themselves  and  soldered  for  greater  strength  or  to  increase 
the  areal  bearing  of  the  clasp  if  necessary.  The  forms  of 
these  clasps  and  their  range  of  application  seem  limited  only 
by  the  ingenuity  of  the  operator. 

In  api)lying  clasps  of  any  type  to  a  partial  denture  the 
fact  should  be  borne  in  mind  that  clasps  are  not  designed  to 
take  up  the  stress  of  mastication,  but  merely  serve  to  keep 
the  denture  seated  on  its  border  in  speaking  and  during  mas- 
ticatory effort.  Thus  it  will  be  seen  that  clasps  of  this  type 
will,  in  very  many  cases,  fulfill  all  the  requirements  efificiently. 

SECURING    THE    RELATION    BETWEEN    CLASPS,    THE 
TEETH  THEY  EMBRACE  AND  THE  BASEPLATE 

When  a  ])artial  clasp  denture  is  finished  and  introduced 
in  the  mouth  it  should  bear  evenly  and  comfortably  on  the 
tissues  and  occasion  the  wearer  no  distress  or  inconvenience. 
Kach  clasji  should  embrace  its  respective  tooth  firmly  and  yet 
subject  it  to  no  leverage,  wedging  or  torsional  strain.  These 
conditions  can  only  be  develojjed  during  the  constructive 
stages,  with  skillful  technic,  by  securing  the  correct  relation- 
ship between  the  clasps,  the  teeth  they  embrace  and  the  base- 
plate or  denture.  The  following  method  is  practical  and  accu- 
rate and  should  be  carried  out  in  the  order  detailed  in  most 
cases.  The  clasps,  having  been  conformed,  preferably  to 
metal  dies,  are  adjusted  to  the  teeth  in  the  mouth.  This  step 
proves  the  acciiracy  of  their  adaptation.  Should  they  shift 
in  any  manner  or  fail  to  grasp  the  tooth  firmly,  correction 
must  be  made  until  satisfactory  adaptation  is  secured  before 
proceeding  further.  They  are  then  removed  and  the  base- 
plate is  introduced  when  each  clasp  is  returned  to  position  on 
its  respective  tooth.  Should  either  clasiJ  fail  to  go  to  correct 
position,  the  baseplate  or  clasp,  or  both,  should  be  filed  away 
at  the  points  of  interference  until  each  factor  can  assume  its 
correct  position  without  disturbing  the  other. 

Usually  the  baseplate  should  fit  snugly  against  all  of  the 
teeth  involved,  including  those  clasped,  the  gingival  margin 


TECHNIC    OF    CLASP    CONSTRUCTION  267 

of  each  clasp  either  resting  on  or  clearing  the  periphery  of  the 
baseplate,  and  occupying  a  iDosition  to  the  occlusal  of  the  lat- 
ter. Variations  from  this  rule  are  sometimes  necessary,  as 
in  case  a  tooth  crown  is  extremely  short,  to  insure  grasping 
properly  it  may  be  necessary  to  extend  the  gingival  margin 
of  the  clasp  slightly  under  the  free  margin  of  the  gum.  In 
such  instances  clearance  for  the  clasp  must  be  gained  by  filing 
the  baseplate  to  accommodate  the  former.  Such  relationship 
between  clasji  and  baseplate,  although  at  times  necessary, 
should  be  avoided  when  possible  because  of  the  liability  of  the 
clasp  to  set  up  gingival  or  peridental  inflammation. 

TAKING  THE  IMPRESSION  OF  THE  CLASPS,  TEETH 
AND  BASEPLATE 

The  clasps  being  in  position  on  the  teeth  and  the  base- 
plate tirmly  seated  on  the  tissues  an  impression  is  taken  in 
jtlaster.  This  need  not  be  extensive,  but  should  fully  embrace 
the  clasped  teeth,  both  bnccally  and  lingually,  and  the  greater 
l)ortion  of  the  baseplate. 

Dn  removal  of  the  inii)ression  each  clasp  that  is  not  re- 
tained in  and  removed  with  it  is  removed  from  its  tooth, 
brushed  free  of  particles  and  returned  to  position  in  its 
matrix.  The  hinged  trays  mentioned  elsewhere  can  be  used  to 
good  advantage  in  taking  impressions  in  this  class  of  work. 
The  ends  of  the  clasp  are  now  sprung  apart  by  means  of  a 
small  peg  of  wood  inserted  between  the  liuccal  and  lingual 
flanges  to  force  them  against  the  matrix  walls  in  essentially 
the  same  relation  they  occupied  in  the  impression  when  on  the 
tooth.  Neglecting  to  carry  out  this  step  usually  results  in  per- 
manently establishing  an  incorrect  relationship  between  the 
clasp  and  baseplate.  In  securing  a  cast  fiiom  the  impression,  a 
clasp  not  properly  forced  against  its  matrix  walls  as  outlined, 
instead  of  embracing  the  axial  walls  of  the  tooth,  will  be  found 
l)artially  imbedded  within  them.  The  extent  to  which  it  is 
imbedded  in  the  lingual  surface  of  the  plaster  tooth  represents 
the  linear  movement  bucally  that  has  resulted  from  the  recoil 
of  the  clasp  on  removal  from  the  tooth.  When  this  error 
occurs,  if  not  corrected,  and  the  clasp  is  permanently  attached 
to  the  baseplate  in  such  relation,  on  introduction  of  the  den- 
ture the  tooth  clasped  will  be  forced  buccally,  oftentimes  to 
such  an  extent  as  to  render  the  i)resence  of  the  denture  un- 
bearable. 

The  clasps  having  been  adjusted  as  described,  the  base- 


26S  TKCHNIC    OK    CLASP    CONSTRUCTION 

plate  is  st't  in  ])lac'e  in  the  impression  and  Inted  firmly  witli 
wax  to  hold  it  in  place  while  secnring  the  east.  When  var- 
nished the  impression  is  filled  with  investment  ('omi)onnd,  and 
the  latter  allowed  time  to  set  hard  before  removing  the  im- 
pression. 

SOLDERING  THE  CLASPS  TO  THE  BASEPLATE 

The  attaehuieut  of  a  clasp  to  l)aseplate  is  accomplished 
by  flowing-  solder  along  the  joint  between  the  two.  The  extent 
of  attachment  shonld  be  limited,  nsnally  to  3-16  of  an  inch,  or 
less.  If  joined  to  a  much  greater  extent  the  clasp  becomes  a 
rigid,  nnyielding  band  and  will  not  fulfill  the  purpose  well 
for  which  designed.  The  attachment  should  be  made  in  as 
nearly  central  a  location  between  the  two  terminals  of  the 
clasp  as  possible,  so  as  to  utilize  and  not  destroy  the  greatest 
grasping  power  of  the  clasp. 

When  clasp  and  baseplate  are  iu)t  in  contact,  connection 
should  be  made  by  inserting  a  strij)  of  clasp  metal  or  a  piece 
of  plate  in  the  space  between  the  two  and  fiowing  solder  over 
all,  so  as  to  make  a  firm  and  rigid  attachment. 

Sometimes  when  the  tooth  clasped  is  long  and  the  space 
between  the  clasp  and  jilate  is  quite  wide,  a  rigid  wire  ex- 
tended lengthwise  between  the  two,  the  connection  being  com- 
pleted with  solder,  will  afford  a  rigid,  self-cleansing  bond 
of  union. 

The  essential  point  to  bear  in  mind  in  securing  the  correct 
relationship  between  clasps,  teeth  and  baseplate  is  that  the 
steps  should  be  carried  out  as  described  by  assembling  the 
appliances  in  the  month  and  securing  the  impression  first  hand 
from  the  tissues  against  which  the  denture  is  to  rest.  Assem- 
bling the  several  jiarts  of  the  denture  on  a  model,  while  some- 
times satisfactory,  more  often  leads  to  error,  sometimes  so 
marked  as  to  require  reconstruction,  or  at  least  reassembling 
of  the  several  parts. 


CHAPTER     XVII 

THE  MASTICATORY  MECHANISM 

At  the  present  time,  more  than  ever  before,  the  fact  is 
realized  that  the  masticatory  organs  are  of  the  most  vital  im- 
portance in  the  maintenance  and  preservation  of  health. 
Partial  or  complete  failure  of  these  organs  to  carry  on  their 
important  functions  in  the  daily  routine  of  life  will,  sooner 
or  later,  result  in  the  permanent  impairment  of  other  functions 
as  well. 

When,  through  accident  or  by  disease,  a  portion  or  all 
of  the  teeth  are  lost,  it  is  imperative  that  they  be  replaced 
with  artificial  substitutes.  Such  substitutes  should  have  the 
appearance  and  perform  the  functions  of  the  normally  ar- 
ranged natural  teeth,  and  no  effort  should  lie  considered  too 
great  in  order  to  accomplish  these  ends. 

The  normal  arrangement  of  the  teeth  in  one  arch  in  their 
relation  to  each  other  and  to  the  centers  of  rotation  of  the 
mandible,  insures  normal  occlusion  and  correct  cusp  clearance 
in  lateral  movements  with  those  in  the  opposite  arch  when 
the  latter  are  also  so  arranged. 

A  single  tooth,  however,  when  elongated,  rotated,  or  out 
of  alignment,  may  impair  the  efficiency  of  the  entire  masti- 
catory apparatus.  It  is  therefore  necessary  to  study  care- 
fully the  normal  human  denture  in  detail,  in  both  passive 
and  active  states,  to  imderstand  what  is  required  in  the  re- 
placement of  the  natural  teeth  with  artificial  substitutes. 

THE  MASTICATORY  APPARATUS 

The  normal  adult  human  masticatory  apparatus  consists 
of  four  principal  factors  or  groups  of  hard  and  soft  tissues 
which,  when  acting  conjointly,  and  in  unison  on  food,  re- 
duce it  to  a  condition  suitable  for  introduction  into  the  di- 
gestive tract.  Ou6  of  these  factors  is  practically  immovable 
or  passive  in  masticatory  effort,  except  as  the  cranium  itself, 
of  which  it  forms  a  part,  moves.  The  other  tliree  groiips  are 
active  or  movable.    They  may  be  classed  as  follows: 

First:     The  upper  maxilla  or  immovable  base. 

Second:     The  mandible  or  principal  moving  factor. 

269 


270  THE    MASTICATORY    MECHANISM 

Third:  The  group  of  muscles  which  control  and  guide 
the  movements  of  the  mandible. 

Fourth:  The  group  of  muscles  which  control  the  po- 
sition of  the  food  and  keep  it  within  the  working  limits  of 
the  teeth  in  masticatory  effort. 

THE   UPPER   MAXILLA 

The  two  superior  maxillary  bones  join  at  the  median  line 
in  a  firm,  strong  suture  to  form  the  maxilla.  This  united 
bone  constitutes  the  anterior  portion  of  the  cranial  base, 
being  directly  and  indirectly  firmly  united  with  all  of  the 
other  cranial  bones  except  the  mandible. 

Since  the  maxilla  moves  only  as  the  entire  cranium  is 
subject  to  movement,  it  may  justly  be  regarded  as  the  base 
or  fixed  factor  of  the  masticatory  apparatus.  The  upper 
teeth  are  imbedded  in  its  alveolar  process,  and  against  these 
the  food  is  forcibly  carried  in  the  process  of  reduction. 

The  body  of  the  bone  in  general  is  composed  of  rather 
thin,  frail  plates,  but  these  are  reinforced  at  various  points 
where  stress  is  heavy  by  what  are  termed  buttresses. 

The  alveolar  process  in  which  the  teeth  are  imbedded  is 
especialh'  heavy  and  resistant  to  stress.  This  process  in 
turn  is  reinforced  by  vertical  ridges  or  columns  running  up- 
ward and  merging  into  the  malar  processes  opposite  the  first 
molars,  while  anterioi^ly  the  cuspid  eminences  pass  upward 
and  merge  into  the  nasal  plates.  The  tuberosities  are  sup- 
ported liy  the  thickened  perpendicular  posterior  walls  of 
the  maxilla  itself. 

Each  maxillary  bone  has  within  its  Iwdy  a  cavity  known 
as  the  maxillary  sinus,  or  antrum..  The  floor  of  this  sinus 
lies  immediately  over  the  roots  of  the  second  and  third  molar 
teeth,  some  of  which  at  times  penetrate  the  bony  plate.  It 
can  thus  be  seen  how  easily  oral  infection  may  be  transmitted 
to  the  tissue  lining  the  antrum  when  these  teeth  contain  dis- 
eased pulps. 

The  several  plates  composing  the  upper  maxilla  enter 
into  the  formation  of  the  floor  and  outer  walls  of  the  nasal 
fossa,  the  palatal  vault,  floor  of  the  orbit  and  spheno  max- 
illary fissure. 

THE  MANDIBLE 

The  mandil)le  is  the  active  working  factor  of  the  mas 
ticatory  apparatus.  In  its  alveolar  process  the  lower  teeth 
are  imbedded,  and  through  its  movements  they  are  brought 


THE    MASTICATORY    MECHANISM  271 

in  forcible  contact  with  the  npper  dcntnre  in  the  reduction  of 
food. 

Wlieu  all  of  the  natural  teeth  are  present  in  a  healthy 

condition  and  normally  arranged,  they  constitute  a  powerful 

,  mill,  capable  of  cutting,  tearing,  crushing  and  grinding  all 

varieties  of  food  taken  into  the  mouth  as  such,  in  a  tlior- 

ouglily  efficient  manner  and  with  comparative  ease. 

The  mandible  is  of  peculiar  form  and  especially  strong 
and  rigid  within  itself,  capable  of  a  wide  range  of  movement 
and  of  fulfilling  various  fimctions. 

AUXILIARY  FUNCTIONS 

The  mandil)le  has  various  functions  and  is  capable  of 
many  movements  other  than  those  concerned  in  masticatory 
effort.  Indirectly,  it  assists  in  iDhonation  by  enlarging  or  re- 
ducing the  size  of  the  oral  cavity,  and  by  gauging  the  dis- 
tance between  the  upper  and  lower  teeth,  the  tongue  is  en- 
abled to  assume  its  proper  position  in  modifying  the  vocal 
tones  as  they  issue  from  the  larynx.  By  its  vax'ious  move- 
ments, the  mandible  assists  in  giving  expression  to  the  face 
in  speaking,  laughing,  and  in  the  exhibition  of  the  various 
emotions.  In  the  lower  animals,  and  occasionally  in  man, 
when  brute  instinct  dominates  his  intellect,  the  masticatory 
a]iparatus  becomes  a  weapon  of  otfence  and  defence. 

GENERAL    DESCRIPTION    OF    THE    MANDIBLE 

A  lever  is  a  rigid  arm,  capable  of  turning  about  a  point 
for  transmitting  force  or  motion  or  for  applying  power  to 
overcome  resistcDice. 

A  device  of  this  type  is  composed  of  three  factors,  viz : 
a  point  or  area  where  power  is  applied,  designated  as  P;  a 
point  or  area  whei'e  that  force  is  made  available  for  work 
or  weight  to  be  overcome,  designated  as  W;  and  a  point  of 
rotation  or  bearing  called  the  fulcrum  and  designated  as  F. 

Levers  are  divided  into  three  classes,  according  to  the 
position  or  arrangement  of  their  factors,  as  follows : 

First     Class,      P F W 

Second-Class,      P W F 

Third     Class,    W P F 

The  mandible  is  a  double  lever  of  the  third  class ;  that  is 
to  say.  being  double,  it  has  two  bearing  points  which  may 
move  in  unison,  forward  or  slightly  backward  at  the  same  or 


272  THIO    MASTU'ATOltY    MKCHANISM 

(litTciciit  liitc's  dj'  Speed,  oi'  one  may  tiiucl  in  a  ileliiiite  patli 
and  the  other  mei'ely  act  as  a  rotation  center. 

'I'he  power  is  applied  ))etween  the  working  area  and  the 
fulcrum  or  bearins'  points.  The  peculiar  form  of  the  bone 
permits  of  the  application  of  great  force,  with  but  little  ten- 
dency to  tip  or  become  unbalanced  in  masticatory  elTort. 

The  mandible  consists  of  a  body,  a  thick,  flat  bone, 
curved  on  itself  in  the  form  of  a  U  and  of  two  perpendicular 
portions,  called  the  ramii,  which  form  the  extremities.     Each 


TTTE    MAXDIELE 


ramus  is  surmounted  by  two  eminences,  the  anterior  called 
the  coronoid  process,  to  which  the  temporal  muscle  is  attached, 
and  the  posterior,  called  the  condyloid  process,  which  forms 
the  articular  or  sliding  joint  surface.  The  upper  extremity 
or  head  of  the  condyloid  process  is  called  the  condyle,  and 
the  constricted  portion  which  connects  it  with  the  ramus  is 
called  the  neck. 

The  upper  or  articular  surface  of  the  condyle  is  convex 
from  before  backward,  as  well  as  from  side  to  side.     It  is 


THE    MASTU'ATOI{Y    MECHANISM  273 

ellii»ti('al  in  ronn,  the  hm.i;'  axis  niiiiiiiii;'  Croiii  witliimt  inward 
and  sliglitly  liat'kward  and  downward. 

In  general  proportions  tlie  niandilile  resembles  an  equi- 
lateral triangle.  Konwill's  researches  led  liim  to  believe  that 
the  average  distance  from  center  to  center  of  the  condyles 
and  from  the  center  of  each  condyle  to  the  mesi-incisal  angles 
of  the  lower  central  incisiors  was  ap})roximately  four  inches, 
these  measurements  forming  an  e(iuilateral  triangle,  and 
hence  this  has  been  termed  the  Bonwill  triangle. 

On  this  basis  of  measurement  he  evolved  his  theory  of 
"anatomical  articulation"  and  constructed  his  "anatomical 
articulator." 

MOVEMENTS  OF  THE  MANDIBLE 

Because  of  its  jteculiar  form  and  the  manner  of  its  at- 
tachment to  the  base  of  the  cranium,  the  mandible  is  capable 
of,  and  subjected  to,  a  great  variety  of  movements.  So  free 
and  varied  are  these  that  r;nless  carefully  considered  they 
may  appear  to  lack  co-ordination. 

Although  callable  of  wide  range  of  action,  there  are  but 
three  definite  movements  of  the  mandible,  however,  that  may 
be  considered  as  important  in  masticatory  effort.  These 
should  be  carefully  studied  and  thoroughly  understood  by  the 
prosthetist  in  order  that  the  product  of  his  hand,  when  con- 
structed and  subjected  to  masticatory  action,  may  perform  in 
an  efficient  manner  the  same  functions  that  are  carried  out 
by  the  natural  teeth. 

The  three  important  movements  mentioned  may  be  out- 
lined as  follows :  First,  a  hinge-like  movement  emjjloyed  in 
opening  and  closing  the  mouth  for  the  introduction,  and  also 
to  a  limited  extent  for  the  crushing  of  certain  varieties  of 
brittle  food. 

Second :  A  protrusive  movement  employed  in  the  grasp- 
ing and  incision  of  food  and  in  rearranging  or  changing  the 
position  of  food  in  the  masticatory  grooves  in  process  of  re- 
duction. 

Third:  Eight  or  left  lateral  movements  employed  in  the 
reduction  of  fibrous,  as  well  as  all  varieties  of  food.  These 
movements  are  the' most  effective  of  any  described,  since  by 
their  action  food  can  be  finely  trituated  with  about  one  half 
the  expenditure  of  muscular  energy  that  is  required  with  the 
hinge  motion. 

To  appreciate  these  movements  in  detail  it  will  be  neces- 
ary  to  consider  the  manner  of  attachment  of  the  mandible  to 


274  THE    MASTICATORY    MECHANISM 

the  eranial  base,  and  the  form  of  artii'ulation  of  the  coudyles 
with  the  temporal  bones. 

THE    TEMPERO-MANDIBULAR    ARTICULATION 

Tlie  condyles  artieulate  \Yith  the  temporal  bones,  being 
received  in  elliptical  concave  depressions,  called  the  glenoid 
fossa?,  and  from  which  they  travel  forward ;  in  some  eases,  to 
a  limited  extent  slightly  backward,  and  from  side  to  side. 
These  depressions  are  situated  immediately  in  front  of  the 
auditory  canals,  from  which  they  are  separated  by  a  tliin, 
bony  partition  which  limits  the  backward  movement.  In  gen- 
eral contour  these  fosste  resemble,  in  reverse,  the  form  of  the 
articular  surfaces  of  the  condyles,  the  adaptation  of  the  two 
surfaces  to  each  other,  however,  not  necessarily  being  exact. 

Between  each  condyle  and  its  dome-shaped  socket  is  in- 
terposed an  inter-art icvilar  fibro-cartilage,  its  upper  surface 
convex,  its  lower  surface  concave.  Synovial  sacs  partially 
enter  between  the  cartilage  and  the  condyle.  The  combined 
thickness  of  the  three  layers  of  tissue  seldom  exceeds  3/32  of 
an  incli,  and  in  many  cases  is  less  than  1/16  of  an  inch. 

By  bearing  in  mind  the  average  thickness  of  these  tis- 
sues, the  thickness  of  the  bony  plate  separating  the  glenoid 
fossa  from  the  auditory  canal  and  the  antero-posterior  diam- 
eter of  the  condyle,  which  is  risually  about  14  of  an  inch,  the 
location  of  the  outer  end  of  the  condyle  in  the  living  subject 
can  be  determined  with  comparative  accuracy. 

The  synovial  sac  contents  lubricate  the  articular  surfaces, 
while  the  inter-articular  fibro  cartilage,  being  l)ut  loosely 
attached  to  and  moving  forward  somewhat  with  the  condyle  in 
its  movement,  reduces  friction  and  acts  as  a  cushion  as  well, 
when  the  mandible  is  subjected  to  heavy  stress. 

At  tlie  anterior  margin  of  the  glenoid  fossa  is  usually  an 
eminence  formed  by  the  middle  root  of  tlie  zygoma  and  called 
the  oiiiiieiitia  articularis. 

THE   CONDYLE   PATH 

Viewed  from  the  side,  the  general  contour  of  tlie  roof 
of  the  glenoid  fossa  with  that  of  the  articular  eminence  at  its 
anterior  margin  and  with  which  it  imperceptibly  merges,  is 
that  of  a  compound  curve. 

The  condyles,  in  the  various  opening,  closing,  protrusive 
and  lateral  movements  of  the  mandible,  are  guided  by  and 
must  take  the  general  direction  of  this  concave-convex  roof 


THE    MASTICATORY    MECHANISM  275 

throughout  the  extent  traversed  by  them  in  each  movement, 
and  hence  this  surface  is  called  the  condyle  path. 

The  condyle  path,  as  before  stated,  is  usually  curved, 
being  concave  posteriorly  and  convex  anteriorly.  The  cen- 
tral portion  is  approximately  a  straight  line.  This  portion, 
the  central  one-half  of  the  path,  may  be  considered,  and 
actually  is,  the  working  surface  which  guides  the  condyle  in  its 
movements  in  carrying  the  lower  against  the  upper  teeth,  in 
their  protrusive  and  lateral  excursions  in  masticatory  effort. 

For  practical  purposes,  in  denture  construction  it  is 
necessary  to  measure  or  record  in  some  manner  the  angular 
inclination  of  the  central  or  straight  portion  of  the  path. 
When,  hereafter,  it  becomes  necessary  to  refer  to  the  in- 


\ARTATIflNS     IN    COXDYl.K    I'ATHS.     ],EFT    SIDE     (TOMKS 


IIDI.I.AMOUEI 


cliiiatidii,  angle  of  inclination,  or  pitch,  of  the  condyle  path, 
these  terms  will  refer  to  the  central  or  woi-king  surface  just 
described,  unless  otherwise  specified. 


VARIATIONS  IN  THE  PITCH  OF  CONDYLE  PATHS 

The  condyle  paths  vary  in  different  individuals  and  fre- 
quently in  the  same  person,  in  their  length,  curvature  and 
angular  inclination. 

Walker,  Christensen,  Gysi  and  many  others  who  have 
investigated  on  the  living  subject,  vary  slightly  in  their  con- 
clusions. Gysi,  whose  work  is  perhaps  the  most  thorough 
because  of  more  accurate  methods  emi)loyed,  estimates  the 
average  inclination  of  the  condyle  path  at  35  degrees. 

Variations  ranging  from  horizontal  to  a  pitch  of  72  de- 
grees, as  recently  recorded  by  the  writer,  have  been  noted. 
It  is  not  uncommon  to  find  a  difference  of  10  degrees  in  the 
pitch  of  the  condyle  paths  of  the  same  individual. 


276  THK    MASTICATORY    MECHANISM 

The  contour  aud  iucliuatiou  of  the  condyle  paths  vary 
in  the  same  individual  from  infancy  to  old  age,  just  as  the 
form  of  the  mandible  is  itself  modified  by  the  lapse  of  time. 

Such  changes  of  the  condyle  path  may  be  ascribed  to 
and  are  influenced  by  the  partial  or  total  lack  or  loss  of  the 
teeth.  Loss  of  all  of  the  teeth  will  result  in  time  in  a  possible 
decrease  in  pitch  of  the  condyle  path,  the  change  in  the  path, 
however,  occurring  quite  gradually. 

The  loss  of  a  portion  of  the  teeth  may  jiroduce  a  directly 
contrary  result.  In  a  specimen  in  possession  of  the  writer 
the  posterior  teeth,  except  third  molars  on  right,  were  lost  a 
number  of  years  prior  to  the  death  of  the  subject.    That  side 


A    SKULL    WITH    ABNORMALLY    DEEP    GLENOID    FOSSA    ON    LEFT    SIDE.      MANDIBLE    THROWN 

TO    LEFT.      TEETH    IN    WORKIXGT  RELATION.      BALANCING    RELATION    BETWEEN 

THIRD    MOLARS    ON    BIGHT.      ALL    BICUSPIDS    AND    MOLARS    ON 

RIGHT.    EXCEI'T   UPPER  AND    LOWER   THIRD    HAVING 

BEEN   LOST 

of  the  mouth  on  which  the  loss  occurred  was  useless  for 
mastication,  and  consequently  it  became  the  moving  arm 
of  the  mandible,  or  the  balancing  side  of  the  masticatory  ap- 
paratus. The  bicusjiids  and  molars  on  the  opposite  side  were 
all  present  and  in  good  condition  and  occlusion,  while  the 
condyle  on  this,  the  working  side,  merely  rotated  in  its  fossa. 
Protrusive  and  lateral  movements  of  the  mandible  on  the 
working  side  in  the  opi)Osite  direction  accomplished  nothing. 
So,  nature,  to  maintain  the  masticatory  function  in  as  per- 
fect a  condition  for  as  long  a  time  as  possible,  increased  the 
depth  of  the  glenoid  fossa  on  the  woi'king  side  by  enlarging 
the  eminentia  articularis  and  by  reducing  the  pitch  of  the 


THK    MASTRATOKY     MECHANISM  277 

condyle  path  on  the  opposite  side,  as  the  eusps  and  planes 
of  the  various  teeth  were  worn  away. 

It  has  been  suggested  that  the  registration  of  the  condyle 
paths  and  the  construction  of  dentures  in  accordance  with 
such  registration  is  unnecessary,  since  time  and  occlusal  con- 
ditions of  the  teeth  modify  the  pitch  and  form  of  the  paths. 

This  view  is  entirely  unscientific  as  well  as  unwarranted 
by  results  in  practice.  In  no  instance  within  the  experience 
of  the  writer  has  any  marked  improvement  in  the  way  of 
additional  lateral  movements  been  observed  with  the  lapse 
of  time,  when  such  movements  were  not  possible  at  first.  It 
is  not  r>easonable  to  suppose,  except  possibly  in  rare  instances. 


that  any  material  change  does  occur,  since  the  artificial 
teeth  in  such  cases  are  almost  invariably  arranged  without 
reference  to  future  possible  lateral  mandibular  movements. 
Consequently,  imless  the  teeth  are  so  assembled  as  to  permit 
of  anatomic  movements  other  than  simple  occlusion  at  the 
time  of  constructing  the  denture,  the  habit  of  confining  mas- 
ticatoi-y  effort  to  the  hinge  movement  alone,  becomes  perma- 
nently fixed  long  before  any  perceiitible  change  occurs  in 
the  condyle  pjxths. 

THE  MUSCLES  OF   MASTICATION 

The  muscles  which  move  the  mandible  in  masticatory 
effort,  particularly  those  which  close  the  jaw,  are  capable  of 


:iTS  THE     MASTICATORY     .MKCHANMSM 

developing  great  jjower.  lu  tests  made  a  uimiber  of  years 
ago  by  Dr.  Black,  with  his  gnatho-dynamometer,  and  since 
verified  each  year  in  class  demonstrations,  it  was  found  that 
a  force  ranging  from  150  to  oOO  lbs.  could  be  developed  by 
these  muscles  and  delivered  between  the  lower  and  upper 
molars. 

The  two  pairs  of  muscles,  the  masseters  and  temporals, 
furnish  most  of  the  power.  The  internal  pterygoids  assist 
in  closing  and  also  in  protrusive  movements. 

THE   MASSETER   MUSCLE 

The  masseter  muscle  is  composed  of  a  superficial  and  a 
deep  portion.  Each  portion  has  a  separate  origin  and  in- 
sertion, and  since  these  vary  in  position,  the  direction  of  the 
fibres  of  the  two  layers  vary  somewhat,  and  the  action  of  each 
portion  is  slightly  ditTerent. 

The  superficial  layer  arises  by  a  tendinous  attachment 
from  the  malar  process  of  the  superior  maxilla  and  from  the 
anterior  two-thirds  of  the  lower  border  of  the  zygomatic  arch. 
The  fibres  pass  downward  and  backward  and  are  inserted  into 
the  angle  and  lower  half  of  the  outer  surface  of  the  ramus. 
Its  action  is  to  draw  the  mandible  upward  and  forward. 

The  deep  portion  of  the  masseter  arises  from  the  inner 
surface  of  the  zygomatic  arch  and  from  the  lower  border  of 
the  posterior  third  of  the  zygoma.  It  is  inserted  in  the  upper 
half  of  the  outer  surface  of  the  ranuis.  Its  fibres  run  perpen- 
dicularly downward  and  its  action  is  to  draw  the  mandible 
upward. 

THE  TEMPORAL  MUSCLE 

The  temporal  muscle  arises  from  the  tem]:)oral  ridge 
on  the  temporal  bone,  from  the  under  surface  of  the  temporal 
fascia,  and  from  the  temjioral  fossa.  It  is  inserted  in  and 
around  the  coronoid  process  of  the  ramus,  some  of  its  fibres 
passing  down  the  anterior  margin  of  the  latter  as  far  as  the 
third  molar.  In  general  outline  it  is  fan-shaped,  its  origin 
representing  a  sweeping  curve,  its  fibres  converging  to  their 
point  of  insertion  in  the  coronoid  process.  Its  action  is  to  close 
the  jaw  and  to  draw  the  condyle  backward  in  its  fossa  when 
protruded,  as  in  unilateral  or  hilateral  position. 

THE   EXTERNAL    PTERYGOID    MUSCLE 

The  external  pterygoid  muscle  has  two  origins  and  two 
insertions.     The  upper  head  arises  from  the  pterygoid  ridge 


THE    MASTICATORY     MECHANISM 


A    CUT    SHOWIXG    THE   DLRECTION    OP    FIBRES    OF    VARIOHS    SDPERFICIAL    MUSCLES    CON- 
CER>rED   IN  FACIAL  EXPRESSION       (ECKLBY'S  REGIONAL  ANATOMY) 


2S0  THK    MASTK'ATOKY     MECHANISM 

of  the  (inter  and  luidci-  Mii-racc  ol'  llic  nicatcr  a!a  of  the  sphe- 
noid Ijoiie.  Its  insertion  is  in  tlie  anterior  margin  of  tiie  in- 
terarticnlar  iiln'o-oartilag'e,  wliieli  covers  the  arlienhir  snrfaee 
of  the  condyle.  Its  fnnetion  is  to  draw  the  cartilage  forward 
in  the  protrusive  movements  of  the  mandible,  tiins  furnishing 
a  concave  cap  for  the  condyle  to  rest  in  as  it  is  carried  forward 
onto  the  eminential  articnlaris. 

Eckley  attributes  the  craclcing  noise  fre(iuently  noticed 
in  the  tempero-mandibular  joint  to  partial  or  complete  paraly- 
sis of  this  portion  of  the  pterygoid,  whicli  results  in  failure  of 
the  muscle  to  draw  the  cartilage  forward  in  unison  with  the 
condyle  and  permits  the  latter,  in  its  forward  excursions,  to 
override  the  anterior  rim  of  the  cartilage. 

The  lower  head  of  the  external  jiterygoid  muscle  has  its 
origin  in  the  outer  surface  of  the  external  pterygoid  plate  of 
the  si^henoid  bone.  It  is  inserted  in  the  anterior  surface  of 
the  neck  of  the  condyle. 

The  function  of  the  muscle  is  extremely  important.  By  its 
action  principally,  the  mandible  is  given  a  lateral  movement 
and  with  its  mate  on  the  opposite  side  protrusion  is  accom- 
plished. These  muscles  are  not  large  as  compared  with  the 
temporals  and  masseters,  nor  do  they  develop  very  great 
power,  since  that  is  unnecessary. 

The  crushing  of  food  is  accomplished  by  the  masseter. 
temporal  and  internal  pterygoid  muscles  in  drawing  the 
mandible  back  to  normal  position,  after  having  been  carried 
laterally  or  forward  by  the  external  pterygoids. 

The  combined  action  of  the  upper  and  lower  portions  of 
the  external  pterygoid  muscle  is  to  draw  the  condyle  and  its 
inter  articular  iibro-cartilege  forward   simultaneously. 

THE  INTERNAL  PTERYGOID  MUSCLE 

The  internal  pterygoid  has  its  origin  on  the  inner  surface 
of  the  external  pterygoid  plate,  from  the  tuberosity  of  the 
palate  bone.  It  passes  downward  and  backward  and  is  in- 
serted in  the  inner  surface  of  the  mandible  from  the  mylohoid 
ridge  and  the  inferior  dental  canal  downward  to  the  angle 
of  the  ramus.  Its  action  is  to  assist  in  closing  the  jaw  and 
bringing  it  back  to  normal  frofn  lateral  position,  in  the  latter 
function  assisting  the  posterior  fibres  of  the  temporal  muscle 
on  the  opposite  side. 


THE    MASTICATORY    MKCHANISM 


282  THE    MASTICATORY    MECHANISM 

MUSCLES    WHICH    DEPRESS    THE    MANDIBLE 

The  jaw  is  opened  by  the  mylohyoid,  genio-liyoid,  genio- 
hyo-glossus,  digastric  muscles  and  gravity.  In  fact,  most 
of  the  supra  and  infra  hyoid  muscles  take  part  in  the  de- 
pression of  the  mandible.  Tlie  hyoid  bone  acts  as  a  movable 
fulcrum  when  the  jaw  is  opened  widely.  The  supra  hyoid 
muscles  contract  and  tend  to  lift  the  hyoid  bone  upward  and 


draw  the  mandible  downward.  This  tendency  is  counter- 
balanced by  the  action  of  the  infra  hyoid  muscles,  which  de- 
press or  at  least  make  rigid  the  hyoid  bone,  so  that  the  upper 
muscles  may  act  effectively. 

Depression  of  the  mandible,  which  is  equivalent  to  open- 
ing the  mouth,  results  in  the  drawing  forward  of  the  con- 
dyles in  their  paths,  as  well  as  in  a  greater  or  less  rotary 
movement  of  their  articular  surfaces. 


THE    MASTICATORY    MECHANISM  283 

111  other  words,  the  centers  of  rotation  in  the  hinge 
action  do  not  lie  in  the  transverse  centers  of  tlie  condyles, 
bnt  are  situated  about  three-fourths  of  an  inch  below  and 
sli^-htly  back  of  the  distal  margins  of  the  rami.  Even  this 
location  is  variable  in  the  same  individual  under  different 
conditions,  depending  on  the  distance  the  mandible  is  de- 
pressed, and  also  whether  it  has  been  subjected  to  protrusive 
as  well  as  opening  movements. 

This  is  explained  by  Gysi  as  follows : 

"If  a  man  were  susjieiided  in  the  air  by  ropes  attached 
to  each  of  his  hands  he  could  be  pulled  hither  and  thither  by 
tugging  at  either  rope.  His  body  would  describe  certain  mo- 
tions accordingly  as  force  was  applied  to  one  rope  or  another. 
If  an  architect  were  to  chart  the  motions  described  by  the 
man's  body,  he  would  find  them  to  be  sections  of  curves,  with 
centers  at  tlic  points  where  the  opposing  curves  met,  not  at 
the  points  to  which  the  ropes  were  attached  to  the  wrists. 
When  he  found  these  imints.  he  would  ])robal)ly  call  them 
'centers  of  motion.' 

"That  illustration  of  the  man  suspended  by  ropes  at- 
tached to  each  wrist  is  not  much  unlike  the  suspension  of 
the  jaw  by  ligaments  attached  to  the  heads  and  necks  of  the 
condyles.  The  articulation  of  the  condyles  with  their  fossa?  is 
very  loose;  a  sort  of  hanging  attachment.  Tlie  jaw  may  be 
pulled  in  any  direction  by  tension  of  the  proper  muscles,  and 
when  it  moves  it  swings  just  as  the  man's  body  did,  not  tvith 
its  center  at  the  condyles,  but  at  the  pointf^  ivliere  opposing 
pulls  meet  and  balance  each  other." 

Bowditch  and  Luce,  in  1899,  and  Walker  in  189-i,  firsb 
called  attention  to  the  fact  that  the  head  of  the  condyle  moved 
forward,  and  the  angle  of  the  ramus  moved  backward,  in  wide 
ojien  movements.  Others  have  since  verified  the  accuracy 
of  these  first  experiments.  No  special  value  attaches  to  the 
registration  of  wide  open  jaw  movements,  since  they  have  no 
bearing  on  occlusion.  Any  movement  of  the  mandible,  how- 
ever, which  can  be  registered,  increases  the  sum  total  of 
knowledge  of  the  human  dental  mechanism  and  aids  in  solving 
this  most  intricate  problem. 

MUSCLES  WHICH  CONTROL  THE  POSITION  OF  FOOD 

This  group  includes  the  lips,  cheek,  palatal  and  tongue 
muscles,  which  when  co-ordinating,  control  the  position  of 
food  and  tend  to  keep  it  within  tlie  working  limits  of  the 
teeth. 


284  THE    MASTICATORY    MECHANISM 

Sjiccilicall}',  the  buccinators  on  the  sides  and  tlic  orbicu- 
laris oris  in  i'ront,  confine  tlie  food  to  a  great  extent  and  pre- 
vent it  from  being  forced  outward  into  tlie  vestibule  during 
masticatory  effort.  Witliin  the  oral  cavity  proper  the  tongue 
moves  the  bolus  of  food  outwardly  and  as  the  mandible  is 
depressed,  moved  laterally,  elevated  and  the  teeth  brought 
together,  the  lingual  marginal  ridges  shear  off  a  portion, 
which  is  caught,  confined,  and  reduced  in  the  masticatory 
groove  between  the  teeth  as  the  mandible  is  returned  to  nor- 
ma! from  the  unilateral  position. 


SUMMARY  OF  MUSCULAR  ACTION  ON  THE  MANDIBLE 


Depression,  or 
opening  of  mouth 


l^]levatiou,  or 
closure  of  month 


Protrusion, 
bilateral 


Protrusion, 
unilateral 

Retrusion, 
bilateral 


Retrusion, 
unilateral 


Mylo-hyoid 
Genio-hyoid 
(lenio-hyo  glossus 
Infra-hyoid  muscles 
Digastric 
Gravity 

Temporals 
Masseters 
Internal  pterygoids 

External  pterygoids 
Internal  pterygoids 
Masseters — superficial  fibres 

External  pterygoid     ]  ( )n  protrud- 
Interual  pterygoid       J  ing  side 
Masseter — superficial  fibres 

Temporals — posterior  fibres 
Masseters — deep  fibres 

Temporal — posterior  fibres 
Masseter — deep  fibres 
Internal  pterygoid  on 
opposite  side. 


THE   MANDIBULAR   LIGAMENTS 

In  addition  to  the  muscles  actuating  the  mandible,  some 
of  which  in  a  state  of  rest  tend  to  hold  the  condyles  in  their 
fossae,  there  are  three  pairs  of  ligaments,  which  limit  its 
range  of  movement  and  yet  permit  a  variety  of  excursions 


THK    .MASTICATORY     MECHANISM  285 

to   be  carried   out   with    freedom.      Tliese   ligaments   are   as 
follows : 

The  capsular  ligament,  divided  into  four  parts — an  an 
terior,  posterior,  external  and  internal  segment. 

The  spheno-mandibular,  or  long  internal  lateral  ligament. 

The  stvlo-mandihular  ligament. 


THE    CAPSULAR    LIGAMENT,    I'STEUXAI.    \IE\V     (DEA\ER) 

THE  CAPSULAR'LIGAMENT 

Tlie  anterior  and  posterior  portions  of  the  capsular  lig 
anient  are  composed  of  thin  layers  of  loose,  flabby  fibres.  An- 
teriorly, these  fibres  are  inserted  into  the  anterior  margin  of 
the  interarticular  fibro-cartilage,  from  which  they  extend  up- 
ward and  downward.     The  upper  fi])res  are  attached  to  the 


X 


^^>-. 


286  THK    MASTICATORY     MECHANISM 

front  of  tlu'  cniiiientia  artienlars,  the  lowci'  (ibrcs  to  the 
anterior  margin  of  the  condyle. 

The  posterior  fibres  are  attached  to  the  margin  of  tho 
glenoid  fissure  and  from  there  extend  to  and  are  inserted  in 
the  posterior  surface  of  tlie  ramus  below  the  neck  of  the 
condyle. 

Since  the  condyle  movements  to  a  great  extent  are  for- 
ward, it  can  readily  be  seen  that  the  anterior  and  posterior 
fibres  of  this  ligament  must  be  loose  to  give  freedom  of  action 
to  the  mandible. 

THE  EXTERNAL  LATERAL  LIGAMENT 

The  external  lateral  ligament  forms  the  outer  portion  of 
the  capsular  ligament,  its  tibres  blending  with  the  anterior 
and  posterior  portions  of  the  latter.  Tliis  ligament  is  the 
strongest  part  of  the  capsule.  It  lias  a  broad  attachment 
above  to  the  zygoma  and  is  inserted  in  the  outer  surface  of 
the  condyle  neck. 

THE  INTERNAL  LATERAL  LIGAMENT 

The  short  internal  lateral  ligament  completes  the  cap- 
sule. Its  fibres  are  attached  above  to  the  inner  margin  of 
the  glenoid  fossa  and  to  the  spine  of  the  sphenoid  lione.  It 
is  inserted  in  the  inner  side  of  the  condyle  neck. 

The  four  portions  of  the  capsular  ligament,  by  the  blend- 
ing of  their  tibres,  encapsule  the  joint.  Within  this  capsule 
is  enclosed  the  iuterarticular  fibro-cartilage,  the  capsular 
tibres  being  more  or  less  closely  attached  to  the  cartilage 
around  its  periphery. 

THE    SPHENO-MANDIBULAR    LIGAMENT 

This  ligament  is  also  called  the  luuci  internal  lateral  lig- 
ament to  distinguish  it  from  tlie  short  internal  lateral  liga- 
ment, which  forms  a  part  of  the  capsule. 

It  Is  attached  to  the  spine  of  the  s]ilienoid  bone,  from 
which  it  extends  downward  and  is  inserted  in  the  mandilnxlar 
spine  and  a  portion  of  the  area  immediately  surrounding  the 
posterior  dental  foramen. 

THE   STYLO-MANDIBULAR    LIGAMENT 

The  stylo-mandibular  ligament  is  attached  to  the  styloid 
process  of  the  temporal  bone,  its  fibres  passing  downward  to 


THE    MASTICATORY    MECHANISM 


fiud  insertion  in  the  posterior  border  and  angle  of  the  ramus, 
between  the  masseter  externally  and  the  internal  pterygoid 
internally. 

These  several  ligaments  being  practically  devoid  of  elas- 
ticity, resemlile  so  many  cables  by  which  the  mandible  is 
suspended  from  the  base  of  the  cranium.  They  limit  the 
action  of  the  various  muscles  concerned  in  protrusion,  lateral 


LXTERXAI,    VIEW    OF    TIIK    SPHEXO-MANDIIiUI.AR    AND    ST\I,0-MA.\1JUUI-AR    LIGAMENTS 
(DEtVVER) 

and  wide-open  movements.  AVithout  their  restricting  in- 
fluence, the  ]iossibilities  of  useless  mandibular  movements  can 
scarcely  be  conceived. 

Usually,  in"  dislocations  of  the  mandible,  the  posterior 
fibres  of  the  capsular  ligament  are  broken  by  the  excessive 
strain  to  which  they  are  subjected,  and  as  they  seldom  if 
ever  again  unite,  recurrent  dislocations  in  the  same  subject 
are  frequent. 


THE    MASTICATORY    MECHANISM 
THE  TEETH 


The  normal  adnlt  denture  consists  of  thirtj'-two  teeth, 
sixteen  in  the  iipper  and  a  like  numl)er  in  the  lower  jaw, 
tile  formula  of  which  is  as  follows : 

M.  B.  C.    I.    I    I.    C.  B.  M. 

3     2122123 

3     2     12     13     13     3 

FKICTIONAL     OK     WORKING    SURFACES     OF     THE     TEETH. 

Those  surfaces  of  the  bicuspids  and  molars  in  one  arch 
presenting  toward  those  in  the  opposite  arch  are  known 
as  occlusal  surfaces,  from  occlude,  which  means  to  shut  or 
close  together. 

Those  surfaces  or  edges  of  the  incisors  and  cuspids  in 
one  arch  presenting  toward  those  in  the  opposite  arch  are 
called  incisal  surfaces  or  edges,  from  incise,  which  means 
to  cut. 

Each  cuspid  tooth  terminates  in  a  i)oint  or  cusi),  with 
incisal  edges,  sloping  away  from  it  mesially  and  distally 
to  the  mesio  and  disto  incisal  angles  of  the  tooth. 

OCCLUSAL  SURFACE  MARKINGS 

The  occlusal  surfaces  of  the  l)icuspids  and  molars  are 
made  up  of  cusps,  inclined  i^lanes,  grooves,  pits  and  ridges, 
displayed  with  more  or  less  definite  regularity. 

THE    CENTRAL   SULCUS    OR    MESIO-DISTAL   GROOVE   OF   THE 
BICUSPID  AND   MOLAR  TEETH 

Traversing  the  occlusal  surface  of  each  bicuspid  and 
molar  tooth,  mesio-distally,  is  a  general  depression,  or 
sulcus,  formed  by  the  planes,  which  slope  linguall.v  from 
the  buccal,  and  buccally  from  the  lingual,  marginal  ridges. 

These  planes  meet  at  varying  angles  near  the  center 
of  the  tooth,  to  form  definite  grooves.  The  grooves,  which 
cross  the  mesial  and  distal  marginal  ridges,  are  accordingly 
named  mesial  and  distal  marginal  grooves,  and  that  which 
divides  the  central  portion  of  the  tooth  is  called  the  cen- 
tral groove. 

In  normal  occlusion  these  general  depressions  or  sulci 
in  the  upper  teeth  receive  the  buccal  cusps  and  marginal 
ridges  of  the  lower  teeth,  while  the  central  sulci  of  the 
lower  teeth  receive  the  lingual  cusps  and  marginal  ridges 
of  the  upper  teeth. 


THE    MASTICATORY     MECHANISM  289 

THE  BUCCO-LINGUAL  GROOVES 

III  additiou  to  the  central  grooves  mentioned,  the  vari 
ons  cusps,  and  planes  sloinng  away  from  them  mesially 
and  distally,  result  in  the  formation  of  other  grooves,  which 
traverse  the   occlusal   surfaces   of  the   teeth   from  buccal   to 


I)IA<iRA.\l     SIK 


SECTION"     OF     MANDIBLE     AND     MAXILLA     SHOWING     UPPER     AND 
LOWEB   TEETH  IN  OCCLOSION.   DISTAL  VIEW 

lingual.  These  .grooves  run  nearly  at  right  angles  to  the 
mesio-distal  grooves,  the  buccal  being  slightly  in  advance  of 
the  lingual  end. 

Each  pair  of  cusps,  as,  for  instance,  the  mesio-buccal 
and  mesio-Iingual  cusps  of  the  upper  first  molar,  are  situ- 
ated approximately  the  same  distance  from  the  mandibular 


290  THE    MASTICATORY    MECHANISM 

rotation  center  of  tliat  side  of  the  arch.  The  phines,  slop- 
ing away  from  these  cusps  mesially  and  distally  until  they 
meet  in  the  central  groove,  and  finally  merging  with  those 
from  the  adjacent  pairs  of  cusps,  enter  into  the  formation 
of  grooves,  which  represent  arcs  of  circles,  also  developed 
from  the  same  rotation  centers.  This  arc-like  or  geomet- 
rical bucco-liugual  arrangement  of  cusps,  ridges  and  grooves 
of  the  upper  teeth  permits  the  cusps  and  sloping  planes  of 
the  occluding  lower  teeth,  which  bear  a   simihir  relation  to 


NTKRKIIl    VIKW 


the   rotation  center,  to  be  moved  freely  back  and  forth,  in 
the  lateral  swing  of  the  mandible,  without  cusp  interference. 

THE  MASTICATORY  OR  RECTANGULAR  GROOVE 

When  the  mandible  is  rotated  laterally,  so  as  to  In'ing 
the  buccal  cusps  and  marginal  ridges  of  the  lower  teeth  on 
the  pivotal  side  outward  from  the  central  sulci  of  the  upper 
teeth,  and  directly  under  the  corresponding  cusps  and 
marginal  ridges  of  the  latter,  a  fairly  close  and  unbroken 
line  of  contact  between  these  wedge-like  ridges  is  effected. 

At  the  same  time  the  lingual  cusps  and  marginal  ridges 
of  both  lower  and  upper  teeth  on  the  same  side  are  brought 
into  similarly  close  contact.  A  rectangular  space  is  thus 
formed,  bounded  above  and  below  by  the  occlusal  surfaces 
of  the  upper  and  lower  teeth,  and  laterally  by  their  buccal 
and    lingual    marginal    ridges.      This    groove    extends    from 


THIO    MASTICATORY    MECHANISM  291 

the  iirst  bicusind  lo  llie  third  molar,  iiichisive,  wlieu  present, 
and  forms  tlie  receptacle  in  which  food  is  held  and  crusheil 
as  the  mandible  is  drawn  back  to  noi'mal  position.  The 
form  and  proi)ortions  of  this  masticatory  groove  is  of  the 
greatest  irajjortance.  The  efficiency  of  tlie  masticatory 
apjjaratiis  is  largely  dependent  on  the  width  of  this  space 
bucco  lingnally;  the  wider  it  is,  within  normal  limits,  the 
greater  the  radial  swing  possible  for  the  mandible  and  the 
more  efficient  its  effort  in  the  reduction  of  food. 

The  detiniteness  of  the  angles  of  the  marginal  ridges 
which  are  formed  by  the  junction  of  the  buccal  and  lingual 
surfaces  of  the  teeth  with  the  various  planes  sloping  to 
the  central  grooves  is  also  important.  These  angles  should 
not  be  too  sharp,  as  the  tongue  and  cheek  muscles  arq^  liable 
to  be  caught  between  them  and  injured  in  masticatory  effort. 

The  closeness  of  apposition  of  the  various  occlusal 
planes  and  marginal  ridges  of  the  lower  to  those  of  the 
upper  teeth,  not  onh^  in  occlusion,  but  in  radial  movements 
of  the  mandible  as  well,  increases  efficiency  in  both  natural 
and  artificial  dentures.  When  loosely  approximated,  or 
possibly  when  only  a  few  cusps  or  surfaces  are  in  actual 
contact,  the  food  is  merely  punctured,  and  the  fibers  are 
not  torn  asunder,  as  is  the  case  when  many  planes  and 
cusps  find  contact  with  those  of  the  opposite  teeth. 

ARRANGEMENT  OF  THE  TEETH  IN  THE  DENTAL 
ARCHES 

OCCLUSAL  VIEW 

Viewed  occlusally,  the  arrangement  of  the  teeth  in  each 
dental  arch  presents  the  general  appearance  of  a  parabolic 
curve,  or  in  some  cases  that  of  a  half  ellipse,  the  central 
incisors  being  at  the  outer  extremity  of  the  major  half  axis. 
The  size  and  outline  form  of  the  curve  varies  in  different 
individuals,  according  to  structural  build. 

Since  normally,  the  upper  overlap  the  lower  teeth  to  a 
greater  or  less  extent,  the  curve  of  the  upper  arch  is  slightly 
larger  than  that  of  the  lower  arch. 

THE  ANTERIOR  CURVATURE,  INCISAL  VIEW 

The  four  incisors  at  their  cutting  edges  iisually  present 
a  symmetrically  curved  arrangement.  The  laterals  may  be 
slightly  in  or  out  of  a  true  curved  alignment,  or,  when  a 


292  Till':     .MASTIC. \T()I;Y     .MKCII.ANIS.M 

tritie  rottitcd,  as  is  l'ic<|Ui'iitl\  tlic  case,  tlicir  iiicsio-liu.nuo- 
iiK'isal  angles  may  overlap  tiie  (listolahial  surfaces  of  the 
central  incisors.  The  variations  noted,  when  not  too  pro- 
nounced, are  pleasinp;  rather  than  other\vis<>,  and  give  cliar- 
acter  and  individuality  to  the  denture. 

The  cutting  edges  of  the  cuspids  usually  are  in  sym- 
metrical lahial  alignment  with  the  incisors.     On  account  of 


the  greater  convexity  of  the  labial  face  of  the  cuspids,  as 
comijared  with  the  incisors,  these  surfaces  stand  out  more 
or  less  prominently  beyond  the  labial  surfaces  of  the  latter, 
especially  at  their  cervices. 

The  cuspids  are  the  corners  of  the  dental  arches,  the 
labial  curvature  of  the  incisors  merging  here  with  the 
straighter   alignment   of  the  posterior   teeth.     The   general 


THE    MASTICATORY    MECHANISM  293 

form,  size  and  position  of  the  (■iis{)ids,  therefore,  give  tliem 
greater  jirominence  than  any  of  tlie  anterior  teeth. 

ALIGNMENT  OF  THE  POSTERIOR  TEETH 

Fi'om  the  cuspids,  to  and  inohidiug  the  first  molars, 
the  teeth  are  arranged  in  practically  straight  lines,  which 
in  passing  backward  diverge.  If  projected,  these  lines 
would  usually  fall  within  and  below  the  inner  ends  of  the 
condyles. 

The  second  and  third  molars  frequently  curve  inward 
somewhat  to  the  lingual  of  these  lines,  an  arrangement 
which  gives  the  general  arch  its  parabolic  or  elliptical  form. 
This  inward  curvature  of  the  second  and  third  molars  is 
necessary  to  avoid  contact  of  thin  buccal  surfaces  with  the 
coronoid  processes  of  the  mandible  in  its  lateral  and  wide- 
open  movements. 

When  viewed  anteriorly,  less  tlian  one-fourth  of  the 
first  bicuspids,  taking  their  bucco-lingual  diameters  as  a 
basis,  are  visible  back  of  the  cuspids.  The  second  bicuspids 
exhibit  about  the  same  amount  of  surface  as  do  the  first 
bicuspids.  This  retiring  jjosition  of  the  bicuspids  adds 
very  much  to  the  esthetic  appearance  of  the  denture,  par- 
ticularly in  the  u])per  arch. 

BUCCAL  VIEW   OF  THE   UPPER   DENTAL  ARCH 
THE  PLANE  OF  OCCLUSION 

In  normal  occlusion  tlie  line  of  contact  of  the  lower 
with  the  upper  bicuspids  and  molars  is  called  the  plane  of 
occlusion,  for  here  tiieir  occlusal  surfaces  meet  in  normal 
closure   as  well  as   in   lateral  movements   of  the  mandible. 

The  general  direction  and  position  of  the  plane  of 
occlusion  is  approximately  parallel  with,  and  about  an  inch 
below,  a  straight  line  extending  from  the  base  of  the  nose 
to  the  center  of  the  condyle. 

CURVATURE  OF  THE  OCCLUSAL  PLANE 

In  reality,  however,  the  occlusal  plane  usually  departs 
from  a  straight 'line,  the  second  bicuspid,  first,  second  and 
third  molars  curving  upward  toward  the  glenoid  fossa,  in 
most  cases,  in  a  fairly  well-defined  arc,  the  convexity  pre- 
senting downward. 

The  amoimt   of  curvature   of  the   occlusal  plane  varies 


294  THE    MAS'l'K'A'I'OltV     MICCHANISM 

ill  (lit'fcrciil  iii<li\itUi;il,s,  iiud  rr(M|uciitly  llicre  is  a  notice 
iihic  <Iift'('reiice  in  tlic  ]ilaiies  cm  the  two  sides  of  llio  arch 
ill   the  same  subject. 

The  cvirvature  varies  from  a  wcll-deiincd  arc  in  most 
case's  to  a  nearly  or  quite  flat  i»Uiiic  in  a  few  instances.  A 
few  cases  liave  come  under  the  notice  of  the  writer  where 
the  curvature  of  the  occlusal  planes  was  reversed.  In 
other  words,  instead  of  the  convexity  presenting  downward, 
the  occlusal  plane  was   conca^'ed  upward.     Such  cases  are 


\L     MKW    OK    'I'lll':     NATniAI.     llENTtrU': 


rare,  however,  and,  within  the  writer's  observation,  only 
occur  when  the  occlusion  is  abnormal,  the  teeth  in  the  lower 
protruding    beyond   those    in    the    upper    arch. 

RELATIONSHIP  OF  THE  PLANES  OF  OCCLUSION  TO 
THE  CONDYLE  PATHS 

The  planes  of  occlusion  and  the  condyle  paths  bear  a 
definite  relationship  to  each  other,  as  the  following  problems 
will  demonstrate : 

First.  On  a  jihotograph  of  a  skull  in  which  the  teeth 
are  normally  occluded,  strike  an  arc  intersecting  the  tips 
of  the  buccal  cusps  of  the  bicuspids  and  molars.  The 
center  from  which  this  arc  is  developed  nuist  be  located  by 
trial.  This  can  easily  be  done  when  the  curvature  is  pro- 
nounced, as  the  center  will  lie  in  the  region  of  the  frontal 


THE    MASTICATORY    MECHANISM  295 

promiueuees.  It  will  Ix'  more  diffieult  to  locate  the  center 
in  those  cases  where  the  occlusal  planes  are  nearly  or  quite 
flat,  because  its  position  will  lie  higher  up,  beyond  the  range 
of  the  ordinary  dividers. 

Second.  Place  one  leg  of  the  divider  on  the  center 
from  which  the  occlusal  arc  was  developed ;  set  ■  the  other 
leg  on  the  margin  of  the  middle  half  of  the  condyle  path, 
and  strike  an  arc  in  this  location.  It  will  be  fomid  that 
the  arc  last  developed  will  coincide  with  the  condyle  patli 
along  its  working  area,  and,  furthermore,  that  it  will  be 
parallel  with  the  occlusal  arc,  since  both  are  developed  from 
the  same  center.  These  arcs  may  coincide,  or,  as  is  more 
commonly  the  case,  be  concentric,  the  condyle  arc  lying 
above  and  witliin  the  one  intersecting  the  tips  of  the  teeth. 

GOVERNING  FACTORS   IN   MANDIBULAR   MOVEMENTS 

The  mandibular  movements  which  are  of  the  greatest 
importance  to  the  jirosthetist  are  those  which  bring  the 
lower  in  contact  with  the  upper  teeth  in  some  of  their  varied 
lateral  and  protrusive  excursions. 

Any  movement  which,  even  to  a  slight  degree,  causes 
separation  of  the  entire  lower  from  the  upper  denture 
can  have  no  bearing  on  occlusal  conditions,  and  therefore 
need  not  here  be  considered.  The  excursions  of  the  con- 
dyles in  their  paths  in  wide-open  movements,  however,  are 
of  importance  in  certain  technical  procedures,  which  will 
later  be  mentioned. 

There  are  three  definite  and  comparatively  fixed  factors 
which  guide  the  mandible  in  its  protrusive  movements. 
These  are  the  incisor  path  and  the  two  condyle  paths. 

THE  INCISOR  PATH 
Protrusion  of  the  mandible  carries  the  incisal  edges 
of  the  lower  anterior  teeth  forward  and  downward  against 
the  lingual  surfaces  of  the  corresponding  upper  teeth.  If 
projected  sufficiently  far  forward  their  incisal  edges  will 
occlude  with  those  of  the .  upper  teeth  in  an  end-to-end 
relation.  The  distance  traversed  by  the  incisal  edges  of  the 
lower  teeth  from  the  position  of  rest,  or  normal  occlusion, 
to  that  of  edge-to-edge  contact  or  incision  is  known  as  the 
incisor  path.  It  is  obvious  that  this  path  controls  the 
movements  of  the  mandible  anteriorly,  since,  with  the  excep- 
tion of  the  last  molars  in  occlusion,  the  remaining  bicuspids 


296  THE    MASTICATORY     MECHANISM 

and    molars    in    one    ardi    arc    nut    nsually    in    contact   with 
those  in  tlic  oppowitc  arch  in  protrnsive  elt'ort. 

THE  CONDYLE  MOVEMENT  IN  PROTRUSION 

As  the  mandible  is  drawn  forward  in  i)rotrusion,  the 
condyles,  being  lield  in  close  contact  with  their  paths  ])y 
the  various  mandibular  muscles  and  ligaments,  must  follow 
closely  the  direction  of  the  condyle  tracts,  whatever  may 
be  their  form  or  })itch.  It  naturally  follows  that  these 
tracts  determine  the  movements  of  the  mandible  posteriorly. 

These  three  guiding  factors  in  protrusive  effort,  the 
incisor  path  and  the  two  condyle  paths,  are  located  one  at 
each  angle  of  thd  equilateral  triangle,  to  which  attention 
has   previously   been   directed. 

THE  FUNCTION  OF  THE  INCISOR  TEETH  IN   PROTRUSIVE 
EFFORT 

Prehension,  or  the  seizing  hold  of  food  liy  the  teeth,  is 
the  first  act  in  masticatory  effort. 

Incision,  or  the  cutting  off  of  a  portion  of  suitable  size 
for  reduction  by  the  bicuspids  and  molars,  is  the  second  act. 

These  functions  are  performed  by  depressing,  protrud 
ing  and  raising  the  mandible  while  protruded,  so  as  to  bring 
the  anterior  teeth  together  in  edge-to-edge  contact,  with 
final  return  of  the  mandible  to  normal  position  and  the  teeth 
to  normal  occlusion.  The  final  act  of  retrusion,  as  outlined, 
shears  off  those  portions  of  the  morsel  of  food  not  com- 
pletely severed  by  direct  incisive  effort.  Only  the  anterior 
teeth  are  concerned  in  the  actual  work  accomplished. 

Since,  then,  the  focus  of  useful  effort  is  confined  solely 
to  the  incisors  and  cuspids,  there  is  no  necessity  for  the 
bicuspids  and  molars  of  the  lower  coming  in  contact  with 
those  in  the  upper  arch  in  the  incisive  act,  except  at  the 
extreme  distal  portion  of  the  arches.  Here  the  last  lower 
molars,  which  normally  occlude  (the  second  molars,  usually 
when  the  third  molars  are  not  fully  erupted  or  are  missing), 
move  forward  in  sliding  contact  with  those  in  the  upper 
arch.  Contact  of  the  molars  in  this  region  does  not  increase 
the  field  of  effort  or  working  area,  since  no  food  is  being 
reduced  here.  It  serves  the  purpose,  however,  of  steadying 
or  balancing  the  denture,  and  further  of  distributing  or 
equalizing  the  force  of  closure,  thus  avoiding  the  imdue 
stress  that  would  be  exerted  on  the  central  portion  of  each 


THK    MASTICATORY     MECHANISM  297 

lateral  hall'  of  the  maiulihle  it'  the  incisur  teeth  ami  condyle, 
without  such  central  bearing  points,  were  required  to  sus- 
tain all  of  the  force   of  masticatory  incisive   effort. 

LATERAL  MOVEMENTS  OF  THE  MANDIBLE 
In  actual  masticatory  effort  the  lateral  mandibular 
movements  are  the  most  important  and  effective  of  any 
of  those  mentioned.  By  such  movements  the  food  is 
crushed,  torn  asunder,  finely  triturated  and  insalivated  as 
it  cannot  be  in  any  other  manner  or  by  any  .other  action. 
Food  subjected  to  the  hinge  action  is  merely  punctured, 
or  at  most  slightly  crushed.  It  cannot  be  torn  and  shredded 
as  when  caught  betweeu  sliding  contact  surfaces,  any  more 
than  can  wheat  be  reduced  to  flour  by  the  lifting  and  drop- 
ping of  the  upper  upon  the  lower  millstone.  Flour  is  pro- 
duced by  the  grains  of  wheat  being  caught  and  broken  up 
from  contact  with  many  sliding  surfaces.  So  food,  when 
caught  and  confined  in  the  masticatory  groove,  is  torn 
asunder  by  being  brought  in  contact  with  the  many  sliding 
planes  of  the  opposing  teeth. 

To  produce  artilicial  dentures  that  will  fulfill  the  func- 
tions of  the  natural  masticatory  organs  it  will  be  necessary 
to  study  the  radial  swing  of  the  mandible  and  the  rela- 
tion of  the  teeth  in  the  lower  to  those  in  the  upper  arch 
when   subjected  to  such  action. 

ANALYSIS    OF    THE    LATERAL    MANDIBULAR 
MOVEMENTS 

In  the  lateral  movements  one  condyle  is  drawn  forward, 
or  protruded  in  its  i)ath,  while  the  other  remains  com- 
jtaratively  stationary,  serving,  in  a  general  way,  as  a 
pivotal  or  rotation  center  to  guide  the  mandible  in  its 
radial  movements. 

THE  CENTERS  OF  MANDIBULAR  ROTATION 

The  centers  of  the  condyles  may  be,  and  frequently 
are,  the  true  centers  of  mandibular  rotation.  Oftentimes, 
however,  the  rotatio'n  centers  are  situated  inside  or  outside 
of  the  condyle  centers  at  varying  distances.  Both  actual 
rotation  centers  may  be  inside,  or  both  outside,  of  the  con- 
dyles, or  one  may  be  inside  and  the  other  outside,  or,  again, 
one  may  be  located  in  the  true  condyle  center  and  the 
other  outside  or  inside  of  the  opposite  condyle.     To  deter- 


208  THE    MASTICATORY    MECHANISM 

mine  their  exact  location  special  appliances  designed  for 
such  iJurjjoses  must  he  used,  the  most  accurate  as  well  as 
convenient  of  wliicli  are  those  suggested  by  Dr.  Gj^si. 

When  the  rotation  centers  are  located  between  the  con- 
dyles the  pivotal  condyle  has  a  slight  l)ackward  movement 
as  the  other  one  is  protruded.  When  the  rotation  centers  are 
located  outside  the  pivotal  condyle  moves  slightly  forward. 

Gysi's  appliances  indicate  that  the  true  rotation  cen- 
ters mav   lie   within    two    and    three-fourth   inches   of   each 


other,  and  varj^  from  that  distance  anywhere  up  to  a  trifle 
over  five  inches  apart. 

The  position  of  the  teeth  in  the  arches  and  of  their 
various  occlusal  surface  markings  in  relation  to  the  rotation 
centers  are  of  extreme  importance.  When  the  teeth  are 
incorrectly  located  co-ordinate  movements  between  those 
in  the  lower  against  those  in  the  upper  arch  will  be 
inhibited. 

RELATION   OF  THE   LOWER   TO   THE  UPPER  TEETH   ON   THE 
PIVOTAL   SIDE 

The  working  limit  of  the  mandible  in  lateral  masticatory 
effort   is   reached   when   the  buccal   and   lingual  cusps   and 


THE    MASTK'ATORY     MECHANISM  299 

marginal  ridges  of  the  lower  bicuspids  and  molars,  on  the 
pivotal  side,  are  directly  under  and  in  contact  with  the  cor- 
responding cusps  and  marginal  ridges  of  the  upi^er  teeth. 
The  amount  of  side  movement  necessary  to  bring  the 
teeth  in  this  relation  to  form  the  masticatory  space  was 
designated  the  "differential  limit"  by  the  late  Dr.  T.  W. 
Pritchett.  Used  in  this  sense,  it  means  the  limit  of  side 
movement  of  the  teeth  for  doing,  effective  work,  and  is 
a  very  appropriate  term.  "Differential"  means  a  differ- 
ence in  rate  or  distances  of  movement  of  the  parts  of  a 
mechanism  in  a  given  period.  In  true  rotary  movements 
of  the  mandible  laterally  the  ])icuspids  travel  a  greater 
distance  in  the  same  jieriod  than  do  the  molar  teeth,  since 
the   former   are   situated   farther   from   the   rotation   center. 

SIDE  MOVEMENTS  OF  THE  MANDIBLE  NOT  CONTROLLED  BY 
THE   ROTATING   CENTERS 

In  reality  the  rotation  centers  do  not  absolutely  contine 
the  mandible  to  an  eiact  radial  swing  at  all  times  or  rmder 
all  circumstances.  Dr.  Bennett  of  Tjondon  has  shown  that 
there  is  frequenth-  a  side  movement  of  the  entire  mandible 
independent  of  the  ordinary  rotation  points. 

In  some  experiments  cari-ied  out  by  the  writer  this 
side  movement  was  found  to  l)e  involuntary,  or  automatic, 
in  some,  and  entirely  volitional  in  other  cases.  In  most 
instances  it  is  so  slight  as  to  be  of  little  importance  in 
general  masticatory  effort,  and  need  not  be  considered  in 
denture  construction  as  a  separate  or  vital  factor. 

A  method  of  adapting  artificial  dentures  to  this  side 
movement,  when  present  and  involuntary,  will  later  on  be 
described. 

RELATION   OF  THE   LOV/ER  TO   THE   UPPER  TEETH   ON   THE 
PROTRUDED   SIDE 

The  lateral  movement  of  the  mandible  carries  the  lower 
teeth  on  the  protruded  side  lingually.  During  this  move- 
ment the  disto-buccal  cusp  of  the  lower  second  molar  moves 
along  the  inclined  planes  leading  from  the  central  sulcus 
to  the  lingual  marginal  ridge  of  the  upper  second  molar, 
and  there  finds  contact  with  its  mesio-lingual  cnsii.  This 
is  known  as  the  hnlaucUifi  covldcl.  and  this,  the  protruded 
side  of  the  mandible,  is  known  as  (he  balancing  side,  in 
contradistinction  to  the  opposite,  or  pivotal,  side,  which 
is  the  masticating  or  ivorking  side. 


300  THK    MASTICATORY     MKCHANISM 

Balaiicui.i^'  contact,  as  just  stated,  is  usually  developed 
between  the  lower  and  upper  second  molars.  Similar  con- 
tact, however,  may  be  developed  between  the  lower  and 
ui)per  third  molars,  when  fully  erupted,  although  it  fre- 
quently happens  that  these  teeth,  even  after  a  lapse  of 
many  years,  fail  to  come  into  normal  occlusion  with  each 
other.  For  this  reason,  therefore,  balancing  contact  is 
most  commonly  develo])ed  and  remains  most  persistent 
between  the  lower  and  u])per  second  molars.  In  radial 
movements  of  the  mandible  no  contact  exists,  nor  is  any 
essential  to  the  balancing  of  the  masticatory  apparatus, 
from  the  second  molar  forward  to  the  opposite  central,  or 
even  lateral,  incisors.  The  actual  work  of  mastication  is 
being  performed  on  the  opposite  of  the  mouth,  and  there- 
fore the  close  interlocking  of  planes  and  cusps  on  the  pro- 
truded side,  exclusive  of  the  balancing  point,  would  tend 
to  disturb,  rather  than  aid,  masticatory  effort. 

THE  COMPENSATING  CURVE 

As  in-eviously  stated,  tlie  tii)s  of  the  buccal  cusps  of 
the  bicuspids  and  molars,  when  viewed  bucally,  assume  a 
curved  arrangement,  the  convexity  being  downward.  This 
curved  arrangement  of  the  teeth  in  the  upjier  arch  is  called  the 
compensating  curve.  The  reason  for  it  being  so  designated 
is  as  follows: 

When  the  occlusal  plane  is  flat,  and  the  condyle  path 
is  inclined  downward  and  forward,  separation  occurs  be- 
tween the  lower  and  upper  bicuspids  and  molars  in  lateral 
movement,  the  lower  teeth  being  carried  downward  to  the 
lingual  and  away  from  the  upper  teeth  on  the  protruded 
side.  Balancing  contact,  therefore,  is  not  jiossible  under 
such  conditions,  because  of  incoordinate  movements  the 
occlusal  planes  of  the  upper  teeth  oeing  practically  hori- 
zontal while  the  occlusal  planes  of  the  lower  teeth  are 
carried  downward  in  an  angular  direction  by  the  condylar 
movements.  When  arranged  on  a  proper  curve,  however, 
the  disto-buccal  cusp  of  the  lower  second  molar  occupies 
a  higher  position  in  the  occlusal  plane  than  the  mesio- 
lingual  cusp  of  the  upper  second  molar,  which  occupies 
a  position  forward,  downward  and  to  the  lingual  in  the 
occlusal  plane.  In  lateral  movements  the  disto-buccal  cusps 
of  the  lower  second  molar  moves  downward,  forward  and 
linguall}%  in  contact  with  the  plane  leading  from  the  central 


THE    MASTICATORY    MECHANISM  301 

groove  to  tlie  mesio-]ingual  eiisp  of  the  upper  second  molar. 

This  balancing  area  is  present,  and  the  diso-buccal 
cusp  of  the  lower  second  molar,  under  normal  conditions, 
is  in  contact  with  it  at  some  point  throughout  the  entire 
lateral  excursion  of  tlie  condyle,  both  out  of  and  back  to 
its  fossa. 

The  curved  arrangement  of  tlic  upper  teeth,  therefore, 
compensaies  for  the  dropping  down  of  tlie  condyle  in  its 
path  in  radial  and  forward  movements,  and  makes  possible 


DIAGRAil    SHOWING    PARAT.I.EL    RELATION    OF    CONriVI.E    PATH    AND    COMPENSATING    CURVE 

the  contact  just  described.  AVhile  the  compensating  curve 
represents  a  fairly  accurate  arc  where  it  intersects  the  tips 
of  the  buccal  cusps  of  the  bicusi)ids  and  molars,  when 
projected  forward,  it  passes  above  the  incisal  edges  of  the 
anterior  teeth  sometimes  as  high  as  the  incisal  third  of  the 
central  incisors.  '  This  is  due  to  the  overlapping  of  the 
upper  anterior  over  the  lower  teeth,  there  being  a  more 
or  less  definite  correlation  existing  between  the  curvature 
of  the  teeth  plane  and  the  overbite.  Variations  as  to 
the  amount  of  overbite  naturally  occur,  one  of  the  most 
common  being  a  deep  overbite,  with  a  comparatively  shal- 


302  THK    MASTU'ATORY    MKCHANISM 

low  or  flat  conipensaling  curve.  In  such  cases  some  space 
must  be  present,  when  the  teeth  are  in  occlusion,  between 
the  lingual  surfaces  of  the  upper  and  the  incisal  edges 
of  the  lower  teeth,  otherwise  interference  will  occur  with 
normal  lateral  and  protrusive  movements. 

THE  CURVE  OF  SPEE 

The  lower  teeth,  including  the  incisors  and  cuspids, 
usually  present  a  very-well-defined  arc-like  arrangement 
when  viewed  buccallv.  This  curved  plane  assumed  by  the 
lower  teeth  is  sometimes  called  the  "Curve  of  Spee,"  be- 
cause Graf  von  Spee,  the  G-erman  anatomist,  first  called 
attention  to  it,  about  1890. 

Spee  says,  in  regard  to  tlie  relation  existing  between 
the  condyle  paths  and  the  teeth  planes :  "In  the  forward 
bite  the  teeth  and  condyles  describe  the  same  circular  move- 
ment. The  steeper  the  ]iath  of  the  condyle  the  more  pro- 
nounced the  tooth  cur\e  will  be,  because  both  will  have 
the  same  radius." 

This  latter  statement  is  incorrect,  for,  while  the  con- 
dyle path  and  the  teeth  plane  may  both  be  arcs  of  circles 
having  a  common  center,  their  radii  may  vary,  and  the  two 
curves  will  often  represent  concentric  arcs. 

Spee's  writings  refer  especiallj'  to  the  curvature  of 
the  lower  teeth  plane  and  its  relation  to  the  condylar  move- 
ments, and  therefore  the  term,  "Curve  of  Spee,"  should 
not  be  applied  to  the  upper  teeth  i)lane. 

MODIFICATION  OF  THE  COMPENSATING  CURVE 

Occasionally  the  occlusal  surfaces  of  the  upper  molars 
present  a  series  of  parallel  planes,  instead  of  assuming  a 
symmetrical  curve,  as  described.  The  second  molar  is 
slightly  higher  than  the  first,  and  the  third  slightly  higher 
than  the  second.  The  lower  molars  assume  a  similar 
relation,  with  the  result  that  the  occlusal  plane  when  analyzed 
presents  a  step-like  instead  of  a  curved  arrangement. 

It  is  claimed  by  some  that  this  is  the  logical  manner 
in  which  to  arrange  teeth  in  the  construction  of  artificial 
dentures.  First,  because  balancing  contact  can  be  more 
easily  secured;  second,  that  there  is  less  liability  of  the 
dentures  becoming  dislodged  in  masticatory  effort.  The 
argument  is  that  the  force  of  muscular  effort  is  delivered 
upon  the  food  more  in  the  nature  of  an  end  thrust  against 


THE    MASTICATORY    MECHANISM  303 

right-angle  surfaces,  rather  than  against  inclined  planes; 
third,  that  such  an  arrangement  of  the  teeth  is  anatomical, 
natural  and  more  common  than  the  curved  arrangement. 

It  is  the  opinion  of  the  writer,  based  upon  the  examina- 
tion of  many  specimens,  first,  that  the  step-like  arrange- 
ment is  the  exception,  and  not  the  rule,  or  at  least  occurs  no 
more  frequently  than  the  curvcil  arrangement;  second,  that 
balancing  contact  can  as  readily  l)e  secured  liy  placing  the 
second  molars  in  a  relation  similar  to  that  which  they 
sustain  in  the  natural  denture,  when  the  curvature  is  well 
defined,  as  previousiy  outlined;  third,  that  the  A'arying 
planes  on  the  occlusal  surfaces  of  the  intercusi^ating  molars 
tend  to  prevent  displacement  of  the  dentures  in  masticatory 
effort;  fourth,  that  better  esthetic  results  can  be  secured 
by  arranging  the  teeth  by  the  curved  rather  than  by  the 
stepping  method.  However,  either  method  is  productive 
of  satisfactory  results  if  due  attention  is  given  to  details, 
so  it  is  largely  a  question  of  esthetics,  in  which  neither  com- 
fort nor  utilitv  is  concerned. 


CHAP  T  K  R     XVIII 

CONSTRUCTION  OF  FULL  DENTURES. 

ANATOMIC  METHOD 

GENERAL  REMARKS 

In  the  eoiLstriictioii  of  good  dentvires,  as  has  ))een  previ- 
ously stated,  the  accomplishment  of  three  objects  is  desirable, 
necessary,  and,  in  most  cases,  possible,  when  careful  atten- 
tion to  detail  is  observed.  These  three  objects — usefulness, 
good  looks  and  comfort — when  attained  in  prosthetic,  as  well 
as  in  all  dental  operations,  represent  that  quality  of  service 
which  our  patients  have  a  right  to  expect,  and  which  the  ten- 
ets of  our  profession  impose  upon  us. 

It  is  therefore  the  duty  of  every  practitioner  to  perfect 
himself  in  the  liighest  degree,  not  only  in  theoretical  knowl- 
edge, but  in  the  acquirement  of  technical  skill  as  well  in  all 
that  pertains  to  his  calling,  whether  it  be  the  general  or  a  spe- 
cialized field  of  dental  practice. 

Anatomic  occlusion  of  artificial  teeth  consists  in  following 
nature's  plan  of  arrangement  as  observed  in  the  normal 
human  masticatory  apparatus. 

Occasions  arise,  Jiowever,  when  this  course  is  not  pos- 
sible, but  such  cases  are  rare.  When  occurring  the  causes 
may  be  traced  to  some  abnormality  of  the  glenoid  forste,  usu- 
ally the  result  of  mandilmlar  movements  having  since  early 
youth  been  restricted  liecause  of  malocclusion  or,  in  some 
cases,  to  the  sequela  of  temporo-mandibular  inflammation. 

Whatever  the  character  of  the  abnormality  an  attempt 
should  be  made  to  discern  the  cause  and  discover  such  useful 
mandibular  movements  as  are  possible.  With  a  thorough 
knowledge  of  existing  conditions  and  the  application  of  an- 
atomic methods  far  better  service  can  be  rendered  a  patient 
than  when  such  almormality  is  ignored. 

By  way  of  introduction  to  anatomic  methods  a  brief  re- 
view of  masticatory  movements  in  general  will  he  in  order. 

MASTICATORY  MOVEMENTS   OF  THE  CARNIVORA 

The  most  effective  masticatory  movements  of  the  carniv- 
ora  (flesh-eating  animals)  are  hinge-like,  no  extensive  lateral 
movements  of  the  mandible  being  possible  for  two  reasons: 

304 


CONSTRUCTION  OF  FULL  UENTHRES  305 

First,  because  of  the  t'orni  oi'  the  temjjoro-iiuuKUbuhir  artieu- 
lation,  which  does  not  permit  of  much  unihiteral  action;  aud, 
second,  because  of  the  excessive  length  and  relation  to  each 
other  of  tlie  upper  and  lower  canine  teeth.  In  general,  the 
posterior  teeth  of  this  class  of  mammalia  liave  strongly 
marked  cusps  which  intercuspate  closely.  Their  function 
is  to  tear  and  ciit  food. 

MASTICATORY    MOVEMENTS   OF   THE   HERBIVORA 

In  the  herbivora  (animals  that  live  on  herbs  and  vegeta- 
tion), the  effective  mandibular  movements  are  almost  exclu- 
sively lateral,  or  from  side  to  side.  The  occlusal  surfaces  of 
the  teeth  are  not  strongly  cusped,  but  are  ridged  for  grinding 
food. 

MASTICATORY   MOVEMENTS    OF  THE   OMNIVORA 

In  the  omnivora  or  herbi-carnivora  (subsisting  on  both 
flesh  and  vegetation),  the  effective  masticatory  movements  are 
hinge-like  as  well  as  from  side  to  side,  or  lateral.  The  occlu- 
sal surfaces  of  the  teeth  consist  of  planes,  ridges,  grooves  and 
cusps,  usually  so  arranged  that  in  unilateral  movements  the 
CUS13S  of  the  lower  may  glide  between  those  of  the  upper  teeth 
in  definite  paths,  without  interference. 

Since  man  is  omnivorous,  the  human  masticatory  ap- 
l^aratus,  while  modified  somewhat  from  that  of  the  lower  ani- 
mals because  of  different  habits  of  life,  corresponds  in  gen- 
eral to  mammalia  of  tJiis  class.  A  more  complete  general  de- 
scription of  the  human  masticatory  apparatus  will  be  found  in 
the  preceding  chapter. 

In  the  chewing  of  meats,  tlie  liinge  action  of  the  mandible 
is  most  effective  at  first  until  the  meat  fibres  have  been  more 
or  less  torn  and  shredded  by  the  cusps  of  the  bicuspids  and 
molars,  after  which  the  lateral  movements  are  just  as  essen- 
tial in  still  further  reducing  the  mass  to  a  pulpy  condition 
suitable  for  action  by  the  digestive  fluids. 

Cereals,  fibrous  vegetables  and  most  all  varieties  of 
starchy  foods  require  active  lateral  movement  for  proper  re- 
duction. Dr.  G.  v.. Black  in  "Phvsical  Characters  of  Hixman 
Teeth"  (Cosmo-s,  1895),  states: 

"In  the  mastication  of  cereal  foods — those  made  from 
grain  of  almost  all  kinds — the  lateral  or  grinding  motions  are 
largely  employed.  This  is  true  also  of  all  of  the  brittle  foods 
of  whatever  nature.    Indeed,  many  of  these  are  so  difficult  to 


306  CONSTRUC'PIOX    OK    FHI-L    DENTTTRES 

cnisli  l)y  dircci  ]irossuf«'  that  it  hcconics  inipract  ical)l('.  Many 
kinds  of  food  will  simply  lie  packed  togethei-  between  the 
teeth,  and  a  stress  of  two  or  three  hundred  pounds  will  be 
insufficient  to  crush  it  out  as  meats  are  crushed.  Many  of 
the  crusts  from  ordinary  baker's  bread,  when  subjected  to 
stress  between  the  molar  teeth,  will  not  be  cut  through  with 
a  stress  of  two  hundred  and  fifty  pounds ;  and  they  are  not 
very  hard  crusts,  either.  They  are  readily  broken  up,  how- 
ever, with  a  much  lighter  stress  combined  with  a  little  lateral 
movement,  especially  as  they  become  moistened  with  the 
secretions.  It  seems  probable,  however,  that  many  persons 
unconsciously  exert  an  enormous  force  upon  such  foods  as  are 
inclined  to  pack  between  the  teeth.  I  am  no  longer  surprised 
at  the  frequent  breaking  of  frail  teeth  on  In'ead  crusts  that, 
are  not  very  hard.  It  is  but  little  wonder  that  porcelain  fac- 
ings on  crowns  and  bridges  are  so  often  broken." 

In  carrying  out  a  line  of  experiments  to  determine  the 
amount  of  direct  stress  required  to  crush  various  kinds  of 
food.  Dr.  Black  used  an  instrument  called  a  p)hago-d3"namome- 
ter.  The  action  of  tliis  instrument  on  the  food  tested  was 
practically  identical  with  that  exerted  liy  the  natural  teeth 
on  food  wlien  the  hinye-like  action  of  the  mandil)le  is  em- 
ployed. 

Some  years  later  Dr.  Joseph  Head  carried  out  a  line  of 
experiments  to  deterjnine  the  amount  of  force  required  to 
reduce  similar  classes  of  food  with  lateral  movements.  He 
used  for  this  purpose  a  Imman  skull  in  which  the  natural 
teeth  were  present  and  occluded  well.  The  following  table 
of  comparison  shows  that  it  requires  only  about  one-lialf  the 
effort  to  reduce  food  under  lateral  movem(>nts  that  is  required 
under  the  hinge  action  of  the  mandible: 

Dr.  Head 's 
Meals  Experiments 

Corned  Beef    18     -22  lbs. 

Tongue   1     -  2    " 

Tenderloin  of  Beef,  very  tender.  8     -  9    " 

Round  of  Beefsteak,  tough 38     -42    " 

Eoast  Beef   20     -.35    " 

Boiled  Ham   10     -14    " 

Pork  Chop   25     -30    " 

Roast  Veal    16     -30    " 

Average    17     -20    "  3214-417/8 


Dr 

•.Black's 

Ex, 

>eriments 

.",0 

-35     lbs. 

;! 

-  5      " 

35 

-40      " 

60 

-80      " 

35 

-50      " 

40 

-60      " 

20 

-25      " 

35 

-40      " 

CONSTRUCTION  OF  FULL  DENTURES  307 

Dr.  Head's  Dr.  Black's 

Vegetables.  Experiments         Experiments 

Raw  Cabbage   16  "  40     -60      " 

Head  Lettuce    16  "  25     -.30      " 

Radish,  whole  broke  at 20     -25    "  20     -25      " 

Radish,  i^ieces  pulverized  at.  ..  .10     -15    "  35     -40      " 

Average    12V--16    ''  30     -383^" 

(Dental  Cosmos,  1906,  P.  1191) 

Dentures  constructed  on  a  plain  line,  or  similar  articula- 
tor, or  on  an  anatomical  occluding  frame,  when  all  of  the  de- 
tails are  not  carefulh-  attended  to.  limit  the  wearer  to  the 
hinge  action  of  the  mandible  in  the  reduction  of  food. 

The  advantage  of  the  anatomic  system  of  denture  con- 
struction over  the  generally  prevailing  methods  wherein 
masticatory  effort  is  limited  to  the  hinge  action  of  the  mandi- 
ble, have  l)ecome  an  established  fact.  Dentures  of  the  ana- 
tomic type  balance  when  in  action,  while  those  constructed 
on  plain  line  articulntors  become  readily  unseated  when 
lateral  movements  are  attempted.  This  fact  alone  is  of  suffi- 
cient importance  to  warrant  the  adoption  of  anatomic  meth- 
ods, because  of  greater  efficiency,  as  well  as  comfort,  derived 
by  the  patient  from  the  use  of  dentures  of  this  type. 

The  normal  human  denture,  and  the  various  relations  the 
lower  sustain  to  the  upi)er  teeth  in  full  and  partial  occlusion, 
is  the  ideal  working  model  for  the  jn-osthetist,  although  at 
times  departure  from  ideal  conditions  must  be  made.  To 
carry  out  the  many  steps  of  denture  construction  by  this 
method  a  knowledge  of  the  mechanism  of  the  masticatory 
apparatus  is  the  first  essential,  while  the  use  of  suitable  ap- 
pliances constitutes  a  second  factor  of  equal  imj^ortance. 

MAIN  FEATURES  OF  ANATOMIC  METHODS 

The  essential  practical  features  of  anatomic  denture 
construction,  therefore,  aside  from  a  knowledge  of  mandi- 
bular movements,  involve  the  use  of  special  appliances  and 
require  that  certain  steps  be  carried  out  in  logical  sequence. 
The  main  factors  Qf  importance  are  as  follows: 

First — An  -occluding  frame  capable  of  reproducing  the 
most  essential  masticatory  movements  of  the  mandible. 

Second — A  face  bow,  or  caliper,  for  mounting  the  casts 
on  the  occluding  frame  in  correct  relation  to  the  lateral  cen- 
ters of  rotation. 

Third — Some   means  for   registering   the    condyle   path 


oOS  CONSTRUCTION'    OF    FULL    DENTURES 

pitch  of  the  i^atieut  and  of  recording'  the  same  on  the  occlud- 
ing frame. 

Fourth — The  selection  ot  t<'eth  of  ai)pi-opriate  size,  shade 
and  anatomic  forms  to  meet  the  requirements  of  each  case. 

Fifth — Ti'ial  of  the  model  dentures  in  the  mouth  under 
masticatory  movements  to  verify  their  efficiency  and  estlietic 
appearance. 

Sixth — Testing  and  correction  of  occhisiou  of  the  jinished 
dentures  l)y  means  of  carl)on  paper  and  engine  stones,  to 
compensate  for  variation  of  the  natural  lateral  mandibular 
rotation  centers  from  those  of  the  occluding  frame  on  which 
the  teeth  were  arranged. 

PRESENT  METHODS  OF  TECHNIC  IN  ANATOMIC 
DENTURE  CONSTRUCTION 

Two  general  methods  of  anatomic  denture  construction 
are  in  vogue  in  this  country  at  the  present  time,  each  of  which 
recjuires  special  appliances  and  the  following  of  a  rather 
closely  defined  system  of  technic. 

The  two  systems  referred  to  are  the  Snow  methods  and 
appliances,  a  logical  outcome  of,  with  improvements  on,  the 
Bonwill  and  Christensen  ideas,  and  the  Gysi  methods  and  ap- 
pliances, which  are  based  on  similar  principles  but  differ  in 
many  important  detail-^.  Both  systems  in  the  hands  of  com- 
petent prosthetists  lead  to  the  same  desired  results,  viz.,  the 
production  of  high-type  dentures,  which  for  efficiency  and 
comfort  far  surpass  those  produced  by  any  other  system  in 
which  lateral  mandibular  movements  are  not  considered. 
Both  methods  involve  the  carrying  out  of  many  steps  in  com- 
mon, in  some  of  which  the  same  technic  is  employed,  while 
in  others  considerable  variation  occurs.  The  essential  details 
of  these  two  sj^stems  will  now  be  rendered  sufficiently  clear, 
it  is  hoped,  to  enable  a  prothetist  of  average  skill,  who  un(Jer- 
takes  the  work,  to  secure  satisfactory  results. 

THE   SNOW  APPLIANCES  AND   METHODS 

The  appliances  used  in  the  Snow  method  consist  of  an 
occluding  frame,  or  as  it  is  termed,  an  "articulator,"  the 
condyle  or  lateral  rotation  centers  of  which  are  four  inches 
apart,  this  being  about  the  average  distance  from  center  to 
center  of  the  human  condyles.  '^Plie  lateral  rotation  centers  of 
the  frame  are  fixed  at  four  inches  and  cannot  be  increased  or 
diminished.     The  condyle  paths  of  the  frame  are  capable  of 


CONSTRUCTION'  OF  FULL  DENTURES  3U9 

adjiistuieiit  and  of  being  clamped  at  various  angles,  depending 
npon  the  pitch  of  the  condyle  paths  of  the  patient,  as  regis- 
tered. The  upper  and  lower  bows  of  the  occluding  frame,  to 
which,  when  the  casts  are  attached,  represent  the  maxilla  and 
mandible,  respectively,  are  adjustable  for  the  accommodation 
of  thick  or  thin  casts.  The  back  spring,  by  its  tension,  holds 
the  mandibular  portion  of  the  frame  in  the  back  end  of  the 
condyle  slots,  or  in  that  jjosition  representing  the  condyles 
at  rest  in  the  glenoid  fossa". 

THE   FACE   BOW 

The  face  bow  is  a  measuring  device  or  caliper  designed 
for  registering  the  antero-posterior,  as  well  as  horizontal 
plane  relationship  of  tlie  alveolar  ridges  to  the  condyles  when 
the  latter  are  at  rest  in  the  glenoid  fossje,  as  in  normal  closure. 
It  is  used  in  conjunction  with  the  wax  bite,  or  with  occlusion 
models.  This  appliance  is  indispensable  in  order  that  the 
casts  may  be  mounted  in  true  relation  to  the  rotation  centers 
of  the  frame.  By  thus  establishing  the  correct  radial  distance 
of  the  casts  from  the  hinges,  the  teeth,  when  occluded  on  the 
frame  and  adjusted  with  clearance  paths  for  the  cusps  of  the 
lower  to  traverse  laterally  between  those  of  the  upper  teeth, 
will  follow  the  same  lines  of  travel  when  the  dentures  are 
completed  and  fitted  in  the  mouth.  Increasing  or  decreas- 
ing the  radial  distance  of  the  teeth  on  the  frame  from  that 
which  they  will  occupy  in  the  mouth,  will  cause  cusp  inter- 
ference in  lateral  movements. 

The  face  bow  consists  of  a  U-shaped  frame,  in  the  ex- 
tremities of  which  are  two  graduated  sliding  rods  to  enable 
the  bow  to  be  evenly  balanced  on  the  face.  These  are  the 
condyle  rods,  the  inner  ends  of  which,  in  adjustment,  are  to 
be  placed  opposite  the  outer  ends  of  the  condyles  and  there 
clamiied  on  points  previously  marked  on  the  integument  be- 
fore adjusting  the  bow.  The  bow  in  its  central  portion  carries 
a  universal  clamp  for  receiving  the  bite  rod  after  the  latter 
has  been  firmly  fixed  in  the  occlusion  model  and  for  clamping 
it  to  the  bow  when  proper  adjustment  of  the  condyle  rods  to 
the  face  has  been  gecured. 

THE   BITE   GAUGES 

Two  small  flat  plates  of  metal  called  hite  gauges,  having 
the  edges  turned  down  to  engage  with  the  lower  wax  rim, 
and  with  tapering  pins  projecting  on  the  upper  surfaces  to 
engage  with  the  upper  wax  rim,  are  used  for  taking  the  pro- 


aiO  CONSTRUCTION    OF    FULL    DENTURES 

trusive  bite — the  means  by  whicli  the  condyle  paths  are  regis- 
tered. The  details  for  the  application  of  these  appliances 
will  be  given  in  the  following  described  case  of  full  upper  and 
lower  denture  construction. 

GENERAL    CONSTRUCTIVE    STEPS 

The  construction  of  full  dentures  anatomically  involves 
the  securing  of  suitable  impressions ;  production  of  casts ; 
development  of  wax  contour  models,  first  on  the  casts  and 
afterward  in  the  mouth,  to  develop  lost  facial  contour  and 


UPPER    MODELING 


establish  the  normal  bite ;  the  mounting  of  the  casts  on  an 
anatomical  occluding  frame ;  registration  of  the  condyle  paths 
of  the  patient  and  the  adjustment  of  the  condyles  of  the  frame 
to  correspond ;  development  of  the  compensating  curve  on 
the  wax  occlusion  model;  selection  of  teeth  of  suitable  form 
and  color  to  harmonize  with  anatomic  and  esthetic  require- 
ments of  the  patient,  and  their  arrangement  in  upper  and 
lower  arches  so  as  to  develo]i  the  greatest  efficiency  and  pre- 
sent the  best  appearance ;  duplication  in  permanent  materials 
of  the  wax  model  dentures,  and  finally,  the  fitting  and  adjust- 
ment of  the  dentures  to  the  respective  arches  within  the  oral 
cavity. 


CONSTRrCTIOX  OP  FULL  DENTURES  311 

Moi'f  tliau  one  limidrcd  iinliviilual  stops  must  be  carried 
out  in  sequence  in  the  production  of  full  dentures  of  any  type. 
It  is  therefore  imperative  that  the  greatest  care  be  constantly 
exercised  to  arrive  at  satisfactory  results,  since  a  single 
error  in  some  particular  step  may  minimize  the  efficiency,  or 
result  in  the  total  faiUire  of  the  substitutes. 

The  technic  of  impression  taking,  east  construction  and 
the  formation  of  base  plates  of  various  kinds,  has  been  pre- 
viously presented.  Also  a  brief  description  of  the  oral  cavity 
and  the  masticatory  movements  has  been  given.  Tliese  vari- 
ous subjects  should  be  thoroughly  considered  by  the  student 
before  undertaking  the  work  now  to  be  presented. 

Assuming  that  suitable  casts  have  been  derived  from  ac- 
curate iinjiressions  of  the  mouth,  tlie  next  step  in  the  coustruc- 


SIDE   VIEW   l)K   IMl'RESSKJN"    UKADV    Fdl!    FI1I!MIX( 


tion  of  a  full  denture  (upper  and  lower)  is  to  form  in  wax, 
or  some  easih"  workable  but  comparatively  rigid  material, 
models  of  the  dentures  to  be  constructed.  These  model -den- 
tures, before  being  duplicated  in  permanent  materials,  are 
tried  in  the  mouth  and  tested  as  to  occlusion,  appearance  and 
comfort.  Should  any  modification  he  required,  such  changes 
as  are  necessary  may  be  accomplished  with  less  effort  and  loss 
of  time  while  the  dentures  are  in  a  plastic  condition  than 
subsequently. 

The  model  dentures  are  developed  in  two  stages:  first, 
base  plates  are  fitted  to  the  casts  before  the  latter  are  mounted 
on  the  occluding  frame,  and  on  these,  rims  of  wax  are  ad- 
justed to  represent  approximately-  in  depth  and  contour  the 
lost  teeth  and  absorbed  borders.  These  are  ordinarily  called 
trial  base  plates. 


:512  (;ONSTRrC"IM().\     Ol'    full    DliNTrRES 

Dr.  G.  II.  Wilson  suggests  Ihc  use  of  the  tonus  Dcrlusion 
uud  contour  }iiodels,  because  by  means  of  them  ocelnsal  rela- 
tions are  determined,  while  snbseqnently  by  additions  to,  and 
trimming  of  the  wax  rims,  the  contour  of  the  faeo  is  restored 


\M)    TltlM.MEI) 


to   normal   outline.     They   also   represent,   in   a  crude   way, 
models  of  the  dentures  to  be  constructed. 

The  second  stage  i?  developed  as  follows:    After  certain 
sequent  steps,  to  be  described  later,  are  carried  out,  sections 


l.dWER    CAST    WITH    BASEPLATE    FITTED    TO    BORDER 

are  cut  out  of  the  wax  rims,  and  in  the  spaces  so  formed  the 
selected  teeth  are  adjusted,  the  lower  to  occlude  with  the  up- 
per. The  gums  are  then  carved  in  the  wax  and  the  surplus 
material  removed,  which  steps  convert  the  wax  occlusion  and 


CONSTRUCTION  OF  FULL  DENTURES  313 

contour  models  into  »v/.r  Diodel  dentures,  by  which  term  they 
will  be  designated  in  this  description  of  denture  construction. 
This  term  is  appro] )riate  l)ecanse  they  are  the  models  by 
means  of  which  the  matrices  are  produced  in  which  the  per- 
manent dentures  are  molded. 

OCCLUSION  AND  CONTOUR  MODELS 

In  the  construction  of  full  dentures  the  upper  and  lower 
occlusion  models  repiesent  two  masses  of  crude  material 
from  which  the  prosthetist  carves  and  shapes  in  outline  and 


DI.STAI.    ^'IE^V    (IF    I'l'TER    AND    I^OWKR    OCl'LISION    MODEI^ 

contour  the  forms  of  the  permanent  dentures,  just  as  a  sculp- 
tor molds  in  clay  the  model  of  a  ijermanent  statue. 

An  occlusion  model  is  usually  developed  in  two  steps 
and  may  be  composed  of  different  classes  of  materials. 

First,  a  base  plate,  either  permanent  or  temporary,  is 
formed  over  a  die  or  cast,  derived  from  an  impression  of  the 
mouth. 

Second,  to  the  base  plate  a  rim  of  plastic  material,  usually 
wax,  is  tirmly  attached  and  by  trial  in  the  mouth  is  carved 
and  molded  to  "the  required  contour  of  the  future  denture. 

REQUIREMENTS  OF  A  BASEPLATE 

The  base  plate,  of  whatever  class  decided  upon,  should 
be  rigid  and  unyielding,  capable  of  withstanding  oral  tern- 


314  CONSTRUCTIOX    OF    FULL    DENTURES 

perature  without  softening  or  bending  under  masticatory 
stress.  It  should  be  olosely  adapted  to  the  oral  tissues  on 
which  it  rests  and  should  not  become  dislodged  by  its  own 
weight,  or  tip  from  the  action  of  adjacent  muscles. 

The  prospect  of  success  of  a  permanent  denture  is  slight 
when  the  base  plate  ol  the  occlusion  model  fails  to  show  an 
equal  amount  of  adhesion  required  in  the  finished  denture. 
The  most  exact  technio,  therefore,  shoiild  be  carried  out  in 
forming  the  base  for  an  occlusion  model,  for  by  this  means 
the  adaptation  of  the  permanent  denture  can  be  determined 
at  a  time  when  corrections  can  be  made  with  little  loss  of  time. 

Wlien  a  permanent  base  plate  of  swaged  gold,  platinum 
or  aluminum  fails  to  show  good  adaptation  and  adhesive  prop- 
erties in  preliminary  trials  it  should  be  reswaged  over  a  new 
die  derived  from  a  new  impression,  since  in  no  case  do  sub- 
sequent steps  tend  to  improve  defective  adaptation,  but  rather 
to  increase  it.  The  same  holds  true  of  vulcanite  or  cast 
metal  bases  and  of  base  plates  constructed  of  the  more  rigid 
temporary  materials.  Under  no  conditions  should  an  elastic 
substance  or  a  material  that  readily  distorts  by  heat  or 
pressure  be  employed  in  the  construction  of  bases  for  oc- 
clusion models,  because  distortion  of  the  pattern  denture 
from  any  cause  will  result  in  similar  errors  in  the  permanent 
denture. 

REQUIREMENTS   OF  THE   OCCLUSION    RIM 

The  wax  used  in  forming  the  occlusion  rim  must  be  of  a 
hard  variety,  not  softening  at  oral  tem]ierature  or  mashing 
down  under  masticatory  stress  either  before  or  after  the 
teeth  are  imbedded  in  it.  The  rim  should  not  l)e  built  up  in 
layers  as  is  frequently  the  case,  but  the  wax  should  be  kneaded 
into  a  compact,  solid  mass  before  l)eing  attached  to  the  base 
plate.  A  rim  composed  of  a  hard  variety  of^pink  wax  will 
present  a  better  appearance  and  enable  the  prosthetist  to  de- 
velop a  more  esthetic  temporary,  or  model  denture,  than 
when  yellow  or  l)rown  waxes  are  employed. 

CONSTRUCTION  OF  OCCLUSION  MODELS 

The  base  plate,  of  whatever  material  determined  upon, 
should  be  formed,  introduced  in  the  mouth  and  tested  as  to 
its  fitness  in  peripheral  outline,  stability  on  and  adhesiveness 
to  the  tissues.  When  found  satisfactory  in  every  respect  the 
occlusal  rim  is  formed  and  attached  to  it  as  follows : 


CONSTRUCTION  OP  FULL  DENTURES  315 

Tlic  wax  tt)  \)c  used  in  forniiiig  the  rim  is  softened  in 
water  not  exceeding  130  degrees  Fahrenlieit.  When  tlioi-- 
oughly  plastic  it  is  kneaded  into  a  compact  mass  with  palm 
and  fingers,  then  transferred  to  a  dry  towel  and  the  kneading 
process  continued  until  all  moisture  is  eliminated. 

The  mass,  while  plastic,  is  then  formed  into  a  roll  about 
one-half  inch  in  diameter  and  four  and  one-half  inches  long. 
This  roll  is  then  bent  around  and  placed  upon  the  maxillary 
portion  of  the  base  plate,  against  which  it  is  only  slightly 
pressed.  A  heated  spatula  is  passed  along  the  line  of  junction 
of  the  roll  with  the  base  plate  on  the  labial,  buccal  and  lingual 
surfaces  to  melt  the  wax  and  cause  it  to  adhere  firmly  to  the 
base  plate  throughout  the  entire  extent  of  the  border.  The 
angles  are  then  filled  in  with  melted  wax  until  approximate 
contour  on  all  surfaces  is  developed.  Considerable  lieat  is  re- 
quired to  properly  attach  the  wax  rim  to  the  base  plate.  When 
the  latter  is  composed  of  temporarj'  material  it  should  rest 
upon  the  cast  on  which  formed  to  prevent  distoi'tion  while  ap- 
plying the  rim  and  melting  the  wax. 

When  the  rim  is  firmly  adherent  and  the  wax  has  cooled 
somewhat,  the  labial,  buccal  and  lingual  surfaces  are  devel- 
oped api^roximately  to  the  desired  contour  liy  additions  and 
trimming  as  indicated. 

APPROXIMATE  DEPTH  OF  OCCLUSION  RIMS 

For  ordinary  cases,  where  an  average  amount  of  absorp- 
tion of  the  borders  has  occurred,  the  rim  should  be  about 
three-eighths  of  an  inch  thick  from  maxillary  to  occlusal  sur- 
faces and  about  the  same  breadth  from  buccal  to  lingual. 
The  occlusal  surface  should  be  flat  from  before  backward, 
as  well  as  from  side  to  side.  This  may  be  accomplished  by 
paring  otf  the  excess  occlusal  wax  with  a  knife,  softening  this 
area  somewhat  and  pressing  against  any  true  flat  surface  as 
a  slab  or  the  top  of  the  bench.  During  this  step  the  base  plate 
should  rest  upon  its  cast  and  the  applied  pressure  should  be 
uniform  to  jirevent  tln'nning  the  rim  more  on  one  side  than 
the  other. 

BUCCO-LINGUAL  POSITION  OF  THE  UPPER  AND  LOWER  WAX 
RIMS  IN   RELATION  TO  THE  BORDER  CRESTS 

The  rim  should  be  set  as  nearly  on  the  border  as  possible 
to  reduce  to  the  minimum  the  tipping  leverage,  which  increases 
in  direct  proportion  to  the  distance  the  teeth  are  placed  labi- 
ally  or  buccally  from  the  maxillary  ridge. 


;UC  CONSTRUCTIOX    OP    FULL    UKNTI'RKS 

Tliero  arc  two  iinjiorlaiit  ract<irs,  luiwcxci',  which  Uirgely 
control  tlio  ]al)ial  and  l)iu'cal  ])ot<itiou  of  the  occlusal  rim  of 
an  npper  occlusion  model.  First,  the  width  of  the  lower  arch 
from  buccal  to  buccal  and  its  relation  to  the  ui)per  border; 
and  second,  the  extent  of  loss  of  the  upper  alveolar  ridge  on 
labial  and  buccal  surfaces  b.y  absorption.  In  h\l\  cases  the 
teeth  in  the  lower  must  occlude  with  those  in  the  upper,  re- 
gardless of  the  disparity  in  size  of  the  two  arches.  When  the 
lower  arch  is  excessively  large  and  the  upper  is  under  size 
in  arranging  the  teeth  on  the  iipper  base  plate  they  must  be 
placed  out  beyond  the  ridge,  while  the  lowers  must  be  set 
inward  as  much  as  possible  without  interfering  with  tongue 


1>ISTAI,  VIKW  Ol'  Ul'l'KK  AND  l.OWKR  OCCLUSION  .MOIJKi.S 

ITRI.U,    PLATES),    SHOWING    THE    UEI-ATFON   Ol'    WAX 

niMS    TO    TITER    AND    I.OWEK    llORDEIl    CRKSTS 

movements.  A  general  rule  to  follow  is  to  so  adjust  the  wax 
rims  in  full  cases  that  the  buccal  and  lingual  surfaces  of  both 
rims  will  be  parallel  with,  and  about  an  equal  distance  from, 
a  line  drawn  between  tiie  crests  of  tlie  two  borders. 

The  second  factor,  which  must  frequently  be  considered 
in  the  development  of  the  labial  and  Iniccal  surfaces  of  an 
upper  occlusion  model,  is  the  extent  of  contour  necessary  to 
develop  on  the  rims  to  restore  lost  facial  profile.  The  amount 
of  such  restoration  varies  in  different  cases,  being  greatest  in 
those  where  the  teeth  were  extracted  early  in  life  and  dentiires 
have  been  worn  continuously  for  many  years,  the  borders  hav- 
ing constantly  become  reduced  in  size.  In  such  cases  the  best 
judgment  of  the  prothetist  must  be  exercised  to  determine 
just  how  far  labially  and  buccally  the  upper  teeth  may  be 
carried  beyond  the  fulcrum  line,  or  crest  of  the  border  in  re- 


CONSTHl'CTIOX    OP    FULL    DENTURES  317 

storiii.y'  lost  facial  conlDur,  witliout  endangering  the  stability 
of  the  substitute.  Since  anatomic  methods  have  been  devel- 
oped, however,  it  is  found  that  in  most  cases  the  teetli  in 
both  arches  can  be  lined  up  in  accordance  with  esthetic  re- 
quirements, the  tendency  to  tip  l>eing  practically  overcome  by 
the  balancing  contact. 

It  is  best,  however,  to  establish  the  parabolic  arch  lines 
conservatively — that  is,  within  rather  than  at  the  extreme 
outer  position  demanded  by  esthetics.  Quite  frequently  in 
these  most  difficult  cases  the  arch  lines  of  the  teeth  mav  be 


SIllK     VIKW    clI'"     FIMSIIKII    (ICI'I.USIOX    IIOIIKI 


kept  within  normal  limits  and  yet  the  required  facial  restora- 
tion may  be  accomplished  by  means  of  plumpers — reflections 
of  the  upper  peripheral  margin  of  the  base  plate.  The  neces- 
sity for  this  means  of  restoration  cannot  be  determined  be- 
forehand and  therefore  in  the  preliminary  formation  of  the 
occlusion  model  it  is  not  attempted.  Trial  in  the  mouth  will 
determine  the  position  and  extent  of  such  reflected  margins 
and  they  can  be  developed  accordingly. 

All  surfaces  of  the  wax  rim  should  now  be  smoothed  up  so 
that  when  introduced  in  the  mouth  the  patient  may  feel  no 
special  discomfort,  and  further,  so  that  the  occlusion  model 
may  present  as  good  an  appearance  as  possible. 

The  foregoing  outline,  although  referring  more  particu- 
larly to  the  construction  of  an  u])per  occlusion  model,  applies 
in  most  essentials  to  the  development  of  a  lower  model  as 
well.    In  lower  cases  the  slant  of  buccal  and  lingual  surfaces 


318  CONSTRUCTION    OK    FULL    DKNTl'lUCS 

of  tli(_'  oc'i'Iusioii  rim  is  usually  Id  the  lingual,  t'roiii  the  border 
crest  ocdusally,  in  order  that  its  periphery  may  coincide  witli 
tliat  of  tlie  upper  rim  at  tlie  common  occlusion  plane. 

TRIAL   OF  OCCLUSION   MODELS   IN  THE   MOUTH 

The  upper  and  lower  occlusion  models  having'  been  de- 
veloped to  approximaie  form,  they  are  introduced  in  the 
mouth.  There  are  a  number  of  important  points  to  be  consid- 
ered and  recorded  by  means  of  the  occlusion  models  before 
they  are  finally  removed  from  the  mouth,  the  usual  order  of 
procedure  being  as  follows : 

First,  testing  the  adaptation  of  the  base  plates  to  their 
respective  ridges. 

Second,  determining  the  correct  occlusal  plane. 

Third,  restoring  disturbed  facial  profile  and  contour. 

Fourth,  marking  the  high  and  low  lip  lines  on  the  wax 
rims. 

Fifth,  marking  the  median  line  of  the  face. 

Sixth,  locating  the  ends  of  the  condyles  and  marking 
same  on  the  integument. 

Seventh,  removing  the  upper  contour  model,  inserting 
and  removing  tlie  bite  rod. 

Eighth,  "taking  the  bite"  and  locking  the  contour  models 
together. 

Ninth,  applying,  adjusting  and  clamping  the  face  bow. 

Tenth,  removal  of  the  occlusal  models  from  the  mouth. 

TESTING    THE    ADAPTATION    OF    EACH    BASEPLATE 
TO  ITS  RIDGE 

Each  occlusion  model  is  independently  fitted  to  its  border 
and  tested  as  to  closeness  of  adaptation,  freedom  from  muscu- 
lar impingement  and  wliether  or  not  it  will  retain  its  position 
on  the  border  under  muscular  action. 

When  the  periphery  of  a  base  plate  impinges  on  the 
fraenum  or  muscular  attachments,  even  tliough  it  may  rest 
firmly  on  the  general  surfaces  of  the  ridge  and  vault  under 
pressure,  yet  displacement  may  readily  occur  when  pressure 
is  discontinued  and  muscular  tension  is  applied.  Any  points 
of  interference  not  previously  disclosed  during  trial  of  the 
base  plate  should  lie  relieved  before  proceeding  with  the  sub- 
sequent steps. 


CONSTRUCTION    OF    Fl'LL    DENTURES  :J19 

DETERMINING  THE  CORRECT  OCCLUSAL  PLANE 

Various  plans  are  suggested  for  determining  the  correct 
position  of  the  occlusal  plane  between  the  two  maxillary  sur- 
faces. One  of  these  is  to  draw  a  line  on  the  face  extending 
from  tlie  tragus  of  the  ear  to  the  ala  of  the  nose  and  trim  the 
planes  of  occlusion  piuallel  with  this  line.  AVhile  perhaps 
in  the  average  case  this  rule  might  apply,  variations  are  so 
frequent  that  it  cannot  be  relied  upon.  Many  cases  have  come 
under  the  writer's  notice  where,  if  this  plan  had  been 
adopted,  the  occlusal  planes,  while  anteriorly  correct,  would 
have  intersected  one  or  the  other  borders  in  the  region  of  the 
second  molars,  thus  unequally  dividing  the  space  between  the 
crests  of  the  two  processes  in  which  the  teeth  are  subsequently 
to  be  placed. 

The  following  plan  is  accurate  and  easy  of  application : 
P^irst  determine  the  correct  length  of  the  occlusal  rim  of  the 
upper  model  auteriorly.  In  the  largest  percentage  of  cases 
the  anterior  teeth  in  normal  arches  extend  about  one-sixteenth 
of  an  inch  below  the  ujjper  lip  when  tlie  latter  is  relaxed,  as 
can  be  seen  when  the  lips  are  slightly  parted.  This  amount 
of  margin  of  the  upper  occlusion  model  should  be  seen  under 
similar  posing  of  the  lips.  Should  the  rim  be  too  short  an 
addition  is  made,  and  when  too  long  the  excess  is  pared  off 
until  the  proper  amount  of  wax  is  exposed.  Whatever  changes 
may  be  made  to  the  rim  anteriorly  should  be  followed  by  cor- 
rections to  the  entire  occlusal  plane,  keeping  it  flat  and  of  uni- 
form thickness  antero  posteriorly  from  incisal  region  to  the 
tuberosities,  until  subsetjnent  changes  are  found  necessary. 

The  length  of  the  upper  rim  having  been  determined  and 
sucli  changes  as  may  be  necessary  effected,  the  lower  model 
is  introduced  and  the  patient  instructed  to  close.  Usually  the 
rims  strike  in  the  molar  region,  while  anteriorly  there  is  more 
or  less  space  between  them.  Instruct  the  patient  to  bring  the 
lips  together  and  notice  the  amount  of  muscular  effort  re- 
quired to  effect  their  closure. 

Both  occlusion  models  are  now  removed  and  pared  off 
equally  at  their,  contact  points,  being  careful  to  preserve  the 
flat  occlusal  i^lanes  by  shaving  off  long  bevel  sliecs  of  wax. 
The  main  point  to  kee]i  in  mind  in  this  trimming  process  is 
to  preserve  an  equal  thickness  of  wax  on  each  side  of  each 
rim  from  occlusal  to  maxillary  surfaces,  so  that  in  occluding 
the  teeth  they  may  be  placed  in  the  space  thus  provided. 


320  CONSTRUCTIOX    OK    FULL    DENTl'RES 

J->rii'tly  stated,  an  cft'oft  should  be  made  to  estalilish  the 
occlusal  plane  midway  between  the  crests  of  the  upper  and 
lower  borders.  Tlie  only  exception  to  this  method  is  in  those 
cases  where  absorption  of  the  borders  has  progressed  un- 
equally, the  teeth  in  one  arch  having  long  been  lost  and  in 
the  other  having  been  extracted  at  a  much  later  date.  In 
such  cases  the  occlusal  plane  must  be  located  nearer  the 
border  showing  the  least  absorption. 

ESTABLISHING    HEIGHT    OF    THE    LOWER    OCCLU- 
SION RIM 

The  depth  of  the  upper  wax  occlusion  rim — that  is,  its 
thickness  from  the  maxillary  surface  of  the  border  to  the 
occlusal  plane — is  to  a  very  groat  extent  determined  by  the 
length  of  the  upper  lip  anteriorly,  while  posteriorly  it  com- 
monly fills  about  one-half  the  space  between  the  crests  of  the 
two  maxillary  borders,  the  mandible  being  in  nomal  position, 
which  position  usually  j^laces  it  parallel  with  the  upper  max- 
illary crest. 

With  these  two  factors  as  a  basis  it  is  a  comparatively 
simple  task  to  develop  the  upper  occlusion  model.  It  is  more 
difificult,  however,  to  develop  a  correctly  proportioned  lower 
occlusion  model,  because  of  the  absence  of  any  fixed  land- 
mark, by  means  of  which  the  height  of  the  lower  rim  can  be 
established. 

Let  us  consider  the  relation  of  the  mandible  to  the  max- 
illa, first,  with  the  natural  teeth  present  and  in  occlusion,  and 
second,  after  the  jaws  become  edentulous.  In  the  first  instance 
the  masticatory  muscles  bring  the  mandible  upward  until 
when  the  teeth  are  in  occlusion  it  is  in  a  state  of  rest.  In  this 
position  the  facial  profile  is  normal;  while  the  lips  rest  easily 
against  each  other  without  apparent  muscular  tension,  or 
conscious  effort  on  the  part  of  the  individual.  Although  while 
it  is  possible  for  the  ]:)atient  to  compress  the  lips  and  give 
them  a  strained  appearance  it  is  purely  a  voluntary  act  of  the 
orbicular  muscles,  in  which  the  mandibular  muscles  take  no 
part,  since  the  teeth  in  occlusion  arrest  the  approach  of  tiie 
mandible  toward  the  maxilla  by  contact  of  their  normal 
occlusion  planes. 

Could  a  registration  of  the  normal  profile  be  made  when 
the  natural  teeth  are  present  and  in  occlusion,  say  by  placing 
one  leg  of  a  caliper  on  the  under  side  of  the  mandible  and  the 
other  on  the  cranium  on  points  that  could  afterward  be  located 


CONSTRUCTION"  OF  FULL  DENTURES  321 

and  the  distance  between  the  two  be  recorded,  this  measure- 
ment would  enable  the  length  of  the  face  to  be  reestablished 
after  loss  of  the  teeth. 

This  method  is  not  practical,  but  the  illustration  shows 
what  we  hope  to  and  should  accomplish  liy  means  of  occlusion 
and  contour  models  of  suitable  height. 

Instead  of  the  calipers  the  esthetic  judgment  of  the  pros- 
thetist  is  the  court  of  last  resort.  His  eye  should  be  so  trained 
as  to  detect  defective  profile  or  contour  and  restore  his 
patient's  face  to  norm.al  appearance. 


THEORETICAJ.  MEASUKEMBNT   OP   FACIAL  PROFILE 

In  edentulous  cases,  there  being  no  teeth  present  to  ar- 
rest the  jirogress  of  mandible  toward  the  maxilla,  restoration 
of  the  normal  pose  of  the  lips  and  the  general  profile  and  con- 
tour of  the  face  must  be  depended  upon  in  establishing  the 
height  of  rim  of  the  lower  occlusion  model.  This  can  only 
be  done  by  repeated  trial  and  testing,  building  up  or  reducing 
the  rim  as  facial  contour  and  the  pose  of  the  lips  indicate. 

The  depth  of  the  upper  rim  having  been  determined  by 
the  length  of  the  upper  lip,  the  height  of  the  lower  rim  is 
established  at  such  point  that  the  lower  lip  may  rest  easily  in 
contact  with  the  upper  without  requiring  muscular  effort  to 
effect  closure.  Pursing  out  of  the  lip  indicates  that  the  rim 
is  too  short,  while  muscular  eft'ort  in  closing  the  lips  indicates 
that  the  rim  is  too  high. 


322  CONSTRUCTION    OF    l^ULL    DENTURES 

When  the  rims  have  been  developed  correctly  labially 
the  contour  models  should  be  tested  posteriorly  to  determine 
whether  there  is  uniform  and  equal  contact  between  them  and 
their  respective  borders.  This  test  is  made  by  having  the 
patient  maintain  moderate  mandibular  pressure  while  the 
prosthetist  endeavors  to  force  the  occlusion  models  apart, 
first  on  one  side  and  tlien  on  the  other.  If  on  moderate 
pressure  the  two  base  plates  separate  while  contact  is  main- 
tained labially,  it  indicates  that  the  occlusion  rims  are  too 
short  where  separation  occurred,  one  or  the  other  of  the  base 
plates  having  tipped  or  left  its  border.  Such  imperfect  con- 
tact should  be  corrected  by  additions  of  wax  to  one  or  both 
rims  until  uniform  bearing  on  both  sides  of  the  mouth  is 
established. 

In  making  such  additions  care  should  be  taken  to  preserve 
the  flat  plane  areas  of  both  occlusion  models. 

Should  the  upper  plane  be  flat  and  the  rim  of  proper 
length  the  lower  rim  on  the  deficient  side  may  be  corrected  by 
adding  a  sheet  of  soft  wax  to  the  occlusal  plane  where  defi- 
cient, introducing  in  the  mouth  and  having  the  patient  exert 
gradual  and  uniform  pressure  upon  it.  The  lower  model  is 
then  removed  and  the  surplus  trimmed  off  to  correct  peri- 
pheral outline. 

RESTORING  LOST   FACIAL  CONTOUR 

One  of  the  most  important  results  of  full  denture  con- 
struction, when  the  steps  are  properly  carried  out,  is  the  cor- 
rection of  disturbed  facial  contour. 

The  teeth,  the  borders  in  which  they  are  imbedded,  with 
the  overlying  soft  tissues  in  the  natural  masticatory  ap- 
paratus, when  viewed  anteriorly  present  a  generally  convex 
appearance  from  side  to  side  and  a  nearly  perpendicular  ar- 
rangement from  above  downward.  The  labial  and  buccal  sur- 
faces of  the  teeth  and  alveolar  arches  support  the  lips  and 
cheeks  and  in  tliis  manner  aid  in  giving  form  and  contour  to 
the  lower  half  of  the  face. 

Wlien  the  teeth  are  lost  and  the  alveolar  borders  absorb 
to  a  greater  or  less  extent  from  without  inward,  as  well  as  in 
height,  the  lips  and  cheeks  lose  their  support  and  fall  back- 
ward and  inward.  The  symmetry  of  the  face  is  thus  disturbed 
to  a  marked  degree  and  unless  corrective  measures  are  re- 
sorted to  the  patient  becomes  disfigured  for  life.  By  the  in- 
troduction of  suitably  formed  dentures  disturbed  facial  profile 
and  contour  can  in  a  great  measure  be  overcome. 


CONSTRUCTION  OF  FULL  DENTURES  32S 

The  first  stage  in  denture  construction,  where  corrective 
measures  can  be  developed  and  tested,  is  during  the  trial 
of  the  wax  occlusion  models  in  the  mouth.  Later  on  the  final 
test  occurs  with  the  introduction  of  the  wax  model  dentures. 
By  molding  and  carving,  varying  the  thickness  of  the  labial 
and  buccal  rims  of  the  wax  occlusion  models,  introducing  them 
in  the  mouth,  having  the  patient  close  and  bring  the  lips  to- 
gether in  a  normal  relation,  or  state  of  rest,  the  prosthetist 
can  determine  the  measure  of  success  attained.  Repeated 
modifications  and  trials  are  sometimes  necessary  to  secure 
satisfactory  results,  while  in  other  eases  but  little  difficulty 
is  encountered. 

The  occlusion  rims,  by  their  perpendicular  height,  estab- 
lish the  profile  and  length  of  the  face.  Their  labial  and  buccal 
surfaces  lift  out  the  sunken  areas,  particularly  from  the  bi- 
cuspids forward. 

In  order  to  correct  the  wrinkles  which  extend  from  the 
alaB  of  the  nose  outward,  over  the  angles  of  the  mouth,  it  is 
usually  necessary  to  extend  the  periphery  of  the  occlusion 
model  upward  in  the  region  of  the  cuspids.  Such  extensions, 
however,  should  be  neither  too  high  nor  too  bulky,  or  they 
will  interfere  with  the  movements  of  buccal  and  orbicular 
muscles  and  displacement  of  the  denture  will  result. 

In  those  cases  where  considerable  restoration  is  required 
and  the  extension  upward  of  the  peripheral  rim  of  the  base 
plate  is  limited  by  muscular  attachment  the  required  contour 
can  usually  be  developed  by  reflecting  the  peripheral  margin 
of  rim,  as  previously  mentioned,  outward  and  downward  in 
the  form  of  flanges,  or  so-called  plumpers.  The  width  and 
slant  of  a  flange  of  this  type  depends  on  the  amount  of  re- 
storation required  and  the  tension  of  the  muscles  jDeripher- 
ally.  In  all  cases  they  must  be  so  disposed  as  not  to  interfere 
with  freedom  of  muscular  action  or  displacement  will  most 
certainly  occur. 

The  usual  prominent  features  of  an  upper  occlusion  model 
when  developed  are  as  follows : 

The  contour  model  is  notched  anteriorly,  to  allow  free 
play  for  the  labial'  frenum. 

There  should  be  slightly  depressed  areas  between  cen- 
trals and  cusiDids  above  the  laterals,  thus  reproducing  the  in- 
cisive fossae  such  as  are  noticeable  in  the  maxilla.  These  de- 
pressions allow  freedom  of  movement  of  the  alse  of  the  nose. 
Prominently  contouring  the  labial  rims  above  the  lateral  in- 


:;24  CONSTRUCTION    OF    FULI,    DICNTUliKS 

cisors  ut'teiitimes  restricts  the  size  of  the  nasal  urilice,  inter- 
feres with  respiration  and  is  generally  uncalled  for. 

Prominent  cuspid  eminences  to  partially,  but  not  usually 
wholh',  obliterate  the  wrinkles  extending  from  the  alae  of  the 
nose  outward  over  the  angles  of  the  mouth.  A  slight  sug- 
gestion of  these  wrinkles  in  persons  of  middle  age,  or  past, 
produces  a  more  esthetic  result  than  when  completely  obliter- 
ated. 

Peripheral  margins,  from  median  line  to  tuberosities 
more  or  less  notched,  as  indicated  by  the  muscle-marking  ex- 
ercise carried  out  in  impression  taking. 

MARKING  THE  HIGH  AND  LOW  LIP  LINES 

The  high  and  low  lip  lines  are  marked  on  the  upper  and 
lower  occlusion  models  respectively,  to  serve  as  guides  in 
determining  the  length  of  teeth  to  select  for  the  case. 

The  upper  central  incisors  should  extend  from  the  incisal 
plane  to  the  high  lip  line,  or  slightly  above  it,  so  that  when 
the  artificial  gum  material  is  applied  over  the  cervical  ends 
of  the  teeth,  the  highest  curves  of  the  gingival  line  coincide 
with  the  high  lip  line.  The  same  arrangement  can  be  fol- 
lowed in  selecting  and  arranging  the  lower  incisors  and  carv- 
ing the  gums,  although  the  gums  of  the  lower  teeth  seldom 
show  to  the  same  extent  as  in  upper  cases. 

The  object  in  selecting  teeth  of  the  length  indicated  by 
the  high  lip  line  is  to  avoid  exposure  of  too  much  artificial 
gum,  as  would  occur  when  shorter  teeth  are  used,  and  also 
to  obviate  the  monotony  which  is  apparent  when  only  the 
jDorcelain  is  visible. 

The  patient  is  instructed  to  raise  the  upper  and  depress 
the  lower  lip  as  in  broadly  smiling,  and  while  in  this  position 
the  prosthetist  marks  on  the  occlusion  models  the  lines  of  lip 
perijiheries  as  they  lie  against  the  wax  surfaces. 

MARKING  THE  MEDIAN  LINE  OF  THE  MOUTH 

The  human  face  is  seldom,  if  ever,  symmetrical.  Usually 
the  nose  is  bent  to  one  side;  one  eye  may  be  slightly  higher 
or  nearer  the  median  line  than  the  other,  or  set  at  a  different 
slant;  the  general  line  of  the  lips  from  side  to  side  may  not 
form  a  right  angle  with  the  perpendicular  lijie  of  the  face. 
In  fact,  the  most  symmetrical  faces,  when  studied  closely,  will 
be  found  unsvmmetrical. 


CONSTRUCTION    OI<^    FULL    DENTURES  325 

it  is  tliL'iH'l'urc  ii  tlil'licult,  uiuUcr  at  times  iu  denture  cou- 
struc'tiou  to  determine  just  wliere  the  two  ceutral  incisors 
should  be  placed  because  tliere  is  no  fixed  landmark  to  serve 
as  a  basis,  or  to  indicate  the  position  once  occupied  by  the 
natural  teeth.  Usually  the  center  of  the  philtrum  of  the  lip 
will  serve  as  a  guide,  but  when  the  nose,  chin  and  other  fea- 
tures are  out  of  alignment  a  general  average  must  be  struck 
to  arrive  at  hannoiiious  results.  This  may  be  done  by  placing 
a  straight  edge,  or  the  edge  of  a  card,  flatwise  against  the  face 
extending  from  the  center  of  the  chin  to  a  point  located  mid- 
way between  the  inner  ends  of  the  eyebrows  and  making  a 
slight  mark  on  the  occlnsion  models.  The  card  is  then  re- 
moved and  a  point  directly  under  the  center  of  the  philturm 
is  marked.  When  there  is  much  variation  in  the  two  lines  a 
third  line  midway  between  the  two,  yet  favoring  a  location 
near  the  philtrum,  will  give  a  harmonious  median  line. 

When  the  correct  position  is  determined  a  perpendicular 
line  extending  across  both  base  plates  should  be  distinctly 
marked  in  the  wax.  Care  should  be  taken  in  subsequent  steps 
not  to  obliterate  it  until  the  arrangement  of  the  teeth  is  be- 
gun. 

LOCATING  THE  OUTER  ENDS  OF  THE  CONDYLES 

Previous  to  taking  the  bite  the  outer  ends  of  the  con- 
dyles should  be  located  and  their  exact  position  indicated  by 
dotting  the  integument  directly  over  their  locations  with  a 
soft  pencil.  The  outer  ends  of  the  condyles  in  most  cases 
approach  the  outer  margins  of  the  glenoid  fossiB,  sometimes 
coming  quite  to  the  margins  so  as  to  be  detected  with  little 
difficulty.  More  frequenth',  however,  they  are  slightly  over- 
hung by  the  glenoid  riras.  When  the  integument  is  thick  and 
the  interarticular  fibrocartilages  and  cai^sular  ligaments  are 
well  developed  it  is  sometimes  difficult  to  locate  them,  either 
at  rest  or  when  in  action. 

In  the  largest  percentage  of  cases  the  condyle  end  will 
be  found  about  one-half  inch  in  front  of,  and  on  a  horizontal 
plane  with  the  upper  jnargin  of  the  external  auditory  meatus. 

The  index  finger  shoiild  be  placed  perpendicularly  against 
the  side  of  the  face,  .with  that  portion  of  the  ball  immediately 
below  the  finger  -nail  resting  on  the  immovable  glenoid  rim. 
The  patient  is  then  instructed  to  open  and  close  slightly  with 
the  hinge  motion.  Wide  open  movements  are  confusing  as  the 
condyle  not  only  rotates  but  moves  foi'ward  in  its  path  as 
well.    By  applying  steady  pressure  with  the  finger  against  the 


S26  CONSTRUCTION    OK    FULL    DKNTIIKES 

glenoid  rim  with  slight  opening  and  closing  movements  of  the 
mandible  a  point  of  iiereeptible  movement  will  be  detected 
close  n]5  along  the  glenoid  margin  and  in  about  the  same  rela- 
tion to  the  external  auditorv  meatus  as  stated.    While  varia- 


GLENOID  MARGIN 


rOSlTIOX   OF   FINGER   IX   LOCATING    rOXDVLE   KXD 

tions  in  position  of  the  condyle  ends  occur  in  different  indi- 
viduals, and  frequently  in  the  same  person,  they  will  not  be 
very  marked  and  usually  are  not  difficult  to  detect. 

The  greatest  care  should  be  exercised  in  determining  the 
correct  antero-posterior,  as  well  as  perpendicular  position  of 
the  condyle  ends  when  at  rest  in  their  foss«,  as  the  measure- 
ment secured  with  the  face  bow  becomes  the  basis  of  radial 
movement  of  the  casts  when  mounted  on  the  occluding  frame. 

APPLICATION    OF   THE   BITE    FORK   TO    UPPER 
OCCLUSION  MODEL 

The  bite  fork,  with  its  crescent-shaped  plate  for  insertion 
into  the  occlusal  model,  is  heated  and  the  plate  inserted  in 
the  labial  surface  of  the  wax  rim.     The  occlusion  model  is 


UPl'EB    OCCLUSION    MODEL   WITH    BITE    FORK    IN   POSITION 

removed  from  the  mouth  during  this  step,  since  if  carried  out 
in  the  mouth  the  melted  wax  caused  by  the  insertion  of  the 
heated  fork  is  liable  to  burn  the  lips. 

The  fork  while  heated  is  pressed  into  the  rim  until  its 


CONSTRUCTION  OP  FULL  DENTURES  327 

entire  inner  peri])hery  engages  with,  and  is  firmly  imbedded 
in  the  labial  surface.  The  rod  should  be  jDarallel  with  the 
occlusal  plane  and  point  as  nearly  forward,  parallel  with  the 
median  line  of  the  occlusion  model,  as  possible,  so  that  the 
universal  clamp  of  the  face  bow  may  grasp  it  firmly  when 
tightened. 

After  insertion  it  will  be  found  most  convenient  to  re- 
move the  bite  fork  from  the  occlusion  model  before  taking  the 
bite,  as  its  weight  tends  to  dislodge  the  upper  occlusion  model. 
When  the  latter  step  is  carried  out  and  the  bite  locks  are  in- 
serted the  fork  is  returned  to  the  groove  previously  made  for 
it,  the  lip  protected  with  a  najikin  and  a  hot  spatula  passed 
around  the  upper  surface  of  the  fork  to  lute  it  firmly  to  the 
occlusion  model. 

MEANING  OF  THE  TERM,  "TAKING  THE  BITE" 

Tahiufi  the  bite  refers  to  establishing  the  correct  antero- 
posterior, as  well  as  perpendicular,  relation  of  the  mandibular 
to  the  maxillary  ridge.  When  the  natural  teeth  are  present 
and  in  normal  occlusion,  the  condyles  are  at  rest  in  the  glenoid 
fossa?.  Since  in  edentulous  cases  the  occlusion  rims,  when  prop- 
erly formed,  take  the  place  of  the  natural  teeth,  they  estab- 
lish the  correct  perpendicular  distance  of  the  mandible  from 
the  maxilla.  The  final  step  of  taking  the  bite  consists  in  hav- 
ing the  patient  close  the  mouth  normally,  that  is,  so  that  the 
condyles  are  at  rest  in  the  glenoid  fossae  while  the  occlusion 
rims  are  in  contact,  ajid  registering  the  relation  of  the  occlu- 
sion models  to  each  other  in  this  position. 

DIFFICULTY  ENCOUNTERED  IN  TAKING  THE  BITE 

More  or  less  difficulty  is  encountered  in  taking  the  bite 
because  of  the  tendency  of  patients  to  unconsciously  protrude 
the  mandible,  either  uni-  or  bi-laterally.  It  is  also  a  notice- 
able fact  that  the  more  interested  the  patient  is  in  this  step, 
and  the  greater  effort  he  displays  in  giving  a  correct  bite,  the 
greater  is  the  liability  of  error  resulting.  It  is  therefore  best 
not  to  inform  the  patient  of  the  importance  of  the  step  about 
to  be  carried  out,  but  merely  instruct  him  at  the  proper  time 
what  to  do. 

VARIOUS  METHODS  OF  SECURING  THE  BITE 

Various  methods  are  adopted  for  securing  a  normal  bite, 
any  one  of  which  might  prove  successful  in  some  cases  and 


328  CONSTRUCTION    OP    FUI.L    DENTURES 

result  ill  failure  in  others.  Some  of  these  methods  are  as 
follows : 

First — Tlie  patient  is  instructed  to  swallow  and  at  the 
same  time  close  the  mouth,  the  culmination  of  this  muscular 
effort  being  supposed  to — and  in  some  cases  does — bring  the 
condyles  back  in  their  position  of  rest  in  the  fossae. 

Second — A  small  pellet  of  wax  is  attached  to  the  distal 
margin  of  the  central  vault  portion  of  the  baseplate.  The 
patient  is  instructed  to  touch  the  pellet  of  wax  with  the  tip 
of  his  tongue,  and  at  the  same  time  close  the  mouth  until  the 
occlusion  rims  are  in  contact. 

Third — A  chin  cup  is  applied  to  the  meiitum,  to  which 
straps  are  attached  which  jjass  around  the  head.  When  these 
straps  are  properly  adjusted,  tension  is  exerted  on  the  mandi- 


THE  GAKBISON   BITE  GUIDE 


ble  to  force  it  backward.  Eepeatedly  opening  and  closing  of 
the  mandible  will  frequently,  but  not  in  all  cases,  result  in 
establishing  the  correct  bite.  An  apparatus  similar  to  the 
one  just  described  is  known  as  Garrison's  Bite  Guide. 

Fourth — Pressure  may  be  exerted  upon  the  point  of  the 
chin,  while  the  patient  repeatedly  opens  and  closes  the  mouth, 
attention  in  the  meantime  being  given  to  the  relation  the 
occlusion  rims  sustain  to  each  other  when  brought  in  con- 
tact. 

Fifth — It  is  a  noticeable  fact  that  when  the  masticatory 
muscles  are  wearied  by  rapid  and  repeated  exertion,  they 
draw  the  mandible  backward  until  tlie  condyles  are  in  normal 
resting  position  in  the  fossa?. 

By  combining  the  two  methods  last  mentioned,  a  correct 
bite  may,  in  practically  all  cases,  be  secured. 


CONSTRUCTIOX    OK    FULL    DENTURES  329 

A    PRACTICAL    METHOD    FOR    SECURING    A    CORRECT 
BITE 

The  jiatieiil  isliuuld  he  instructed  to  open  and  close  the 
mouth  rapidly  many  times,  say  for  a  period  of  one-half  to  one 
minute,  the  operator  in  the  meantime  paying  but  little  atten- 
tion, further  than  to  see  that  his  instructions  are  followed. 
He  will  then  say  to  the  patient,  "Relax  your  muscles  and  let 
me  open  and  close  your  mouth. ' '  The  point  of  the  chin  is  then 
grasped  lightly  with  the  tips  of  the  fingers  and  thumb  so  as 
not  to  displace  the  lower  occlusion  model,  and  the  mandil}le 
is  moved  up  and  down,  the  lips  being  raised  to  note  position 
in  which  the  occlusion  rims  strike.  Slight  pressure  may  also 
be  applied  on  the  mandible  to  force  it  upward  and  backward. 
Undue  pressure  should  be  avoided,  as  it  would  result  in  com- 
pression of  the  tissues  in  the  temporo-mandibuiar  joint,  and 
thus  give  a  slightly  backward  or  retruded  bite. 

Under  the  slight  pressure  exerted,  together  with  repeated 
opening  and  closing  movements,  the  occlusion  rims  will  finally 


^^^ 


niiijii 


ISITE     LOCKS.        LEFT,      FORMED     OF 

WIRE        RIGHT,     1)K.     SNOWS 

DESIGN 

meet  each  time  in  the  same  relation  to  each  other.  The 
patient  is  then  instructed  to  "keep  the  mouth  closed."  The 
bite  locks  are  then  warmed  and  forced  into  tlie  upper  and 
lower  occlusion  models,  about  in  the  region  of  the  bicuspid 
teeth.  Care  should  bo  taken  in  placing  them  to  avoid  en- 
croaching on  the  groove  previously  made  for  the  bite  fork. 
A  third  bite  lock  is  sometimes  inserted  in  the  labial  region  to 
prevent  possible  change  of  relation  between  the  baseplates  in 
removal  from  the  mouth. 

In  some  cases  where  the  wax  occlusion  models  are  large 
and  the  oral  opening  small,  it  is  impossible  to  remove  the 
two  models  when  '  locked  together.  By  cutting  cross 
grooves  in  both  occlusion  rims  opposite  each  other,  one  on 
either  side  and  one  anteriorly,  placing  small  pellets  of  warm 
wax  directly  over  them,  and  having  the  patient  bite,  the  wax 
will  be  forced  in  the  grooves  and  will  serve  as  guides  in  plac- 
ing the  models  in  correct  relation  to  each  other  on  removal 
from  the  mouth. 


330  CONSTRUCTION    OK    FULL    DENTURES 

The  bite  lock  having  been  inserted  or  the  grooves  cut  as 
described,  the  next  step  is  to  return  the  bite  fork  to  position. 

INSERTING  THE  BITE  FORK  IN  THE  UPPER  OCCLUSION 
MODEL 

The  bite  fork  is  now  warmed  slightly,  the  lips  opened 
and  the  fork  inserted  in  the  groove  previously  made  by  it, 
and  from  which  it  was  removed  previous  to  taking  the  bite. 
To  secure  it  firmly  in  place,  a  heated  spatula  should  be  passed 
along  the  upper  surface  of  the  fork,  the  upper  lip  being  held 
up  and  the  lower  protected  with  a  iia|)kin.  When  firmly  fixed 
the  face  bow  can  be  applied. 

ADJUSTING  THE   FACE   BOW  TO  THE   OCCLUSION 
MODELS 

As  will  be  seen,  the  bite  has  been  established,  although 
the  occlusion  models  have  not  yet  been  removed  from  the 
mouth.    The  face  how  is  now  applied  so  that  when  the  hase- 


ADJUSTIXG    THE   CONDYLE  RODS 


plates  are  removed  from  the  mouth,,  and  the  casts  are  in- 
serted each  in  its  respective  baseplate  and  attached  to  the 
occluding  frame,  their  maxillary  surfaces  will  bear  the  same 
relation  to  the  frame  hinges  that  the  natural  ridges  sustain 
to  the  condyles  ivhen  the  later  are  at  rest  in  the  glenoid  fossae. 
The  condyle  rods  of  the  bow  are  now  drawn  outward  so 
as  to  allow  them  to  pass  on  either  side  of  the  face  without  in- 
terference. The  universal  clamp  in  the  center  of  the  bow  is 
carried  over  the  projecting  rod  of  the  bite  fork,  and  the  back 


CONSTRUCTION    OF    FULL    DENTURES  331 

ends  of  the  bow  are  dropped  down  nntil  the  condyle  rods  are 
opposite  the  points  previously  marked  in  pencil  to  indicate 
the  condyle  ends.  The  condyle  rods  are  then  pressed  inward 
until  their  ends  rest  on  the  points  marked. 

Care  should  be  tiiken  to  see  that  the  condyle  rods  show 
the  same  number  of  gradations  between  their  inner  ends 
which  rest  on  the  face  and  the  inner  sides  of  the  bow.  Should 
the  bow  be  unequally  balanced  when  clamped,  the  casts  will,  as 
a  result,  be  mounted  to  one  side  instead  of  on  the  center  of 
the  occluding  frame,  and  their  radii  of  movement  will  be  in- 


PATIENT   TIGHTENING   THE   BITE   FORK   CLAMP 

correct.  When  balanced,  the  clamps  which  lock  the  condyle 
rods  are  tightened,  the  rods  readjusted  to  the  natural  con- 
dyle ends  by  springing  the  bow  away  slightly  to  allow  the 
integument  to  assume  its  normal  position,  then  returned  to 
place  and  held  in  correct  relation  by  the  operator  while  the 
patient,  or  assistant,  is  instructed  to  tighten  the  central  clamp, 
thus  fixing  the  relation  of  the  bite  fork  to  the  face  bow.  The 
operator  should  forcibly  tighten  the  clamp  to  insure  against 
any  possible  change  from  stress  while  removing  the  occlu- 
sion models.  The  condyle  rods  are  now  released  and  drawn 
outward,  the  patient  instructed  to  open  the  mouth  and  the 
occlusion  models  and  face  bow  are  removed,  using  the  bite 
fork  as  a  handle. 


332  CONSTRUCTIOX    OF    FULL    DENTIFRKS 

ADJUSTMENT  OF  THE   FACE   BOW,  WITH   OCCLUSION 
MODELS  ATTACHED,  TO  THE  OCCLUD- 
ING FRAME 

(Dn  removal  of  contonr  models  from  the  mouth,  the  con- 
dyle rods  of  the  face  bow  are  pressed  inward  their  full  ex- 
tent, and  tightly  clamped. 


OCCLDSIOX    MODELS.    ATTACHED    TO    FACE    HOW.    nEMO\ED    FROM    MOUTH 

The  sheet  metal  base  is  slipped  on  the  lower  bow  of  the 
occluding  frame,  to  prevent  the  latter  tipping  backward.  The 
occlusion  models  are  carried  between  the  upper  and  lower 
bows  of  frame,  the  ends  of  the  face  liow  sprung  apart,  and 


FACE   liOW,    WITH   OCCHSIOX    .MODELS    ATTAf'HED.    AD.ILSTEJ)    TO    OCCLUDING    FRAME 

the  condyle  rods  ai'e  attacliod  to  tlie  projectin.g  lugs  of  the 
frame  hinges. 

The  face  bow  should  be  made  parallel  with  the  bench  on 
which  the  occluding  frame  rests.    This  may  be  done  by  plac- 


CONSTRUCTION  OP  FULL  DENTURES  333 

ing  a  cork,  or  small  block  of  suitable  thickness,  under  the  cen- 
tral clamp  as  illustrated. 

ATTACHING  THE  CASTS  TO  THE  OCCLUDING  FRAME 

The  upper  bow  of  the  frame  is  thrown  back,  the  upper 
cast  is  seated  in  its  baseplate  and  luted  with  wax,  if  neces- 
sary, to  hold  it  steadily  in  place.     The  bow  is  now  dropped 


IIIUoUN    BACK   TO   RECEIVE   UrPER    CAST 


UI'I'EK    CAST    SEATED    IN    ITS    BASEPLATE 


down  on  the  base'  of  the  cast,  to  which  a  mix  of  moderately 
thin  plaster  is  applied.  The  bow  should  be  fully  enclosed  in 
plaster  and  the  latter  i!iven  time  to  set  before  mounting  the 
otlier  cast. 

The  face  bow  and  frame  are  now  inverted,  the  sheet 
metal  base  removed,  the  lower  bow  thrown  back,  the  lower 


CONSTRUCTION  OP  FULL  DENTURES 


UPPER    I'AST    ATTACIlEIl    TO    FRAME    BOW 


OCCLUDING   FRAME   INVERTEP      BOW  THROWN  BACK  TO   RECEIVE  LOWER  CAST 


LOWBE   CAST   SEATED   IN   ITS   BASEPLATE 


CONSTRUCTION     OF    FULL     UENTLHF; 


CASTS   MOUNTED    READY    FOR    REMOVAL    OF    FACE    r.OXV 


CASE  «1TH  FACE    HOW.    BITE   FORK    AND    RITE   LOCKS    REMOXED.    BUCCAL    VIEW 


336  CONSTRTICTIOX    OF    FUL[.    DKNTURKS 

cast  iusortc'tl  and  lute<,l  to  its  baseplate,  aud  the  mandibular 
bow  dropped  down  upon  the  base  of  cast. 

By  loosening  the  set  screws  of  the  mandibular  bow,  the 
latter  may  be  raised  or  lowered  in  the  frame  sockets  until  it 
lays  flat  upon  the  base  of  the  cast.  When  adjusted,  the  set 
screws  of  the  bows  should  all  be  tightened  so  that  the  rela- 
tion of  casts  to  frame  hinges  may  not  lie  disturbed  by  slipping 
of  the  bows  in  subsequent  steps.  The  lower  bow  and  cast  are 
united  with  plaster,  as  in  the  preceding  step,  the  plaster  al- 
lowed to  harden  and  the  frame  righted. 

The  face  bow  is  3-emoved  first,  then  the  bite  fork,  and 
finally   the  bite   locks,   after  which    the    surplus    plaster    is 


LABIAL    "ilBW    OF    MOnXTEU    I'ASTS    AND    OCCLUSION    MODELS 

trimmed  from  the  casts  and  occluding  frame  bows.  This  lat- 
ter step,  although  apparently  unimportant,  adds  to  the  ap- 
pearance of  the  case,  and  where  much  surplus  is  present, 
enables  the  frame  to  be  handled  more  conveniently. 

REGISTERING  THE  CONDYLE  PATHS  OF  PATIENT 

There  are  two  fundamental  steps  of  vital  importance  in 
the  construction  of  anatomic  and  scientific  dentures  that  can- 
not be  ignored  without  lessening  the  quality  and  efficiency  of 
the  substitute. 

The  first  is  mounting  the  casts  in  correct  horizontal  plane 
relationship  to,  and  radial  distance  from,  the  rotation  cen- 
ters of  the  occluding  frame.     This  step  just  described  is  ac- 


CONSTRUCTION  OF  FULL  DENTURFS  337 

complished  by  means  of  the  face  bow  or  some  similar  device. 
The  second  consists  in  registering  the  pitch  of  the  con- 
dyle paths  of  the  patient,  and  setting  the  condyle  paths  of 
the  occlnding  frame  at  corresponding  angles.  This  may  be 
accomplished  by  two  somewhat  different  methods,  the  very 
simple  Christensen-Snow  plan  and  appliances,  and  the  more 
elaborate  registration  suggested  by  Gysi  by  means  of  his 
Condyle  Begister.  The  first  method  will  be  described  here, 
the  second  subsequently  in  connection  with  the  Gysi  appli- 
ances. 

CHRISTENSEN'S  METHOD 

Dr.  Carl  Christeusen  of  Copenhagen  noticed  that  when 
correctly  formed  occlusion  models  were  introduced  in  the 
mouth  and  the  mandible  was  protruded,  that  in  all  cases  where 


4^ 


the  condyle  paths  inclined  downward,  the  occlusion  models 
separated  in  the  molar  region,  while  anteriorly  they  remained 
in  contact. 

He  further  noticed  that  the  amount  of  separation  of  the 
occlusal  planes  in  the  molar  region  increased  in  direct  ratio 
to  increased  pitch  of  the  condyle  paths. 

He  then  conceived  the  idea  that  by  rigidly  fixing  the  occlu- 
sion models  together  while  in  the  mouth,  in  the  separated  re- 
lation produced  by  mandibular  protrusion,  that  on  returning 
them  to  the  occluding  frame  and  seating  each  cast  in  its  re- 
spective baseplate,  the  condyle  paths  of  the  frame,  which  pre- 


CONSTRUCTION  OF  FULL  DENTURES 


viously  were  released,  would  assume  the  same  angular  in- 
clination as  those  of  the  patient.  The  condyle  paths  of  the 
frame  thus  automatically  adjusted  were  then  fixed  in  this 
position. 

While  subject  to  errors  from  various  causes,  in  the  main 
points  the  idea  is  practical.  Christensen's  efforts,  there- 
fore, have  contributed  much  to  solving  the  problem  of  ana- 
tomic occlusion. 

To  hold  the  occlusion  models  in  their  separated  relation, 
he  introduced  rolls  of  soft  wax  in  the  molar  region,  instructed 
the  i)atient  to  protrude  and  close,  after  which  the  occlusion 
models  were  locked  together  with  staples  or  bite  locks.  By 
exercising  care  in  carrying  out  the  steps,  this  method  is  accu- 


CHRISTrNSE\  1 


lllh     (ONDIXE 


rate,  but  lack  of  precision  on  the  part  of  the  prosthetist  will 
usually  result  in  a  distorted  relation  between  the  occlusion 
models  in  the  various  steps  of  removal  from  the  mouth  and 
readjustment  on  the  occluding  frame. 

Dr.  Geo.  B.  Snow  devised  "bite  gauges"  to  take  the 
place  of  the  rolls  of  wax,  and  by  means  of  these  simple  appli- 
ances the  liability  of  error  occurring  is  greatlv  reduced. 


TECHNIC  OF  CONDYLE  REGISTRATION 

The  occlusion  models  are  now  removed  from  their  casts 
on  the  frame,  the  two  bite  gauges  heated  slightly  and  pressed 
downward  into  the  occlusal  surface  of  the  lower  wax  rim 
about  five-eighths  of  an  inch  in  front  of  the  distal  ends.    The 


CONSTRUCTION  OF  FULL  DENTURES  339 

metal  plate  of  the  bite  gauge  should  rest  on  the  occlusal  plane 
of  wax. 

The  object  in  i^lacing  the  bite  gauges  forward  of  the  dis- 
tal ends  of  the  baseplate  is  to  prevent  the  lower  occlusion 
model  from  sliding  forward  when  the  patient  closes.  Placed 
in  the  position  mentioned,  the  pressure  on  closure  comes  be- 
tween the  two  extremities  of  the  model.    Before  introducing 


THE   SNOW   BITE   GAnGES 


in  the  mouth,  the  patient  should  be  shown  the  occlusion 
models,  his  attention  called  to  the  bite  gauges,  and  a  brief 
explanation  be  made  of  what  is  expected  of  him. 

The  occlusion  models  are  now  introduced  and  the  pa- 
tient instructed  to  protrude  the  mandible,  or  "bite  forward" 
until  the  occlusion  rims  touch  anteriorlj',  while  the  pyramidal 
pointed  pins  of  the  bite  gauges  presenting  upward  enter  the 
upper  and  keep  the  occlusion  models  apart  at  their  distal  ex- 
tremities, in  direct  proportion  to  the  drop  of  the  condyles  in 


LOWER   OCCLUSION    MODEL    WITH    BITE   GAUGES    IN    POSITION 

their  paths.  The  occlusion  models  are  now  locked  together 
with  three  bite  locks,  one  on  either  side  and  one  anteriorly,  and 
when  firmly  fixed  are  removed  from  the  mouth. 


LIMIT  OF  PROTRUSIVE  MOVEMENT  OF  MANDIBLE 

The  extreme  forward  limit  of  mandibular  protrusion 
varies  greatly  in  different  individuals,  the  average  distance 
being  about  one-fourth  inch.    When  the  protrusive  movement 


340  CONSTRUCTION  OF  FULL  DENTURES 

exceeds  this  amoimt.  the  condyle-beariiig  surfaces  in  some 
eases  pass  beyond  tlie  normal  working  slant  of  the  condyle 
paths,  onto  the  more  nearly  horizontal  surfaces  of  the  articu- 


TEitsi'icrTivK  viF.u   (ii-  rrrioit  and  i,(i\vi:ii  hcch  sion  mouei^s.    i'i.umi'ers  ox  the  upper 

MODEL.       TIIESIO    Alil>lTlu.NS    AUK    USUALLY    SITUATE11    51()I!E    TO    THE    DISTAL 
THAN    AS    SHOWN    IN    CUT 

lar  eminences,  and  an  incorrect  registration  will  result,  the 
l)itch  of  the  condyle  paths  of  the  frame  being  less  than  in  the 
actual  working  area  of  the  natural  paths. 


SCHEMATIC  DRAWING  OF  WHAT  OCCUBS  IN  TAKING  THE  PROTltUSIVE  BITE  AND  ADJUSTING 
THE  LOCKED.   PROTRUDED.   OCCLUSION  MODELS   TO  THE  FRAME 

On  the  other  hand,  a  protrusive  movement  of  one  eightli 
inch  or  less,  while  capable  of  being  registered,  will  not  be 
suflScient  to  properh'  adjust  the  condyle  slots  of  the  occluding 


CONSTRUCTION    OP    FULL    DENTURES  341 

frame,  ou  account  of  the  short  distance  the  hinge  pin  will 
travel  in  the  slot  in  adjustment  of  the  casts  to  their  occlusion 
models.  A  slight  amount  of  lost  motion  also  contributes  to 
further  error,  the  hinge  pins  being  a  trifle  less  in  diameter 
than  the  width  of  the  slots. 

It  may  be  stated  definitely  that  the  amount  of  protrusion 
should  range  between  three-sixteenths  and  one-fourth  inch,  in 
order  that  a  correct  record  may  be  made  on  the  occluding 
frame. 

Some  patients  cannot  ])rotrude  the  mandible  directly  for- 
ward to  any  extent,  bi;t  usually  are  capable  of  moving  it  to 


SEATED    IN    THEIR    RESPECTIVE 


either  side  in  lateral  effort.  In  such  case  the  bite  gauges 
are  inserted  as  usual,  and  the  patient  is  instructed  to  "bite  to 
one  side."  The  bite  locks  are  then  inserted,  the  occlusion 
models  removed  and  returned  to  the  occluding  frame.  The 
condyle  slot  of  the  frame  on  the  protruded  side  is  adjusted 
and  locked,  the  clamps  on  both  sides  of  the  frame  being  re- 
leased while  seating  the  casts  in  their  baseplates.  The  bite 
locks  are  then  I'emoved,  the  occlusion  models  returned  to  the 
mouth,  and  the  patient  instructed  to  "bite  sideways"  in  the 
()p])Osite  direction.  The  occlusion  models  are  again  locked  to- 
gether, ]'emo\ed  from  the  mouth,  returned  to  the  frame,  and 
the  other  condyle  slot  adjusted  and  locked  as  before. 


342  CONSTRUCTION  OK  KULL  UENTUKES 

ADJUSTING  THE  CONDYLE  PATHS  TO  THE  OCCLUDING 
FRAME 

The  condyle  slot  clamps  of  the  occluding  frame  are  re- 
leased and  the  back  spring  unhooked,  as  a  preliminary  step  in 
the  adjustment  of  the  casts  to  the  occlusion  models  in  their 
protruded  or  unilateral  relation. 

The  lower  occlusion  model  is  now  set  upon  its  cast,  the 
upper  bow  of  the  frame  is  moved  backward  until  the  upper 
cast  enters  its  baseplate  and  is  accurately  seated. 


JIAJ>JNEK    OF   Al'PLYING   rRESSUBE   TO    AVOID    TIPPING    IN'    SEATING    CASTS    IN    PBOTRDDED 
AND   LOCKED   OCCLUSION    MODELS 

In  seating  the  casts  in  their  baseplates  care  should  be 
taken  to  direct  the  pressure  upon  them  in  line  with  their  cen- 
ters, to  prevent  tipping.  Grasping  the  bows  of  the  frame  near 
the  hinges  will  unseat  the  casts  anteriorly  and  reduce  the 
pitch  of  the  condyle  slots  below  that  recorded  by  the  pro- 
trusive bite,  while  exerting  pressure  on  the  casts  anteriorly 
will  increase  the  pitch  of  the  paths. 

The  most  accurate  method  of  adjustment  is  to  place  the 
thumb  in  the  center  of  the  base  of  the  lower  cast,  the  middle 
finger  in  the  center  of  the  upper,  and  exert  sufficient  pressure 
to  firmly  seat  and  hold  the  casts  in  their  baseplates  while 


CONSTRUCTION  OF  FULL  UENTUKKS  343 

adjusting  and  clamping  the  condyle  slots.  The  casts  being 
seated  and  held  firmly  in  their  baseplates  as  described,  the 
projecting  end  of  one  condyle  slot  plate  should  be  grasped 
with  the  thumb  and  index  finger  of  the  other  hand,  and  sub- 
jected to  gentle  traction  imtil  a  position  of  rest  is  found, 
where  neither  side  of  the  condyle  slot  impinges  on  the  hinge 
pin  of  the  frame.  When  correctly  adjusted,  the  condyle  slot 
plate  is  clamped  in  that  position,  and  similar  steps  carried  out 
in  adjusting  the  opposite  condyle  slot. 

The  condyle  paths  of  the  frame  being  adjusted  in  the 
manner  described,  the  bite  locks  and  gauges  are  removed  from 
the  occlusion  models  and  the  back  spring  again  hooked  on  its 
pin,  the  tension  of  which  returns  the  hinge  pins  of  the  frame 
to  the  distal  ends  of  the  condyle  slots,  the  same  position  they 
occupied  when  the  casts  were  first  mounted. 

The  occlusion  models,  therefore,  sustain  the  same  rela- 
tion to  each  other  as  before.  The  only  change  effected  by 
adjusting  the  occlusion  models  in  their  protruded  relation  to 
the  unlocked  frame  is  in  the  slant  of  the  condyle  paths  which, 
if  the  steps  have  been  accurately  carried  out,  now  coincide 
with  the  pitch  of  the  condyle  paths  of  the  patient. 

DEVELOPING  THE  COMPENSATING  CURVES 

Wliile  it  is  not  absolutely  essential  to  the  correct  arrange- 
ment of  teeth  anatomically,  it  will  be  found  much  more  con- 
venient for  the  beginner  when  the  condyles  move  downward, 
to  change  the  occlusion  rims  from  flat  to  curved  planes,  thus 
indicating  the  alignment  of  the  teeth  from  before  backward. 
When  properly  developed,  these  curved  planes  represent  a 
plane  section  of  a  convex  sphere  in  the  upper,  and  of  a  corre- 
sponding concave  sphere  in  the  lower  occlusion  model,  which 
may  be  moved  against  each  other  in  protrusive  and  lateral 
effort  without  loss  of  contact.  Theoretically,  the  working 
area  of  the  condyle  paths  also  represent  sections  of  a  convex 
sphere  which  have  a  common  center  with  the  occhisal  sphere 
sections. 

In  taking  the  protrusive  bite,  the  condyles  traversed  a 
distance  along  the  condyle  path  sphere  equal  to  the  forward 
movement  of  "the  mandible.  Tlie  incisal  plane  of  the  lower 
occlusion  model  traveled  a  like  distance  along  the  occlusal 
sphere  incisally. 

Now  since  the  condyle  spheres  are  fixed  factors,  and  the 
incisal  rim  need  not  be  modified,  these  areas  become  the  basis 


344  CONSTRUCTION  OF  FULL  DENTURES 

Tor  develupiiiK  the  compensating  curves  in  tlie  occlusion  rims, 
or  in  correcting  tiie  flal  planes  of  the  upper  and  lower  occlu- 
sion models  so  that  they  will  remain  in  contact  in  lateral  and 
protrusive  elTort. 

FUNDAMENTAL  PRINCIPLES  OF  DEVELOPING  THE 
COMPENSATING  CURVE 

While  the  following  example  is  not  exactly  applicable  to 
developing  the  compensating  curves,  it  will  serve  to  illustrate 
the  fundamental  principle  involved. 

Tn  developing  a  cylindrical  colunm  from  a  S(|nare  piece  of 


timber,  when  for  any  reason  it  cannot  be  turned  in  a  lathe, 
the  woodworker  will  first  square  the  ends  of  the  material,  and 
on  each  end  describe  a  circle  of  the  same  diameter  as  the  col- 
umn to  be  developed.  Around  these  circles  he  will  circum- 
scribe polygons — usually  octagons — the  sides  of  which  touch 
the  circles  tangentially  and  are  parallel  to  each  other.  By 
drawing  connecting  lines  from  the  angles  of  the  polygon  on 
one  end,  to  the  corresponding  angles  of  the  polygon  on  the 
opposite  end,  the  surplus  is  marked  off,  which,  when  removed, 
reduces  the  square  timber  to  polygonal  form.  Accurate  me- 
chanical reduction  of  the  remaining  surplus  may  be  accom- 
plished by  again  drawing  polygons  having  twice  the  number 


CONSTRUCTION  OP  FULL  DENTURES  345 

of  sides,  on  each  end  of  the  timber,  their  sides  also  tangential 
to  the  circles,  connecting  their  angles  and  reducing  the  sur- 
plus in  a  similar  manaer.  The  remaining  surplus  is  then  re- 
duced by  planing  off  tlie  line  angles  and  testing  with  templets 
of  proper  curvature  as  the  work  proceeds. 


CONVEX   AND   CONCAVE   SPHERE   OCCLnSION   MODELS.    DIAGRAJQIATIC 

In  a  similar  manner  the  sculptor  blocks  out  his  statue  in 
the  rough,  and  the  lapidist  grinds  otf  the  rough  and  super- 
fluous parts  of  gems,  after  which  both  apply  the  finishing 
touches. 

A  simple  yet  comparatively  accurate  plan  of  blocking  out 
the  compensating  curves  in  the  rough  is  as  follows : 


DIAGltAM   OF   STEI'S    IN 


■UJXIJIUCAT>   FIGIKE 


The  slight"  protrusive  mandibular  effort  required  to  bring 
the  teeth  in  working  and  balancing  relation  seldom  exceeds 
one-eighth  of  an  inch.  This  distance  represents  the  forward 
movement  of  the  protruded  condyle  in  its  path,  which  for  all 
jjractical  purposes  can  be  considered  as  a  straight  line  tan- 


346  CONSTRUCTION  OF  FULL  DENTURES 

gential  to  the  condyle  path  sphere.  The  slight  deviation  from 
a  horizontal  line  of  th-.'  lower  occlusion  model  in  the  incisor 
region  in  its  protruded  position  is  scarcely  perceptible,  there 
being  only  one  two  hundred  and  fifty-sixth  of  an  inch  of  sep- 
aration, one-eighth  of  an  inch  from  the  labial  surface  of  the 
wax  when  the  drop  of  the  condyle  in  its  path  is  one-eighth 
of  an  inch. 

The  flat  plane  of  occlusion  in  the  incisor  region  may 
therefore  be  considered  as  another  line  or  plane,  tangent  to 
the  compensating  curve. 

Since  the  only  object  in  developing  the  compensating 
curve,  aside  from  esthetics,  is  to  secure  balancing  contact, 
and  since  balancing  contact  is  developed  between  the  upper 
and  lower  second  molars,  it  follows  that  if  a  tangent  can  be 
correctly  located  in  the  area  to  be  occupied  by  the  second 
molars,  the  plane  thus  developed  will  serve  as  a  guide  in  set- 
ting the  occlusal  surfaces  of  these  teeth. 

The  average  distance  from  the  condyle  centers  to  the 
mesio-incisal  angles  of  the  lower  incisor  teeth  is  four  inches 
in  a  straight  line.  The  second  molars  are  situated  practically 
half-way  between  these  two  points,  but  being  below  a  straight 
line,  drawn  between  the  points  mentioned,  they  are  usually 
about  two  and  one-fourth  inches  from  the  second  molar 
position. 

The  problem  then  mav  be  stated  as  follows :  Given  two 
tangents  of  arcs  developed  from  a  common  center  from  which 
to  develop  a  third  tangent  between  the  two,  having  a  similar 
angular  inclination  to  each,  or  an  angular  mean  between  the 
two.  This  is  an  extremely  simple  ]3roblem  to  solve  on  a  sheet 
of  paper,  and  is  accomplished  as  follows: 

Project  the  two  gixen  tangents  until  they  intersect.  From 
the  point  of  intersection  lav  off  a  point  on  each  tangent  equi- 
distant from  the  point  of  intersection  and  connect  the  points 
so  located  with  a  strai2;ht  line.  If  for  anv  reason  the  two  tan- 
gents cannot  be  extended  to  intersect,  lines  drawn  parallel 
to  them,  which  will  intersect,  may  be  developed,  and  the  line 
of  direction  of  the  third  tangent  can  easily  be  determined  by 
these  construction  lines. 

Now  the  difficulty  met  with  in  developing  the  third  tan- 
gent on  occlusion  models  is  that  the  condyle  path  tangent  if 
projected  may  strike  the  occlusion  tangent  too  far  forward  in 
case  of  slight,  or  not  at  all  in  case  of  steep,  pitch  of  the  former. 
Neither  is  there  a  flat  surface  on  which  to  make  the  meas- 
urements required.    Yet  with  these  difficulties  encountered,  a 


CONSTRUCTION  OK  FULL  DENTURES  347 

knowledge  of  a  few  fundamental  facts  will  enable  the  pros- 
thetist  to  develop  the  third  tangent  in  a  very  short  time. 

The  first  fundamental  fact  to  keep  in  mind  is  that  under 
any  and  all  conditions  the  occlusal  plane,  whether  flat  or 
curved,  should  be  so  located  as  to  divide  the  space  as  equally 
as  possible  between  the  crests  of  the  two  borders,  in  order 
that  there  may  be  room  for  placing  the  teeth  in  each  arch. 

The  second  relates  to  how  this  space  may  be  ap- 
proximately divided  evenly.  Since  the  flat  occlusal  rims 
have  previously  been  formed  in  most  cases  so  as  to  divide 
the  space  between  the  borders  equally,  it  follows  that  if  the 
flat  plane  is  to  be  changed  to  a  curved  plane,  the  change  must 


LOCATING  POINT  A 


be  effected  by  modifying  both  occlusion  rims,  paring  off  the 
upper  and  adding  to  tlje  lower  at  the  distal  terminal,  and  re- 
ducing the  lower  and  adding  to  the  upper  in  the  bicuspid 
region. 

The  third  point  is  that  the  condyle  path  and  the  occlusal 
plane  represent  short  tangents  of  a  common  arc,  or  concentric 
arcs  having  a  common  center,  and  therefore  since  they  are 
tangents  of  common  or  parallel  arcs,  the  position  of  the  third 
tangent  may  be  determined  bj'  developing  one  or  more  lines 
parallel  to  the"m  to  find  the  angle  of  intersection. 

The  direction  of  the  third  tangent,  or,  as  it  may  be  called, 
the  second  molar  tangent,  may  be  determined  in  several  ways, 
the  simplest  being  to  jiroject  the  occlusal  plane  backward  be- 
yond the  point  of  intersection  with  the  condyle  path  plane,  and 


IMS  CONSTIUICTION    OF    FULL    DFNTIIRIia 

liiscrt  the  included  angle,  (lie  hisoctioii  lino  nivini;,-  the  direc- 
tion of  tile  tliird  tangent,  hut  tiie  liiu;  when  developed  may  he 
too  far  forward  or  back  of  llu'  required  positioiL 

Again  the  line  of  direction  of  the  second  molar 
tangent  may  bo  determined  by  laying  off  equidistant  points 
from  the  point  of  intersection  on  both  condyle  path  and 
occlusal  plane  tangent,  and  connecting  the  two  points,  as 
stated  previously.  This  method  places  the  position  of  the 
second  molar  tangent  above  and  at  times  too  far  forward  or 
back  of  the  required  position. 


MAliKINXi    LINE    I!-C    CONTINUOUS    WITH    OR    P.iltALLKL    TO    TIIE    CONDYLE    PATH 

The  objections  mentioned,  together  with  the  fact  that 
the  point  of  intersection  is  often  back  of  the  distal  ends  of 
the  occlusion  models,  and  therefore  in  space,  frequently  ren- 
der both  of  these  methods  impracticable. 

By  the  use  of  one  or,  in  some  cases,  two  parallel  lines, 
these  objections  are  overcome  and  the  second  molar  tangent 
can  be  laid  in  its  proper  position  without  difificulty.  The  plan 
is  as  follows: 

PRACTICAL  STEPS 

Locate  on  the  upper  occlusion  model  at  its  distal  termina- 
tion point  a,  through  which  the  compensating  cnrve  miist 
and  should  pass.  This  point  should  be  about  one-sixteenth  of 
an  inch  above  the  flat  occlusal  plane  since  the  latter,  when 


CONSTRUCTION  OF  FULL  DENTUKFS  34'J 

changetl  l<i  a  curved  piano,  must  be  so  developed  as  to 
divide  the  space  between  the  upper  and  lower  border  crests 
equally,  or  as  nearly  so  as  is  possible  with  a  cui'ved  plane. 


WI.IPERIXG 


INDYT.K    I.IN'E 


LAYING    OFF    DISTAXCE    A-F    ON    SUB-OOCLUSAL    LINE 

This  is  necessary,  as  before  stated,  in  order  that  space  may  be 
preserved  for  reception  of  the  lower  teeth.  When  the  compen- 
sating curve  is  developed  so  that  its  distal  termination  coin- 


:i60  CONSTRUCTION  OK  FULJ-  DENTUKES 

cides  with  the  flat  plane  of  occlusion,  its  curvature  is  devel- 
oped at  the  expense  of  the  lower  occlusion  model  entirely. 

Through  point  A  draw  line  B,  C,  continuous  or  parallel 
with  the  condyle  paih,  extending  it  diagonally  across  the 
lower  occlusion  rim.  With  a  pair  of  dividers  scribe  line 
D,  E,  on  the  buccal  surface  of  lower  occlusion  model,  and 
about  one-fourth  inch  below  the  flat  occlusal  plane.  This 
subocclusal  line  intersects  the  projected  condyle  path  line 
at  F. 

Place  one  leg  of  a  divider  on  F,  the  other  on  A,  with  this 
as  distance  set  off,  F,  G,  on  D,  E.  Draw  line  A,  G,  which  rep- 
resents a  short  tangent  of  an  arc  developed  from  the  same  cen- 


CONNEOTING  A-G. 


ter  as  the  comijensating  curve  and  condyle  path.  At  a  point 
one-fourth  inch  in  front  of  the  distal  terminal  of  line  A,  G, 
project  a  symmetrical,  curved  line  forward,  terminating  it  just 
in  front  of  the  cuspid  eminence. 

The  distal  one-fourth  inch  of  line  A,  G,  represents  the 
second  molar  tangent,  both  in  position  and  line  of  direction, 
and  is  not  changed  in  this  blocking  out  of  the  compensating 
curve.  Later  it  may  or  may  not  be  slightly  modified  in  the 
final  correction  of  the  curved  occlusal  plane. 

With  a  condj'le  path  pitch  of  35  degs.,  the  compensating 
curve  will  cut  into  the  upper  wax  rim  about  one-sixteenth  of 
an  inch,  as  stated,  and  in  the  lower  occlusion  model  about  the 
same  amount.     When  the  condyle  pitch  is  greater  than  the 


CONSTRUCTION  OP  FULL  DENTURES  351 

average,  the  curvature  should  be  increased,  and  when  less, 
decreased  proportionately. 

With  the  exception  of  the  second  molar  areas,  the  curved 
line  is  developed  with  the  eye.     With  a  little  experience  a 


COMPLETED   DIAGRAM    SHOWING   ALL   LINES    EXCEI'T   THE   Cl.ll\E    FROM    SEC- 
OND MOLAB  FOKWABD  TO  MESLAl,  OP  CUSPID 


just  estimate  of  the  correct  curvature  can  be  almost  instantly 
determined. 

A  thin,  hot  blade  spatula  is  used  to  divide  the  wax  along 
line  marked,  from  distal  to  cuspid  terminals.    That  separated 


i!52  CONSTRUCTION'  OP  FULL  DENTURES 

from  each  occlusion  model  by  the  blade  is  transferred  to  the 
opposite  occlusal  surface,  and  there  attached  with  a  hot 
spatula. 

Test  the  accuracy  of  the  balancing  area  of  the  blocked- 
out  compensating  curve  by  subjecting  the  occluding  frame 
to  protrusive  and  lateral  movements. 

By  warming  the  occlusal  surfaces  of  the  rims,  and  rub- 
ing  talcum  power  on  them  to  ])revent  adhesion  when  brought 


COMPENSATING  CURVE  DE\ELOPED.   Bl  . 


together,  corrections  can  readily  be  made  by  subjecting  them 
to  slight  pressure  in  lateral  movements  of  the  occluding  frame. 


THE  ULSAVER  METHOD 

Dr.  E.  S.  Ulsaver  suggests  attaching  a  softened  mass  of 
wax  on  the  distal  end  of  the  lower  occlusion  rim,  throwing 
the  frame  forward  on  that  side  to  a  distance  of  an  eighth  of 
an  inch  or  jDossibly  a  little  more,  and  closing  the  frame  in  this 
protruded  lateral  position. 

Separate  the  occlusion  models  and  trim  off  the  excess  wax, 
buccally  and  lingaiallj".  On  closing  the  frame,  it  will  be  seen 
that  the  occlusion  rims  are  prevented  from  striking  by  the  wax 
addition,  which  presents  the  form  of  an  inclined  plane,  the 
distal  end  being-  the  thickest. 


CONSTRUCTIOX    OF    FULL    DENTUKKS  ■So?. 

The  upper  wax  vim  is  now  triimiied  to  accommodate  itself 
to  the  form  of  the  built  up,  distal  end  of  the  lower  rim.  This 
is  doue  by  paring  away  with  a  knife,  a  little  at  a  time,  nntil 
the  two  rims  again  occlude. 

With  this  incline  as  a  basis,  which  is  really  the  beginning 
of  the  compensating  curve,  it  is  a  comparatvely  simple  matter 
to  develop  symmetrical  curves  on  both  rims.  The  opposite 
side  is  developed  in  a  similar  manner.  The  addition  of  talcum 
powder  to  the  rims  iirevents  the  softened  wax  from  sticking 
in  lateral  and  jirotrnsive  movements. 


L-I.l.SlclN   .M( 


in  Air  111..    LABIAL 


The  only  serious  drawback  to  this  otherwise  excellent 
method  of  developing  the  compensating  curve  is  that  the  curve 
is  usually  formed  entirely  at  the  ex])euse  of  the  uiqier  rim. 


OMITTING  DEVELOPMENT  OF  COMPENSATING  CURVE 

It  is  a  fact  that  the  teetli  c;in  be  arranged  to  occlude, 
and  balance  as  well,  without  previously  developing  the  com- 
pensating curve  on  the  occlusion  models.  To  do  so,  however, 
departure  from  the  tint  occlusal  plane  must  be  made,  either  in 
the  initial  arrangement  of  the  teeth  or  subsequently.  This 
change  involves  the  development  of  a  similar  curvature  of 
the  general  occlusal  sui'faces  of  the  teeth  to  that  developed  in 
the  wax  rims,  as  detailed.  Comparison  of  the  merits  of  the 
two  methods  is  largely  in  favor  of  preliminary  development  of 


354  CONSTRUCTION    OP    FULL    DENTURES 

the  compensating  curve  in  the  occlusion  models,  both  from  the 
standpoint  of  accuracy  of  result,  and  saving  of  time  as  well. 

A  method  of  developing  balancing  contact  and  which  does 
not  require  the  changing  of  the  flat  occlusion  rim  to  curved 
planes  has  been  suggested  by  Dr.  G.  H.  Wilson. 

This  consists  in  stepping  the  upper  second  molar  slightly 
above  the  first  and  raising  the  lower  second  molar  correspond- 
ingly. In  lateral  movements,  the  mesial  margin  of  the  lower 
second  molar  engages  with  the  distal  margin  of  the  upper 
first  molar  and  in  this  manner  balancing  contact  is  secured. 
In  reality,  this  method  of  arrangement  is  a  curve  of  steps. 


CHAPTER     XIX 
THE  ESTHETICS  OF  TOOTH  SELECTION 

GENERAL    CONSIDERATION 

One  of  the  most  difficult  problems  of  esthetics  in  pros- 
thetic dentistry  relates  to  the  selection  of  teeth  of  such  size, 
form  and  color  as  will  harmonize  with  the  features  of  edentu- 
lous patients. 

Could  the  human  race  be  classitied  into  a  few,  or  even 
many  groupS;  the  face  forms  of  the  individual  members  of 
each  group  being  alike,  or  so  closelj*  similar  that  when  the 
peculiarities  of  one  were  known  all  of  the  other  members  of 
that  group  would  immediately  be  recognized,  the  problem 
would  be  simple.  As  a  matter  of  fact,  the  faces  of  no  two 
individuals  in  all  probability  were  ever  exactly  alike  in  con- 
tour, proportion,  disposition  of  lines  or  color  effects  of  the 
complexion ;  hence  the  difficulty  of  establishing  an  accurate 
classification. 

Numerous  attempts  have  been  made  since  Hippocrates' 
time,  2,400  years  ago,  to  classify  the  human  race  into  groups 
according  to  dominant  characteristics.  Practically  all  of  these 
classifications  were  based  upon  the  form,  color  and  activity  of 
the  individuals. 

In  the  older  classifications,  the  cause  of  the  differences 
noted  in  various  individuals  was  attributed  to  the  influence  of 
four  fluids,  or  humours,  of  the  system,  viz.,  the  blood,  phlegm, 
yellow  and  black  bile.  These  several  fluids,  it  was  supjDosed, 
tempered  or  influenced  both  the  form  and  habits  of  the  indi- 
vidual, according  to  their  relative  predominance  and  potencies. 

The  older  classification  of  temperaments  was  given  as 
follows : 

Sanguine    (full  blooded). 

Phlegmatic  (excess  of  watery  fluids  supposed  to  be  elab- 
orated in  the  brain). 

Choleric  (excess  of  yellow  bile  from  the  liver). 

Melancholic  -or  atrabilious  (black  bile  supposed  to  come 
from  the  spleen). 

Within  the  last  century,  when  physiological  functions  be- 
came better  known,  the  fallacy  of  this  ancient  temperamental 
basis  was  disclosed,  and  various  writers  on  this  subject  have 


:!5(;  TIIIO    h:STllKTlCS    OF    TOOTH    SIOLKCTION 

at  (lilTcrciit  tinu's  suggested  nioditieatious.  Auiuiig  those  most 
promineiitl.y  identified  in  tliis  field  may  be  mentioned  Gregory, 
Jacqiie,  Laycock,  Hutchinson  and  Spnrzheim.  A  classifica- 
tion suggested  by  the  latter  is  the  best  known  of  any  at  the 
present  time,  and  is  here  i^resented  with  an  abbreviated  table 
in  which  the  fundamental  points  of  interest  to  the  prosthetist 
are  outlined : 

Sanguine    (dominance   ol'  circuhitoiy   system). 

Nervous   (preponderance  of  nervous  element). 

Bilious   (excess  of  bile  in  system). 

Lymphatic  (superabundance  of  lym])h). 

CLASSIFICATION  OF  TEMPERAMENTS 


Teeth 

merits 

Color 

Shape 

Lymphatic 

Pale  blue  or 
gray 

Fine    and    silky, 

but  without 

luster 

Pallid,    opaque 
or  muddy  yellov 

Poorly    shaped, 
broad  and  flat 

Sanguine 

Blue,    brilliant 
and    expressive 

Blond-red    or 
chestnut,  seldom 
dark   or   black 

Cream-yellow, 
darker    at    neck 

Well    propor- 
tioned,   curved 
and  rounded 

Nervous 

Light   gray   or 

blue,     restless, 

often    morbidly 

Ibrilliant 

Fine,    light    and 
soft 

Peail-gray,    or 
blue   tinge 

iMng,  conical 
and  rounded 

Bilious 

Blacli  or  brown.J    Coarse,  dark, 
small  and           often    black, 
piercing           and    abundant 

Strong,    bronze 
lyellow 

Conical,  long 
and  angular 

That  tile  classification  of  temperaments  just  outlined,  as 
a  basis  for  the  selection  of  teeth,  is  not  without  glaring  de- 
fects, and  very  imperfect,  cannot  be  denied;  yet  until  quite 
recently,  although  much  has  been  written,  lint  little  advance- 
ment has  l)een  made  in  this  field. 

Dr.  Hutchinson,  as  quoted  by  Dr.  Ivy,  says:  "Are  we 
not  obliged  to  confess  that  we  have  but  little  to  guide  us  in 
a  classification  excepting  the  conditions  which  ,go  to  make  up 
what  we  mean  liy  complexion?  In  complexion  we  include  the 
color  of  the  hair  and  eyes,  the  state  of  the  skin  as  regards 
thickness,  thinness  or  transparency,  and  the  various  degrees 
of  freedom  of  distribution  of  blood  in  the  capillaries  of  the 
face.  It  is  easy  to  apply  with  tolerable  accuracy  such  words 
as  blond,  fair,  dark,  brunette,  sallow,  pale,  florid,  clear,  muddy, 
and  the  like,  and  these  and  many  others  are  epithets  aijpli- 
cable  to  the  complexion.  Temjierament,  however,  although  to 
a  large  extent  indicated  by  complexion,  is  generally  held  to 
include  sometliing  more.  If  it  did  not,  I  fear  we  should  find 
it  but  a  sorry  basis  upon  which  to  build  a  knowledge  of  the 


THE  ESTHETICS  OF  TOOTH  SELECTION  :J57 

vital  peculiarities  of  the  individual.  Yet  again  I  ask  what 
have  we  to  which  we  can  make  appeal!  We  may  examine  a 
man's  features,  note  the  size  of  his  bones,  the  shape  of  his 
jaws,  the  brilliancy  of  his  eyes,  the  coarseness  or  fineness  of 
his  hair,  his  stature,  his  muscularity,  his  abundance  or  other- 
wise of  cellular  tissue  and  fat;  ln;t  in  observing  all  these 
things  we  shall  be  reminded  that  some  of  them  are  simply 


LyinpAatic 


DIAOBAMMATIC 


peculiarities  of  family  or  of  race,  and  have  little  or  nothing 
to  do  with  healtli,  while  others  are  conditions  which  may 
vary  much  at  different  periods  during  the  same  life."  (Amer- 
ican System  of  Dentistry,  p.  1031.) 

Because  of  tlie  comparatively  rare  occurrence  of  true 
basal  types  of  temperament  as  given,  and  the  innumerable 
variations  from  these  types  observed,  the  Spurzheim  table 
is  extremely  limited  in  its  scope.  That  it  has  served  a  useful 
purpose  in  a  general  way  cannot  be  denied ;  first,  in  suggest- 


358  THE    ESTHETICS    OF    TOOTH    SELECTION 

ing  the  possibility  of  form  and  color  harmony  of  teeth  with 
the  individual,  although  lacking  in  adequate  data  for  ac- 
complishing the  desired  results;  and,  second,  by  keeping  be- 
fore the  eyes  of  the  dental  profession  the  need  of  a  better 
and  more  scientific  method  for  the  selection  of  teeth. 

With  the  recognized  imperfections  of  the  temperamental 
table  and  the  daily  growing  demands  on  the  prosthetist  in 
the  esthetic  field,  some  solution  of  this  most  intricate  problem 
of  tooth  selection  is  not  only  desirable,  but  imperative.  The 
basis  of  the  solution  lies  apparently  in  a  proper  application  of 
the  laws  of  harmony  of  form  and  color,  regardless  of  the  age, 
nationality,  race  or  temporary  physical  condition  of  the  in- 
dividual. 

HARMONY  DEFINED 

Harmony  is  defined  as:  "Completeness  and  perfection 
resulting  from  diversity  in  unity;  agreement  in  relation;  or- 
der; in  art,  a  normal  state  of  completeness  and  order  in  the 
relation  of  things  to  each  other;  an  essential  in  form  as  an 
element  of  beauty;  as  the  harmonies  of  nature;  the  harmony 
of  a  plan  well  thought  out;  the  harmony  of  a  ship's  lines." 
(Standard  Dictionary.)  "Any  arrangement  or  combination 
of  related  parts  or  elements  that  is  consistent  or  esthetically 
pleasing;  agreement  of  particulars  according  to  some  stand- 
ard of  consistency  or  the  esthetic  judgment."  (Century  Dic- 
tionary.) 

ESTHETICS  DEFINED 

Esthetics  is  defined  as  "The  philosophy  of  the  beautiful." 
(Standard  Dictionary.)  "Esthetics,  the  science  which  de- 
duces from  nature  and  taste  the  rules  and  principles  of  art; 
the  theory  of  the  fine  arts ;  the  science  of  the  beautiful,  or  that 
branch  of  philosophy  which  deals  with  its  principles ;  the  doc- 
trine of  taste."     (Century  Dictionary.) 

INTUITIVE  AND   ACQUIRED   ESTHETICS 

We  look  upon  certain  recurring  things  in  the  material 
world  as  right  and  natural,  because  we  are  accustomed  to  them 
and  because  they  are  associated  together.  When  one  thing 
is  mentioned,  other  things  which  usually  occur  with  it 
are  brought  to  mind.  When  mountains  are  spoken  of,  or 
seen  in  the  distance,  wo  immediately  think  of  a  range  of  them 
varying  in  elevation,  more  or  less  covered  with  foi'ests,  the 


THE    ESTHETICS    OF    TOOTH    SELECTION  359 

home  of  flowers  and  birds  and  beasts,  and  through  which 
streams  flow. 

When  a  particular  color  is  seen,  as,  for  instance,  green, 
an  artist  will  think  of  that  color,  its  components,  yellow  and 
blue,  and  its  complementary  color  red. 

Wlaen  an  architect,  or  one  familiar  with  architecture, 
sees  a  structure,  say,  of  the  Grecian  Doric  order,  even  at  a 
distance,  he  immediately  recognizes  it  as  such,  and  recalls  to 
mind  its  massive,  well-proportioned  columns,  its  plain  sub- 
stantial capitals,  its  undecorated  architrave,  the  decorated 
frieze,  the  cornice,  the  triangular  ends  of  the  structure — usu- 
ally sculptured — called  the  pediment,  bounded  above  by  the 
sloping  cornice  of  the  roof,  and  below  by  the  horizontal  cor- 
nice of  the  entablature.  Structures  of  this  type,  as  the  Parthe- 
non at  Athens  before  its  partial  destruction,  are  conceded  to 
be  the  most  pleasing  and  perfect  from  an  esthetic  standpoint, 
of  anv  that  the  hand  of  man  has  ever  produced. 

The  production  of  such  structures  was  rendered  possible 
only  by  the  gradual  a'rowth  and  development  of  the  artistic 
sense  and  esthetic  judgment,  beginning  with  the  dawn  of  civ- 
ilization— a  growth  in  development  of  the  sense  of  propor- 
tions, harmonv  and  fitness  of  things.  To  combine  in  such  a 
structure  as  the  Parthenon  some  of  the  more  radical  elements 
of  the  BA'zantine  or  other  dissimilar  styles  of  architecture, 
would  detract  from  its  dignity  and  grandeur,  and  shock  the 
esthetic  sense  of  all  beholders. 

In  these  and  innumerable  other  examples,  the  esthetic 
judgment  is  a  law  unto  itself.  It  cannot  be  formulated  by  rule, 
but  is  dependent  upon  and  has  its  origin  in  man's  innate  sense 
of  the  fitness  of  things.  This  sense  of  harmony,  although 
totallv  dormant  in  some  and  a  natural  gift  in  others,  is  capable 
of  cultivation,  and  in  no  profession  or  calling  is  there  more 
need  for  its  enhancement  than  among  the  members  of  our 
profession.  The  prosthetist  must  be  able,  not  only  to  keenly 
appreciate  beautiful  things  and  recognize  them  when  har- 
moniously arranged,  but  he  must  be  able  to  execute  them  as 
well. 

These  examples,  although  apparently  abstract,  have  a 
direct  bearing  on  the  subject  under  discussion — the  selection 
of  teeth  of  appropriate  size,  form  and  color  for  each  edentu- 
lous patient  who  presents.  Since,  as  is  generally  conceded, 
the  temperamental  table  affords  only  the  most  meager  assist- 
ance in  this  regard,  some  other  means  must  be  employed. 


360  THK    KSTHKTICS    OF    TOOTH     SELECTION 

BASIS  FOR  TOOTH  SELECTION 

The  basis  of  tootli  sck'ctioii,  as  previously  states  1,  consists 
in  judging  wliat  size,  form  and  color  of  teeth  will  hannonize 
with  the  facial  lineaments  and  color  scheme  of  the  individual. 
Just  as  in  architecture,  the  openings  of  a  building,  the  lines 
of  its  doors  and  windows  must  harmonize  with  the  more  mass- 
ive lines  of  structure,  so  must  the  teeth,  in  their  size  and  out- 
line form,  harmonize  with  tlie  more  massive  lines  of  the  face. 

Again,  in  the  decoration  of  a  building,  the  color  schemes 
employed  must  harmonize.  Violent  contrasts  are  oppressive 
and  should  be  avoided,  while  lack  of  contrasts,  or  absence  of 
complementary  colors,  i)roduces  a  sense  of  dull  monotony.   • 

In  the  selection  of  teeth,  the  first  two  factors,  size  and 
form,  are  determined  by  the  sense  of  proportion,  the  third 
by  color  judgment. 

The  teeth  occupy  a  comparatively  central  position  in  the 
face,  and  since  observation  clearly  shows  that  there  is  a  gen- 
eral similarity  in  form  between  face  outline  and  tooth  outline 
in  the  same  individual,  a  study  of  facial  outlines  is  essential 
as  a  basis  in  tooth  selection. 

FACIAL  OUTLINES 

In  Dr.  Wilson's  ''Dental  Prosthetics"  is  an  illustration 
reproduced  from  a  work  published  100  years  ago  on  the  "Sci- 
ence of  Beauty"  by  an  English  writer,  Mme.  Schimmelpen- 
nick,  and  which,  by  his  permission,  has  been  here  introduced. 
The  outlines  of  faces  here  shown  are,  of  course,  diagrammatic, 
and  conform  too  rigidly  to  geometrical  forms ;  yet  they  em- 
brace practically  all  of  the  types  of  faces  one  sees  nowadays, 
with  perhaps  the  exception  of  the  ovoid,  and  even  that  is  a 
combination  of  the  square  with  the  round.  Other  combina- 
tions are,  of  course,  possible,  as  the  tapering  with  the  roimd, 
or  square  or  rectangular. 

Naturally  a  tapering  face  indicates  a  tapering  tooth. 
Since  the  outlines  of  such  a  face  converge  from  forehead  to 
chin  and  the  taper  of  the  tooth,  when  in  position,  is  reversed, 
harmonious  results  will  be  secured  if  color  and  size  are 
right. 

An  oval  face  calls  for  an  o\al  tooth — one  with  sides 
slightly  convex  and  angles  rounded. 

A  square,  or  rectangular  face,  recjuires  a  tooth  with 
nearly  parallel  sides,  and  with  moderately  well-defined  angles, 


THE    ESTHETICS    OF    TOOTH    SELECTION  361 

sometimes  sharply  angular,  as  in  cases  where  the  incisal  edges 
are  reduced  to  stimulate  wear. 

The  width  of  a  tooth  should  liear  a  similar  relation  to  its 
length  as  the  correspoiidiiiii'  dimensions  of  the  face  bear  to 
each  other. 

The  prolilem  of  harmony  in  form  and  shade  of  teeth,  with 
the  individual,  is  of  vital  interest  to  both  yiatient  and  pros- 


tanc/i 


REPRODUCTION    OK    MADAME    SCnrMMELPEXMC'K'S    ■KAe^IAT.    FORMS'- 

thetist.  To  the  patient,  because  the  denture  is  a  pari  of  him- 
self, to  be  worn  iir  public  and  private  life.  To  the  prosthetist, 
if  inharmonious,  the  denture,  like  Banquo's  Grliost,  which 
would  not  down,  rises  up  at  most  inopportune  times  to  remind 
him  of  his  deficient  technic  and  lack  of  esthetic  judgment.  It 
is  furthermore,  liguratively  speaking,  a  standing  monument, 


362  THE    ESTHETICS    OF    TOOTH    SELECTION 

before  the  world  at  all  times,  of  inartistic  and  misapplied  den- 
tal effort. 

Since  human  faces  vary  in  outline,  form,  contour  and 
general  proportion,  and  since  there  are  no  fixed  measurements 
available,  to  indicate  with  precision  the  exact  length  and  width 
of  teeth  to  select  for  edentulous  cases,  the  necessity  for  culti- 
vating the  sense  of  proportion — esthetic  judgment — -becomes 
plainly  apparent. 

Every  practitioner  and  student  should  interest  himself 
in  the  collateral  studies  of  clay  modeling,  free  hand  drawing 
and  coloring,  to  acquire  a  rudimentary  knowledge,  at  least, 


TIIK  TIIHEi:   TVI'Al,  F(II[.\IS   (IF   TKK'I  II    (DR.    J.    LEON    \VIU.IAMS) 

to  serve  as  a  working  basis  in  this  most  esthetic  branch  of 
dental  science — prosthetic  dentistr_v. 

NATURAL  TOOTH  FORMS 

Within  recent  years  Dr.  J.  Leon  Williams  in  his  studies 
of  natural  forms  has  shown  quite  conclusively  that  although 
there  are  many  variations  in  form  and  proportion  in  the  teeth 
of  different  individuals  of  many  races,  there  are  but  three  dis- 
tinct typal  forms. 

While  variation  from  these  three  types  are  of  frequent 
occurrence,  such  variations  show  certain  characteristics  com- 
mon to  the  more  distinctly  marked  t^^^es.  Dr.  Williams  has 
classified  these  three  most  persistent  typal  forms,  together 
with  certain  variations,  as  follows : 


THE    ESTHETICS    OF    TOOTH    SELECTION  363 

r  Mesial  and  distal  sides  straight  and  par- 
Class    or    Type    I.J    allel  for  one-half  or  more  of  the  length  of 
Square  Type]   crown    from    incisal    edge    toward    the 
I    cervix. 


CLASS    I,    FOKM    1.    SEl'EREST    MODIFICATION"    OF    THE    SQUAKE    TYPE 


CLASS  I,   FOKM   4,    SOFTEST    MODIFICATION   OF  THE   SQUARE  TYPE 

niooc,         T         TT  r  Mesial  and  distal  surfaces  comparatively 

i^iass  01    J-Vpe  ii.  ^     •  i  ^   t          i    j                 •        ;          i 

Taperino-  Type.  I  '^^^'^^S'"*   'i"«"^'    but    converging   toward 

'^             \  each  other  from  incisal  edge  cervicallv. 


TRUBYTE   FORM  I      CLASS  n 
SIZES  AS  MOULDS    I  L-IM  -  I  N- IP- I  R 


ff?f!t 


CLASS    II,    FOBM    I.    SE\  EKEST    MODIFICATION    OF    THE    TAPEBING    TYPE 


THE    li^STHIOTlCS    OF    TOOTH     SKLhX'TlON 


CI-ASS   II.  FOKM   4,    SOFTEST    MODIFICATION  OF   THE   TAPERINt!   TVI'E 


Class  or  Tj'pe -III. 
Ovoid  Type 


Mesial  surface  slightly  convex,  distal 
surface  a  compound  curve,  convex  in- 
cisally,  changing  to  concave  as  it  passes 
toward  the  cervix. 


CLASS  III,    FORM    1.    SEXHIilC   Monil-ICATION   OF  THE   OVOID   T'iTE 


CLASS    III,    F0R5I    4,    SOFTEST    .MODIFICATION    OF    THE    OVOID    TYPE 


REPRODUCTION  OF  NATURAL  TOOTH  FORMS  IN 
PORCELAIN 

Using  Dr.  Williams'  data  as  a  basis,  the  Dentists'  Supply 
Co.  have  reproduced  in  porcelain,  from  models  carved  by  Dr. 
Williams  himself,  the  three  typal  forms  of  teeth  enumerated, 
in  varying  sizes,  together  witli  a  sufficient  number  of  modified 
types  to  meet  average  prosthetic  requirements. 

Class  1  contains  five,  Class  II,  four,  and  CUass  III,  four 
modifications  of  form.    Since  each  class  and  each  modification 


THE    ESTHETICS    OF    TOOTH     SELECTION  365 

is  produced  in  several  graded  sizes,  a  large  variety  of  sizes 
are  thus  available  for  use. 

Dr.  Williams '  efforts  have  been  devoted  to  the  production 
of  typal  forms  and  modifications  of  the  anterior  teeth,  and 
in  this  field  he  has  arrived  at  most  commendable  and  esthetic 
results. 

Dr.  Gysi,  whose  distiuguislied  work  in  the  field  of  anatomic 
occlusion  is  most  widely  and  favora])ly  known,  has  collaborated 
with  Dr.  Williams  in  the  designing  of  full  sets  of  typal  forms 


of  teeth  in  porcelain.  The  patterns  for  the  bicuspids  and 
molars  were  furnished  by  Dr.  Gysi.  The  upper  and  lower 
teeth  of  these  classes  are  so  proportioned  in  their  mesio-distal 
diameters  and  their  occlusal  surfaces  so  formed  that  close- 
locking  occlusion  can  be  secured  with  comparative  ease. 

Clearance  paths  for  the  cusps  of  the  lower  between  those 
of  the  upper  teeth  can  be  developed  with  Irat  little,  and  in  some 
cases  no  change  of  form,  thus  leaving  the  occlusal  surfaces, 
which  are  strongly  ridged  and  grooved,  undistui-bed  for  the 
more  effective  reduction  of  food. 


366  THE    ESTHETICS    OF    TOOTH    SELECTION 

OBSERVED  OUTLINES  OF  NATURAL  TEETH  IN 
THE  MOUTH 

The  fact  should  be  borne  in  mind  that  in  the  living,  hu- 
man subject  the  typal  forms  of  teeth,  as  illustrated,  do  not 
show  as  distinctly  as  in  extracted  teeth,  or  in  skull  dentures, 
from  around  the  teeth  of  wliich  the  i>um  tissues  have  been 


removed,  because  these  tissues,  particularly  in  early  life, 
often  cover  some  of  the  characteristic  or  determining  class 
lines.  Later  on,  or  when  gingival  absorption  at  any  time  oc- 
curs, the  class  to  which  tlie  teeth  belong  becomes  apparent. 

To  know  the  typal  forms  of  natural  teeth  is  of  vital  im- 
portance, and  time  spent  in  analyzing  these  forms  and  varia- 
tions will  be  well  expended.  Such  knowledge  will  enable  the 
prosthetist  to  produce  esthetic  effects  not  otherwise  possible. 

In  the  literature  which  the  Dentists'  Supply  Co.  furnish, 
descriptive  of  these  typal  forms  of  teeth,  are  also  illustra- 


OCCLUSAL   VIEW   OF   MOLAR    Sl^RFACE   MARKINGS 

tions  showing  not  only  mold  forms  of  the  teeth  themselves, 
but  of  types  of  faces  for  which  each  mold  is  appropriate. 

While  a  few  of  the  illustrations  referred  to  are  here  in- 
troduced, a  perusal  of  the  literature  and  a  study  of  the  entire 
series  will  prove  most  beneficial  to  the  prosthetist  in  the  selec- 
tion of  teeth  of  suitable  forms  for  individual  cases. 


THE    ESTHETICS   OF    TOOTH    SELECTION  367 

The  accompanying  half-tones  of  noted  statues  in  the 
various  galleries  and  museums  of  Europe  and  the  United 
States,  illustrates  quite  plainly  the  types  of  faces  to  which 
Madame  Sehimmelpeunick  called  attention  a  century  ago. 

"Admiral  Farragut,"  "Saphira,"  and  "Vulcan"  repre- 
sent the  square  tj'pe  and  would  require  the  parallel-sided  tooth 
of  Class  I. 


■ADMIRAL   FAKEAGUT' 


THK  KSTHKTICS  OF  TOOTH  SELECTION 


THE    ESTHETICS    OF    TOOTH    SELECTION  309 

"Cicero,"  the  "\'estal  \'iri;iii,"  and  the  statue  of  "A 
Youug  Woman"  i-e]iv('sent  the  tapering  face  and  would  re- 
quite taperina'  teeth  wcic  ih'iitures  to  be  supplied  tlieni.  Class 
II. 


THE    ESTHETICS    OF    TOOTH    SELECTION 


■A    MCSTAI.   YIRi;lN" 


■•STATUE  OF  A  YOUNG   WOMAN" 


THE    ESTHETICS    OF    TOOTH    SELECTION  371 

"Juno,"  "Aphrodite,"  and  "David"  represent  the  oval 
type  and  would  require  the  ovoid  tooth  of  Class  III. 


■APHRODITE" 


a72  THK    ESTH1<]T1CS    OK    TOUTll     SELECTION 

"Nero"  represents  a  circle,  \cr\  iieai-ly,  and  cdnid  he  su| 
plied  with  a  sliort,  wide  tcmtli  el'  Class  III. 


The  head  of  "A  liNunan  ijad\ 
though  liarmonious  facial  line. 


shows  a  severely  straight 


•A    HOMAN   LATiy 


THE    ESTHETICS    OF    TOOTH     SELECTION  373 

THE  COLOR  PROBLEM  IN  TOOTH  SELECTION 

The  problem  of  selection  of  artificial  teeth  that  will  har- 
monize with  the  general  color  scheme  of  the  individual's  com- 
plexion is  a  vital  factor  in  the  production  of  dentures  of 
esthetic  value. 

That  this  subject  is  given  too  little  consideration  is  appa- 
rent from  observing  the  prosthetic  restorations  seen  in  the 
mouths  of  persons  in  all  conditions  of  life.  Many  of  these  sub- 
stitutes are  out  of  harmony  in  color.  The  reason  for  this  can 
only  be  found  in  the  prosthetist's  lack  of  knowledge  of  color 
principles. 

The  most  logical  means  of  avoiding  such  inharmoin-  in 
this  line  as  is  daily  apparent  is  by  a  study  of  the  rules  of 
harmony  relating  to  colors,  their  complements  and  con- 
tracts. 

In  Vander]>oel's  "Color  Problems,"  we  find  the  follow- 
ing: 

"The  relation  of  color  to  light  is  much  the  same  as  that 
of  music  to  sound.  Color  has  its  many  hues,  its  long  scales  of 
tints  and  shades,  its  true  and  false  chords.  Mere  sound  gives 
us  but  little  pleasure;  when  developed,  however,  into  its  high- 
est form,  music,  we  are  thrilled,  as  by  the  song  of  a  bird,  a 
favorite  ballad,  or  a  Beethoven  symphony.  So  in  light,  our 
enjoyment  culminates  at  the  glories  of  color  in  a  flower  or  a 
sunset,  at  the  shadows  that  play  over  the  hills,  or  at  the  varied 
hues  of  a  salt  marsh.  Hence,  we  may  aptly  term  color  the 
music  of  light;  and  when  we  think  of  the  wonderful  ways  in 
which  it  has  been  used  and  combined  liy  painters  and  design- 
ers for  hundreds  of  years,  it  must  seem  strange  to  us  that  its 
harmonies  have  not  been  as  tlioroughly  studied  and  classified 
as  those  of  sound." 

It  must  not  be  inferred,  however,  from  the  above  quota- 
tion that  a  classified  system  of  color  science,  capable  of  being 
utilized  by  anyone  who  so  desires,  is  not  available.  As  a  mat- 
ter of  fact,  many  valuable  scientific  works  have  been  written, 
some  in  the  simplest  language  possible,  in  which  the  funda- 
mental i)rinci]3les  of  color  harmony  are  fully  explained. 

That  these  works  have  not  been  extensively  recognized 
and  more  generally  utilized  in  the  past,  particularly  in  spe- 
cialized lines,  as  in  prosthetic  esthetics,  is  largely  due  to  pre- 
vailing educational  methods. 

A  brief  outline  of  some  of  the  principles  of  color  har- 
mony will  now  be  given  in  the  hope  that  it  may  not  only  be 


374  THE    ESTHETICS    OF    TOOTH    SELECTION 

beneficial  in  a  practical  way,  but  prove  an  incentive  to  further 
study  in  this  most  interesting  field. 

A  SYNOPSIS   OF  COLOR  PRINCIPLES 

DEFINITIONS 

"Color  is  the  immaterial  result  of  the  decomposition  of  light. 
A  ray  of  light  in  passing  through  a  triangular  prism  is 
decomposed  into  a  series  of  colors  the  same  as  a  rain- 
how. 

" Paivt  or  Piginent  is  the  material  hasis  which  decomposes 
light  so  as  to  reflect  only  some  of  its  constituent  colors. 

"Shade  refers  to  the  chromatic  composition  of  a  color.  Cobalt 
and  cerulium  offer  us  different  shades  of  hlue. 

"Tint  is  the  condition  of  a  shade  of  color  which  arises  from 
its  admixture  with  water  or  white.  It  becomes,  thereby, 
more  or  less  intense  without  any  change  in  its  chromatic 
composition. 

"Tone  is  the  condition  of  a  color  in  which  it  appears  other 
than  it  is.  A  light  blue  under  the  effect  of  a  bright  or 
dull  light  will  appear  a  light  blue,  yet,  in  the  representa- 
tion of  these  different  conditions,  different  shades  must 
be  used;  different  tints  would  fail  to  convey  a  just  idea 
of  the  color. 

"Harmony  is  the  effect  of  a  proper  arrangement  of  colors  in 
a  picture. 

"Contrast  is  the  etfect  arising  from  different  colors  being 
adjacent  to  one  another,  as  red  beside  blue  or  yellow,  etc." 
— (Bacon). 

COLOR 

The  i^rincipal  source  of  terrestial  light  is  the  sun.  Under 
ordinary  conditions,  light  emanating  from  this  source  is  white, 
or  colorless. 

By  a  process  called  dispersion,  sunlight,  as  well  as  that  de- 
rived from  artificial  sources,  can  be  resolved  into  a  series  of 
different  colors,  known  as  spectrum  colors. 

Dispersion  of  light  is  accomplished  by  directing  a  ray  of 
sun  or  artificial  light  through  a  shutter,  into  a  darkened  room, 
passing  it  through  a  horizontally-fixed  prism,  or  over  a  dif- 
fraction grating,  and  allowing  it  to  fall  upon  a  white  screen. 

By  fixing  the  prism  in  such  position  that  the  light  enters 
it  at  a  slant,  the  beam  will  be  bent  twice  in  its  course,  first  on 
entering,  and  second,  on  leaving  the  crystal.    As  a  result,  in- 


THE    ESTHETICS    OP    TOOTH    SELECTION  375 

stead  of  showing  as  a  spot  on  the  screen  it  sliows  as  a  perpen- 
dicular band,  or  line,  presenting  a  series  of  juxtaposed  colors. 

This  indicates  that  certain  colors,  of  wliieh  white  light  is 
composed,  have  different  refractive  indices,  that  is,  the  rays 
of  one  color  will  be  bent  at  a  different  angle  from  those  of 
another. 

The  colors  and  their  order  from  above  downward,  as  they 
appear  on  the  screen,  are  as  follows: 

Purple. 

*Blue. 

Green. 

*Yellow. 

Orange. 

*Eed. 

Purple. 

Formerly  the  top  color  was  rated  as  two  colors,  violet 
and  indigo,  but  in  1890  the  discovery  was  made  that  indigo 
was  composed  solely  of  blue  and  black,  and  as  black  is  not  a 
component  of  sunlight,  indigo  is  not  a  possible  prismatic  color. 

Each  pair  of  juxtaposed  colors  blend  almost  imiier- 
ceptibly  into  each  other  so  as  to  present  different  shades  and 
varying  tints,  just  as  they  appear  in  the  rainbow,  yet  tlie 
center  of  each  color  is  clear,  distinct  and  unmixed. 

A  distinction  must  be  made  between  white  light,  which  is 
immaterial  or  intangible,  including  the  colors  resulting  from 
its  dispersion,  and  pigment  colors,  which  are  composed  of 
material  substances. 

Since  we  cannot  distinguish  the  color  of  an  object  in  the 
dark  it  naturally  follows  that  either  sun  or  artificial  light  must 
fall  upon  it  to  disclose  its  tint. 

The  reason  why  one  object  appears  one  color  and  another 
object  a  different  color  in  the  same  light  and  under  similar 
conditions  is  due  to  some  inherent  quality  of  the  substances 
themselves  for  absorbing  certain  spectral  colors  and  reflecting 
others. 

For  example,  a  red  substance  absorbs  all  the  other  colors 
of  the  spectrum  but  red  which  is  reflected.  A  green  substance 
absorbs  all  the  spectrum  colors  but  blue  and  yellow,  which, 
when  mixed,  produce  green. 

PRIMARY  COLORS   (PIGMENTS) 

A  primary  color  is  one  which  cannot  be  formed  by  combin- 
ing other  colors.     Blue,  yellow  and  red  are  considered  as 


:i7(i  THE    lOSTHlOTICS    OK    TOOTH     SIOLKCTION 

primaries,  in  lioili  prismatic  and  pigment  colors.  From  these, 
b}'  their  admixture  in  proper  proportions,  practically  all  other 
colors  except  white  and  black  can  be  produced,  and  a  very 
close  api)roximati()n  to  these  are  i»ossible. 

SECONDARY  COLORS 

A  secondary  color  is  mailc  by  coinldiiing  two  primary 
colors  in  ecpial  parts.  There  are  three  secondary  colors : 
Green,  orange  and  purple,  wJiich  are  formed  as  follows: 

Grreen — from  blue  and  yellow. 

Orange — from  yellow  and  red. 

Purple — from  blue  and  red. 

TERTIARY   COLORS 

A  tertiary  color  is  made  bj'  mixing  two  secondary  colors 
in  equal  parts.  There  are  three  secondary  colors:  Citrine, 
russet  and  olive,  which  are  formed  as  follows: 

Citrine — from  orange  and  green. 

Eusset — from  orange  and  purple. 

Olive — from  i^urple  and  green. 

The  formation  of  a  tertiary  color,  by  mixing  two  sec- 
ondaries in  equal  parts,  is  equivalent  to  mixing  two  parts  of 
one  primary  to  one  each  of  the  other  two  primaries.  For 
example,  olive  is  formed  from  purple  and  green.  Since  pur- 
ple contains  one  part  of  blue  and  one  of  red,  and  green  is  com- 
posed of  one  part  of  blue  and  one  of  yellow  it  naturally  fol- 
lows that  olive  is  composed  of  two  parts  of  blue  to  one  each 
of  red  and  yellow. 

INTERMEDIATE  COLORS 

When  a  primary  and  a  secondary  color  are  combined  in 
equal  parts  they  form  what  is  known  as  an  intermediate  color. 
These  are  named  and  formed  as  follows : 

Sulphur  (vellow-green),  three  parts  yellow  to  one  of 
blue. 

Saffron  (yellow-orange),  three  parts  yellow  to  one  of  red. 

Nasturtium  (red-orange),  three  parts  red  to  one  of  yellow. 

Graimet  (red-purple),  three  parts  red  to  one  of  blue. 

Cami^anula  (blue-purple),  three  parts  blue  to  one  of  red. 

Turquoise  (blue-green),  three  parts  blue  to  one  of  yellow. 

By  A^arying  the  proportions  of  the  constituent  pigments, 
it  is  possible  to  jiroduce  an  almost  endless  variety  of  colors. 


THE    ESTHETICS    OF    TOOTH     SELECTION  377 

COMPLEMENTARY  COLORS 

Certain  colors  are  pleasing  to  the  eye,  or  liarniovize, 
when  jolaced  alongside  each  other,  while  others  are  displeas- 
ing, or  inharmonious.  Those  which  are  most  pleasing  are 
termed  complementary  colors.    Now,  why  is  this  so? 

As  has  been  shown,  the  most  satisfying  light  to  tlic  visual 
organs  is  simlight,  subdued  or  diminished  in  its  intensity  to 
such  degree  as  the  optic  nerve  can  tolerate  with  comfort.  The 
same  holds  true  of  the  more  brilliant  white  varieties  of  artifi- 
cial light. 

Both  natural  and  artificial  light,  as  has  been  shown,  when 
passed  through  a  prism  or  over  a  diffraction  grating  are 
dispersed  into  the  primary  and  secondary  spectral   colors. 

It  therefore  follows  that  harmony  in  colors  results  from  so 
mixing  them  or  placing  them  in  juxtaposition  that  all  are  re])- 
resented,  as  in  white  light,  thougli  not  necessarily  in  balanced 
proportions. 

A  complementary  color  is  defined  as  one  which  sui)i)li('s 
those  colors  tliat  are  lacking  in  another  color.  There  are 
various  ways  of  producing  complementary  effects,  some  com- 
plicated, and  others  quite  simple.  It  is  to  tlie  sim])lest  of 
these  that  attention  will  now  be  directed. 

The  complement  of  red  is  green,  because  green  is  com- 
posed of  blue  and  yellow,  and,  therefore,  it  sup]ilies  these  two 
colors,  which  are  lacking  in  red.  Likewise  the  rule  works 
both  ways,  for  red  is  the  complement  of  green. 

The  complement  of  lilue  is  orange,  and  of  orange, 
lilue. 

The  complement  of  yellow  is  ])urple,  and  of  ])urple,  yel- 
low. 

As  a  general  rule  more  harmonious  results  are  produced 
when  the  complementary  color  is  less  ]:)ronounced  than  the 
principal  color.  When  too  conspicuous  it  lessens  the  ])roini- 
nence  of  the  main  color. 

COLOR  FUNCTIONS   OF  THE   VISUAL   ORGANS 

These  statements  in  regard  to  colors  and  their  comple- 
ments are  not  arbitrary  rules,  promulgated  for  convenience, 
but  are  based  npou  physiologic  functions  of  the  visual  or- 
gans, and  can  be  demonstrated  by  anyone  to  his  own  satisfac- 
tion. 

For  example,  when  one  gazes  intently  at  a  red  object  foi' 
two  or  three  minutes,  until  the  eyes  become  saturated  with 


378  THE    ESTHETICS    OF    TOOTH    SELECTION 

tliat  folor,  and  then  closes  the  eyes  an  image  of  the  object  will 
still  be  seen,  not  in  red,  however,  but  in  green. 

If,  instead  of  closing  the  eyes,  one  continues  to  gaze  at  the 
same  or  other  red  objects,  a  greater  or  less  sense  of 
monotony  and  visual  fatigue  is  experienced,  which  is  im- 
mediately relieved  on  looking  at  something  green.-  The  same 
holds  true  of  the  other  colors  and  their  complements. 

The  tiring  of  the  visual  organs,  when  compelled  to  gaze 
continuously  at  incomplete  spectral  colors,  together  with  the 
automatic  foi'mation  of  complementary  colors  within  the  eyes, 
clearly  indicates  that  white  light,  which  contains  all  of  the 
prismatic  colors,  is  normally  and  naturally  demanded  by  the 
organs  of  vision. 

When  the  principal  color  viewed  is  not  intense,  but  rep- 
resents a  more  or  less  dilute  tint  of  a  primary,  secondary  or 
intermediate  color,  the  corresponding  complement  will  be  pro- 
portionately reduced. 

Whatever  the  color  scheme  may  be,  the  strength  or  tone 
of  the  various  colors  should  accord.  "The  note  struck  may 
be  high  or  low,  but  should  be  maintained  throughout  the  color 
scheme.  A  crude,  strong  color,  though  othei'wise  harmonious, 
will  clash  discordantlv  among  delicate  tints  of  a  notably 
lighter  tone."     (Sanford.) 

The  question  may  arise  in  the  reader's  mind.  "Of  what 
value  is  this  discourse  on  the  physics  of  light,  and  the  harmony 
of  colors,  to  the  prosthetist?"  Simj^lv  this:  Without  a  rudi- 
mentary knowledge  of  the  physics  of  light,  and  the  natural 
laws  of  the  harmonv  of  crude  colors  and  their  complements, 
the  selection  of  teeth  of  appropriate  shade,  or  tint,  becomes 
a  difPcult,  and  in  some  cases,  an  impossible  task. 

The  artist,  or  artisan,  can  lighten  or  strengthen  the  prin- 
cipals or  complementaries  of  the  color  scheme  he  is  creating, 
and  arrive  at  a  just  balance  of  harmony  between  the  two. 

The  color  scheme  which  presents  to  the  prosthetist, 
which  he  works  with,  and  he  cannot  change,  is  the  pa- 
tient's face.  Here  the  flesh  tints  of  the  complexion  display 
themselves  in  the  integument  according  to  the  general  char- 
acteristics, habits  of  life  and  health  of  the  individual. 

The  prevailing  tones  are  gray  and  yellow,  tinged  with 
red  and  brown.  Now  since  gray  consists  of  white  and  black, 
the  degree  of  grayness  determines  the  tone  of  the  complexion, 
whether  light  or  dark.  The  reds  and  browns  always  appear 
in  more  or  less  attenuated  form,  and  usually  are  modified  by 


THE    ESTHETICS    OF    TOOTH    SELECTION  379 

admixture  with  other  colors  to  suggest  secondaries  or  inter- 
mediates. 

The  hair,  to  a  marked  degree,  contributes  to  the  general 
color  scheme  of  the  individual.  In  color  it  may  range  from 
white  to  black,  including  intermediate  shades  of  yellow,  red 
and  brown.  As  a  rule,  light  hair  and  light  complexions  are 
associated,  while  dark  or  black  hair  usually  implies  a  more 
strongly  pigmented  integument  in  which  perceptible  tints  of 
reds  and  browns  more  or  less  diluted,  yet  plainly  apparent, 
are  noticeable. 

The  lips  range  in  color  from  a  gray,  which  at  times  is 
scarcely  distinguishable  from  the  integument,  through  vary- 
ing shades  of  pink,  red,  brown  to  purple,  depending  largely  on 
the  vitality  and  age  of  the  individual.  They  form  the  imme- 
diate setting,  or  frame  work,  for  the  teeth. 

In  addition  to  the  usually  pronounced  color  of  the  lips 
in  which  the  teeth  are  framed,  the  shadows  of  the  lips  and 
oral  cavity  must  also  be  considered.  These  shadows  tend  to 
soften  the  lighter  teeth  and  blend  them  with  the  more  darkly 
shaded  integument. 

Dr.  G.  W.  Clapp,  who,  with  the  aid  of  a  color  expert,  ex- 
amined many  individuals,  in  an  effort  to  determine  the  per- 
centage of  various  colors  present  in  natural  teeth,  gives  the 
following  data  of  one  case  as  follows : 

Miss  D.  A.  Wt.  119  lbs. 

Ht.  5.6  In. 

Eyes 

Hair 

UPPERS  Skin 

TT    T.    /-I     i     1  (  Cervical 

U.  R.  Central |  j^^j^^j 

COLORS  FOUND   IN   NATURAL  TEETH 

According  to  Dr.  Clapp 's  analyses,  many  colors  are  to  be 
found  in  the  natural  teeth.  With  gray  as  a  foundation,  the 
predominance  of  some  one  of  the  primary  or  secondary  colors 
gives  the  tooth  its  color  individuality.  He  says:  "Natural 
teeth  exhibit  every  color  of  the  rainbow.  The  primary  colors, 
red,  blue  and  yello.w,  are  found  in  every  human  tooth.  At 
least  one  of  the-  secondary  colors,  orange,  green  or  violet,  is 
found  in  every  tooth,  generally  with  an  excess  of  some  prim- 
ary color  which  gives  to  the  tooth  its  recognized  color  as  a 
blue,  a  yellow  or  a  pink.  Gray  teeth  occur  when  there  is  no 
excess  of  primary  color." 


Red     Yellow  Blue 

Color  Developed 
Black     Orange 

17.5       43.0     16.0 

16.0 

1.5       25.5    yeL 

Dead  Black 

4.1         3.0         .88 

.88 

2.12       1.1    red 

1.1         1.4         .20 

.20 

.90         .3    yel. 

1,1         1.35       .34 

.34 

.76         .25  yel. 

380  THE    KSTHETICS    OP"    TOOTH     SKLECTION 

SUGGESTIONS 

In  the  selection  of  teeth  for  a  given  ease  no  specific  rules 
can  be  laid  down,  because  of  the  wide  variation  in  color 
schemes  of  different  individuals.  Persons  with  complexions 
showing  pronounced  reds  or  browns,  and  with  dark  hair,  re- 
quire comparati\('1y  dark  teeth,  in  wliich  orange  or  ]iink  tints 
predominate. 

Persons  are  frequently  seen  whose  general  color  scheme 
is  neutral,  no  pronounced  primary  or  secondary  colors  appa- 
rent. Either  a  very  dark  or  a  light  tooth  for  such  a  case 
would  be  inappropriate,  by  attracting  too  much  attention  to 
the  mouth.  Teeth  of  gray  shade  or  neutral  tint  should  be 
selected  and  of  such  dei)tli  of  tint  as  will  coincide  with  the 
complexion. 

Fair  or  light  complected  persons  recpiire  correspondingly 
light  teeth,  tinged  with  yellow  or  blue,  sometimes  almost 
neutral  as  to  primaries  and  secondaries. 

White  teeth  are  inappropriate  in  all  cases,  although  pa- 
tients frequently  demand  them.  Natural  teeth  are  never 
white,  the  nearest  approach  being  a  light  shade  of  gray.  The 
harmony  and  esthetic  appearance  of  many  otherwise  good 
dentures  is  frequently  spoiled  by  the  use  of  teeth  of  too  light 
shade. 

As  has  been  shown,  the  color  scheme  of  an  individual  may 
range  from  i^ronounced  primaries  or  secondaries,  through 
imperceptibly  attenuating  gradations  to  neutral  grays,  in 
which  none  of  the  prismatic  colors  are  discernible. 

This  color  scheme,  painted  by  nature's  hand,  is  the 
prosthetist's  canvas,  in  which  he  must  place  a  central  set- 
ting, the  teeth.  How,  then,  can  he  hope  to  attain  esthetic  re- 
sults without  a  knowledge  of  the  laws  of  harmony  of  colors? 

The  physiologic  color  function  of  the  eye,  previously  re- 
ferred to,  which  automatically  creates  the  complementary  of 
a  pronounced  color,  is  an  aid,  in  the  selection  of  teeth,  to  those 
deficient  in  a  knowledge  of  the  laws  of  harmony. 

In  some  individuals  this  infiiifioii,  if  it  might  be  so  called, 
is  an  efficient,  though  unrecognized,  guide  in  choosing  teeth 
that  will  "look  well,"  while  the  results  attained  throiigli  this 
means  are  at  times  pleasing  and  harmonious. 

More  often,  however,  when  the  physiologic  function  is 
imperfectly  developed  or  totally  lacking,  as  in  the  color  blind, 
most  inharmonious  selections  result,  a  fact  plainly  apparent 
to  anvone  in  whom  this  facultv  is  not  deficient. 


THE    ESTHETICS    OF    TOOTH    SELECTION  381 

The  selection  of  teeth  for  edentulous  cases  is  not  a  prob- 
lem of  matcliing  shades,  Inxt  of  harmonizing  colors  by  grada- 
tions and  complementaries,  the  general  color  scheme  of  the 
patient  affording  the  basis  for  such  selection. 

It  is  hoped  that  this  discourse  on  color  and  form,  brief 
and  imjiei'fect  as  it  is.  has  disclosed  its  importance  in  the 
field  of  dental  prosthetics,  and  that  it  will  create  in  the  mind 
of  the  reader  an  interest  in  and  a  desire  for  more  extended 
knowledge  in  the  esthetic  field. 


C  H  A  P  T  E  R     X  X 

ARRANGING  AND  OCCLUDING  THE  TEETH 
UPPER  ARCH 

ARRANGING  THE  SIX  ANTERIOR  TEETH 

The  full  upper  set  of  fourteen  teeth  should  be  first  ar- 
ranged, beginning  witli  the  central  incisors.  A  section  of  waN 
is  removed  from  the  upper  occlusion  rim  of  sufficient  width, 
length  and  depth  to  r(;ceive  a  central  incisor.  Into  the  si^ace 
so  formed  a  central  incisor  is  set,  its  mesio-labial  angle  in 
line  with  the  median  line  previously  marked  on  the  wax  rin; 


DIAGRAMMATIC    CUT    SHOWING     SECTION    OP    WAX    KEMOVED    WITH    TOOTH     IN    CORHECT 
LAUIAL   AND    INCISAL    POSITION 

Its  labial  contour  should  coincide  with  the  general  labial  con- 
tour of  the  rim,  the  two  undisturbed  margins  of  wax  on  either 
side  of  the  space  serving  as  guides  in  securing  correct  align- 
ment. Its  incisal  edge  is  brought  even  with  the  incisal  rim  of 
wax.  When  set,  the  tooth  should  occupy  the  space  of  and  re- 
store the  disturbed  contour  occasioned  by  the  removal  of  the 
section  of  wax.  In  nearly  all  cases  the  long  axes  of  the  cen- 
trals, when  viewed  labially,  should  diverge  slightly  from 
incisal  to  gingival,  away  from  the  median  line,  the  horizontal 
alignment  mesio-distally  of  the  incisal  edge  serving  as  a 
guide,  or  at  least  strongly  indicating  the  amount  of  such 
divergence.  When  in  proper  position,  a  hot  spatula  is  passed 
in  back  of  the  tooth  so  as  to  melt  the  wax,  not  only  around  the 
pins,  but  against  the  entire  lingual  surface  as  well,  and  thus 
firmly  fix  it  in  place. 

In  like  manner  a  section  of  wax  is  removed  and  the  lat- 
eral incisor  is  set  in  position,  the  central  just  placed  on  its 

382 


ARRANGING    AND    OCCLUDING    THE    TEETH  383 

mesial  side,  and  the  undisturbed  wax  in  the  cuspid  area  on  the 
distal  serving  as  g'uides  for  its  correct  labial  alignment.  The 
cuspid  is  then  set  and  fixed  in  similar  manner. 


VIEW    OF    rlM'ER     LEFT    CENTHAL    INCISOR    ADJUSTED    IN    OCCLUSION    RIM 


UPPER    CENTRAI.    LATEK^VL,    AND    CUSPID    ARRANGED 

It  will  usually  be  best  to  return  to  the  median  line  and 
place  the  other  three  anterior  teeth  in  the  order  mentioned, 
so  that  should  rearrangement  for  esthetic  reasons  be  neces- 


384  AKKANGINCI     ANU    OC'CLUDING    THE    TEETH 

sary,  it  can  he  more  readily  aeeoiiiplislied  now  tiian  after  any 
of  the  posterior  teeth  are  phu-ed. 

ARRANGING  THE  POSTERIOR  TEETH 

The  first  and  seeouel  iMcusjiids  and  lirst  and  seeond  mol- 
ars on  one  side  are  set  in  a  similar  manner  in  the  order  named, 
followed  by  the  arrangement  of  the  teeth  on  tlie  opposite  side. 

After  remoA-ing  the  section  of  wax  for   each  posterior 


^1X    ANI'EHKII!.' 


iKl)    AMI    \VAXEI>    IN    l'< 


tooth,  the  walls  of  the  matrix  so  formed  should  be  thoroughly 
softened  with  a  hot  spatula,  the  tooth  pressed  into  buccal 
alignment,  and  the  frame  closed.  This  Inings  the  occlusal  rim 
of  the  lower  occlusion  model  up  in  contact  with  the  tooth, 
which,  if  longer  than  normal,  establishes  its  correct  incisal 
or  occlusal  length. 

If  shorter  tJiau  required,  it  nuist  Ije  brought  down  in  close 
contact  with  the  lower  wax  rim  when  closed.  In  fact,  the  tips 
of  the  cusps  of  all  of  the  npper  bicuspids  and  molars  should 
be  sunk  one-half  their  depth  in  the  lower  occlusion  rim.  This 
may  readily  be  done  by  softening  the  wax  slightly  where  the 
cusps  strike,  as  each  tooth  is  placed.  The  reason  for  this  is 
that  when  the  tips  of  the  upper  bicuspids  and  molars  are  not 
imbedded  as  described,  but  are  allowed  to  rest  on  the  undis 


ARRANGING    AND    OCCLUDING    THE    TEETH  385 

turbed  lower  wax  rim,  in  arranging  tlie  corresponding  lower 
teeth  they  must  be  raised  the  full  dei)th  of  their  cusi)s,  and 
even  higher,  in  order  to  bring  them  into  occlusion  with  the 
upper  teeth.  This  raises  the  occlusal  plane  of  the  denture  in 
the  bicuspid  and  molar  region  from  one-sixteenth  to  one- 
eighth  of  an  inch  above  the  line  established  by  trial  of  the 
wax  occlusion  models. 

By  following  the  plan  outlined,  the  cusps  of  the  upper 
teeth  pass   slightly  below,   and  those  of  the  lower  slightly 


FULL   UPPER   DENTTRE   OCCLUDED 


abo\e,  the  wax  occlusal  plane,  thus  maintaining  the  normal 
])osition  of  the  plane  as  previously  determined. 

ARRANGING    THE    LOWER    TEETH    IN    OCCLUSION    WITH 
UPPER  TEETH 

The  arrangement  of  the  teeth  in  the  lower  arch  should  be- 
gin with  the  lower  second  bicuspid  because  better  interlocking 
of  the  various  planes  and  cusps  can  be  secured  with  the  occlud- 
ing teeth  than  when  the  same  order  of  arrangement  is  fol- 
lowed as  in  the  uppe'-  arch,  viz.,  centrals,  laterals,  cuspids,  etc. 

A  section  of  wax  is  removed  from  the  lower  occlusion  rim 
directly  opposite  the  distal  one-half  of  the  upper  first  and 
mesial  one-half  of  the  upper  second  bicuspids.  A  heated  spa- 
tula is  thrust  deeply  into  the  floor  of  the  space,  and  the  side 


■.iW  ARRANGING    ANIJ    OCCLUDING    THK    TKBTH 

walls,  particularly  toward  the  lingual,  are  thoroughly  softened. 

The  lower  second  bicuspid  is  set  in  this  softened  matrix, 

its  occlusal  surface  considerably  above  normal  position.    The 


LOWEB  SECOND   BICUSPID   SET  IN  SOFTEKED   WAX,   BUT   SLIGHTIiT  ABOVE 

POSITION.     BY  CLOSURE  OF  THE  PRAJIE  IT  IS  FORCED  DOW'NWARD 

AND    IN    APPROXIMATELY    COSRECT    OCI'LtTSION 


CUT    SIIOWINC    PROPKR    CONTACT     I  >E\i:i.OPEn    BETWEEN'    THE    MARGINAL    RIDGES 

frame  is  then  carefully  and  slowly  closed,  using  reasonable 
force  if  necessary  to  bring  the  ui^per  teeth  in  contact  with 
the  lower  occlusion  rim.  The  wax  in  which  the  upper  teeth 
are  imbedded  should  be  thoroughly  chilled,  previous  to  and 


AKKANGING    AND    OCCLUDING    TH1<;    TKETH  387 

diiriug  tins  step,  to  prevent  llicir  (lis|i|;icciiii'nl  iiihIci-  Ihe  ap- 
plied pressure. 

The  closiug  of  the  frame  brings  tlie  upper  bicuspids  in 
contact  with  the  elongated  lower  second  bicuspid,  and  forces 
it  down  to  place.  If  carefully  carried  out  and  the  wax  is  suf- 
ficiently plastic,  the  i^arious  planes  of  the  teeth  will  become 
closely  interlocked,  as  in  normally  occluded  natural  teeth. 

Care  should  be  taken  to  see  that  in  closing  the  frame  the 
lower  bicuspid  is  not  forced  outward  gingivally.  This  will 
most  certainly  occur  on  account  of  the  slope  of  the  ridge  lap 


KRAME  THROWN  TO  LEFT  TO  TEST  CONTACT  OF  BUCCAL  MARGINAL  RIDGES.     IN  THIS 

CASE   THERE    IS    IMPERFECT   CONTACT  BETWEEN   MESIAL   RIDGE   OF   LO«T,B 

SECOND,    AND   DISTAL  RIDGE    OF    TPPER    FIRST   BICUSPID 

acting  as  an  inclined  plane,  thus  directing  the  tooth  outward 
as  it  settles  into  the  wax,  unless  counter-pressure  is  applied 
gingivally  to  keep  it  in  proper  alignment. 

TESTING    THE    OCCLUSAL    SURFACES    FOR    WORKING 
EFFICIENCY 

Before  placing  the  next  tooth  the  relation  of  the  lower 
second  to  the  upper  first  and  second  bicuspids  should  be  tested 
as  to  its  working  efficiency.  This  is  done  by  drawing  the 
lower  portion  of  the  frame  outward  on  the  side  being  tested, 
so  as  to  bring  the  buccal  marginal  ridge  of  the  lower  second 
bicuspid  outward  and  directly  under  the  corresponding  ridges 
of  the  occluding  teeth. 

Usually,  although  in  full  occlusion  the  tooth  maj'  have 
interlocked  well  with  the  opposite  teeth,  it  will  be  found  that 


.■!88  Al{KANGIN(i    AND    OCCLll  DINC     •rillO    'I'KKTH 

while  the  mesial  or  distal  slope  of  the  buccal  marginal  ridge 
linds  contact  with  the  opposite  tooth,  the  other  slope  does  not 
strike,  a  space  of  greater  or  less  width  being  apparent. 

This  defect  may  be  remedied  by  holding  the  frame  in  lat- 
eral position,  and  moving  the  lower  bicuspid  bodily  forward 
or  backward,  as  required,  until  the  planes  are  brought  in 
close  contact  and  the  wax  surrounding  the  tooth  chilled,  when 
the  frame  is  allowed  to  spring  back  to  position. 

A  piece  of  carbon  paper  inserted  between  the  occlusal 
surfaces  will,  imder  pressure,  disclose  the  points  of  interfer 
ence  in  normal  occlusion,  which  can  be  ground  away  with  a 


l.llWEI!    iUClSrill   IN 


small  engine-stone.  The  mesial  and  distal  marginal  ridges  of 
the  opposing  teeth  ai'e  usually  the  points  needing  correction. 
Another  method  quite  as  efficient  in  some  cases,  particu- 
larly where  but  little  correction  is  required,  is  to  soften  the 
wax  in  which  the  three  teeth  are  imbedded  so  that  with  slight 
pressure  they  may  change  their  position.  By  carefully  sub- 
jecting the  frame  to  lateral  movements,  at  the  same  time  ex- 
erting slight  pressure  io  keep  the  teeth  in  occlusion,  the  posi- 
tion of  both  upper  and  lower  teeth  may  be  modified  so  as  to 
correct  the  defects  mentioned,  without  much,  if  any,  grinding. 

SECURING    CONTACT    OF   THE    LINGUAL    MARGINAL    RIDGES 

Now,  while  occlusal  requirements  may  be  perfectly  de- 
veloped and  contact  of  the  mesial  and  distal  slopes  of  the 


ARRANGING    AND    OCCLUDING    TIIK    TEETH  SS'J 

buccal  marginal  ridges  may  he  secured,  it  is  frequently  the 
case  that  contact  of  the  lingual  marginal  ridges  is  defective 
or  entirely  lacking.  Since  the  efficiency  of  the  masticatory 
apparatus  depends  upon  close  contact  of  both  buccal  and  lin- 
gual marginal  ridges  quite  as  much  as  upon  good  occlusal  con- 
tact, it  is  necessary  to  work  out  tlie  required  contact  of  the 
lingual  marginal  ridges  also. 

Failure  to  develop  contact  lingually  in  the  first  steps  of 
arrangement  is  usually  the  resiilt  of  too  long  buccal  cusps  of 
the  lower,  or  too  short  lingual  cusps  of  the  upper  teeth.  When, 
however,  the  teeth  are  well  proportioned,  lack  of  contact  may 


THE    LEFT    LOWER    BKTSI'IDS    AND    MOLARS   OCCLUDED 

be  due  to  inclining  or  lipping  the  teeth  in  one  or  both  arches 
too  far  lingually,  that  is  to  say,  while  tlieir  cervical  position 
may  l^e  correct,  their  occlusal  ends  may  incline  too  much  to 
the  lingual.  Correction  may  be  made  in  the  former  case  by 
reducing  the  length  of  the  cusps  by  grinding,  and  in  the  lat- 
ter by  changing  the  inclination  of  tlie  teeth  in  the  wax.  The 
time  required  for  effecting  such  clianges  as  noted  is  very 
slight,  and  when  corrected  as  soon  as  discovered,  and  as  each 
tootli  is  set,  usually  obviates  more  general  or  extensive  modifi- 
cations later  on. ' 

A  section  of  wax  is  now  removed  for  the  reception  of  the 
lower  first  molar,  the  matrix  walls  softened,  the  tooth  set  in 
a  slightly  elevated  position,  pressure  exerted  on  its  cervix, 
and  the  occluding  frame  closed  to  force  it  into  position  as 


390  AltKANOlNO    AND    OCCLUDING    THE    TEETH 

previously  dcscrilH'd.  In  lil^c  ruaiiiu'r  siiiiilai'  IcsIh  aru  ap- 
plied, and  (•(•ri'cdions  madi'  to  iniiirovc  occlusion  and  contact 
between  the  buccal  and  lingual  marginal  ridges.  Similar 
steps  are  carried  out  iji  adjusting  tlie  second  molar  and  first 
bicusi)id  in  the  order  named,  after  which  the  l)icuspids  and 
molars  on  the  oi^posite  side  are  arranged  in  similar  order 
and  manner. 

ARRANGING   THE   SIX    LOWER   ANTERIOR   TEETH 

The  six  anterior  teeth  can  now  be  set  in  position.  These 
are  placed  in  the  wax  rim  in  the  following  oi-dcr:  cuspids, 
laterals  and  centrals. 


BDCCAI.  VIEW  OP  FULL,   DENTURE  OCCLUDED.     GUMS  NOT   CARVED 

Should  the  teeth  prove  too  narrow  to  fill  the  space  when 
aligned  in  proper  curvature,  a  wider  set  of  sixes  should  be 
substituted,  or  if  too  wide,  a  narrow  set  can  be  used.  When 
only  slightly  excessive  in  width,  correction  may  be  made  by 
grinding  the  distal  surfaces  of  the  cuspids  and  the  mesial 
surfaces  of  the  first  bicuspids  at  their  points  of  contact.  This 
procedure  reduces  the  length  of  the  arc  described  by  the  six 
anterior  teeth,  and  increases  the  distance  between  the  first 
bicuspids,  so  that  teeth  which  at  first  glance  appear  too  wide 
to  be  practicable,  can  be  utilized  with  very  little  effort. 

As  each  tooth  is  set,  the  frame  should  be  subjected  to 
lateral  movements  to  test  their  incisal  relationship.  Fre- 
quently by  grinding  the  incisal  edge  of  the  lower  teeth  at  the 


ARRANGING    AND    OCCLUDING    THE    TEETH  oMl 

expense  of  the  labio-mcisal  angle,  clearance  space  may  be 
developed  without  shortening  the  teeth  or  placing  them  to 
the  lingual  of  their  former  position. 


BIAGKAM  SHOWIXC  TUK  HELATION  OV  LOWEK  TO 
UPPER  MOLARS  IX  THE  INITIAL  ACT  OF  MAS- 
TICATION. BALANCING  SIDE  ON  BIGHT.  WORK- 
ING  SIDE  ON  LEFT. 

Where  much  overbite  of  the  upper  over  the  lower  teeth  is 
deemed  necessary,  the  arc  descrilied  by  the  latter  must  be 
correspondingly  reduced,  in  order  to  secure  clearance  space 
in  lateral  movements.  In  ordinary  cases  an  overbite  of  one- 
sixteenth  of  an  inch  will  prove  sufficient  for  practical  pur- 
poses, and  produce  satisfactory  esthetic  results  as  well. 

DEVELOPING  BALANCING  CONTACT 

In  the  arrangement  of  the  teeth,  so  far  nothing  has  been 
said  of  the  balancing  contact.     This  lias  ]nirposely  been  left 


DISTAL    VIEW    OF    A    FULL    DENTURE    SHOWINti    RELATION    OF    TEETH    ON    WORKING 
SIDE.   LEFT.   AND  BALANCING   SIDE.   RIGHT 

until  the  teeth  have  been  occluded,  since  balancing  adjust 
ment  must  always  be  carefully  developed  in  all  cases  as  a 
final  step.     Test  is  now  made  as  follows: 


392  AKKANGINU    AND    OCCLUDING    THK    TEETH 

Tlie  frame  is  drawn  to  one  side  until  tlie  teeth  on  the 
working  side  are  carried  to  their  differential  limit,  i.  i'.,  the 
l)uocal  and  lingual  marginal  ridges  of  the  upi)er  and  lower 
teetli  are  in  contact.  While  in  this  position  the  relation  of 
the  ujjper  and  lower  second  molars  on  the  opposite  side  should 
he  observed.  Tlie  disto-buccal  cusp  of  the  lower  second  molar 
should  rest  against  the  mesio-lingual  cusp  of  the  upper  sec- 
ond molar,  or  in  the  case  of  disproportion  in  the  mesio-distal 
diameters  of  the  molar  teeth,  it  sometimes  finds  contact  with 
the  disto-lingual  cusp  of  the  upper  first  molar. 

If  on  throwing  the  frame  sidewise  as  described,  the  sec- 
ond molars  do  not  meet,  an   instrument   should  lie  inserted 


LEFT    BUCCAL    VIEW    OF    CASE.      TKKTU    IX    WORKING    RELATION 

under  the  distal  end  of  the  lower  second  molar  and  the  latter 
raised  until  contact  is  established.  The  frame  should  now 
l)e  opened  without  distiirbing  the  molar  in  its  raised  position, 
a  heated  s])atula  passed  under  it  to  melt  the  wax  and  form  a 
new  base  on  which  to  rest,  and  the  wax  allowed  to  cool. 

The  lower  are  now  brought  into  occlusion  with  the  upper 
teeth  by  closing  the  occluding  frame,  if  this  can  be  done  with- 
out disturbing  the  lower  second  molar  in  its  corrected  position 
and  the  position  of  the  upper  molar  changed  to  occlude  with 
the  lower.  Wlien  on  testing  the  lower  and  upper  teeth  do  not 
occlude,  being  held  apart  by  the  modified  i^osition  of  the  sec- 
ond molars,  the  wax  under  the  upper  molar  should  be  softened 
and  the  teeth  brought  together  under  pressure.  The  use  of 
carbon  paper  will  also  disclose  points  of  interference. 


ARRANGING    AND    OCCLUDING    THE    TEETH  393 

It  should  be  kept  in  miiiil  that  baUiHciiiy  contact  is  devel- 
oped between  the  upper  and  lower  second  molars  in  almost 
every  instance,  and  when  developed  no  other  contact  is  re- 
quired on  that  side  between  that  point  and  the  opposite  lateral 
or  cuspid  tooth.  The  teeth  on  tlie  balancing  side  are  not  in 
such  relation  to  each  other  as  to  form  a  masticatory  mill  or 
to  hold  food,  the  actual  work  being  accomplished  on  the  oppo- 
site or  working  side. 

It  will  be  found  by  reference  to  the  diagram  that  the  gen- 
(>r;d  contact  between  the  t(>etli  in  the  two  arches,  in  the  initial 


lilGHT   BUCCAL    VIEW    OF    (."ASE,      SECOND    .MOI 


act  of  masticatory  effort,  i.  e.,  the  position  where  the  teeth 
begin  their  return  to  normal  occlusion,  is  as  follows : 

The  buccal  and  lingual  marginal  ridges  of  the  lower  and 
upper  teeth  on  the  working  side  from  the  cuspid  to  the  second 
molars  inclusive,  are  in  contact.  On  tlie  opposite  side  con- 
tact exists  between  the  second  molars.  These  points,  if  con- 
nected by  imaginary  lines,  represent  a  triangle,  the  teeth 
along  the  working  side  occupying  the  base,  the  second  molars 
on  the  opposite  side  the  apex  of  the  figure. 

The  fact  that 'contact  is  thus  ranged  along  the  sides  and 
at  the  angles  oi  a  three-sided  figure  no  doubt  gave  rise  to  the 
term  three-point  contacl.  This  term  is  misleading  because,  as 
a  matter  of  fact,  there  are,  or  should  be,  many  points  of  con- 
tact between  the  teeth  on  tlie  working  side  of  the  mouth,  but 
not  necessarily  more  tlian  one  on  the  balancing  side. 


ARRANGING    AND    OCGLUDING    TIIIC    TlOI-nil 


HUMAN  DEXTUIIE  SIIOWIXG   BUOKEX  CONTACT  OF  LOWER  WITH    Ul'I'EK 
TEETH    FBOM   FIRST  MOI,AnS  TO   CUSPIDS   OF   OPl'OSITE   SIDE 


ARRANGING    AND    OCCLUDING    THE    TEETH  395 

This  is  Nature's  plan,  as  cau  be  seen  by  examiuiDg  the 
natural  teeth  in  a  normally  arranged  denture.  Stress,  there- 
fore, is  laid  upon  this  fact  because  many  in  attempting  to 
occlude  teeth  anatomically,  endeavor  to  secure  close-locking 
contact  between  the  upper  and  lower  bicuspids  and  molars 
on  the  entire  balancing,  as  well  as  working,  side  in  lateral 
movements. 

FINAL  TEST  WITH   CARBON   PAPER 

When  the  arrangement  of  the  teeth  has  been  concluded 
and  balancing  contact  has  been  secured,  a  final  test  of  all  sur- 
faces with  carbon  paper  is  made,  and  the  high  points  thus 
disclosed  removed  with  engine-stones.      This  test  should  be 


DIAGR;U.I  SHOWING  HOW  CONTACT  ON  WORKING  AND 

BALANCING   SIDES    OCCURS   ALONG   BASE   AND 

AT  APEX   OF    A   TRIANGLE 

repeated  until  smooth- gliding  contact  in  lateral  and  protru- 
sive movements  is  developed. 

DEVELOPING  THE  CONTOUR  OF  THE  DENTURES  IN  WAX 

Strips  of  wax  are  now  placed  on  the  labial  and  buccal 
surfaces  of  the  denture,  one  strip  against  and  parallel  with 
the  periphery,  and  another  overlaying  the  cervices  of  the 
teeth.  The  round  end  of  the  heavy  burnishing  spatula  is 
heated  and  passed  rapidly  back  and  forth  along  the  strips  to 
soften  and  burnish  them  into  close  contact  with,  and  cause 
them  to  adhere  to,  the  outer  surfaces  of  the  wax  denture. 
The  wax  should  overlay  the  cervices  of  the  teeth  about  one- 
twentieth  of  an  inch  in  depth  and  cover  the  gingival  thirds 
at  this  time,  the  idea  being  to  apply  a  slight  surplus  every- 


396  ARRANGING    AND    OCCLUDING    THE    TEETH 

where,  from  wliicli,  by  carving,  the  gum  festoons  and  general 
contours  are  developed  to  proper  curvature  and  thickness. 

It  has  been  previousl}^  shown  by  the  presentation  of  Dr. 
Williams'  work  that  tliere  are  three  typal  forms  of  Imman 
teeth,  each  type  presenting  certain  modifications. 


To  one  who  lias  gi\en  this  subject  any  consideration,  it 
is  a  comparatively  simple  matter,  according  to  the  data,  to 
select  teeth  of  appropriate  form  for  any  individual  case,  since 
the  manufacturers  are  supplying  artificial  teeth  closely  re- 
sembling tlie  tyjial  forms  of  the  natural  organs. 


Now,  granting  that  teeth  of  correct  form  and  size  have 
been  selected  and  occluded,  it  does  not  follow  that  esthetic 
results  will  inevitably  follow  their  use.  In  fact,  in  the  carv- 
ing and  festooning  of  the  gums  one  class  may  be  easily  made 
to  resemble  another,  or  any  form  may  be  so  distorted  as  to 


CARVING   TOOL   SUITABLE  FOB   IISi:   IN  WAX.    \UIA'ANITE  OR  PORCELAIN 

be  unrecognizable.  Clearly,  then,  it  is  the  prosthetist  and  not 
the  manufacturer  who  finally  detei'mines  the  class  of  tooth 
the  finished  denture  presents. 

As  an  artist,  the  prosthetist  should  recognize  the  type  of 
tooth  required.    As  a  sculptor,  he  should  be  able  to  so  mold 


ARRANGING    AND    OCCLUDING    THE    TEETH  397 

the  pliant  materials  around  the  rigid  porcelain  as  to  frame 
them,  as  it  were,  to  meet  the  esthetic  requirements  of  the  case. 

It  requires  quite  as  much  judgment  to  fashion  the  arti- 
ficial gums  around  teeth  of  appropriate  form  in  order  not 
to  distort  their  type,  as  to  develop  reasonably  appropriate 
forms  from  types  of  teeth  that  do  not  strictly  conform  to  the 
requirements  of  a  given  case.  In  either  case  the  prosthetist 
nuist  possess  a  well-developed  esthetic  sense  to  produce  har- 
monious results. 

The  advantage  in  using  teeth  of  suitable  typal  forms  is 
that,  although  the  prosthetist 's  esthetic  judgment  must  be 
none  the  less  well  developed,  the  teeth  themselves  indicate 
the  form  of  the  gum  festoons,  and  therefore  serve  as  pat- 
terns in  the  carving  of  the  case.  When  teeth  are  used  which 
do  not  strictly  conform  in  typal  outline  to  the  case,  the  pros- 
thetist must  be  able  to  see  a  mental  picture  of  the  require- 
ments of  the  case,  and  develop  those  forms  by  the  disposition 
of  his  wax  around  the  teeth. 

As  an  artisan,  the  prosthetist  must  reproduce  in  per- 
manent materials  the  modeled  wax  form  of  the  denture  and 
maintain  in  clearness  and  purity  during  the  finishing  stages 
the  outlines  of  the  typal  forms  of  teeth  he  set  out  to  develop. 

The  dentures  at  this  stage  are  in  the  rough,  as  it  were,  as 
slight  surplus  allowance  of  wax  should  be  made  for  loss  in 
tinal  finishing.  They  should,  however,  represent  in  general 
detail,  though  roughly  blocked,  the  typical  outline  forms  of 
the  finished  dentures,  just  as  the  work  of  a  sculptor,  as,  for 
example,  the  statue  of  Tolstoi,  by  Mucha,  represents  the 
characteristic  features  of  the  man.     (See  page  398.) 

The  attainment  of  esthetic  results  along  these  lines,  as 
well  as  in  the  arrangement  of  the  teeth,  is  of  the  utmost  im- 
portance. The  denture  which  the  prosthetist  produces,  and 
which  is  fitted  in  the  patient's  mouth,  is  not  like  a  garment 
which  can  be  worn  at  pleasure  or  put  oft"  for  something  more 
attractive.  It  literally  becomes  a  part  of  that  patient's  body, 
to  be  worn  for  j^ears,  or  until  further  tissue  loss  or  accident 
requires  renewal.  It  corrects  impaired  phonation,  disturbed 
facial  contour,  and  by  its  use,  when  properly  constructed,  the 
patient  is  enabled  to.  masticate  and  assimilate  food,  thereby 
enabling  normal  lx)dily  functions  to  be  carried  on.  The  health 
of  the  patient,  his  well-being,  comfort  and  good  looks  de]iend 
upon  the  etiticiency  of  the  prosthetist 's  efforts. 

He,  therefore,  who  undertakes  this  specialty  should  have 
the  ambition,  or  be  required,  to  develop  more  than  (average 


398  AKKANGING    AND    UCCLUDING    THK    TEETH 

skill,  since  conditious  of  sucli  vital  importance  depend  upon 
the  results  of  his  efforts. 

DEVELOPING  THE  GUM  FESTOONS 

When  teeth  of  approximately  the  right  form  have  been 
selected  and  arranged,  and  the  wax  has  been  applied  and  bur- 
nished against  the  labial  and  buccal  surfaces  of  the  denture 


STATUE    OP    TOLSTOI    (BY   MUCHA)    SHOWING    CHjVRACTERISTIC    LINES 
WITHOUT  FULLY  DEVELOPED  DETAILS   (SEE  PAGE  397) 

slightly  thicker  than  required,  the  gum  festoons  are  developed 
as  follows: 

With  a  sharp  carving  tool,  or  the  pointed  blade  end  of 
the  burnishing  spatula,  the  surplus  wax  is  removed  from  the 
labial  face  of  each  tooth.  The  instrument,  applied  at  right 
angles  to  the  surfaces  of  the  tooth,  should  be  held  with  the 
pen  grasp — thumb,  index  and  middle  fingers — the  fourth  and 


ARKANUING    ANU    OCCLUDING    THK    TEETH  39« 

little  tiugers  rostiug  at  some  couveiueul  jioiiit  on  tlie  ease  so 
as  to  control  the  movements  of  the  bla<h'. 

The  gingiva  of  each  tooth  is  then  carefully  outlined  with 
the  blade,  the  surplus  wax  removed,  and  the  correctness  of 
form  noted.  It  is  usually  better  to  remove  too  little  than  too 
much  wax  in  the  first  outlining,  since  more  time  is  lost  in  mak- 
ing additions  than  is  required  in  going  over  the  case  a  second 
time  after  inspection.  The  wax  should  be  allowed  to  fill  the 
embrasures  to  as  great  an  extent  as  is  consistent  with  the 
development  of  correct  typal  forms,  to  avoid  the  formation 
of  unnecessary  food  i30ckets. 

This  fact,  however,  should  be  kept  in  miml :  When  teetli 
are  selected  for  a  given  case  whicli  conform  in  length  to  the 
distance  between  the  incisal  rim  of  wax  and  the  liigh  lip  line, 
and  in  typal  form  to  the  requirements  of  the  case,  they  must 


not  be  distorted  and  their  esthetic  value  impaired  by  the  ex- 
cessive use  of  wax  in  gum  festooning. 

The  round  end  of  the  spatula,  or  a  similar  carving  tool, 
is  now  used  to  develop  the  varying  siirfaces  of  the  gum  fes- 
toons above  the  embrasures  and  between  the  gingivae  and 
]ieriphery  of  the  denture. 

It  is  not  possible  to  describe  accurately  the  outline  of 
these  uniform,  yet  plainly  marked,  undulating  surfaces  swell- 
ing out  over  the  rounded  labial  and  buccal  curves  of  the  teeth 
and  sinking  into  the  embrasures  and  areas  as  between  the 
roots  of  the  natural  teeth,  were  they  present.  Many  in  the 
attempt  to  reproduce  the  gum  festoons  and  surfaces  extend 
grooves  from  the"  embrasures  toward  the  periphery.  While 
these  are  decidedly  better  from  an  esthetic  standpoint  than 
mechanically  rounded,  convex  ridges,  they  lack  that  inde 
scribable  and  delicate  variation — the  imperceptible  fading  of 


400  ARRANGINC!     AND    OCCJLUDINfi    THIC    TKKTU 

oue  suvfju'c  iii1(i  iiiiollici-  SO  (it'toii  seen  ill  iKiniiiil,  licjiltliy  ,ti;um 
tissue. 

One  who  is  really  interested  in  tliis  work  eau  lind  no 
better  ideals  than  can  be  gained  by  taking  impressions  of  the 
labial  and  buccal  surfaces  of  the  teeth  and  gums  of  normal 
mouths,  securing  casts  of  the  same,  and  studying  the  forms 
and  variations  there  represented. 

TRIMMING   THE   PERIPHERAL   OUTLINE    OF   THE   DENTURES 

When  the  festooning  of  the  gums  has  been  completed,  and 
frequently  liefore,  the  excess  peripheral  wax  should  be  re- 
moved so  as  to  disclose  the  general  outlines  of  the  dentures. 
The  attention  should  be  directed  to  the  form  of  the  denture 
as  a  whole,  as  well  as  to  specific  details,  and  by  early  outlining 
them  the  proportion  of  the  parts  to  the  whole  can  be  more 
easily  determined. 

FINISHING   TOUCHES    IN    CARVING 

Attention  has  iireviously  been  called  to  certain  prom- 
inent points  in  the  develoi)ment  of  the  wax  contour  and  occlu- 
sion models.  These  will  bear  In-ief  repetition,  since  the  final 
touches  are  given  thern  at  this  time  before  trial  in  the  mouth. 

The  central  notch  providing  for  the  unrestricted  action 
of  the  frenum  is  cleared  of  excess  wax,  and  the  margins 
smoothly  rounded. 

The  incisive  fossae  or  depressions  should  be  developed 
above  the  lateral  incisors.  In  most  cases,  in  order  to  develop 
these  depressions,  it  will  be  necessary  to  set  the  cervices  of 
the  laterals  inward  so  that  a  straight  edge  applied  to  the 
cervices  of  the  central  and  cuspid  on  either  side  will  clear 
those  of  the  laterals.  This  does  not  require  that  the  incisal 
edge  of  the  lateral  shall  be  set  within  the  anterior  curve  of  the 
arch,  but  merely  necessitates  the  slanting  inward  or  liackward 
of  tlie  long  axis  of  the  lateral. 

When  set  directly  upright  the  incisive  fossae,  if  developed, 
will  form  an  abrupt,  and  usually  an  unsightly,  depression, 
while  the  monotonous  curvature  of  the  labial  surfaces  and 
the  parallel  arrangement  of  the  central,  lateral  and  cuspid,  do 
not  produce  as  fine  esthetic  effects  as  where  the  alignment  is 
varied.  The  cuspid  eminence  is  usually  plainly  developed, 
sometimes  strongly  marked,  as  conditions  demand.  It  is 
usually  most  prominent,  though  not  always  so,  at  the  peri- 
pheral margin,  slightly  concave  from  above  downward,  and 


ARRANGINC    AND    OCCLUDING    THE    TEETH  401 

again  proiuiiicnt  as  tlio  ji'iiin  tVsloon  will  ]ic!iuit  at  the  ccivix 
of  the  tooth. 

Usually  back  of  the  euspid  emiueiioe  the  periphery  of  the 
denture  drops  down,  frequently  sufficient  to  form  a  decided 
notch,  to  permit  the  free  play  of  the  buccal  muscles.  The 
perijihery  of  the  baseplate  in  the  region  of  the  tuberosities 
should  extend  as  high  as  tissue  attachment  will  permit,  to  give 
stability  to  the  denture  in  masticatory  eiTort. 

It  is  best  in  all  cases  to  so  form  the  baseplate  as  to  em- 
brace practically  all  of  the  tuberosities,  not  only  on  the  buccal 
surfaces,  but  distally  as  well.  When  roiuided  or  somewhat 
spherical,  as  the  tuberosities  frequently  are,  the  baseplate, 
when  enclosing  them,  is  prevented  from  sliding  forward  in 
masticatory  stress. 

FINISHING   THE    LINGUAL    SURFACES    OF    THE    WAX    MODEL 
DENTURES 

The  excess  wax  should  l)e  removed  from  the  lingual  sur- 
faces of  the  dentures  and  any  depressions  filled  in  to  effect 
the  desired  contour. 

In  many  cases  it  is  advisable  to  develop  in  wax  the  lin- 
gual forms  of  the  incomj^lete  porcelain  teeth  so  as  to  repre- 
sent the  forms  of  natural  teeth.  By  applying  tinfoil  to  the 
palatine  area  and  biirnishing  it  carefully  against  the  lingual 
wax  contours  of  the  various  teeth,  the  work  of  final  finishing 
in  vulcanite  is  reduced  to  the  minimum. 

t'are  should  be  taken  to  see  that  the  baseplate  is  not  ex- 
cessively thick  at  any  point,  and  that  the  border  portion  is 
not  bulky  or  over-developed.  Special  care  should  be  bestowed 
on  the  correct  development  of  the  surfaces  to  the  lingual  of 
the  incisors.  If  unnecessarily  thick,  the  patient's  speech  will 
be  thickened  to  a  marked  degree,  while  if  deficient  a  whistling- 
tone  is  apt  to  be  produced.  This  is  because  in  phonation  the 
tongue  does  not  find  normal  contact  with  the  denture,  or,  in 
those  cases  where,  in  the  production  of  certain  tones,  the 
tongue  does  not  touch  the  teeth  or  the  baseplate,  the  space 
through  which  the  air  passes  is  of  abnormal  outline. 

Tests  should  be  made  as  to  the  efficiency  of  the  denture 
in  phonation  during  trial  in  the  mouth.  Frequently  the  re- 
moval or  addition  of  a  li-ttle  wax  will  correct  what  othei'wise 
might  prove  a  serious  defect.  Such  changes  are  usually  re- 
quired to  be  made  back  of  the  incisor,  and  occasionally  along 
the  lingual,  surfaces  of  the  bicuspids. 


402  ARRANGING    AND    OCCLUDING    TlIK    TKlflTH 

THE    DEVELOPMENT    OF   THE    RUGiE 

When  the  ruga?  are  plainly  marked  in  the  i)alale  the\- 
are  easily  reproduced  in  tlie  denture  by  carefully  adapting 
the  softened  baseplate  to  the  case  in  such  manner  as  to  force 
it  into  the  depressions  between  the  folds,  and  yet  not  thin  it 
on  the  ridges. 

In  preparing  an  impression  for  the  production  of  a  cast, 
the  rugas  should  in  most  cases  be  slightly  exaggerated  by 
scraping  the  bottom  of  the  grooves  impressed  by  the  high 
ridges  with  a  discoid  excavator.  This  not  only  allows  the 
denture  to  become  more  firmly  seated  on  the  vault  tissues, 
but  clearly  indicates  the  position  and  form  of  these  folds  so 
that  they  may  be  easily  reproduced  in  the  baseplate  when 
desired. 

Just  what  the  function  of  the  rugae  may  be  is  not  known. 
In  the  lower  animals  they  aid  in  prehension.     In  man  their 


SECTION  OP  LOWER  DENTURE  SHOWING  LINGUAL 

SURFACE,  A,  CONCAVED  TO  INCREASE 

TONGUE  SPACE 

roughened  surfaces  may  assist  in  separating  triturated  from 
imperfectly  masticated  food,  and  may  result  in  a  keener  ap- 
preciation of  taste  as  well. 

When  ruga5  are  developed  in  a  denture  special  care  must 
be  taken  to  have  the  baseplate  of  the  exact  thickness  required 
in  the  finished  substitute,  to  cover  the  cast  with  thin  tinfoil 
before  vulcanizing,  and  the  lingual  surface  of  the  wax  model 
also  before  flasking  the  tin  lining  remaining  in  the  matrix 
side  of  the  flask.  This  procedure  forms  an  improvised  metal 
matrix  between  which  the  rubber  is  vulcanized,  and  when 
carefully  carried  out,  the  surfaces  of  the  vulcanite  in  contact 
with  the  foil  are  practically  finished  when  removed  from  the 
flask. 

The  lower  wax  model  denture  is  finished  in  much  the 
same  manner  as  the  upper,  the  prominent  points  of  the  lat- 
ter, however,  being  developed  to  a  lesser  degree  liecause  the 


ARRANGING    AND    OCCLUDING    THE    TEETH  403 

surface  markings  of  the  lower  natural  denture  are  not 
strongly  marked.  Special  care  should  be  observed  to  avoid 
unnecessary  bulk  of  wax  on  the  lingual  of  lower  cases,  for 
unless  remo\'ed  in  finishing  the  vulcanite,  tongue  movements 
are  liable  to  be  impeded.  When  finished  in  the  manner  de- 
scribed, the  wax  model  dentures  are  ready  for  trial  in  the 
mouth. 

TRIAL   OF  THE   DENTURES   IN   THE   MOUTH 

The  following  points  should  l)e  observed  in  the  trial  of 
the  wax  model  dentures  in  the  mouth : 

First,  occlusion.  The  patient  is  instructed  to  open  and 
close  the  mouth  a  number  of  times,  and  in  doing  so  to  avoid 
the  application  of  excessive  masticatory  force,  which  tends 
to  displace  the  teeth  in  the  wax. 

Observe  the  following: 

Whether  or  not  tlie  teeth  rest  against  each  other,  as  in 
normal  occlusion. 

See  that  they  intercuspate  properly. 

That  the  overhang  of  the  buccal  marginal  ridges  of  the 
upper  bicuspids  and  molars  over  the  lower  teeth  is  the  same 
on  both  sides. 

Note  whether  the  median  lines  of  the  upper  and  lower 
dentures  coincide. 

Observe  the  pose  of  the  lips  when  at  rest  and  in  smiling, 
and  finally,  the  profile  and  fullness  of  the  face,  to  see  whether 
addition  or  reduction  of  wax  in  any  area  is  required. 

Second,  lateral  movements.  The  patient  is  instructed 
to  move  the  mandible  from  side  to  side  to  test  the  clearance 
paths  of  the  teeth. 

Usually  it  is  best  at  the  beginning  of  this  test  to  intro- 
duce carbon  paper  between  the  occlusal  surfaces  of  the  two 
dentures,  and  by  this  means  iinder  lateral  movements  the 
high  points  are  disclosed.  These  should  be  ground  away  with 
engine  stones.  Repeated  trials,  followed  by  grinding,  first 
on  one  side  and  then  on  the  other,  should  be  made  until  the 
cusps  of  the  lower  denture  glide  smoothly  between  those  of 
the  upper  teeth  without  interference. 

When  there  is  much  variation  of  the  lateral  mandibular 
rotation  centers  from  those  of  the  occluding  frame,  consider- 
able grinding  will  be  required.  When  the  rotation  centers 
are  approximately  four  inches  apart,  but  few,  if  any,  cor- 
rections will  be  necessary. 


404  ARRANGING    AND    OCCLUDING    THE    TEETH 

111  carrying  out  the  lateral  movemeiitss  the  patient  should 
be  cautioned  against  exerting  much  force  u^Don  the  teeth, 
since  hy  these  side  movements  they  are  much  more  readily 
displaced  than  under  direct  stress. 

The  necessity  for  using  hard  wax  tiiat  will  not  soften 
readily  at  oral  temperature,  for  the  rims  in  which  to  imbed 
the  teeth,  becomes  apparent  at  this  stage  of  construction. 

Tliird,  balancing  contact  may  be  tested  by  placing  car- 
bon paper  between  the  upper  and  lower  second  molars  on 
the  protruded  side.  If  porcelain  is  not  discolored  by  the  car- 
bon, there  is  lack  of  proper  contact.  Correction  is  made  by 
removing  the  lower  denture,  raising  the  second  molar  dis- 
tally,  higher  than  the  actual  required  position,  melting  wax 
in  the  space  underneath  to  serve  as  a  foundation,  returning 
the  denture  to  the  mouth  while  the  wax  is  still  plastic,  and 
having  the  patient  throw  the  dentures  into  balancing  relation 
and  close.  The  elongated  tooth  will  thus  be  forced  down  into 
correct  relation,  the  plastic  wax  underneath  preventing  the 
tooth  from  settling  to  its  former  shortened  position. 

One  other  test  still  remains  to  be  carried  out.  The  change 
of  position  of  the  lower  second  molar,  particularly  when  ele- 
vated as  described,  in  order  to  develop  balancing  contact, 
usually  requires  that  the  central  groove  and  sloping  planes 
leading  to  it,  of  the  upper  second  molar  be  deepened  corre- 
spondingly to  receive  the  buccal  marginal  ridge  of  the  lower 
second  molar  when  the  teeth  are  in  normal  occlusion.  This 
test  and  the  correction  is  made  with  carbon  paper  and  stones, 
or  the  wax  under  the  upper  second  molar  is  softened,  the 
lower  baseplate  removed,  chilled  and  returned  to  place,  and 
the  patient  instructed  to  close  with  sufficient  effort  to  force 
the  upper  molar  into  the  softened  wax  a  sufficient  depth  to 
bring  the  remaining  teeth  into  full  occlusion. 

The  latter  method,  although  practicable  at  times,  fre- 
(piently  results  in  loss  of  balancing  contact,  because  the  point 
of  contact  previously  established  by  elevating  the  lower  molar 
is  moved  upward  in  gaining  normal  occlusion.  Correction 
by  grinding,  therefore,  is  preferable. 

When  satisfied  that  the  various  important  requirements 
of  the  dentures  have  been  developed  as  outlined,  tests  of  the 
patient's  aliility  to  phonate  correctly  should  be  made,  as 
previously  mentioned. 

It  is  difficult  to  correctly  estimate  the  exact  amoimt  and 
general  form  of  contour  in  a  denture  required  for  the  cor- 


ARRANGING    AND    OCCLUDING    THE    TEETH  4U5 

rect  artioiilatioii  of  sounds  in  all  eases,  except  ))y  careful 
trial.  In  fact,  in  certain  cases,  as  where  the  patient  has  never 
before  worn  artilicial  dentures,  the  use  of  any  appliance  hav- 
ing a  baseplate  in  excess  of  bulk  of  normal  lost  tissue  will 
cause  a  thickening  of  speech  for  some  time  after  its  intro 
duction. 

In  all  cases  an  effort  should  lie  made  to  develop  as  nearly 
as  possible  the  normal  surfaces  seen  in  natural  dentures  by 
avoiding  either  excessive  hulk  or  deficient  contour. 

FINAL   FINISHING  OF  THE  WAX    MODEL   DENTURES 

After  the  various  tests  and  corrections  have  been  car- 
ried out  as  outlined  until  satisfactory  results  have  been  se- 
cured, the  dentures  are  removed  from  the  mouth  and  returned 
to  the  casts  on  the  occluding  frame. 

If  during  trial  in  the  mouth  the  position  of  any  of  the 
teeth  have  been  purposly  changed,  care  should  be  taken  to 
avoid  closing  the  frame  with  any  degree  of  force  or  the  cor- 
rections made  in  the  mouth  are  liable  to  be  disturbed. 

Each  denture  is  now  carefully  inspected  to  see  that  the 
gum  festoons  and  general  contour  are  as  desired,  or,  if  not, 
corrected. 

The  surfaces  of  wax  are  carefully  smoothed  with  a 
burnisher  and  all  minute  fissures  or  holes  obliterated,  since 
in  subsequent  flasking  the  plaster  will  enter  them  and  show 
as  rough  points  on  the  matrix  walls. 

The  surfaces  of  wax  may  be  rendered  very  smooth  by 
carefully  rubbing  them  with  a  pellet  of  cotton  moistened  with 
chloroform.  Since  chloroform  is  a  slow  solvent  of  wax,  care 
should  be  taken  to  avoid  covering  the  teeth  with  the  dissolved 
wax  carried  by  the  cotton.  When  this  occurs  the  teeth  will 
readily  loosen  in  the  matrix  in  the  removal  of  the  wax. 

The  case  is  sometimes  passed  quickly  through  a  Bunsen 
flame  to  smooth  the  surfaces,  but  this  method  should  not  be 
generally  adopted,  since  the  flame  affects  high  points  more 
readily  than  depressions  and  finely-carved  surfaces  and  deli- 
cate festoons  are  qui.ckly  obliterated. 

Before  removing  the  casts  from  the  occluding  frame  care 
should  be  taken  to  see  that  each  wax  model  denture  is  firmly 
attached  to  its  cast. 

This  is  done  by  placing  a  little  extra  wax  at  various 
points  around  the  periphery  of  the  baseplate  and  with  a  hot 


406  ARRANGING    AND    OCCI>UDlNG    THE    TEETH 

spatula  melting  it  along  the  junction  of  the  baseplate  with 
the  cast. 

REMOVING  THE  CASTS   FROM   THE   OCCLUDING   FRAME 

With  a  sharp  knife,  the  plaster  which  was  built  around 
the  bows  and  against  the  base  of  the  cast  in  mounting,  is  pared 
away  so  as  to  expose  and  undermine  the  bows,  after  which 
the  cast  is  easily  detached.  The  adherent  plaster  is  then 
removed  so  as  to  reduce  the  cast  to  its  original  form  before 
attachment  to  the  occluding  frame. 


C  H  A  P  T  I]  K     X  X  I 

REPRODUCTION    OF    THE   WAX   MODEL   DENT- 
URES IN  PERMANENT  MATERIALS 

The  duplicatiou  of  the  wax  model  dentures  iu  perma- 
nent materials  may  be  roiio'hly  divided  into  tive  stages,  as 
follows : 

Flasking  the  wax  model  denture. 

Packing  the  matrix  witli  rnbber. 

Closing  the  flask. 

Vulcanizing. 

Finishing. 

A  wax  model  denture  usually  presents  a  very  irregular 
outline  and  many  varying  surfaces.  It  is  also  composed  of 
some  of  the  permanent  factors  of  the  denture,  viz.,  the  teeth, 
and  sometimes  the  baseplate.  The  wax  portion  of  the  model 
denture  must  be  replaced  with  rubber  applied  in  a  plastic 
condition  and  afterward  hardened.  The  problem  is  how  to 
replace  the  wax  with  vi;lcauite  without  losing  the  relation 
between  the  teeth  and  oast  of  the  mouth. 

SECTIONAL  MOLDS 

The  reproduction  of  a  pattern  or  model  in  metal  or  other 
materials  capable  of  being  rendered  plastic  is  usually  ac- 
complished by  surrounding  the  object  it  is  desired  to  repro- 
duce with  a  sectional  mold,  so  formed  as  to  part  from  irreg- 
ular surfaces  without  breaking,  removing  the  model  from  th^ 
mold,  replacing  the  various  sections,  and  filling  the  space 
formed  by  the  removal  of  the  model,  with  the  plastic  material. 

To  carry  out  such  work  accurately  some  means  must  be 
provided  for  holding  tlie  several  parts  of  the  sectional  mold 
in  exact  relation  to  each  other  after  removal  of  the  pattern 
or  model,  and  while  filling  the  matrix. 

Iron  and  brass  founders  use  what  is  termed  a  flask  or 
molding  box,  consisting  of  two  or  more  sections,  iu  each  of 
which  a  portion  of  the  mold  is  formed.  These  various  sec- 
tions of  the  molding  box  are  held  in  position  by  means  of 
accurately  fitted  guides,  so  that  when  separated  and  the  model 
is  removed,  the  several  parts  of  the  mold  can  be  reassembled 

407 


408  KLASKINC     WAX     MODl^L     OKNTUKKS 

and  held  in  the  same  iclalioi:  tlicv  (iccniii(Ml  wiicri  the  pat- 
tern was  enclosed  within. 

When  a  pattern  composed  entirely  of  wax  is  used,  and 
the  object  is  to  be  reproduced  in  metal,  as  an  inlay,  crown, 
bridge  or  denture,  the  mold  can  be  made  in  a  single  piece 
and  the  wax  model  dissipated  by  heat,  thus  clearing  the 
matrix  and  obviating  the  necessity  for  forming  the  mold  m 
sections. 

In  prosthetic  operations  the  reproduction  of  a  wax  model 
denture  is  usually  accomplished  by  forming  of  plaster  a  two- 
piece  sectional  mold  in  a  metal  box  termed  a  flask.  Some- 
times in  complicated  cases,  as  in  the  construction  of  obtura- 
tors and  artilicial  vete,  a  three  or  four  section  mold  is  re- 
quired, involving  the  use  of  flasks  of  special  forms. 

FLASKS 

Vulcanite  flasks  used  for  dental  purposes  are  made  of 
brass  or  cast  iron.  They  usually  cousist  of  a  lower  section 
in  which  the  base  of  the  cast  is  invested,  and  an  upper  sec- 
tion in  which  the  mold  containing  the  teeth  and  representing 


in  reverse  the  gum  and  lingual  areas  of  the  denture  is 
formed.  The  lower  section  may  or  may  not  have  a  removable 
bottom,  while  the  top  of  the  upper  section  is  always  remov- 
able, to  facilitate  the  flashing  of  the  case. 

These  varioiis  parts  of  the  flask  are  provided  with  pins, 
or  lugs,  which  fit  into  holes  or  slots  in  the  corresponding  op- 
posite parts,  for  accurately  guiding  and  holding  them  in  cor- 
rect relation  to  one  auother  while  flasking,  and  during  the 
final  closing  of  the  packed  case. 


FLASKING    WAX    MODEL    DKXTURES  4oy 

Two  general  styles  of  flasks  are  in  oommou  wae: 
First — Flasks  to  whicli  screw  bolts  are  fitted,  for  clos- 
ing and  holding  the  packed  case  together  during  vulcaniza- 
tion. 

Second — Flasks  which  are  closed  and  held  together  by 
means  of  a  spring  clamp  or  ]>ress. 


Cl'T    SHOWING    THE    KLASK    SlOI'AItATKl) 


An  appliance  called  a  flask  press  is  frequently  employed 
for  closing  packed  cases,  the  bolts  or  clamps  being  used  for 
holding  the  flask  together. 

The  usual  methods  followed  in  closing  flasks  and  hold 
ing  them  together- during  vulcanization  will  yield  satisfactory' 
results  if  reasonable  care  is  observed  in  carrying  out  the  se\'- 
eral  steps.  If  carelessly  performed,  errors  are  liable  to  occur 
during  this  o])eration  which  may  result  in  destroying  denture 
adaptation.  Attention  will  be  called  to  these  sources  of  error, 
and  means  for  obviating  the  same,  under  the  heading.  Clos- 
ing the  Packed  Flcsk. 

Most  of  the  flasks  offered  by  the  supply  houses  are  too 
small  to  receive  average  and  large  sized  casts.  Since  no  ad- 
vantage is  gained  in  the  use  of  small  flasks,  the  larger  sizes 
should  be  used. 


410 


PLASKING    WAX    MODEL    DENTURES 


FITTING  THE   CAST  AND   WAX   MODEL   DENTURE  IN   THE 
FLASK 

In  uppei'  cases  the  cast  with  wax  model  denture  attached 
is  now  set  in  the  lower,  or  shallow,  section  of  the  flesk.  If 
too  large  peripherally  to  rest  upon  the  bottom  of  the  flask, 
the  margins  of  the  cast  should  be  pared  away  at  points  of 
interference  until  it  drops  into  position.  Usually  reducing 
the  distal  end  of  a.  cast,  when  trimming  in  this  location  is 
permissible,  will  be  all  that  is  required. 

The  upper  section  of  the  flask  is  now  set  in  position  to 
test  the  depth  of  cast  and  denture  as  compared  to  the  depth 
of  the  entire  flask.     Should  the  incisal  ends  or  occlusal  sur- 


A    Sl'ECIAI.   SIZED   FLASK    KOK   \U1.(  AXIZIXG    I.AUGE    CASES 

faces  of  the  teeth  project  above  the  upper  plane  of  the  second 
section,  they  will  interfere  with  the  top  plate  going  to  place, 
and  the  teeth  are  liable  to  become  disj^laced.  This  is  obviated 
by  reducing  the  base  of  the  cast  sufficiently  to  lower  the  teeth 
below  the  upper  plane. 


FLASKING  THE  WAX  MODEL  DENTURE 

The  upper  portion  of  the  flask  is  now  set  aside  and  the 
cast  and  denture  removed  from  the  lower  section.  A  mix  of 
plaster  of  medium  consistency  and  containing  no  accelerator 
is  applied  over  the  bottom  and  around  the  inside  periphery 
of  the  first  section  of  the  flask. 

The  east  should  be  set  in  water  for  ;i  sliori  time  just 
previous  to  investment  to  partially  fill  the  pores,  then  set  in 
position  in  the  flask  and  pressed  down  into  the  soft  plaster 


FbASKINC     WAX    .MODEL    DENTURES 


tu  tlie  positiou  previously  detenuiued.  With  a  slioit,  stifL' 
blade  spatula  the  plaster  between  the  sides  of  the  flask  and 
the  peripheral  line  of  the  wax  model  denture  is  smoothed 
down  where  high,  and  built  in  where  deficient,  so  as  to  form 
a  continuous  surface  from  the  denture  margin  to  the  upper 
plane  of  this  first  section.  This  surface  of  plaster  forms  the 
dividing  line  between  the  two  halves  of  the  invested  case. 

Care  should  be  taken  to  see  that  none  of  the  gum  por- 
tion of  the  denture  is  imbedded  in  the  plaster  investment  of 
the  first  section,  or  the  packing  of  the  case  becomes  difficult. 
Under  no  circumstances  should  the  line  of  separation  of  the 
two  halves  of  the  flask  occur  near  the  cervices  of  the  teeth 
or  the  basic  rubber  will  most  certainly  find  its  way  through 
to,  and  mix  with,  the  gum  material. 


DIAGRAM   OF    DPPEB   WAX    MODEL    DENTURE    INVESTED    IN    FIRST    OR    LOWER    SECTION    OF 

FLASK 

The  plaster  is  built  against  the  distal  margin  of  the  base- 
plate, but  not  so  as  to  overlay  it  at  any  point.  When  set,  the 
surplus  plaster  is  trimmed  off  and  the  surfaces  surrounding 
the  cast  smoothed  up  with  a  piece  of  sandpaper.  Particu- 
lar attention  should  be  given  to  removing  all  plaster  from 
the  flask  margins  and  from  the  holes  or  grooves  which  receive 
the  lugs  of  the  second  section.  This  is  necessary  in  order  that 
the  metal  edges  of  the  two  sections  may  come  together  with- 
out interference.  Wlien  smoothed  up  and  the  loose  debris 
is  removed,  the  plaster  surfaces  are  varnislicd  with  a  good 
separating  medium  and  allowed  to  dry. 

The  second  section  of  the  flash  is  now  set  in  j^osition, 
into  which  plaster  of  medium  consistency,  too  thick  to  pour, 
is  introduced  with  a  spatula,  placing  it  on  the  incisal  and 
occlusal  surfaces  of  the  teeth.  By  jarring  the  flask  on  the 
bench,  the  plaster  is  vibrated  down  between  the  labial  and 


412  FLASKINU    WAX    .\l(M)IOL    DKNTURKS 

liiiccjil  sui'Taccs  1)1'  llic  ilcntiirc  :iiiil  ll;isk  ;iii<l  oxci-  the  liii.nual 
iii'cas  as  well. 

Special  care  slioiild  he  taken  in  lillini;'  tlie  upper  liali"  of 
the  flask  to  avoid  eonliiiing  tiie  air  in  the  embrasures,  or  any- 
where throughout  the  plaster  investment.  When  air  spaces 
are  present,  pressure  of  th(>  surphis  rubber  in  the  matrix 
is  liable  to  force  the  teeth  into  them  in  closing  the  flask,  or 
result  in  uncontrolled  loss  of  rubber  from  the  matrix.  Elon- 
gation of  the  teeth  from  this  cause  is  of  frequent  occurrence, 
particularly  when  the  matrix  contains  much  surplus  rubber. 

To  obviate  this  difficulty,  a  mcfal  occlusion  reiainer  sug- 
gested by  Dr.  rxreeno,  is  lieni  to  lay  in  contaet  with  the  oc- 


clusal surfaces  of  the  teeth  and  extend  over  the  labial  and 
buccal  surfaces  as  well.  In  the  second  stage  of  flasking  when 
the  plaster  has  assumed  a  level  even  with  the  occlusal  sur- 
faces of  the  teeth,  the  occlusion  retainer  previoiisly  conformed 
to  the  arch  is  quickly  liiled  with  plaster,  inverted  and  pressed 
down  until  in  contact  with  the  teeth  at  many  points.  The 
remaining  space  in  the  flask  is  now  filled  with  plaster  slightly 
above  its  upper  margin. 

The  top  of  the  flask  is  now  adjusted  and  pressure  ap- 
plied to  force  out  the  excess  plaster  while  it  is  still  plastic. 
Care  should  be  taken  to  see  that  the  projections  of  the  top 
enter  their  respective  guides  of  the  flask. 


FLASKING    WAX    MODEL    DENTURES  41:! 

Siuce  rubber  is  easily  soiled  from  dirty  lingers,  and 
siuce  the  flask  as  well  as  the  rubber  must  be  handled  more  or 
less  in  packing  the  matrix,  to  obviate  discoloration  of  the 
rubber,  the  outer  surfaces  of  the  flask  should  be  cleaned  with 
a  scrub-brush  and  water.  The  holes  and  grooves  which  re- 
ceive the  bolts  should  also  be  cleared  at  this  time,  for  if  de- 
ferred until  the  case  is  packed,  some  of  the  debris  is  liable 
to  become  intermixed  with  the  contents  of  the  matrix.  This 
scrubbing  and  cleaning  of  the  flask  can  be  carried  on  while 
the  plaster  is  hardening. 

From  fifteen  to  twenty  minutes'  time  should  be  given 
the  plaster  in  the  upper  portion  of  the  flask  is  set,  or  a  longer 
time  if  necessary  when  slow-setting  material  is  used.  The 
plaster  must  be  thoroughly  hardened  before  separating  the 
flask,  to  prevent  displacement  of  tlie  teeth. 

SEPARATING  THE  FLASK 

The  flask  and  contents  should  he  warmed  to  render  the 
wax  soft,  but  not  sufiiciently  heated  to  melt  it.  This  is  neces- 
sary so  that  the  wax  may  part  readily  from  the  teeth  with- 
out dislodging  them  from  the  matrix.  Heating  is  best  ac- 
complished in  a  warming  oven,  the  temperature  of  wliich  does 
not  exceed  120  degrees  Fahrenheit.  This  method  requires 
but  a  short  time,  while  the  danger  of  melting  the  wax  is  en- 
tirely obviated.  In  case  the  warming  oven  is  not  available, 
the  flask  may  be  heated  over  a  Bunsen  stove.  When  so  done, 
it  should  not  be  allowed  to  rest  in  one  position  for  any  length 
of  time,  particularly  when  the  case  is  invested  in  a  closed- 
bottom  flask.  AVith  a  pair  of  flask  tongs  it  may  be  turned 
so  that  its  various  surfaces  can  all  be  heated  without  ovei- 
heating  any  part. 

The  principal  advantage  of  using  dry  heat  in  softening 
the  wax  is  that  the  plaster  of  both  cast  and  matrix  as  well 
is  rendered  harder  and  more  resistant  to  stress  than  when 
saturated,  as  it  is  by  the  usual  method  of  placing  in  hot 
water. 

Since  iilastei'  is  low  in  conductivity,  sufficient  time  sliould 
be  allowed  for  the  heat  to  penetrate  the  interior.  When  over- 
heated and  the  wax  is  melted,  it  soaks  into  the  plaster  mat- 
rix and  cannot  well  be  removed  by  the  usual  means.  Its 
presence  impairs  the  quality  of  the  vulcanite,  frequently  pre- 
venting it  from  fuUv  hardening,  as  well  as  modifying  its  color. 


114  FLASHING    WAX    MODICL    DRNTURRS 

OPENING  THE  FLASK 

The  lieated  flask  resting  upon  tlie  beiieli  is  set  edgewise 
and  with  a  folded  towel  steadied  with  one  hand.  The  point 
of  a  knife  is  inserted  between  the  line  of  jinietion  of  the  two 
sections  just  sufficiently  to  gain  a  hold.  A  slight  i-otary  or 
prying  motion  is  applied  until  the  sections  show  a  slight  line 
of  separation.  The  flask  is  then  turned  and  the  knife  applied 
to  the  opposite  side.  The  sides  of  the  flask  by  tlie  guides, 
especially  when  the  latter  fit  closely,  are  the  logical  points 
to  apply  the  wedging  ]jressure. 

The  force  at  the  start  should  be  very  light  and  gradual, 
to  permit  the  wax  to  yield  without  endangering  any  over- 
hang that  may  be  present,  either  on  the  cast  or  matrix  walls. 


FIRST    SECTION  OF    FLASK    CONTAINING    CAST.      AFTER    SErARATION 

When  the  two  sections  show  a  line  of  separation  around  their 
entire  pei'ipheries,  with  a  folded  towel  in  each  hand  the  flask 
is  picked  up,  and  with  a  steady,  rocking,  manual  force,  the 
lower  and  upper  halves  are  gradually  parted. 

InsufiScient  warming  of  the  wax  within  the  matrix,  or 
undue  force  exerted  in  separating  the  flask,  frequently  results 
in  fracturing  the  matrix,  or  the  cast,  or  in  dislodging  some 
of  the  teeth. 

When  separated,  the  cast  will  be  found  enclosed  within 
the  lower  section  of  the  flask,  and  the  teeth  covered  by  the 
wax  in  the  upper  section. 

CLEARING  THE  MATRIX  OF  WAX  AND  BASEPLATE  MATERIAL 

When  Ideal  Baseplate,  or  any  hard  special  material  Is 
used  as  a  baseplate,  it  can  best  be  removed  by  insei'ting  the 
point  of  a  knife  at  the  back  under  the  central  vault  portion, 


FIvASKING    WAX    MODEL    DENTURES  415 

when  by  prying  upward  it  may  be  readily  fractured  and  the 
broken  pieces  removed. 

With  a  spoon-shaped  instrument,  such  as  a  medium-sized 
Kingsley  Scraper,  the  wax  enclosing  the  teeth  can  be  started 
at  one  tuberosity,  and  if  of  sufficient  cohesiveness,  can  be 
gradually  released  from  the  teeth  and  matrix,  en  masse. 

When  somewhat  hardened,  it  should  again  be  rendered 
plastic  or  removed  in  sections;  otherwise  the  teeth  will  be 
displaced.  When  overheated,  but  not  actually  melted,  a 
dash  of  cold  water  will  restore  its  cohesiveness  without  en- 
tirely destroying  its  plasticity.  When  melted  and  partially 
absorbed  by  the  matrix,  the  entire  elimination  of  the  wax 
is  not  possible  without  the  application  of  dry  heat  sufficient 
to  lower  the  resistance  of  the  plaster  to  stress;  therefore 
such  means  should  not  be  used. 

The  bulk  of  wax  having  been  removed,  such  smaller  por- 
tions as  are  adherent  to  the  pins  of  the  teeth  and  in  the  em- 
brasures should  be  i)icked  out  with  a  delicate  instrument,  care 
being  taken  not  to  mar  the  matrix  or  dislodge  the  teeth. 

The  flask  is  now  set,  tuberosities  up,  at  an  angle  of  about 
45  degrees,  in  the  sink,  and  a  small  stream  of  boiling  water 
allowed  to  fall  from  a  height  of  ten  or  twelve  inches  against 
the  molar  and  bicuspid  teeth  on  each  side.  A  small  teakettle 
is  very  convenient  for  this  purpose,  the  spout  producing  a 
small  stream  which  is  easily  directed  where  desired.  A  pan 
with  handle  and  having  a  sharp  lip  will  answer  the  same 
purpose. 

To  rid  the  matrix  quickly  of  wax,  and  prevent  excessive 
absorption  of  water  by  the  latter,  the  water  must  be  boiling 
hot,  must  fall  from  a  considerable  height,  must  be  directed 
where  needed,  the  flask  inclined  so  that  the  water  will  readily 
flow  from  the  matrix  and  carry  the  melted  wax  with  it,  and 
the  process  carried  out  as  quickly  as  possible  and  stopped 
as  soon  as  all  wax  is  removed.  The  plan  adopted  by  some, 
of  placing  tlie  flask  section  in  a  pan  of  water  and  bringing 
to  a  boil,  is  an  incorrect  and  careless  procedure,  resulting 
in  full  saturation  of  the  plaster  with  water  and  frequently 
of  a  film  of  wax  adhering  to  the  flask,  matrix  surfaces  and 
teeth. 

The  matrix  section  is  now  emptied  of  the  water  in  its 
deeper  parts,  a  thorough  examination  made  to  see  that 
the  pins  and  embrasures  are  clear  of  debris  and  that  the 
plaster  has  not  found  its  way  into  interproximate  spaces 
through  crevices  in  the  wax  model  denture  while  filling  the 


416  FLASKING    WAX    MODEL    DENTURES 

second  section.  Slimild  any  he  pn^sent,  it  is  ])icke(l  ont  with 
a  delicate  instrument,  and  tlie  defective  ])arts  carved  to  cor- 
rect form. 


TOP   VIEW   OF    PnEPAREn    MATIilX    P.EADY    FOR   PACKING 


TOP    VIEW   OF    FIRST    SECTION    OF    FLASK    CONTAINING    CAST 


FLASKING    WAX    MODEL    DENTURES  417 

Auy  delicate  overhanging  margins  of  the  matrix  sliould 
be  trimmed  away  to  prevent  fracture  while  closing  the  packed 
case.  Its  removal  only  slightly  increases  the  bulk  of  excess 
peripheral  vulcanite  subsequently,  while  if  allowed  to  re- 
main, and  fracture  does  occur,  the  broken  pieces  are  liable 
to  become  intermixed  witli  the  rubber.  Tlic  correct  order  of 
procedure  is  to  remove  the  peripheral  overhang  of  the  matrix 
margin  before  washing  out  the  wax,  since  the  latter  step  will 
thus  clear  the  matrix  of  the  cuttings. 

Should  any  teeth  become  dislodged,  they  may  be  ce- 
mented in  place  by  varnishing  those  surfaces  which  rest  in 
the  matrix  with  liquid  silex,  and  returning  them  to  place  un- 
der pressure. 

Should  the  case  have  become  overheated  before  opening 
the  tlask  and  the  wax  melted,  the  order  of  procedure  just  out- 
lined should  be  carried  out.  In  addition  and  at  this  stage 
the  use  of  chloroform  applied  with  tweezers  and  cotton 
pellets  will  remove  some  of  the  superficial  wax. 

TREATMENT   OF   FIRST   SECTION   OF   THE   MOLD 
CONTAINING  THE  CAST 

Since  plaster  when  dry  is  much  more  resistant  to  stress 
than  when  moist,  the  application  of  water  to  the  cast  for  the 
removal  of  adherent  wax  should  be  avoided  if  possible.  When 
rigid  baseplate  material  has  been  employed  and  the  case  is 
not  overheated,  the  cast  is  free  from  wax  on  all  areas  except 
around  the  margins  where  the  ]ieriphery  of  the  baseplate  has 
been  luted  to  it.  A  slight  amount  of  wax  in  this  location  can 
usually  be  removed  by  careful  scraping,  followed  by  wash- 
ing of  the  areas  so  covered  with  chloroform. 

PROVIDING  FOR  THE  ESCAPE   OF   SURPLUS   RUBBER 

Since  no  two  bodies  can  occupy  the  same  space  at  the 
same  time,  some  means  must  be  ]n-ovided  for  the  reception 
of  the  surplus  rubber  during  the  closing  of  the  flask.  When 
no  provision  is  made  for  the  purpose  stated,  and  any  excess 
of  rubber  is  present  in  the  matrix,  then  when  the  two  sections 
of  the  flask  are  brought  together  under  pressure,  compression 
of  some  portioi>  of  the  matrix  will  occur.  The  amount  of 
space  so  formed  will  be  in  direct  lu'oimrtinn  to  the  excess  of 
rubber  retained  within  the  flask. 

To  overcome  danger  of  distortion  of  the  cast  or  matrix, 
a  shallow  depression  extending  from  the  inner  wall  of  the 
flask  inward  to  within  onc-sixteeiith  of  nil   indi   of  the  cast 


418  KLASKINO    WAX    MODEL    DENTURES 

margin  should  be  made  around  the  entire  peripliery  in  the 
first  section  of  the  flask.  Tliis  de]iression  should  not  be  con- 
nected at  any  point  with  the  matrix,  the  idea  being-  to  leave 
a  narrow  line  of  contact  at  the  peripheral  margin  of  the 
denture  between  the  surfaces  of  plaster  in  the  two  sections 
when  the  flask  is  closed. 

This  line  of  contact  retards  the  ready  escape  of  the  rub- 
ber during  the  closing  of  the  flask,  and  subsequently  during 
vulcanization.  Furthermore,  sliould  much  excess  be  present, 
this  peripheral  line  of  contact  being  so  much  more  limited  in 
area  than  the  cast  or  matrix  walls,  will  yield  slightly  and 
l^ermit  the  surplus  to  escape  into  the  groove,  thus  relieving 
undue  pressure  within  the  matrix. 

The  cutting  of  waste  gates  leading  from  the  periphery 
of  the  matrix  to  the  outer  groove  is  unnecessary,  and,  in  fact, 
detrimental,  as  when  ]iresent  they  permit  the  too  ready 
escape  of  surplus  rubber. 

The  groove  having  been  formed,  the  debris  is  brushed 
off  and  this  section  is  set  aside  until  the  matrix  is  packed 
with  rubber. 

STEPS  PREPARATORY  TO   PACKING  THE   MATRIX 

Dental  rubber,  while  more  or  less  plastic  and  adhesive, 
is  not  sufficiently  so  to  be  formed  into  a  homogenous  mass 
as  it  is  introduced  into  the  matrix.  In  adding  one  piece  of 
pink  rubber  to  another,  or  in  introducing  tlie  basic  material, 
spaces  are  liable  to  result  from  the  overlapping  of  one  piece 
on  another.  Unless  these  spaces  are  eliminated  while  pack- 
ing, an  intermixture  of  the  pink  and  basic  rubber  will  often 
occur.  Such  mishaps  alwa^'s  detract  from  the  esthetic  ap- 
pearance of  the  finished  denture. 

There  are  two  methods  in  vogue  for  rendering  the  rub- 
ber more  plastic  preparatory  to  packing,  viz.,  first  heating 
the  rubber  before  introduction,  and  second,  heating  the  mat- 
rix, by  which  means  the  rubber,  although  cold,  is  immediately 
rendered  plastic  when  carried  to  place. 

HEATING   THE   RUBBER   BEFORE   INTRODUCING   IT   IN   THE 
MATRIX 

This  is  usually  accomplished  by  placing  the  pink  aud 
basic  rubber  on  a  plate,  as  it  is  cut  in  pieces  of  suitable  size 
for  packing.  The  plate  is  placed  over  a  pan  of  water  and 
the  latter  heated  over  a  burner.  The  greatest  amount  of  heat 
l)Ossible  to  develop  by  this  method  will  not  exceed  212  degrees 
Fahrenheit,  not  sufficient  1o  injure  the  rubber,  yet  ample  to 


FLrASKlNG    WAX    MODEL    DENTURES  419 

reuder  it  plastic  and  workable.  Tlio  ubjection  to  this  method 
lies  in  the  fact  that  the  rubber,  although  heated,  is  carried 
to  a  cold  matrix  where  it  immediately  becomes  chilled,  and 
is  almost  as  difficult  to  condense  as  though  it  had  not  been 
so  treated. 

HEATING  THE  MATRIX  PREPARATORY  TO  PACKING  THE 
RUBBER 

The  second  and  umch  more  practical  method,  when  one 
becomes  accustomed  to  it,  consists  in  heating  the  matrix  side 
of  the  flask  to  about  212  degrees  Fahrenheit,  or  until  steam 
begins  to  escape  from  the  plaster.  A  matrix  so  heated  will 
usually  retain  sufficient  heat  to  permit  the  rubber  to  be  con- 
densed, but  should  the  packing  of  the  case  prove  tedious,  it 
may  be  re-heated  without  injury  to  the  rubber  already  packed. 

The  advantages  of  this  method  are  twofold,  viz.,  first, 
drying  and  hardening  of  the  plaster  matrix,  rendering  it  more 
resistant  to  stress,  thus  reducing  its  liability  to  distortion  in 
closing  the  flask ;  and  second,  the  absorbed  heat  of  the  matrix 
not  only  softens  the  rubber  as  soon  as  placed,  but  keeps  it 
plastic  so  that  it  may  be  united  into  a  homogeneous  mass  en- 
tirely free  from  spaces,  tlius  obviating  the  danger  of  inter- 
mixture of  the  basic  and  gum  material. 

The  disadvantages  of  this  method  consist  in  danger  ot 
overlieating  the  flask,  thus  injuring  the  plaster,  and  the  ne- 
cessity for  exercise  of  greater  care  in  manipulation  to  avoid 
burning  the  fingers.  In  all  other  respects  this  method  of  ren- 
dering the  rubber  plastic  is  preferable  to  the  former,  and  bj' 
observing  reasonable  care  the  objections  mentioned  can  be 
obviated. 

To  prepare  the  matrix  for  packing  by  the  second  method, 
the  flask  should  1k'  placed  on  a  metal  plate  or  sheet  of  gauze, 
over  a  Bunsen  flame,  and  heat  applied  gradually  so  as  not 
to  disintegrate  the  plaster  in  the  bottom  of  the  flask.  Since 
plaster  is  a  poor  conductor  of  thermal  changes,  the  process 
should  be  continued  a  sufficient  time  to  heat  the  entire  matrix 
throughout.  Care  should  be  taken  not  to  force  the  heat- 
ing too  strongly,  or  the  rapid  accumulation  of  steam  next  the 
bottom  and  walls  of  .the  flask  may  disturb  the  plaster  contents. 
In  the  meantime  while  the  flask  is  heating,  the  rubber  may 
be  prepared  for  packing. 

PREPARING  THE  RUBBER  FOR  PACKING  THE  MATRIX 

A  good-sized  sheet  of  clean  paper  is  laid  on  the  bench; 
the  i^acking  instruments,  a  pair  of  ball  .pointed  pliers,  a  thin- 


420  KLASKIN(!     WAX     .\1()1)I01>     I  JlOXTIIIilOS 

hliidc  liiiniislicr,  ;i   sliiirp  poiiilcd   iiisl  niiiiciil    niid   llic   lieavv 
wax  burnisliiun'  spatula  are  laid  coiivcniciitly  at  hand. 

Tlio  muslin,  (■(tvcrin^-  both  sidos  of  a  slieot  of  granular 
gum  facing  or  jiink  rulibcr,  is  strii)|H'd  liiick  so  as  to  expose 


THIS   CUT  SHOWS   Till     1     si  Nil  \1        1(  I     1    \    1    1  I  111     LEU    AAD  lOllllM     \I1I 

THE    INSTRUMENTS    1111(111111  II     111]     IJll  llll  I       I  RUNf  ULAU  I  11  1  I  s 

OF    PIMv   OB  (  KVMl  \lt       I  \I    Kl  1  1  HI       (  N    rill     ltl<  1 1  1    SI  III      STRIPS   01 

liASK     Runi  1  R       I  (IWl  11  RI(  IIT     \SIMirilI     I       II     I    \sl       RUB 

HI  R  FOR   (IM  RI  \^1N(      lllr    \  \l  IT   I  ORTI<l\    dl'    M  \TRI\ 

from  oue-lialf  to  two-thirds  of  the  sheet.  Eight  or  ten  strips 
three-sixteenths  of  au  inch  wide  are  cut  from  across  the  slieet 
and  allowed  to  fall  on  the  paper,  but  should  not  touch  each 


^^ 


other  because  of  their  tendency  to  adhere.  From  one  or  more 
of  these  strips  are  cut  about  twenty-eight  triangular  pieces 
for  filling  the  embrasures  between  the  teeth.  These  also 
should  be  kept  separate. 


FLASKINCi     WAX    .MODEL    DENTURES  421 

BASIC  RUBBER 

Several  strips  of  the  red,  maroou  or  black  rubber,  which 
is  to  constitute  the  base,  are  cut  and  laid  to  one  side  of  the 
pink.  As  tlie  packing  proceeds,  wider  strips  will  be  required, 
but  they  can  lie  cut  as  needed  and  of  a  width  suitable  to  the 
requirements  of  the  case.  The  rubber  being  cut  as  described, 
and  the  matrix  side  of  the  flask  heated,  the  case  is  now  ready 
for  packing. 

PACKING  THE  MATRIX 

Since  the  outer  matrix  wall  of  a  vulcanite  case,  being 
perpendicular  or  nearly  so,  is  most  difficult  to  adapt  the  rub- 
ber to  and  hold  in  position  until  the  flask  is  finally  closed,  this 
portion  of  the  matrix  is  packed  first  because  more  accessible 
before  the  introduction  of  the  basic  material. 

The  one  essential  point  to  keep  in  mind  during  the  pack- 
ing of  the  rubber  is  to  so  place  it  as  to  avoid  intermixture 
of  the  gum  material  and  the  basic  portion.  The  gum  facing 
must  be  applied  piece  by  piece  and  formed  into  a  solid  homo- 
geneous mass  free  from  spaces.  It  miist  lay  in  close  contact 
with  the  matrix  walls  and  show  no  tendency  to  draw  awaj' 
from  them.  It  must  entirely  fill  the  embrasures  between  the 
teeth  from  the  deepest  portions  represented  by  the  interproxi- 
mate  spaces  in  the  bottom  to  the  extreme  upi^er  periphery  of 
the  matrix.  ', 

PACKING  THE  GUM   FACING 

With  the  sharp  packing  instrument,  or  a  pair  of  ball 
pointed  pliers,  a  triangular  piece  of  granular  gum  or  pink 
rubber  is  carried,  pointed  end  down,  into  the  embrasure  be- 
tween two  teeth,  and  with  a  suitable  thin-bladed  burnisher 
is  forced  into  the  deepest  and  narrowest  portion.  Another 
piece  is  carried  to  the  adjoining  embrasure  and  adapted  in 
a  similar  manner.  The  adjacent  angles  of  the  two  are 
pressed  between  the  matrix  walls  and  the  labial  cervix  of  the 
tooth,  and  if  sutlficiently  long  to  meet,  are  united  together 
by  pressure.  If  too  short,  a  third  piece  can  be  laid  above 
the  cervix  of  the  tooth  and  the  three  united. 

The  other  embrasures  are  similarly  filled,  each  triangular 
piece  of  rubber  as  it  is  added  being  closely  conformed  to  the 
walls  and  its  upper  end  united  with  the  adjoining  piece  al- 
ready placed.  The  embrasures,  interproximate  spaces  and 
the  space  between  the  cervix  of  each  tooth  and  the  matrix 
wall  for  an  eighth  of  an  inch  above  the  teeth  shoiild  be  filled 


•122  KLASKINC    WAX    MODKN    DENTUHKS 

solidly  with  triiiii,i;iilar  pieces  of  gimi,  mikI  all  well  condensed 
so  as  to  eliminate  all  openings. 

A  strip  of  pink  or  granular  facing  rubber  is  now  applied 
against  the  lingual  surfaces  of  the  teeth,  and  pressed  against 
that  which  alread.y  fills  the  embrasures.  Its  lower  margin 
should  not  approach  the  pins  of  the  teeth  closer  than  one- 
sixteenth  of  an  inch,  nor  should  it  ever  enclose  them,  since 
teeth  anchored  in  pink  vulcanite  are  gradually  dislodged  un- 
der stress. 

The  strips  of  rubber,  when  cut  crosswise  of  the  sheet,  are 
not  of  sufficient  length  to  pass  around  the  matrix  wall  from 


<KII     IN     TlIK 


oue  tuberosity  to  the  other;  therefore  to  complete  the  first 
layer,  a  second  strip  is  abutted  or  allowed  to  slightly  overlap 
the  end  of  the  first  piece,  after  which  it  is  adapted  to  the  cor- 
responding unfinished  part  of  the  matrix  above  the  tooth  pins 
on  the  opposite  side.  In  placing  these  and  all  other  strips  of 
the  gum  material,  care  should  be  taken  to  avoid  stretching 
them,  as  the  tendency  of  the  mass  of  gum  facing  to  leave  the 
matrix  wall  is  very  noticeable  if  the  strips  are  stretched  as 
applied. 

Another  stri^D  of  facing  is  placed    above    that    already 
packed,  its  lower  slightly  overlapping  the  upper  margin  of 


PLASKING    WAX    MODEL    DENTURES  423 

the  first.  When  by  pressure — usually  with  the  round  end  of 
the  burnishing  spatula,  slightly  heated — it  is  adapted  to  the 
matrix  wall  and  underlying  rubber,  other  strips  are  added 
and  pressed  to  place  in  like  manner,  one  layer  overlapping 
another,  until  the  entire  wall  of  the  matrix  is  covered.    When 


care  has  been  exercised  in  carving  the  wax  gums  to  correct 
contour,  two  layers  of  pink  rubber  will  furnish  ample  thick- 
ness to  obviate  exposure  of  the  basic  material  on  the  gum 
surfaces  in  the  final  finishing  of  the  case. 

As  a  final  step  in  the  condensation  of  the  gum  portion, 
a  folded  towel  should  be  placed  against  the  outer  surface  of 


A   CONVENIENT  RUBBER   I'ACKINO    INSTIUMENT    (IVORY) 

the  flask  to  protect  the  thumbs  from  the  heated  metal,  and 
finger  pressure  should  be  applied  to  the  rubber  built  against 
the  matrix  wall,  the  force  exerted  being  outward  and  slightly 
downward. 

Some  prosthetists.  before  introducing  the  gum  material, 
paint  the  matrix  wall  with  a  solution  of  pink  chloro-rubber, 
which  serves  to  cement  the  layers  of  gum  material  closely 
to  the  walls.  When  applied  in  a  thin  layer,  and  the  chloro- 
form is  allowed  to  evaporate  before  packing,  it  serves  a  use- 
ful purpose,  but  is  more  often  harmful  than  beneficial,  as  at 
times  it  seems  to  retard  the  hardening  of  the  pink  rubber  in 
vulcanizing.  It  is  also  liable  to  change  the  color  of  the  outer 
surfaces  of  the  gum  facing  to  a  slight  extent. 


■124  PLASKINti    WAX    MODEL    DENTURES 

PACKING  THE  BASIC  RUBBER 

The  entire  outer  wall  of  the  matrix  having  been  packed 
and  condensed  as  described,  the  next  step  is  to  introduce  the 
basic  rubber. 

A  narrow  strip  is  laid  in  tiie  bottom  ot  the  matrix  and 
pressed  under  the  pins  of  the  teeth,  care  being  taken  not  to 
displace  the  gum  facing  which  tills  the  deepest  portions  of 
the  interproximate  spaces.  This  strip  of  basic  material,  al- 
though placed  under  the  pins,  should  lay  to  the  lingual  of  the 
gum  facing. 

A  wider  strip  is  now  laid  over  the  first  one  and  pressed 
solidly  against  it,  so  as  to  eliminate  any  s])aces  that  may  be 


THE    CillM    FACIV 


present.  The  bottom  of  the  matrix  is  filled  in  this  manner 
so  as  to  represent  in  bulk  the  amount  of  wax  and  baseplate 
material  that  formed  the  bulk  of  the  wax  contour  model. 

In  upper  cases  the  palatine  portion  is  covered  with  one, 
sometimes,  though  seldom,  two,  thicknesses  of  rubber  cut  so 
as  to  overlay  this  area  and  extend  on  and  attach  to  that  fill- 
ing the  deeper  part  of  the  matrix. 

A  pattern  can  quickly  be  cut  from  the  muslin  removed 
from  the  sheet  rubber,  and  its  size  tested  by  placing  in  the 
matrix.  When  properly  formed,  it  is  laid  on  the  sheet  of 
rubber,  a  piece  cut  according  to  outline,  the  mu.slin  removed, 
and  the  rubber  i^laced  in  position  and  firmly  condensed  at 


FIvASKING     WAX     MODKL    DKXTUKKS  425 

its  margins  to  that  already  packed  around  and  to  the  lingual 
of  the  pins  in  the  hottom  of  the  matrix.  A  strip  of  basic 
material  wide  enough  to  line  the  gum  portion  of  the  matrix 
is  cut  and  stretched  to  I'educe  its  thickness.     This  is  then  laid 


THE    TINS    KNTIKKl.V    CIlVERKll    WITH     IIA.SIC    IUHHER 


•At'I/T    AREA    CnVERKl)    WITH    A    SINGLE   LAYER   OK    liASIC    ItUHKER 


against  the  gum  facing  and  firmly  pressed  against  it.  This 
lining  of  basic  material  strengthens  the  gum  portion,  and  fur 
ther  insures  the  entire  palatine  and  border  surfaces  of  the 
denture,  being  composed  of  the  same  colored  vulcanite,  a 
point  of  considerable  esthetic  importance. 


t2(i  KLASKINC     WAX     .\l()|)i:i,     lilOXTUKKS 

A  second  layer  ol'  iuIiIxt,  usually  a  strip  about  one-half 
inch  wide  and  long  enougli  to  extend  from  anterior  to  pos- 
terior limits  of  the  matrix,  is  laid  in  the  central  palatine  area, 
to  insui'e   slioht  surplus  in   this   i-egion   on   closing  the  flask. 


MATRIX    PACKKD    liKADY    FOR    CLOSING    THE    FLASK 

When  both  basic  rubber  and  gum  facing  have  been  introduced 
and  thoroughly  condensed,  the  case  is  ready  for  the  final 
steps  preparatory  to  closing  the  flask. 

When  diatoric  teeth  are  used  it  is  necessary,  in  packing 
the  matrix,  to  fill  the  central  depressions  of  the  bicuspids  and 


molars  with  small  pieces  of  basic  rubber.  This  is  an  essential 
part  of  the  packing  process  and  is  necessary  in  order  that  the 
anchorage  spaces  within  the  teeth  for  the  rubber  may  be  per- 
fectly filled  in  the  final  closing  of  the  flask. 


PbASKING    WAX    MODEL    DENTURES  427 

GAUGING  THE  AMOUNT  OF  RUBBER  REQUIRED 

Tlie  amount  of  basic  material  required  is  entirely  de- 
pendent on  the  extent  to  which  absorption  of  the  residual 
ridge  has  progressed.  AVhen  extensive,  more  rubber  will  be 
required  than  when  the  ridge  is  prominent. 

A  simple  method  of  testing  approximately  the  proper 
amount  of  rubber  required  to  till  the  matrix,  is  to  collect  all 
of  the  wax  and  baseplate  material  removed  from  the  matrix, 


WATEK     GAUGE     FOR     DETERMINING     THE 

VOLUME   OF   RUBBER   REQUIRED   TO 

FILL   THE   SL\TRIX 


work  it  up  into  a  solid,  compact  mass  and  test  its  bulk  by 
displacement  of  water  as  follows : 

A  glass  is  filled  to  overflowing  with  cold  water.  Into 
this  the  wax,  held  on  the  point  of  a  small  instrument,  is  im- 
mersed, which,  of  course,  displaces  an  equal  bulk  of  water. 
The  wax  is  then  removed,  the  required  amount  of  gum  fac- 
ing— usually  about  one-half  sheet — is  placed  in  the  glass,  and 
sufiScient  basic  material  is  added  to  again  bring  the  water  to 
the  point  of  overflow  of  the  glass.  A  slight  addition  should 
be  made  to  compensate  for  the  wax  that  adhered  to  the  pins 
and  was  lost  by  washing  the  matrix  with  hot  water. 

Dr.  E.  T.  Starr  suggested  the  use  of  a  glass  vessel  hav- 
ing two  adjustable  pointers  attached  to  a  perpendicular  post 
held  by  means  of  top  and  bottom  bands.  The  top  pointer 
was  set  at  high-water  mark,  as  established  by  the  introduc- 
tion of  the  wax.     The  lower  pointer  was  set  at  low- water 


428  FbASKING    WAX    MODEL    DENTURES 

mark,  determined  by  removal  of  the  wax.  Sufficient  rubber, 
both  facing  and  basic  material,  was  added  to  raise  the  water 
to  the  upper  pointer.  The  use  of  this  appliance  obviated  the 
overflow  of  the  water. 

FLASK  CLOSING 

PRELIMINARY   CONSIDERATIONS   RELATIVE   TO   FLASK 
CLOSING 

Previous  mention  has  been  made  of  the  crystalline  char- 
acter of  plaster,  its  tendency  to  crush  under  pressure  when 
the  modulus  of  resistance  to  stress  of  the  crystals  has  been 
reached,  and  of  its  greater  resistance  to  stress  when  in  a  dry 
condition  than  when  saturated,  or  even  slightly  moistened 
with  water. 

These  facts  are  of  vital  importance  in  vulcanite  denture 
construction,  for  when  disregarded,  distortion  of  the  cast,  of 
the  matrix  side  of  the  flask,  or  of  both,  is  very  liable  to  occur. 
When  so  occurring,  the  result  is  frequently  a  partial  or  total 
loss  of  adaijtation  of  the  denture  to  the  tissues. 

ESTIMATING  THE  FORCE   EXERTED   BY  THE   SCREW 

Few  prosthetists  realize  the  enormous  pressure  capable 
of  being  exerted  on  both  the  cast  face  and  the  opposite  matrix 
walls  when  the  latter  contain  a  considerable  quantity  of  ex- 
cess rubber,  the  flask  being  completely  closed  at  a  rapid  rate 
and  under  direct  screw  pressure.     The  rule  for  estimating 
the  force  exerted  by  a  screw  is  stated  as  follows : 
distance  between 
P  :  W  : :  contiguous  threads  =  ir  X  twice  the  length  of 
lever. 
Explanation 

P  =  power,  indicates  the  amount  of  force  exerted  on 

the  end  of  the  lever  or  wrench  handle. 
W  =  weight,  indicates  the  load  moved  by  the  screw  in 
advancing  through  the  nut  or  the  force  ap- 
plied against  the  excess  rubber. 
Distance  between  contiguous  threads  of  screw  refers  to 

pitch  of  screw. 
IT  =  pi,  is  the  Greek  letter  used  to  indicate  that  num- 
ber— 3.1416 — which,  when  multiplied  by  the 
diameter  of  a  circle  =  the  circumference. 
The  lever  or  wrench  represents  the  radius  of  the  circle 
described  by  the  end  of  the  handle  in  revolving  the  nut  around 


FLASKING    WAX    MODEL    DEXTUKES  429 

the  screw.  To  fiud  the  diameter  of  the  circle,  the  radius  must 
be  doubled. 

Ill  applying  this  rule  to  determine  the  force  exerted  by 
the  flask  screws,  the  principal  factors  concerned  are  as  fol- 
lows: 

First.  The  power  delivered  on  the  end  of  the  wrench 
handle  by  the  hand. 

The  record  of  over  two  hundred  tests  made  by  pros- 
thetists  under  the  writer's  observation,  with  a  specially  de- 


DIAGItAlI    SHOWING    .Mil'    DESC'IilBEI)    ISY   FLASK    WRENCH 

signed  wrench  capable  of  registering  the  pounds  pressure  ap- 
plied, showed  a  range  of  from  15  to  80  pounds  exerted  on  the 
end  of  the  four-inch  handle.  The  low  average  of  the  total  was 
50  pounds. 

Second.  The  ivcight,  or  second  factor,  represents  the 
force  exerted  )jy  the  surplus  rubber  against  the  cast  in  one 
side,  and  the  matrix  walls  and  teeth  in  tlie  opjtosite  side  of  the 
flask,  as  tli(!  screw  jiressure  forces  out  the  excess  material. 
This,  of  course,  is  an  unknown  quantity,  but  is  determined  I'y 
the  rules  of  proportion  in  the  usual  manner. 


430  PLASKING    WAX    MODEL    DENTURES 

Third.  The  distance  between  tivo  continuous  threads 
represents  the  approach  of  the  two  halves  of  the  flask  to  each 
other  in  revolving  the  nut  once  around  by  means  of  the 
wrench.  The  threads  on  the  average  flask  bolts  are  1-20  of 
an  inch  apart,  or,  as  ordinarily  spoken  of,  the  'pitch  of  the 
screw  is  1-20. 

Fourth.  The  fourth  term  of  the  proportion  is  deter- 
mined as  follows:  Multiply  the  length  of  the  wrench  by  2, 
which  gives  the  diameter  of  the  circle,  in  inches,  traversed  by 
its  outer  end.  This  multiplied  by  .3.1 41G  will  give  the  circum- 
ference of  the  circle  in  inches. 

With  three  factors  known,  the  fourth  can  easily  be  found. 
The  following  example  will  serve  to  illustrate  the  enormous 
force  commonly  delivered  against  the  cast  face  in  flask  clos- 
ing: 

Number  of  pounds  applied  to   the  end  of  the 

wrench  handle  -t  inches  long 50 

Force  exerted  against  cast  face  by  excess  rubber 

under  pressure X 

Distance  between  two  contiguous  threads 

1-20  of  an  inch 

Circumference  of  circle  described  bv  end  of 
wrench   3.1416  X  2  X4  =  25  +. 

Formula,  50  :  X  : :  1-20  :  25  -f . 

Multiplying  the  two  extremes  =  1250. 

Dividing  1250  by  1-20  to  determine  the  other 
mean  =25000.' 

Deducting  2-3  for  friction,  gives  8333  pounds  ex- 
erted on  cast  face. 

Accompanying  tests  made  by  tlie  writer  in  a  specially 
designed  compression  dynamometer  revealed  the  fact  that  a 
face  plate  with  one  inch  superficial  area  could  be  forced  from 
1-16  to  l^  inch  into  hardened  and  comparatively  dry  plaster 
at  2,000  pounds  pressure,  and  14  to  %  inch  in  well  hardened 
plaster,  set  four  hours.  It  will  thus  be  seen  that  distortion  of 
both  cast  and  matrix  may  readilj''  occur  under  the  pressure  of 
over  four  tons  as  ordinarily  applied. 

The  only  redemption  from  failure  in  denture  construc- 
tion in  every  case  is  due  to  the  fact  that  the  rubber  is  plastic 
and  does  not  resist  the  force  of  the  screw,  as  would  a  hard, 
unyielding  material.  When  the  closing  of  the  flask  is  forced 
too  rapidly,  however,  with  a  large  amount  of  excess  rubber 
present,  the  effect  is  practically  equivalent  to  that  produced 
with  a  hai'd,  unyielding  material  interi^osed.     This  is  often 


PLASKING    WAX    .MODEL    DENTURES  4ai 

seen  in  fractured  casts  and  distorted  surfaces  in  the  tinal 
opening  of  the  flask. 

Five  pounds  of  power  on  the  end  of  the  wrench  handle 
represents  the  maximum  force  that  should  he  applied  in  flask 
closing.  Even  this  amount,  limited  as  it  is,  yields  a  pressure 
of  over  800  pounds  on  fhr  cast  face. 

TEST  CLOSING  OF  THE  FLASK 

To  insure  a  sufficient  quantity  of  rubber  in  the  matrix 
and  yet  obviate  distortion  of  the  cast  face  and  matrix  walls, 


as  a  result  of  undue  force,  the  following  method  will  be  found 
satisfactory : 

The  matrix  should  contain  very  little  excess  rubber.  The 
proper  amount  ma.v  be  determined  with  comparative  accuracy 
by  means  of  the  water  glass  test  previously  described. 

The  flask  should  be  gradually  raised  in  tempei'ature  to 
212  deg.  F.,  dry  heat,  the  two  halves  brought  together  by 
tightening  the  bolt  nuts  slowly,  being  careful  not  to  exceed 
five  pounds  force  on  the  wrench  handle,  and  when  closed  the 
bolts  are  removed  and  the  flask  separated. 

To  prevent  adhesion  of  the  rubber  to  the  cast  surfaces 
a  square  of  muslin  slightly  larger  than  the  area  of  the  matiix 
should  be  interposed  between  the  two  halves  of  the  flask.  A 
piece  of  the  cloth  removed  from  the  sheet  rubber,  when  freed 
from  the  sizing  or  starch,  will  answer  this  purpose.  On  opening 


432  PLASKfN(i     WAX     AKJDKL    DK.XTURKS 

flu!  closed  lia.sk  the  imislin  can  readily  be  removed  from  the 
condensed  rubber  within  the  matrix  without  distortinj^-  the 
latter  by  moistening  it  with  a  pellet  of  wet  cotton. 

Close  examination  should  be  made  to  see  tbat  the  matrix 
contains  sufficient  rubber,  usually  determined  by  observing  the 
perijijieral  surplus  and  by  ajjplying  i)ressure  interiorly.  If 
delicient.  additional  rubber  should  l)e  placed  wliere  required 
anil  tlie  flaslc  closed  without  relieating. 

TREATMENT   OF  THE   CAST   SURFACES   FOR   VULCANIZATION 

Just  before  tlic  linal  closing  of  the  flask  the  surfaces  of 
the  plaster  cast  should  be  well  saturated  with  liquid  silex,  a 
thick  coating  being  applied  and  allowed  to  remain  undisturbed 
for  two  or  three  minutes,  when  the  surplus  may  be  removed 
with  a  cloth  or  pellets  of  cotton.  This  film  of  silex  penetrates 
the  surface  of  the  plaster  to  a  slight  extent,  fills  the  minute 
openings  between  the  crystals  as  well  as  the  smaller  air 
spaces  and  gives  a  smooth,  hard  finish  to  the  cast.  As  a  result 
the  vulcanite  will  present  a  much  smoother  surface  than  when 
pressed  and  hardened  against  an  untreated  plaster  surface. 

Casts  formed  from  Spence's  plaster,  which  on  account 
of  its  greater  resistance  to  stress  is  preferable  to  plaster, 
should  bo  covered  with  a  layer  of  thin  tin  foil,  usually  No.  4. 
The  foil  is  first  applied  to  the  cast  surfaces  with  the  fingers, 
the  surplus  removed  with  shears  and  final  adaptation  secured 
with  a  soft  napkin  or  pellets  of  cotton  and  pressure. 

When  adapted  the  foil  is  removed,  the  surface  of  the  cast 
is  coated  with  a  film  of  LePage's  glue,  the  foil  returned  to 
place  and  by  pressure  and  burnishing  conformed  closely  to 
all  surfaces  of  the  cast.  Sandarac  or  shellac  varnish  may  also 
be  employed.  Whatever  adhesive  agent  is  used  it  should  be 
applied  in  a  thin  coat  and  allowed  to  become  somewhat  sticky 
before  returning  the  foil  to  the  cast. 

To  aid  in  the  removal  of  the  tin  foil  from  the  vulcanized 
case  the  former  should  be  covered  with  a  film  of  soap,  either 
lather  or  liquid,  the  surplus  being  removed  with  pellets  of 
cotton  and  the  film  allowed  to  dry  before  closing  the  flask. 

In  case  the  tin  foil  cannot  be  readily  stripped  from  the 
denture  after  vulcanization  it  can  be  removed  by  the  applica- 
tion of  mercury,  rubbing  it  into  the  tinned  surfaces  with 
chamois  leather. 

Casts  formed  from  magnesium  oxy-chloride  require  no 
coating  or  preliminary  treatment,  the  surfaces  being  suffi- 


FLASKlXd     WAX     .\U)I)KI>     DK.XTURKS  4S;} 

cieiitly  siiKMitli  1(1  iiii|iart  a  dense  and  jiolislicd  surface  to  the 
vulcauite. 

The  steps  ha\iii,i;-  lieeii  earried  eut  as  deserilied,  tlie  pUis- 
tei'  contents  of  the  tiask  are  now  in  a  eomparatively  dry  and 
hardened  condition,  the  matrix  liUed  ^Yithout  distortion  of 
its  walls  or  the  east  face. 

To  prevent  the  rapid  saturation  of  the  now  dry  piaster 
investment  in  the  flask  during  vulcanization,  the  latter 
should  be  placed  above  the  water  in  the  vulcanizer,  and 
hardened  in  steam  instead  of  under  water,  as  is  the  usual 
method.  ( 'ases  so  manipulated  often  come  from  the  vulcan- 
izer with  the  plaster  almost  as  hard  and  capable  of  resisting 
stress  as  when  first  introduced. 

SCREW  PRESSES 

Screir  -presses  are  frecjuently  employed  for  closing 
flasks.  These  appliances  have  screws  of  different  pitches, 
ranging  from  1-10  to  1-16.  which  with  a   sliort  handle  vield 


DOUBLE    HAXni.E    FI.ASK    CLOSING    riU:SS 


1  HEW    1    12    I'lTCH 


less  force  than  a  screw  of  less  pitch,  as  1-20.  The  handles 
of  most  flask  jiress^s,  however,  are  double,  permitting  the 
use  of  both  hands  in  closing,  so  that  an  equal,  or  gi-eater, 
amount  of  force  can  be  developed  by  means  of  the  press  with 
double  handle  than  with  the  flask  wrench. 

Spring  devices,  as  the  Donham  or  Wilson  flask  presses, 
are  designed  for  maintaining  the  partially  closed  over-packed 


KLASKINC     WAX     MOIJKL    UKNTUKKS 


FbASKING    WAX    MODEL    DENTURES  435 

flask  under  continuous  pressure  until  the  elevation  of  tem- 
perature within  the  vulcanizer  renders  the  rubber  sufficiently 
plastic  to  escape  into  the  space  provided,  without  subjecting 
cast  or  matrix  to  excessive  pressure  or  crushing  strain. 

In  the  vulcanization  of  thick,  bulky  masses  of  rubber, 
spring  closing  devices  are  of  decided  advantage,  for  the  rea- 
son that  when  excessive  expansion  of  the  mass  occurs,  the 
spring  yields,  allowing  the  flask  to  open  slightly,  thus  re- 
lieving the  matrix  walls  and  east  face  from  undue  stress. 
Later  on  when  contraction  sets  in,  the  resiliency  of  the  spring 
will  again  force  the  flask  together. 


C  II  A  PT  K  If     X  XII 

VULCANITE 

In  prostlietie  operations,  ndvaiilzathni  is  ilic  process  1j\' 
wliicli  rubber  as  prepared  for  dental  i)urposes  is  changed 
from  a  plastic  state  to  a  hardened  condition  capable  of  re- 
taining its  molded  form  and  of  resisting  stress. 

Eubber  so  treated  is  termed  vulcanite,  and  the  apparatus 
by  means  of  which  the  i)rocess  is  carried  out  is  called  a  vul- 
canizer. 

In  order  to  have  a  clear  understanding  of  the  process  of 
vulcanization  it  will  be  necessary  to  learn  something  of  the 
origin  and  physical  properties  of  both  crude  and  manufac- 
tured rubber,  and  of  the  chemical  changes  which  occur  dur- 
ing the  liardening  process. 

RUBBER 

Eubber  is  a  colloidal  substance  obtained  by  evaporating 
the  juice  derived  from  various  sjoecies  of  tropical  trees, 
shrubs,  vines  and  creepers.  The  first  importations  of  im- 
portance of  this  material  into  Europe,  in  the  form  of  bags 
and  bottles,  occurred  in  the  early  part  of  the  eighteenth  cen- 
tury, but  its  real  origin  was  apparently  unknown.  From  the 
fact  that  it  was  foiind  very  useful  in  rubbing  out  lead-pencil 
marks  it  was  called  rubber.  The  name  India  was  applied  to 
it  because  the-early  jshipments  came  from  the  West  as  well 
as  the  East  Indies. 

Brantt  states  that  "In  1735  La  Condamine  first  discov- 
ered that  the  substance  was  the  dried  milky  juice  of  a  tree 
which  the  Indians  on  the  coast  of  the  Amazon  River  called 
Caout-Chouc  and  from  which,  from  time  immemorial,  they 
had  been  making  waterproof  fabrics,  shoes,  vessels,  etc." 

CAOUTCHOUC 

It  is  a  long  story — the  history  of  investigation  concern- 
ing the  physical  and  chemical  properties  of  caoutchouc.  More 
than  one  hundred  and  seventy-five  years  have  elapsed  since 
La  Condamine  first  discovered  that  it  was  of  vegetable  origin. 
Many  eminent  chemists  have  devoted  a  great  deal  of  time  to 


VULCANITE  437 

investigating  this  natural  product,  and  yet  to-day  there  are 
some  problems  arising  from  the  necessary  mixture  of  caout- 
chouc with  other  substances  for  commercial  purposes,  but 
partially  solved. 

Carl  0.  Webber,  Ph.  D.,  Crumpsall,  Eng.,  whose  work 
is  perhaps  the  most  logical  and  up-to-date,  in  "The  Chem- 
istry of  India  Rubber"  (1909),  says  in  regard  to  the  diffi- 
culties attending  investigations  of  this  material: 

"No  class  of  bodies  otters  such  formidable  manipulative 
difficulties  to  the  investigating  chemist  as  the  remarkable 
group  of  colloids  comprised  under  the  collective  name  of 
India  rubber.  These  difficulties  are  physical  rather  than 
chemical — that  is  to  say,  they  do  not  so  much  consist  in  the 
functional  complexity  of  the  molecules  of  India  rubber  as  in 
the  circumstance  that  these  molecules  are,  at  any  rate  at  pres- 
ent, known  only  with  the  colloidal  state  superimposed  upon 
them.  Matter  in  this  state  does  not  exhibit  the  abrupt 
changes  of  physical  condition  which,  in  crystalloids,  take  the 
form  of  melting  points,  boiling  points  and  solution.  The 
physical  changes  induced  in  colloids  by  heat,  or  by  solvents, 
are  perfectly  continuous  changes  as  long  as  the  underlying 
chemical  molecule  or  configuration  remains  intact.  As  a 
consequence  the  characterization  and  identification  of  the  col- 
loids and  their  derivatives,  and  their  isolation  and  purifica- 
tion from  mixtures  of  them,  offers  frequently  almost  insuper- 
able difficulties." 

Crude  caoutchouc  as  it  comes  to  market  is  of  varying 
and  uncertain  composition.  A  lot  produced  in  a  given  local- 
ity will  oftentimes  differ  slightly  in  composition  from  another 
lot  from  the  same  species  of  trees  in  a  nearby  localitv. 

The  juice  when  it  first  issues  from  the  tree  is  milklike  in 
appearance  and  is  termed  lafex.  It  consists  of  more  than  50 
per  cent  water.  On  exposure  to  the  air  it  loses  most  of  the 
moisture,  is  reduced  in  bulk,  turns  brown  and  becomes  more 
or  less  elastic. 

The  rubber  gatherer  in  the  native  forests  dips  a  clay- 
covered  paddle  in  the  collected  latex,  gives  it  a  few  turns  and 
subjects  the  adhering  film  to  the  heat  and  smoke  of  an  open 
fire  to  evaporate  the  moisture  rapidly,  repeating  the  process 
many  times  unt^l  a  good  sized  oval  mass,  termed  a  "biscuit," 
is  formed. 

In  this  as  well  as  various  other  crude  methods  of  prepara- 
tion, sand,  dirt  and  other  foreign  matter  become  incorporated, 
while  covering  an  imperfectly  evaporated  layer  with  a  fresh 
one  causes  the  retention  of  excess  moisture. 


r.K  VULCANITE 

Recent  methods  whereby  the  latex,  when  freshly  col- 
lected, is  subjected  to  the  action  of  chemicals  for  the  extrac- 
tion of  nndesirable  constituents,  have  resulted  in  the  produc- 
tion of  rubber  of  a  superior  quality. 

One  formula  for  Para  latex  and  another  for  the  rubber 
after  evaporation  of  the  moisture  are  given  below: 

Latex  Evaporated  Juice 

Water    55.15  Caoutchouc    94.6 

Caoutchouc    41.29  Resin    2.66 

Proteids    •  2.28  Proteids   1.75 

Sugar    0.36  Ash    0.14 

Ash  (Salts)    0.41  Moisture    0.85 

Loss   0.51 


100.00  100.00 

Caoutchouc  of  commerce  is  prepared  for  manufacturing 
purposes  by  first  shredding  it  and  washing  to  remove  the 
contained  soluble  constituents  and  foreign  matter.  It  is  then 
thoroughly  dried  and  passed  through  heated  rolls  to  render 
it  again  homogeneous.  Caoutchouc  prepared  in  this  manner, 
although  comparatively  pure,  is  adaptalile  to  but  few  pur- 
poses because  of  its  tendency  to  stick  to  objects  it  comes  in 
contact  with,  or  when  folded  on  itself.  It  also  deteriorates, 
and  in  time  loses  its  elasticity  and  liecomes  hard. 

The  discovery  of  a  method  of  rendering  soft  rubber  less 
adhesive  and  more  permanent  was  made  by  Charles  Goodyear 
of  Boston  in  1839,  and  Thomas  Hancock  of  England  in  1842, 
Goodyear  iDatented  his  process  in  1843.  While  the  methods 
of  these  men  eliminated  the  stickiness  and  improved  the  qual- 
ity, the  rubber  was  not  hardened  appreciably.  Nelson  Good- 
year discovered  a  process  of  hardening  rubber  in  1849,  which 
process  was,  and  is  still,  termed  vulcanization. 

The  hardening  of  all  varieties  of  rubber  is  rendered  pos- 
sible by  the  addition  of  sulphur.  In  the  actual  process  of 
hardening,  the  rubber  may  be  subjected  to  the  action  of  heat 
and  usually  moisture,  in  a  specially  designed  boiler  termed 
a  vulcanizer.  "Thin  articles  may  be  vulcanized  cold  by  dipping 
them  in  a  cold  mixture  of  100  parts  carbon  disulphide  and 
2V2  parts  of  bichloride  of  sulphur  for  from  IV^  to  3  minutes, 
according  to  the  thickness  of  the  articles."  (Braunt.) 

The  first  experiments  with  rubber  in  denture  construction 
were  made  by  Mr.  Bevan  of  the  Goodyear  Rubber  Company, 
in  conjunction  with  Dr.  Putnam  of  New  York,  and  Dr.  Mal- 
lett  of  New  Haven  in  1853.  Their  vulcanizer  weighed  1,200 
pounds.     (Harris,  1871.) 


VUIA'ANITE  431) 

FORMULAS  FOR  DENTAL  RUBBERS 

The  following  formiilae  for  various  colored  rubbers  used 
for  dental  purposes  are  those  furnished  by  Dr.  Wildman: 

Dark  Dark  Grayish  Jet     Ma- 

Brown    Red    Pink  White  Black  Black    roon 

Caoutchouc    48        48        48        48        48        48        48 

Sulphur    24         24        24        24        24         24         24 

Vermilion  36         10         30 

White    Oxide    of 

Zinc 30        96         

Ivory    or    Drop 
Black 24        48  6 

Per  cent  of  Caout- 
chouc in  mass. .  66         44        43      22.6         50        40        44 
Various  shades  of  red  and  pink  rubber  are  produced  by 
modifying-  the  percentage  of  vermilion;  maroon,  by  increas- 
ing or  decreasing  the  black  pigment. 

VULCANIZABLE  RUBBER  EMPLOYED  FOR  DENTURE 
BASES 

Red,  maroon  and  black  varieties  of  rubber  of  the  best 
quality,  in  addition  to  sulphur,  contain  a  comparatively  small 
percentage  of  inert  material  usually  represented  by  the  col- 
oring pigments  employed.  Because  of  their  greater  strength 
and  elasticity,  the  better  grades  of  rubber  should,  as  a  rule, 
be  employed  for  baseplate  purposes. 

Cheap  grades  of  basic  rubber  are  heavilj-  loaded  with 
foreign  material  to  reduce  the  cost.  When  present  in  any 
considerable  quantity  they  reduce  the  elasticity  of  the  finished 
product  and  render  it  brittle  as  well. 

The  cheaper  grades  of  rubber,  however,  show  less  tend- 
ency to  become  porous  in  vulcanizing  than  do  the  better 
grades  because  of  the  comparatively  low  percentage  of  caout- 
chouc present,  grayish  white  in  the  table  of  formulas,  show- 
ing only  22  per  cent  of  rubber. 

PINK   RUBBER  EMPLOYED   FOR   GUM   FACING 

Since  the  "oasis  of  all  vulcanized  rubbers  is  a  combination 
of  sulphur  and  caoutchouc,  and  the  color  of  this  mixture  is 
brown,  it  follows  that  in  order  to  produce  a  pink  the  base 
must  be  lightened  by  the  addition  of  a  white  pigment.  Wliite 
oxid  of  zinc,  and  sometimes  kaolin  are  used  for  this  purpose, 
to  which  vermilion  is  usually  added  for  producing  a  pink 


440  VUIA'ANITIO 

tint.  Varying  shades  of  this  color  may  be  produced  l)\'  modi- 
fying the  proportions  of  tlie  pigments.  The  best  products, 
however,  are  but  poor  imitations  of  the  natural  gum  tissues, 
being  dense,  opaque  and  flat. 

In  full  cases  where  the  gum  tissues  are  not  visible  the 
dissimilai'ity  is  not  so  striking  as  in  partial  cases  where  the 
natural  gums  are  exposed  to  view.  When  possible  to  avoid 
it,  pink  vulcanite  should  not  be  a]3plied  when  the  line  of  junc- 
tion of  the  artificial  gum  with  the  natural  tissues  will  be 
plainly  apparent. 

To  overcome  the  objection  of  the  fiat,  lifeless  appearance 
of  pink  vulcanite,  various  substitutes  have  been  offered,  one 
of  the  most  satisfactory  of  which  is  that  known  as  Granular 
Gum  Facing. 

PINK  GRANULAR   GUM  FACING 

This  gum  facing  consists  of  many  minute  particles  of 
various  colored  rubbers,  pink,  white,  red  and  possibly  a  little 
yellow,  the  pink  largeh^  predominating,  so  united  as  to  form 
a  homogeneous  mass,  yet  not  so  blended  that  the  particles 
lose  their  individual  tints. 

As  prepared  for  use  it  is  lighter  than  the  natural  tissues 
but  darkens  slightly  during  vulcanization.  Although  opaque 
it  does  not  appear  as  flat  as  the  ordinary  pink  vulcanite,  on 
account  of  the  variegated  colors  of  which  it  is  composed. 

When  this  material  is  used  for  artificial  giim  facing,  the 
carving  and  polishing  having  been  properly  accomplished,  it 
presents  the  very  best  appearance  of  any  of  the  pink  varieties 
of  vulcanite  and  should  be  used  in  preference  to  the  latter. 

If  on  vulcanizing  it  presents  a  darker  appearance  than 
desired,  it  may  be  lightened  or  solarized  by  placing  in  a  glass 
vessel,  covei'ing  with  alcohol  and  bleaching  in  the  sun  for  one- 
half  to  three-fourths  of  an  hour.  Pink  viilcanite  can  also  be 
lightened  in  the  same  manner.  The  tint  so  imparted  will  in 
time  disappear,  but  the  favorable  impression  produced  on  the 
mind  of  the  patient  is  well  worth  the  time  expended. 

THE  CHEMICAL  CONSTITUENTS  OF  RUBBER 

Caoutchouc  is  classed  as  a  colloidal  hydrocarbon.  When 
subjected  to  the  action  of  the  best-known  solvents  the  greater 
portion,  about  ninety-five  per  cent,  is  brought  into  solution, 
while  about  five  per  cent  remains  insoluble.  The  chemical 
formula  of  the  soluble  portion  is  CoHie,  while  that  of  the  in- 
soluble constituent  is  C3oH„„Oin.  The  percentage  of  carbon 
and  hydrogen  in  the  insoluble  portion  is  the  same  as  in  the 


VULCANITE  441 

soluble   portion,   as   is   seen   in  the   following:      C3oHgsOio= 

(C,oHio)a  +  10H,O. 

Webber,  whose  researches  in  this  field  are  perhaps  the 
most  elaborate  of  any,  refers  to  the  insoluble  constituent  of 
rubber  as  follows: 

"In  brief  I  suggest  that  this  insoluble  compound  is  a  link 
between  India  rubber  and  the  complex  carbohydrates,  the 
celluloses  in  particular,  which  I  am  inclined  to  consider  the 
raw  material  from  which  the  plant  produces  all  the  terpenes, 
including  India  rubber." 

There  is,  on  the  other  hand,  no  doubt  that  India  rubber 
absorbs  oxygen  when  exposed  to  the  atmosphere,  and  this 
oxygen  absorption  finally  always  results  in  the  conversion 
of  the  India  rubber  into  a  brittle  resinous  body,  generally 
described  as  Spiller's  resin.    Spiller  has  published  an  analysis 
of  this  bodv  and  gives  the  following  figures : 
C— 64 
H—  8.46 
0—27.54 

"It  is  interesting  to  note  that  these  figures  very  exactly 
agree  with  the  composition  of  a  body  of  the  for- 
mula GinHisOio,  the  relation  of  which  to  our  insolu- 
ble constituent,  CaoHssOio,  is  obviously  significant.  Equal- 
ly interesting  to  observe  is  the  fact  immediately  de- 
ducible  from  the  above  given  percentage  composition 
of  Spiller's  resin,  that  this  oxidation  of  India  rubber  consists 
purely  and  simply  in  the  addition  of  oxygen  to  the  unsatur- 
ated India  rubber  molecule,  and  that  consequently  the  car- 
bon-hydrogen ratio  of  India  rubber — 10:16 — remains  un- 
affected in  this  process. "  *  *  *  "  From  this  we  maj^  infer 
that  the  oxygen  percentage  of  India  rubber  in  its  free  resin 
state  of  purity  is  due  to  two  factors,  one  of  which  is  the 
presence  of  the  insoluble  constituent,  CsoHcsOu,,  the  other  to 
the  formation  of  oxygen  addition  products  of  India  rubber." 

He  further  states  that  the  insoluble  constituent  does  not 
seem  to  be  present  in  all  varieties  of  rulilier,  and  when  present 
it  occurs  in  very  small  quantities. 

CHEMISTRY  OF  VULCANIZATION 

Webber  further  sums  up  the  observations  and  results  of 
many  experiments  in  the  vulcanization  of  rubber  as  follows : 

"From  these  facts  we  are  justified  in  drawing  the  fol- 
lowing conclusions: 

"First — The  India-rubber  hydrocarbon,  polyprene  CioH,,, 
combines  with   sulphur  without   evolution   of  hydrogen   sul- 


442  VULCANITE 

])lii(l('.  The  vulcanization  jn'occss  of  India  rubber  is,  there- 
fore, an  addition  process. 

"Second — The  insoluble  constituent  of  India  rubber, 
which  forms  only  an  insignificant  jDroportion  of  the  chemical 
])roduct,  not  exceeding  five  per  cent  of  the  total,  combines 
with  sulphur  under  vulcanizing  conditions  at  a  very  slow  rate, 
with  the  evolution  of  hydrogen  sulphide  and  with  the  forma- 
tion of  a  substitution  product. 

"The  process  of  vulcanization  consists  in  the  formation 
of  a  continuous  series  of  addition  products — of  polyprene 
and  sulphur,  with  probably  a  polyprene  sulphide  CiooHic„S  as 
the  lower  and  CmdHie^jSoi.  as  the  upper  limit  of  series.  Phys- 
ically this  series  is  characterized  by  the  decrease  in  distensi- 
bility,  and  increase  in  rigidity  from  the  lower  to  the  upper 
limit.  Which  term  of  the  above  series,  i.  e.,  which  degree  of 
vulcanization,  is  produced  is  in  every  case  only  a  function  of 
temperature,  time,  and  proportion  of  sulphur  present." 

"There  arises  now,  of  course,  at  once  the  question  as  to 
the  nature  of  the  process  by  which  siilphur  enters  into  com- 
bination with  the  polj^orene,  whether  the  polyprene  sulphide 
or  sulphides  formed  are  addition  or  substitution  products. 
Certainly  what  we  already  know  respecting  the  chemical  na- 
ture of  India  rubber  leads  us  to  infer  that  the  vulcanization 
in'ocess  consists  essentially  in  the  formation  of  an  addition 
])roduct  of  sulphur  and  polyprene.  This  assumption,  how- 
ever, requires  further  support  in  view  of  the  fact  that  quite 
a  number  of  writers,  from  Payen  to  most  of  the  recent  authors, 
declare  tliat  vulcanization  is  accompanied  by  the  evolution  of 
sulphuretted  hydrogen,  thereby  implying  that  the  process  is 
a  substitution  and  not  an  addition  process.  Indeed,  most  of 
the  recent  authors  on  this  subject  state  this  in  so  many  words. 
We  shall  therefore  have  to  subject  this  point  to  a  careful 
examination. 

"Assuming  the  compound  of  polyprene  and  sulphur, 
which  indisputably  forms  in  the  vulcanization  process,  to  be 
a  substitution  product,  it  follows  with  absolute  necessity  that 
for  each  32  parts  of  sulphur  combining  with  the  polyprene  we 
must  obtain  34  parts  of  hydrogen  sulphide.  Now  in  the  proc- 
ess of  vulcanization  as  practically  carried  out,  we  obtain  on 
an  average,  say,  2.5  per  cent  of  combined  sulphur.  Conse- 
quently, the  vulcanization  of  one  ton  of  India  rubber,  on  the 
above  assumption,  would  be  bound  to  yield  very  nearly  60 
pounds  of  hydrogen  sulphide,  or  approximately  18,000  litres. 
Considering  that  in  a  number  of  factories  the  amount  of  India 


VULCANITE  448 

rubber  vulcanized  daily  largely  exceeds  one  ton  weight,  we 
should  expect  to  iiud  the  vulcanizing  rooms  of  these  factories 
reeking  with  this  gas.  As  a  matter  of  fact,  however,  there  is 
scarcely  ever  a  trace  of  this  gas  to  be  discovered  in  the  rub- 
ber works  atmosphere,  and  the  very  rare  cases  in  which  its 
presence  becomes  noticeable  may  always  be  considered  as  an 
indication  of  something  'having  gone  wrong.'  " 

Webber 's  work  may  be  briefly  summed  up  as  follows : 

That  the  hardening  of  rubber  by  vulcanization  is  brought 
about  by  a  chemical  union  of  CioHie  or  polyprene  with  sul- 
phur, resulting  in  the  formation  of  a  series  of  polyprene  sul- 
phides, not  bj^  the  breaking  up  of  the  CioHio  molecules,  but 
by  the  addition  to  them  of  sulphur;  that  the  formation  of 
hydrogen  sulphide  during  the  process  of  vulcanization  is  not 
an  essential  chemical  reaction,  necessary  to  the  hardening 
of  rubber;  that  when  formed  it  is  due  to  the  presence  of  the 
insoluble  constituent — CsoHcsOjo — in  the  rubber;  that  when 
the  process  of  vulcanization  is  properly  conducted,  such  slight 
amount  of  hydrogen  sulphide  as  is  formed  does  not  seriously 
interfere  with  the  quality  of  the  hardened  product;  and, 
finall}',  that  when  hydrogen  sulphide  is  formed  in  excessive 
quantity  it  is  an  indication  that  something  "has  gone  wrong," 
and  the  quality  of  the  vulcanite  is  impaired. 

While  Webber's  observations  seem  generally  logical, 
there  are  some  peculiarities  occurring  in  the  vulcanization  of 
certain  classes  of  cases  that  require  further  study.  For  ex- 
ample, thick  cases  in  which  there  is  a  large  bulk  of  rubber 
present,  frequently  come  from  the  vulcanizer  in  a  porous  con- 
dition and  with  a  strong  odor  of  hydrogen  sulphide,  an  indi- 
cation of  something  having  gone  wrong.  The  same  grade  of 
rubber  may  be  employed  in  thin  or  even  medium  thick  cases, 
vulcanized  under  the  same  conditions  of  temperature,  time, 
and  moisture,  or  at  the  same  time  in  the  same  apparatus,  yet 
show  no  porosity,  nor  will  the  odor  of  hydrogen  sulphide 
be  perceptible. 

The  cause  of  this  is  not  clear.  If  Webber's  observations 
are  correct  that  the  development  of  hydrogen  sulphide  is  due 
to  the  presence  of -the  insoluble  constituent  in  the  rubber,,  and 
the  same  grade  of  rubber  is  used  in  both  cases,  why  should 
not  the  case  containing  less  bulk  show  at  least  a  proportion- 
ate amount  of  porosity,  accompanied  by  an  appreciable 
amount  of  hydrogen  sulphide? 

Two  hundred  blocks  of  vulcanite,  %x%x%  inches,  in  all 


144  VULCANITE 

oi'  wliicli  iiiartically  the  .same  grade  of  rubber  was  used,  when 
sawed  throTigh  the  center,  sliowed  tlie  following  results: 

125  blocks,  very  ]Joroias. 
25  blocks,  slightly  porous. 
50  blocks,  non-porous. 

These  cases  were  all  vulcanized  in  the  same  apparatus, 
and  under  as  nearly  the  same  conditions  of  time  and  tem- 
perature as  possible,  yet  seventy-five  per  cent  were  porous, 
while  twenty-five  per  cent  were  solid.  The  most  porous  blocks 
were  bulged  out  slightly,  while  some  of  the  semi-i^orous  and 
all  of  the  solid  blocks  showed  some  contraction.  The  above 
tests  were  made  for  the  purpose  of  illustrating  the  variation 
in  liorosity  of  the  dilTerent  blocks  and  were  not  tested  for 
dimensional  change. 

Wilson  suggests  that  the  expansion  of  the  rubber  in  the 
matrix,  which  occurs  before  and  possibly  continues  for  a 
short  time  after  the  vulcanization  point  is  reached,  depletes 
the  matrix  of  some  of  the  solid  material.  This  having  escaped 
beyond  the  bounds  of  the  matrix  cannot  return  when  con- 
traction later  occurs,  being  prevented  from  doing  so,  first,  by 
the  natural  sluggishness  of  the  rubber,  and,  second,  because 
as  soon  as  vulcanization  sets  in  the  rubber  next  the  outer  sur- 
faces of  the  matrix  forms  a  constantly  hardening  crust,  which 
effectually  prevents  its  return,  and,  third,  the  surplus  itself 
being  usually  disposed  in  thin  layers  is  quickly  hardened  by 
the  vulcanizing  process. 

Now,  as  vulcanization  proceeds,  the  interior  of  the  bulky 
mass  not  yet  hardened  continually  contracts,  usually  toward 
the  hardened  outer  shell,  resulting  in  the  development  of  many 
internal  spherical  spaces,  the  formation  of  a  partial  vacuum, 
and  on  account  of  the  heat  attained,  the  hydro-carbon  may 
be  decomposed  and  unite  with  the  sulphur  to  form  sufficient 
HoS  gas  to  fill  the  space. 

Whatever  the  cause,  the  fact  remains  that  porous  condi- 
tions frequently  develop  during  vulcanization,  oftentimes  to 
such  an  extent  as  to  require  reconstruction  of  the  denture. 

POROSITY  OF  VULCANITE  AND  HOW  TO  OVERCOME  IT 

Any  means,  therefore,  that  can  be  employed  for  reducing 
the  excessive  bulk  of  rubber  without  materially  increasing  the 
weight  or  disturbing  the  required  contour  of  the  case  might 
be  advantageously  used  for  overcoming  porosity. 


VUIA'ANITB  44G 

Several  methods,  haviiis;-  tliis  end  in  view,  will  here  he 
mentioned : 

Firf:f — The  haseplate  itself  may  be  formed  in  wax  so  as 
to  represent  one-half  or  more  of  the  required  bulk  of  the  fin- 
ished denture.  This  may  then  be  vulcanized,  after  which  the 
teeth  are  occluded  upon  it,  the  deficient  contour  developed  in 
was  and  the  case  revulcanized. 

This  method  is  specially  applicable  to  lower  cases  where 
the  alveolar  border  is  almost  completely  absorbed  and  where 
the  establishment  of  normal  profile  and  bite  requires  that  the 
teeth  shall  be  set  high  above  the  border  crest.  It  may  also  be 
used  to  advantage  in  badly  absorbed  ridges  in  upper  cases. 
While  this  method  does  not  reduce  the  bulk  of  rubber,  the 
process  of  vulcanization  is  divided  into  two  stages,  which  in 
practically  every  case  will  avert  porosity. 

Second — When  for  any  reason  the  double  vulcanization 
method  is  not  considered  advisable,  these  and  similar  cases 
may  be  carried  out  as  follows : 

The  wax  model  denture  is  flasked  in  the  usual  manner. 
Pink  gum  facing  is  applied  to  the  labial  and  buccal  walls  of 
the  matrix.  Tlie  lingual  wall  of  the  matrix  is  lined  with  basic 
material  which  sliould  be  carefully  applied  so  as  to  leave  no 
open  spaces  in  the  lining.  This  leaves  the  central  portion  or 
body  of  the  matrix  still  unfilled.  Into  this  space  blocks  of  old 
vulcanite,  cut  in  such  manner  as  to  fit  into  the  opening  with- 
out disturbing  the  packed  rubber,  are  placed.  The  blocks 
should  not  extend  so  high  as  to  interfere  with  the  alveolar 
ridge  of  the  cast  when  the  two  halves  of  the  flask  are  closed. 

Additional  basic  rubber  is  now  laid  over  the  blocks,  ex- 
tending from  the  inner  to  outer  periphery  of  the  matrix,  thus 
entirely  covering  or  sealing  them  in,  so  that  none  of  the  old 
rubber  will  be  exposed  to  view  when  the  case  is  finally  fin- 
ished. Sufficient  excess  should  be  present  to  insure  all  spaces 
between  the  blocks  and  matrix  walls  being  filled  on  closure 
of  the  flask. 

Third — Blocks  of  aluminum  or  tin  may  be  employed  in- 
stead of  vulcanite,  the  technic  of  application  being  similar  to 
that  just  described.-  When  a  considerable  space  is  to  be  filled, 
aluminum  is  preferable  to  the  tin  on  account  of  its  lighter 
specific  gravity.  When  either  of  these  or  similar  metals  are 
inclosed,  the  weight  of  the  denture  will  increase. 

Fourth — The  interior  of  the  matrix  may  be  filled  in  with 
pink  or  white  rubber,  each  of  which  is  heavily  loaded  with 


446  VULCANITIO 

iiiorl  I'oreii;.'!!  inalciial,  as  tlic  oxide  ui'  zinc  or  white  kaoliu. 
These  rubbers,  even  in  excessive  bulk,  seldom  ever  become 
porous  in  vulcanization. 

CLOSING  FLASKS  WITH  SPRING  PRESSURE 

To  compensate,  in  part  at  least,  for  the  excessive  con- 
traction which  occurs  iu  bulky  cases  during  vulcanization,  the 
closing  of  the  flask  with  spring  pressure  is  advised. 

The  matrix  is  ]jacked  in  the  usual  manner,  slightly  in 
excess  of  the  amount  actually  required  to  fill  the  space.  The 
flask  is  set  in  a  spring  press  of  the  Wilson  or  Donham  type, 
and  the  screw  turned  to  develop  sufficient  tension  in  the  spring 
to  force  the  flask  together,  as  the  rubber  becomes  semi-liquid 
with  rise  of  temperature. 

Since  closure  of  the  flask  is  not  accomplished  immedi- 
ately but  is  extended  over  a  considerable  period  of  time,  in 


FI,ASK    WITH    BOI-T    SPRINGS    IX    TOSITION 


many  cases  not  until  the  hardening  process  begins,  it  is  argued 
that  the  expansion  in  the  mass  of  rubber,  due  to  heating,  is 
over  before  all  of  the  excess  is  removed  from  the  matrix. 
Space  is  thus  provided  for  some  of  the  last  excess  by  the  eon- 
traction  of  the  mass  of  rubber  which  begins  with  the  harden- 
ing process. 

Stated  differently,  some  of  the  excess  rubber  is  thus  fed 
into  the  constantly  contracting  mass  until  the  hardening  proc- 
ess is  well  under  way.  The  resulting  vulcanite  shows  greater 
density  with  less  contraction  than  when  the  flask  is  completely 
closed  before  introduction  into  the  vulcanizer. 

All  forms  of  spring-flask  closing  devices  are  designed, 
primarily,  to  partially  compensate  for  excessive  contraction  in 
the  mass  of  rubber  by  prolonging  the  closing  process  through- 
out the  greater  portion  of  the  contractile  period.  Second- 
arily, the  use  of  springs  obviates  excessive  stress  on  the 
matrix  walls  and  thus  reduces  the  tendency  toward  distortion. 


VULCANITE  447 

Dr.  Geo.  B.  Snow  suggests  the  use  of  small  spiral  springs 
interposed  between  the  nuts  and  flask  top.  When  applied,  the 
flask  need  not  be  fully  closed,  but  the  springs  must  be  com- 
pressed so  that  as  the  rubber  becomes  plastic  with  rise  in  tem- 
perature, the  resiliency  in  the  springs  will  effect  complete 
closure. 

DIMENSIONAL  CHANGES  OCCURRING  IN  RUBBER  DUR- 
ING VULCANIZATION 

EXPANSION 

Two  distinct  changes  occur  in  rubber  during  the  vulcan- 
izing process,  viz.,  tirst,  expansion,  followed  by  contraction. 

The  expansive  movement,  which  is  very  decided,  begins 
with  the  first  application  of  heat  and  continues  until  shortly 
after  the  hardening  process  sets  in.  The  lowest  point  at 
which  rubber  begins  to  vulcanize  or  harden  is  approximately 
around  240  degs.  F.,  while  the  highest  point  at  which  it  may 
safely  be  conducted,  without  causing  detrimental  chemical 
change,  is  320  degs.  F. 

During  the  initial  heating  of  a  ]iacked  and  closed  flask, 
up  to  the  lowest  point  of  vulcanization,  the  matrix  having  been 
full  and  waste  gates  formed  as  described,  the  rubber  flows 
outward  into  the  spaces  so  provided  as  a  result  of  expansion 
due  to  rise  in  temperature  of  the  mass. 

In  case  no  waste  gates  are  jn-esent  and  the  flask,  fully 
packed,  is  closed  before  introducing  into  the  vulcanizer,  dis- 
tortion of  the  matrix  will  usually  occur,  the  amount  depending, 
first,  upon  the  excess  of  rubber  present,  and  second,  upon  the 
tendency  of  the  matrix  walls  to  yield  under  stress  or  com- 
pressive force,  and  third,  upon  the  temperature  of  the  applied 
heat. 

That  the  ex])ansive  force  of  rubber  is  very  positive  and 
powerful  as  well  is  frequently  seen  in  the  distortion  of  matrix 
walls  and  cast  surfaces,  which  distortion  if  wrought  directly 
would  require  the  application  of  heavy  mechanical  force. 

CONTRACTION  OF  RUBBER 

The  contractile  movement  sets  in  shortly  after  the  rub- 
ber begins  to  harden  and  continues  throughout  the  vulcanizing 
process  in  a  moderately  definite  ratio,  the  amount  depending 
upon  the  functions  of  time   and  tem])erature  of  applied  heat. 

Since  no  appreciable  amount  of  excess  rubber,  which  from 
anj'  cause  has  been  expelled,  can  return  to  the  matrix,  it  natu- 


44S  VULCANITE 

rally  follows  that  as  contraction  of  the  essential  body  of  ma- 
terial occurs,  there  being  no  means  of  replenishing  it  as  it 
becomes  reduced  in  bulk,  warpage  of  the  baseplate  is  very 
liable  to  occur  since  the  mass  no  longer  completely  fills  the 
matrix  space. 

At  times  contraction  of  the  rubber  is  so  marked  that 
spaces  develop  between  the  vulcanite  and  the  teeth,  while 
that  enclosing  tlie  pins  contracts  in  such  manner  as  to  almost 
release  the  latter.  When  such  a  condition  arises  the  teeth  will 
frequently  he  found   loose,   can   rc^adily   be  moved    in    their 


THIS  CUT  SHOWS  A  FLASK  FORCED  AND 
HELD  APART  ONE-EIOHTH  INCH  BY  THE  EX- 
PANSION  OP  RUBBER  DURIXC  VULCANIZA- 
TION. THE  SPRING  EXERTED  A  PRESSURE 
OF   OVER    500   LBS. 

matrices,  and  will  be  easily  displaced  under  stress.  When  the 
denture  is  subjected  to  use,  the  spaces  become  filled  with  food, 
which,  as  it  decomposes,  gives  rise  to  disagreeable  odors. 
Cases  in  which  marked  contraction  occurs  usually  require  re- 
construction. 

VULCANIZERS 

The  apparatus  in  which  the  flasks  containing  the  packed 
rubber  are  placed  while  hardening  is  called  a  vulcanizer.  It 
consists  of  a  l)oiler  usually  large  enough  to  hold  two  or  three 
flasks,  and  is  commonl>-  made  of  seamless  hammered  copjier, 
the  walls  of  which  are  about  one-eighth  of  an  incli  tliick. 


VULCANITE  449 

The  top  margin  of  the  boiler  is  turned  true  and  polished 
and  to  this  a  cap  or  cover  is  fitted  for  confining  the  steam. 
The  cap  is  usually  grooved  to  receive  a  packing  of  graphite, 
steam-proof  fiber  or  metallic  lead,  to  seal  the  boiler  tightly 
and  prevent  the  escape  of  steam  during  vulcanization. 

Various  method.s  are  employed  for  fastening  the  top  to 
the  boiler,  the  most  convenient  of  which  is  by  means  of  a  cross- 
bar hinged  to  one  side  of  the  boiler.  When  the  cover  is  ad 
justed,  the  bar  rests  upon  it  and  is  bolted  to  the  opposite  side 
with  a  single  bolt. 

As  before  stated,  the  boiler  is  usually  made  of  hammered 
or  pressed  copper,  without  brazed  or  soldered  joints,  so  as 
to  resist  the  expansive  force  of  steam  to  which  it  is  subjected 
during  vulcanization.  Cast  boilers  of  copper,  brass  or  iron, 
unless  made  specially  heavy,  are  liable  to  prove  defective  and 
leak  or  burst  with  use.  Explosions  are  by  no  means  rare,  and 
such  accidents  are  always  dangerous.  Every  precaution, 
therefore,  should  be  taken  to  obviate  them,  first,  in  the  selec- 
tion and  use  of  the  most  trustworthy  and  well-constructed 
appliance  it  is  possible  to  secure,  and  second,  in  bestowing  the 
proper  care  upon  it  while  in  use. 

SAFETY  DEVICES 

To  tlie  lid  of  the  vulcanizer  is  usually  attached  various 
devices  for  registering  temperature  or  indicating  pressure 
within  the  appliance,  those  most  commonly  employed  being 
the  thermometer  and  the  steam  gauge. 

THE  THERMOMETER 

An  attached  thermometer  enclosed  within  a  metal  case 
indicates  the  temperature.  The  base  of  the  thermometer  case 
screws  over  a  projection  on  the  vulcanizer  cover. 

The  center  of  the  projection  is  bored  out  to  make  a  reser- 
voir for  containing  mercury.  In  this  mercury  bath  the  ther- 
mometer bulb  rests  and  by  tliis  means  the  thermometer  has 
a  direct  metallic  connection  with  the  interior  of  the  vulcanizer 
through  the  mercury  and  the  metal  cover.  The  metal  casing 
of  the  thermometer  -should  be  removed  from  the  vulcanizer 
cap  from  time  to  ■+ime  to  see  that  the  depression  contains  the 
required  quantity  of  mercury,  i.  e.,  sufficient  to  surround  the 
thermometer  bulb.  When  the  bulb  does  not  rest  in  the  mer- 
cury bath  the  temperature  reading  will  be  much  lower  than 
the  temperature  of  the  steam  within  the  vulcanizer.    The  re 


■150  VULCANITE 

suit  in  such  cases  is  that  if  the  temperature  is  raised  to  the 
vulcanizing  point  as  indicated  by  the  thermometer,  the  con- 
tents of  the  flask  will  in  all  probability  be  ruined  by  overheat- 
ing. Deficient  mercury  in  the  depression  oftentimes  accounts 
for  the  safety  valve  of  the  vulcanizer  blowing  off  before  the 
thermometer  registers  the  vulcanization  point. 

THE  STEAM  GAUGE 

Since  a  definite  ratio  exists  between  steam  pressure  and 
temperature,  a  steam  gauge  of  ordinary  type  and  connected 
to  the  vulcanizer  cover  in  the  usual  way  may  be  used  in  con- 
junction with  or  independent  of  other  registering  devices. 

TABLE  OF  STEAM  PRESSURE 

The  following  table,  showing  the  relation  of  temperature 
to  pressure  of  heated  or  unconfined,  and  superheated  or  con- 
fined steam,  is  furnished  by  the  Buffalo  Dental  Manufactur- 
ing Co.: 

Degrees  Steam  pressure 

Fahrenheit  per  square  inch 

212  0 

220 2 

230  6 

240   10 

250  15 

260  21 

270   27 

280   34 

290  43 

300   52 

310  63 

320  75 

330   89 

340   104 

350   120 

360   140 

370   160 

380   180 

390   205 

400  234 

410   264 

420  296 

430   335 


VULCANITE  451 

Degrees  Steam  pressure 

Fahrenheit  per  square  inch 

440  375 

450  410 

460  455 

470  515 

480  565 

490  603 

500  663 

510  721 

520  798 

530  864 

540  937 

550  1015 

It  will  be  noted  that  the  elastic  force  of  steam  increases  at 
a  rapid  rate  and  not  in  direct  proportion  to  rise  of  tempera- 
ture.   For  example: 

At  220°  F.  the  pressure  is      2  lbs.    By  steps  of  50  degrees  the 
increase  is  very  marked. 

270°  F.  the  pressure  is    27  lbs.,  an  increase  of    25  lbs. 

320°  F.  the  pressure  is    75  lbs.,  an  increase  of    48  lbs. 

370°  F.  the  pressure  is  160  lbs.,  an  increase  of  85  lbs. 

420°  F.  the  pressure  is  296  lbs.,  an  increase  of  136  lbs. 

470°  F.  the  pressure  is  515  lbs.,  an  increase  of  219  lbs. 

520°  F.  the  pressure  is  798  lbs.,  an  increase  of  283  lbs. 

Without  suitable  means  for  controlling  the  temperature, 
or  without  almost  constant  watching  of  the  vulcanizer,  over- 
heating or  burning  of  the  rubber  during  the  hardening  process 
is  very  liable  to  occur. 

GAS  REGULATORS 

To  avoid  the  necessity  of  constant  supervision  of  the  vul- 
canizer when  in  use  and  still  maintain  a  uniform  and  effective 
working  temperature,  an  appliance  called  a  gas  regulator  can 
be  used  for  controlling  the  amount  of  gas  supplied  to  the 
burner.  By  proper  adjustment  of  the  regulator  the  gas  sup- 
ply to  the  burner  will  be  reduced  when  the  temiDerature  rises 
above  the  point  of .  vulcanization  determined  upon  and  at 
which  the  pointer  of  the  regulator  was  previously  set. 

TIME  REGULATORS 

To  further  reduce  the  responsibility  of  the  prosthetist,  a 
time  regulator  can  be  attached  to  the  gas  supply  pipes,  which 


152  VUhCANI'I'K 

will  mitomatically  out  off  the  fuel  at  wliatevcr  time  tlie  eluek 
is  set.  By  combining  the  gas  regulator  with  the  time  regula- 
tor, the  prosthetist  introduoes  the  flask,  closes  the  vulcanizer, 
turns  on  and  lights  the  gas  and  leaves  the  apparatus  to  itself, 
when,  without  furtlier  attention,  the  case  is  vulcanized  and 
the  gas  automatically  shut  off.  Before  lighting  the  gas  the 
lever  arm  of  the  clock  which  controls  the  gas  valve  should 


f 


AUTOMATIC  GAS  BEGtLATOR 


VULCAHIZER   WITH  GAS  AND  TIME 
KEGULATOK    ATTACHMENTS 


be  set  on  the  threaded  spindle  of  the  hour  hand  at  such  point 
as  to  allow  time  for  the  temperature  to  rise  to  vulcanizing 
point  and  further  to  allow  time  for  vulcanization  to  occur  as 
well. 

Appliances  of  this  type  are  not  a  luxury  but  a  necessity 
in  every  well  equipped  dental  laboratory. 


THE  SAFETY  VALVE 

Every  vulcanizer  should  have  attached  to  it  a  device 
called  a  safety  i^nhe,  which,  when  the  pressure  within  the 


VULCAN' ri'K 


boiler  exceedb  soiin^wliat  the  high  vulcanizing  picssiue,  will 
automatically  open  and  release  the  steam. 

The  simplest  device  of  this  type  consists  of  a  tube  screwed 
into  the  top  of  the  vulcanizer.  The  outer  end  of  the  tube  is 
fitted  with  a  screw  cap  having  a  hole  in  the  center.  The  open- 
ing through  the  cap  and  tube  leads  directly  into  the 
vulcanizer.  By  removing  the  cap,  placing  a  disc  of  thin 
copper  foil  over  the  end  of  the  tube  and  replacing  the  cap 


SAFETY    VALVE    AND    BLllW  OFF    ATTAl'IIMEXT    FOR   A'ULCANIZER 


Screw  Cap 

Brass  Washer- 
Safety  Disk dgSB 

Styd 

DETAIL  OF   SAFETY  VAL^•E 


DETAIL  OP   HLOW  OFF    VALAE 


tightly,  the  vulcanizer  chamber  is  thus  sealed.  The  copper 
foil  disc  usiTally  breaks  when  the  pressure  exceeds  350°  F., 
considerably  above  vulcanizing  temperature,  but  well  below 
the  tensile  limits  of  the  boiler,  thus  avoiding  danger  of 
explosion.  This-  safety  valve  is  independent  of  thermometer, 
gas  or  time  regulator  or  steam  gauge  and  will  work  when 
other  means  fail,  providing,  however,  that  reasonable  atten- 
tion is  given  it  to  see  that  the  tube,  both  internally  as  well  as 
externally,  of  the  disc  does  not  become  clogged. 


454  VULCANITIO 

VULCANIZATION    OF    CASES    IN    WHICH    AUTOMATIC 
FLASK  CLOSING  DEVICES  ARE  USED 

rractieally  all  doiitai  riihlxTs  are  su  compouiKled  that 
when  heated  to  320°  F.  and  maintained  at  that  temperature 
for  one  hour  thej-  will  vulcanize.  From  twenty-iive  to  forty 
minutes  are  usually  required  to  raise  the  temperature  within 
the  apparatus  to  the  vulcanizing  point  so  that  the  actual  time 
consumed  in  the  process  of  hardening  the  rubber  ranges  from 
eighty-five  to  one  hundred  minutes.  Bulky  cases  should  be 
vulcanized  at  the  same  temperature,  but  for  a  somewhat 
longer  period,  since  large  masses  of  rubber  naturally  require 
more  time  to  harden  than  do  those  of  less  bi;lk. 

It  is  the  opinion  of  the  writer,  based  upon  many  experi- 
ments in  the  vulcanization  of  all  classes  of  cases,  bulky  and 
otherwise,  that  the  use  of  automatic  springs  for  closing  the 
flask  in  the  preliminary  stages  of  vulcanization  will  result, 
first,  in  less  dimensional  change  of  the  matrix;  second,  in  a 
thicker  external  shell  being  formed,  and  third,  in  a  denser 
quality  of  vulcanite  when  hardened. 

These  observations  coincide  very  closely  with  extensive 
experimental  work  carried  on  liy  Dr.  Gr.  H.  Wilson,  and  which 
is  described  in  detail  in  his  work,  Dental  Prosthetics.  (1914, 
Lea  &  Febiger.) 

When  automatic  closing  devices  are  used,  space  should 
be  provided  for  the  escape  of  surplus  rubber.  This  should 
be  in  the  form  of  a  groove  of  ample  size,  close  to  and  extend- 
ing entirely  around  the  periphery  of  the  matrix,  but  with  no 
gateway  connections  leading  from  the  mati'ix  to  the  space. 

VULCANIZATION    OF    CASES    IN    WHICH    THE    FLASKS 

ARE   CLOSED   AND    BOLTED    BEFORE    PLACING 

THEM  IN  THE  VULCANIZER 

To  avoid  excessive  dimensional  change  in  the  matrix  dur- 
ing vulcanization,  in  those  cases  in  which  the  flask  is  closed 
and  bolted  before  placing  in  the  vulcanizer,  the  following  con- 
ditions must  be  observed: 

The  case  should  be  treated  as  described  under  the  head- 
ing, "Test  Closing  of  the  Flask." 

In  this,  as  in  all  methods  of  vulcanization,  the  case  should 
be  placed  above  water  and  the  process  conducted  in  an  at- 
mosphere of  steam. 

From  thirty  to  forty  minutes'  time  should  be  allotted  in 
raising  the  case  to  vulcanizing  temperature,  which,  in  this 
instance,  is  lower  than  by  the  method  just  described. 


VULCANITE  455 

Vulcanization  should  be  conducted  at  a  temperature  rang- 
ing from  290°  F.  to  300°  F.  and  for  a  period  varying  from 
two  to  two  and  one-half  hours. 

It  is  the  belief  of  the  writer  that,  although  the  rubber  is, 
in  all  probability,  in  the  most  liquid  condition  at  the  highest 
temperature,  it  also  exerts  the  greatest  expansive  force  be- 
tween 300°  F.  and  320°  F. 

If  this  assumption  is  true,  it  will  thus  be  seen  that  by  this 
method  the  matrix  is  relieved  of  considerable  expansive  force, 
which,  if  permitted  to  develop,  would  result  in  distortion. 

SUMMARY  OF  FACTS  OF  IMPORTANCE  IN  REGARD  TO 
VULCANIZATION 

The  important  facts  in  regard  to  vulcanization  may  be 
summed  up  as  follows : 

When  automatic  flask-closing  devices  are  used,  cases  may 
be  satisfactorily  vulcanized  at  320°  F.  for  a  period  of  one 
hour,  or,  when  bulky,  at  the  same  temperature  for  a  longer 
period. 

When  flasks  are  closed  and  locked  before  introducing  in 
the  vulcanizer  the  process  should  be  conducted  at  a  tem- 
perature not  exceeding  300°  F.,  preferably  slightly  lower, 
and  for  a  sufficient  length  of  time  to  induce  the  proper  de- 
gree of  hardness  in  the  vulcanite.  The  time  may  range  from 
two  to  three  hours,  depending  on  the  bulk  of  material  and  the 
quality  of  the  ru1)ber  employed.  The  actual  time  can  only  be 
determined  by  suitable  tests  for  any  particular  rubber.  Such 
tests,  when  once  made  and  recorded,  serve  as  a  basis  for  sub- 
sequent operations. 

REMOVAL  OF  THE  FLASK  FROM  THE  VULCANIZER 

From  ten  to  fifteen  minutes  should  elai)S(',  after  vulcan- 
izing a  case,  before  opening  the  blow-off  valve  for  the  release 
of  the  steam.  It  should  then  be  opened  but  slightly  so  that 
the  pressure  may  be  gradually  reduced.  Wiien  opened  widely, 
so  that  the  steam  pressure  within  the  vulcanizer  is  lowered 
suddenly,  before  that  within  the  flask,  the  contents  of  the  lat- 
ter will  frequently -become  distorted. 

REMOVAL  OF  THE  DENTURE  FROM  THE  FLASK 

On  removal  of  the  flask  from  the  vulcanizer,  and  before 
opening,  it  should  be  placed  in  cold  water  for  another  ten  or 


456  VUbCANITK 

lifteen  inhiutcs,  or  until  the  jilaslcr  and  (Icnluri'  ari'  thor- 
oughly C'hill(Ml.  otlicrwise  warpagc  ol'  the  case  will  occur  at 
this  stage. 

When  chilled,  the  bolts  are  removed  and  the  fiask  care- 
fully pried  apai't.  Sometimes  it  is  advisable,  when  the  plaster 
contents  of  the  fiask  have  not  become  softened  to  any  extent 
in  vulcanizing,  to  remove  the  top  of  the  flask  and  with  a  knife, 
carefully  remove  the  plaster  from  the  outer  surfaces  of  liu' 
denture,  being  careful  while  doing  so  not  to  mar  the  denture 
base  or  fracture  the  teeth. 


VULCANITE  LATHE   BUItS 

The  fiask  is  then  separated,  the  plaster  beneath  the  den- 
ture nndermined  and  the  cast  and  denture  pried  ont.  Re- 
moval of  the  surrounding  plaster  is  a  simple  matter.  The 
case  should  then  be  thoroughly  scjubbed  with  a  stiff  brush 
to  remove  all  remaining  portions  of  i)laster  when  it  is  ready 
for  final  finishing. 


POLISHING  THE  DENTURE 


With  a  coarse  saw  the  suri)lus  vulcanite  is  tiimnied  from 
the  periphery  of  the  baseplate.  Further  shaping  of  the  mar- 
gins to  correct  peripheral  ontline  can  be  done  with  the  double 


VUIX'ANITIC 


end  vuleauitc  lile  and  xulcanilc  lallu'  bars.  The  liiiul  sniootli 
iug  of  the  margins  and  general  surfaces  can  he  ([niekly  aeeoni- 
plished  witli  emery  hands  on  the  lathe  arbor. 


A*^ 


EMEI'.Y  BAXII    LATHE    MANDKEL 


When,  in  the  final  waxing  of  a  denture,  the  correct  gingi- 
val outline  is  given  the  gums,  so  that  they  represent  the  type 
of  teeth  recjuired  for  that  particular  case,  hut  little  effort  will 
be  required  in  finishing  the  vulcanite. 


DIt.    Ull.SON'S  SET    OK    VII.L'AMTE    FINISHERS 

The  right  and  left  bevel  chisels  are  used  to  true  up  the 
gum  festoons  and  develop  clean,  symmetrical,  lingual  margins 
of  vulcanite  against  these  surfaces  of  the  teeth.  The  set  of 
chisels  and  scrapers  suggested  by  Dr.  G.  H.  Wilson  are  excel- 


VUIX'ANITK 


\  lew  uF  rrrKR  and  i,(i\vei',   iikxtii'.i:  siiowixi!  lingi:ai.  siufaces  cif  teeth  de\T5E- 

OPED  IN   VULCANITE.      CONSTRUCTED   FOR   DR.    JOHN  BAWUNGSON.   A   NOTED 

ENGLISH   SURGEON.    B^'   DR.    GENESE   IN   1864.      LOANED   BY   IIR. 

SYKES    OE    C.    ASH    &   SONS 


BUCCAL     VIEW     OF     THE    RAWXINGSON    CASE.       THIS 

SHOWS   WELL-PROPORTIONED   UPPER   AND    LOWER 

TEETH    AND     FINE    OCCLUSAL    RELATIONS 


VUbCANITK  459 

lent  for  this  purjiose.  This  set  contains  a  small  pointed  in- 
strument for  removing  vulcanite  from  constricted  spaces  in 
the  embrasures  and  interproximate  spaces. 

It  is  frequently  advisable  to  develop  in  vulcanite,  the  lin- 
gual forms  of  the  natural  teeth,  after  the  method  introduced 
by  Dr.  Genese,  in  1860,  and  later  described  by  Dr.  Fine,  in 
1906.  Three  advantages  are  gained  liy  this  manner  of  contour 
development :  First,  the  bulk  of  vulcanite  is  materially  re- 
duced without  impairing  the  strength  of  the  baseplate;  sec- 
ond, the  teeth  are  given  approximately  their  true  lingual 
forms  and  consequently  feel  natural  and  comfortable  to  the 


SEl'TioNA!,     Mi;\V     (IK     AX      IPI'KR     DENTURE. 

LINGUAE     SUnFACE.S     OF     THE     TEETH    DEVET.- 

OPED    IN    VULI'ANITE    (FINE) 


SEUTIONAI.       VIEW       OF       UPPEIl 

DENTURE.     SHOWING     FORII     OF 

INSTRUIIF-NT    USED    IN    CARVING 

THE   WAX 


wearer;  third,  such  a  form  of  denture  aids  materially  in  cor- 
rect phonation.  The  only  objections  are  the  time  required  in 
the  carving  and  the  difficulty  encountered  in  finishing  the  vul- 
canite in  the  linguo-gingival  angles  and  embrasures. 

Bj'  developing  the  lingual  forms  of  the  teeth  in  the  final 
carving  of  tlie  wax  and  lining  the  vault  portion  of  the  wax 
model  denture  with  tinfoil  before  flasking  the  case,  the  finish- 
ing steps  are  comparatively  simple.  The  tinfoil  margins  next 
the  teeth  should  be  turned  away  from  the  latter  so  as  to  be 
caught  in  the  plaster  investment  in  the  upper  half  of  the  fiask. 
Wlien  No.  30  foil  ov  heavier  is  used  it  can  readily  bo  stripped 
from  the  vulcanite  or  the  thinner  gauges  can  be  quickly  re- 
moved bv  rubbing  with  mercurv. 


■1()U  VULCANITE 

Kultlici-  \ulcai]i/,c(l  against  tinfoil  comes  I'l-oin  the  liaslc 
clean,  poJisliecl  and  more  dense  than  wlien  vulcanized  a.gainst 
plaster,  and  when  care  is  used  in  waxing  a  case  hut  little  linal 
])olishin,<j'  is  re(|nired. 

REPRODUCTION    OF   THE    RUGAE 

When  re])r()(luction  of  the  I'Ugac  has  been  can'ied  out, 
small  scrapers  of  the  Kingsley  type  are  most  useful  for  fresh- 
ening the  depressions  hetween  these  irregular  ridges.  If 
proi^erly  developed  in  wax,  however,  and  the  tinfoil  is  applied 
as  described,  care  being  taken  to  burnish  it  into  the  dejires- 
sions,  the  i^olishing  wheels  will  complete  the  finish  without 
resorting  to  other  means. 

USE  OF  THE  CALIPERS 

To  avoid  iniduc  thinning  and  conse(juent  weakening  of  the 
baseplate,  the  calipers   should   ))e  ajiplied   at  various   times 


REIilSTEUlN 


during  the  finishing  process.     The  instrument  shown  in  the 
illustration  is  the  type  most  commonly  used. 

FINAL   POLISHING    OF   THE   DENTURE 

The  general  finish  is  given  the  vulcanite  with  various 
grits  of  abrasive  powders  and  water,  in  the  form  of  a  medium 
paste,  and  applied  with  brush,  felt  and  muslin  wheels  of  vari- 
ous sizes,  on  the  lathe.  For  rajDid  cutting,  a  rather  coarse 
grit,  pumice  stone,  followed  by  a  liner  to  remove  the  slight 
scratches  left  by  the  former,  is  the  usual  method  of  reducing 
the  irregular  surfaces  and  slight  angles  left  by  the  chisels, 
scrapers  and  emery  bands. 

The  scratches  left  by  the  jiuniice  powdei'  are  removed 
with  whiting  and  water.  A  still  highei-  polish  may  be  given 
the  vulcanite  by  coating  it  with  vaseline  or  heavy  lubricating 
oil,  dipping  it  in  dry  plaster,  and  applying  lightly  to  a  soft 


VULCAiNlTK 


bristle  wheel,  ruuuiug  at  high  speed.  The  application  of  dry 
plaster  is  continued  until  all  of  the  nil  has  been  removed  from 
the  various  surfaces. 

FINISHING  TOUCHES 

The  polished  denture  should  be  cleansed  with  soap  and 
water,  applied  with  a  medium  stiff  brush  and  afterward  in 
clear  water. 


462  VULCANITE 

It  may  then  be  ijlaced  in  a  small  glass  vessel  covered  with 
alcohol  and  set  in  the  sun  to  solarize  or  lighten  the  pink  vul- 
canite when  this  step  is  considered  necessary.  About  one  hour 
will  be  required  to  complete  the  bleaching  process,  the  posi- 
tion of  the  denture  being  changed  from  time  to  time  so  that 
all  surfaces  may  be  of  uniform  color.  After  solarizing,  the 
denture  should  again  be  cleansed  in  water. 

FINAL   FITTING  IN   THE  MOUTH 

When  the  patient  presents,  the  upper  denture  is  intro- 
duced and  tested  as  to  adhesion.  When  sealed,  the  finger 
should  be  passed  a  number  of  times  from  front  to  back,  apply- 
ing considerable  on  the  lingual  surface  of  the  baseplate.  This 
to  a  considerable  extent  forces  the  air  from  between  the  con- 
tact surfaces,  after  which  the  patient  is  instructed  to  apply 
the  tonque  to  the  baseplate  and  "draw  the  air"  from  beneath 
it. 

Should  the  peripheral  margins  impinge  on  the  muscles  or 
soft  tissues  to  any  marked  degree  the  denture  should  be  re- 
lieved at  such  points  and  the  marred  surfaces  polished. 

The  lower  denture  is  introduced  and  seated  on  its  border 
by  drawing  the  lip  and  cheeks  away  from  its  lower  margins 
and  by  applying  downward  pressure  to  partially  expel  the  air. 

Tests  of  the  excursions  of  cusps  of  lower  against  upper 
teeth  in  lateral  movements  sliould  be  made,  first  without  and 
later  with  interposed  carbon  paper.  The  high  points  are  re- 
duced with  engine  stones  until  no  interference  can  be  de- 
tected. The  final  finish  is  given  the  vulcanite  mth  whiting 
and  water  applied  with  clean  felt,  muslin  and  brush  wheels, 
free  from  grit.  All  scratches  should  be  removed  and  a  highly 
polished  surface  developed,  not  only  in  the  lingual  and  outer, 
but  in  the  palatine  areas  as  well. 

FINISHING   THE    PALATINE    SURFACES    OF    A    DENTURE 

To  avoid  subsequent  irritation  of  mucous  tissues  against 
which  the  denture  will  rest,  the  palatine  surfaces  should  be 
freed  from  all  nodules,  the  roughened  areas  smoothed,  and  a 
uniform  polish  given  them. 

Pumice  stone  applied  with  a  stiff  brush  wheel,  rmi  at 
high  speed,  using  but  little  pressure,  followed  with  whiting 
and  water,  will  accomplish  desired  results  without  in  any 
way  interfering  with  denture  adaptation. 

Judgment  must,  of  course,  be  used  as  to  the  amount  of 


VTJIvCANITE  i  463 

pressui'f  ai)plied  to  avoid  cliangiiig  the  form  of  the  palatine 
or  i)eriplieral  surfaces. 

Many  avoid  polishing  the  palatine  and  boi'der  areas  of 
dentures,  under  the  mistaken  idea  that  such  a  step  will  im 
pair  adaptation. 

The  experience  of  the  writer  of  twenty  years  or  more, 
together  with  that  of  many  others,  is  offered  as  evidence  that 
the  polishing  of  all  areas  of  a  denture,  and  particularly  those 
which  l)ear  the  liurden  of  masticatory  effort,  is  not  only  possi- 
ble but  imperative,  and  can  be  accom]ilislied  without  per- 
ceptible interference  to  adaptation. 

The  use  of  tinfoil  on  the  surface  of  casts  reduces  to  the 
minimum  the  amount  of  polishing  required.  The  use  of  artifi- 
cial stone  for  casts  and  the  coating  of  cast  surfaces  with  silex 
aid  in  the  product  of  smooth  vulcanite  surfaces. 

A  final,  high  polish  can  be  given  all  surfaces  by  saturating 
the  denture  in  thick  oil  and  applying  dry  plaster  freely  while 
holding  it  against  the  soft  bristle  lathe  wheel.  The  applica- 
tion of  the  plaster  must  be  continued  until  all  oil  is  removed. 

The  regrinding  of  teeth  in  final  trial  in  the  mouth  is  of 
utmost  importance.  Such  procedure  corrects  errors  of  occlu- 
sion occasioned  by  dissimilarity  between  mandibular  and 
occluding  frame  movements,  as  well  as  slight  errors  arising 
from  change  in  relation  of  teeth  during  flask  closure  and  vul- 
canization. 

The  prosthetist  should  keep  in  mind  during  the  final  trial 
and  adjustment  of  dentures  to  the  mouth  the  three  principal 
objects  he  endeavored  to  accomi)lish  when  the  case  was  under- 
taken, viz.,  to  give  his  patient  dentures  that  would  be  useful, 
look  ivell,  and  feel  comfortable. 

CONSTRUCTION   OF  A   FULL  UPPER   OR   LOWER 
DENTURE 

With  slight  variation  in  technic,  from  that  described  for 
full  cases,  either  upper  or  lower  dentures  may  be  constructed 
b}^  the  anatomic  method,  the  natural  teeth  in  the  opposite  arch 
being  present. 

The  principal,  departure  is  in  the  method  of  taking  the 
bite  and  in  registering  the  protrusive  bite.  To  illustrate,  the 
construction  of  a  full  upper  denture  will  be  outlined. 

The  impression,  cast,  and  wax  occlusion  model  for  the 
upper  arch  are  formed  as  for  an  upper  model  in  a  full  case. 

Developing  uniform  contact  of  the  wax  rim  with  oeclud- 


Kii  vui.cANi'ri': 

illy  teeth  is  esseutially  the  same  as  between  two  occlusion 
models.  The  median  and  high  lip  lines  are  determintid  in  the 
same  manner,  as  is  also  facial  contour. 

The  condyle  ends  are  located  and  points  marked  on  the 
face. 

The  bite  fork  is  inserted  in  tlie  occlusion  rim  and  removed. 

An  impression  in  compound  is  secured  of  the  occlusal 
half  or  more  of  all  of  the  lower  teeth,  when  it  can  be  removed 
without  distortion,  and  from  this  a  lower  occlusion  cast  is 
formed. 

A  layer  of  softened  wax  one-eighth  of  an  inch  thick  is 
now  cut  to  the  form  of,  and  added  to  the  occlusal  surface  of  the 
upper  occlusion  rim  which  should  be  chilled.  The  occlusion 
model  is  introduced  in  the  mouth,  and,  by  trial,  the  normal  bite 
is  determined,  the  patient  biting  into  the  softened,  added  layer 
when  instructed,  until  the  natural  teeth  come  in  contact  with 
the  chilled  occlusion  rim. 

The  bite  fork  is  returned  to  position  and  tirmly  h;ted  in 
the  occlusion  model,  after  which  the  face  bow  is  adjusted  in 
position  and  the  several  clamps  tightened. 

The  occlusion  model,  attached  wax  bite  and  face  bow  are 
removed  and  the  latter  set  in  position  on  the  occluding  frame. 
The  upper  cast  is  seated  in  upper  occlusion  model  and  at- 
tached to  the  upper  bow  of  occluding  frame.  The  impression 
is  removed  from  the  lower  cast  and  the  latter  seated  in  the 
wax  bite,  care  being  taken  to  see  that  the  occlusal  surfaces 
of  the  plaster  teeth  rest  flat  on  the  corresponding  surfaces  of 
wax  bite.  To  be  certain  that  this  step  may  be  carried  out 
accurately,  the  inner  and  outer  margins  of  the  wax  bite  should 
be  cut  away  so  as  to  leave  little  more  than  the  occlusal  sur- 
face markings  of  the  natural  teeth. 

The  lower  cast  is  then  attached  to  the  lower  bow  of  the 
occluding  frame  and  the  face  bow  and  wax  bite  are  removed. 
Since  the  bite  locks  cannot  be  applied  in  taking  the  protrusive 
bite,  the  latter  step  may  be  carried  out  as  Christiansen  first 
described  it,  viz.,  placing  a  roll  of  wax  on  either  side  between 
the  bicuspids  and  molars,  and  having  the  patient  close  the 
mandible  while  in  a  protruded  position. 

The  occlusion  model  should  be  notched  in  the  molar  region 
so  that  on  removal  the  protrusive  wax  bites  will  be  correctly 
guided  to  place.  The  condyle  paths  of  the  frame  are  released, 
the  back  spring  unhooked,  the  upper  occlusion  model  set  on  its 
cast,  the  two  wax  bites  placed  in  their  respective  locations  and 
the  final  adjustment  of  the  several  factors  accomplished  by 


VUl.CANITK  4Gr, 

exertiuy   light   Init   sicady   lux's^urc,    tlirougli    the   ceutcr   ol" 
upper  and  h^wer  casts,  as  in  full  cases. 

When  proper  relation  is  established,  the  condyle  paths 
are  clamped,  the  wax  bites  removed,  the  back  spring  hooked 
and  the  case  is  ready  for  arrangement  of  the  teeth,  which 
step  is  similar  to  the  arrangement  of  teeth  in  full  cases. 

FULL   LOWER  DENTURES 

In  constructing  a  full  lower  denture,  the  upper  natural 
teeth  being  present,  the  stei)s  are  similar  in  detail,  except  that 
the  bite  fork  is  attached  to  the  lower  occlusion  model.  In 
mounting  the  casts,  the  occluding  frame  should  lie  inverted 
and  the  lower  cast  mounted  first. 

THE  GYSI  SYSTEM  OF  ANATOMIC  APPLIANCES 

The  Gysi  System  of  appliances  for  anatomic  denture  con- 
struction atTords  means  of  registering  certain  movements  of 
the  mandible,  not  possible  by  any  other  method.     The  appli- 


THE    GYSI    ADAI'TABLE    ARTICULATOR 


ances  consist  of  ffn  articulator  having  adjustable  condyle 
paths,  adjustable  lateral  rotation  centers,  an  adjustable  side 
movement,  and  the  ordinary  hinge  movement  common  to  all 
occluding  frames ;  also  a  condyle  path  register,  a  lateral  con- 
dyle path  register,  an  incisor  path  register,  and  varioiis  other 
aceessoi'v  appliances. 


4«G  VULCANITE 

APPLICATION    IN    DENTURE    CONSTRUCTION 

111  constructing  dentures  with  these  appliances,  tiie  steps, 
up  to  the  ap]ilication  of  the  face  bow,  are  practically  the  same 
as  detailed  in  the  preceding  chapters.  Although  the  order  of 
procedure  may  be  varied,  tlie  following  will  be  convenient  and 
practical : 

Eegister  the  condyle  paths. 

Take  the  bite. 

Mount  the  casts  on  the  articulator. 

Adjust  the  condyle  paths  of  tlic  articulator.  (Protrusive.) 

Register  the  incisor  path. 

Set  the  rotation  centers  of  the  articulatoi-. 

Eegister  the  lateral  condyle  i^aths. 

Adjust  the  lateral  condyle  paths  of  the  articulator. 

REGISTERING  THE   CONDYLE   PATHS,  FORWARD   MOVEMENT 

The  condyle  path  register  records  the  downward  and  for- 
ward movement  of  the  condyles,  and  also  fulfills  the  purpose 
of  a  face  bow  in  mounting  easts  on  the  occluding  frame.  It 
is  applied  as  follows: 

The  horseshoe  plate  is  adjusted  to  the  lower  occlusion 
model,  the  pins  of  the  plate  being  forced  into  the  wax  rim 


HORSESHOE    I'LATE    ADAPTED    TO     LOWER    OCl'LUSIOX     MODEL 

until  the  plate  rests  flat  upon  its  occlusal  surface.  The  an- 
terior portion  of  the  plate  should  extend  about  three-eigbtbs 
of  an  inch  labially  of  the  rim,  so  that  later  it  may  serve  as  a 
table  for  recording  the  incisor  path. 

The  occlusion  models  are  now  introduced  in  the  mouth, 
the  condyle  path  register  adjusted  to  the  anterior  projec- 
tions of  the  horseshoe  plate,  and  the  pencils  on  the  liori- 


VULCANITE 


467 


zoutal  arms  of  the  register  brought  iu  eoutaet  with  face, 
agaiust  the  previousl_v  marked  condyle  ends.  The  adjustment 
is  accomplished  by  raising,  lowering  or  rotating  the  pencil 
posts  in  their  sockets  and  locking  them  firmly  with  the  set 
screws;  the  pencils  are  moved  inward  by  means  of  the  rack 
and  pinion  adjustment  on  the  ends  of  the  register. 

A  card,  about  two  by  three  inches  in  size,  is  now  inserted 
and  held  firmly  Ix'twoeii  tlie  ]i(Mi('il  point  and  the  face.     Its 


REGISTERING    THE    CONDYLE    PATH 


lower  edge  should  be  parallel  with  the  horizontal  arm  of  the 
condyle  register. 

The  patient  is  instructed  to  bite  sidewise,  so  as  to  project 
the  condyle  next  the  card.  During  this  movement,  the  pencil 
point  moves  synchronously  with  the  condyle  and  marks  on  the 
card  the  direction  of  its  path.  A  card  is  now  applied  to  the 
opposite  side  of  the  face,  and  a  similar  registration  of  the 
opposite  path  secured  in  like  manner. 

A  straight  edge  is  laid  on  the  card,  parallel  with  the 
working  part  of  the  condyle  path,  and  a  line  drawn  along 
it  to  the  lower  margin  of  the  card.     The  protractor  is  then 


VULCANITE 


applied  to  the  card,  by  means  of  wliicli  the  inclination  of  the 
condyle  path  in  degrees  is  determined.  The  condyle  paths  of 
the  frame  are  set  according  to  the  readings  obtained  from  the 
two  cards. 


TAKING  THE  BITE 


The  bite  is  now  taken  as  outlined  in  Chapter  XIX,  the 
horseshoe  plate  being  firmly  affixed  to  the  lower  occlusion 
model,  for  by  this  means  the  occlusion  models  are  attached  to 
the  condyle  register  for  securing  their  correct  relation  to  the 
condyles  in  normal  or  resting  position  in  the  glenoid  fossre. 


VULCANITE  469. 

AVlien  the  normal  bite  is  deteniiiued,  the  bite  locks  are 
iutroduced,  the  condyle  register  adjusted  as  before,  and  the 
occlusion  models  removed  from  the  mouth. 

In  this  sj'stem,  it  is  found  more  convenient  to  seat  each 
cast  in  its  baseplate  and  hold  them  in  proper  position  by  pass- 
ing ]'ul)ber  bands  around  both  casts  and  occlusion  models. 

MOUNTING  THE  CASTS   ON  THE  ARTICULATOR 

The  condyle  register  to  which  the  occlusion  models  are 
attached  is  set  upon  its  base,  the  goose-neck  rod  being  raised 
or  lowered  as  required  to  bring  the  pencil  points  opposite  the 
condyle  points  of  the  articulator. 

Tlie  iron  stand,  with  condyle  register  and  occlusion  mod- 
els attached,  is  now  moved  forward,  clear  of  the  articulator. 


Plaster  is  applied  around  and  over  the  lower  bow,  and  the 
iron  base  pushed  back  until  the  pencil  points  of  the  register 
are  opposite  the  condyle  ends  of  the  frame;  further  additions 
may  be  made  to  the  plaster  around  the  lower  cast,  to  firmly 
attach  it  to  the  frame. 

The  upper  cast  is  attached  to  the  upper  bow  by  applying 
plaster  in  the  usual  manner.  When  set,  the  condyle  register 
and  bite  locks  are  removed,  the  rubber  bands  cut,  and  the 
occlusion  models  removed  from  the  casts. 


REGISTERING  THE   INCISOR   PATH 

A  pellet  of  cotton  saturated  in  oil  of  cloves  is  ignited  and 
the  anterior  end  of  the  horseshoe  plate  held  over  it  to  blacken 


VULCANITE 


CASTS    AND     CONDYLE     KEGISTER     ADJUSTED     TO     ARTICULATOR 

the  surface.     A  thin  film  of  wax  is  flowed  over  the  smoked 
surface  to  prevent  its  being  rubbed  off. 

The  incisor  path  register  is  now  attached  to  the  upper 
occlusion  model  so  that  the  pin  will  project  slightly  below 
the  occlusal  surface.    The  register  must  not  be  set  so  low  as 


PENCIL  FOR   REGISTERING 

LATERAL  PATH  OF  LATERAL  PATH 

CONDYLE  SET  SCREW 


RACK  AND   PINION 

FOR   LATERAL  ADJUSTMENT 

OF  PENCILS 


i;xi>i,ANATonv   CUT  showing  the  various   adjustments  of  the  gysi  adaptable  articulator 


VULCANITK  471 

to  obscure  a  view  of  tlie  ]iiii  iioiiit  in  its  I'xoursions  over  the 
waxed  surface  of  the  liorseshoe  plate. 

The  occlusion  models  are  uow  introduced  in  the  mouth 
and  the  patient  instructed  to  move  the  mandible  sidewise,  at 
the  same  time  holding  the  horseshoe  plate  in  close  contact 
with  the  upper  occlusion  rim. 

By  this  movement  the  pin  of  the  register  on  the  upper 
occlusion  model  marks  an  arc  on  either  side  of  the  median 
line  of  the  horseshoe  plate,  the  centers  of  which  represent  the 
centers  of  rotation  of  the  mandible.  The  logic  of  this  is  appa- 
rent, for  the  condyles  represent  centers  from  which  the  arcs 


KEGISTEItlXG   THE    IXCISOU   PATH 


are  developed.  Usually,  several  movements  will  be  required 
to  mark  distinct  lines  on  the  horseshoe  plate. 

When  the  record  is  sufficiently  sharp,  the  occlusion  models 
are  removed  from  the  mouth,  returned  to  the  casts  on  the 
frame,  and  the  latter  subjected  to  lateral  movements.  The 
direction  taken  by  the  pin  of  the  incisor  register  should  be 
closely  observed.  If  it  follows  the  arc,  the  rotation  center  of 
the  fra^e^is  correct,  and  the  latter  may  be  fixed  accordingly. 
If  not,  the  rotation  center  of  the  frame  should  be  moved  out- 
ward or  inward- as  required,  until  the  point  accurately  follows 
the  arc  it  made  while  in  the  mouth.  The  rotation  center  on  the 
opposite  side  of  the  frame  is  determined  in  like  manner. 

The  object  in  carrying  out  the  steps  as  described  is 
to  insure  correct  lateral  movements  to  the  frame,  so  that  when 


172  VinX'ANITK 

tliL'  teeth  are  aii;uij;('<l  in  the  wax  rims,  tlie  cusp  (.'learauce 
there  devehjped  will  reiiuire  but  little  chauge  when  tlie  den- 
tures are  introduced  in  the  mouth.  It  is  a  step  nearer  true 
anatomic  movements  than  can  be  secured  from  a  frame,  the 
rotation  centers  of  which  are  fixed  the  average  distance  apart. 

REGISTERING    THE    LATERAL    CONDYLE    PATH 

The  lateral  paths  must  not  be  confused  with  the  lateral 
rotary  movements  of  the  condyles.  Naturally,  when  one  con- 
dyle is  the  actual  center  of  rotation,  the  other  condyle  in  mov- 
ing forward  describes  an  arc,  the  radius  of  which  corresponds 
to  the  distance  between  the  two  condyles.  It  is  found,  how- 
ever, that  the  radius  of  the  arc  described  by  a  projected  con- 
dyle is  sometimes  greater  or  less  than  the  distance  between 
the  condyle  centers. 

Again,  in  some  persons,  the  mandible  moves  bodily,  side- 
wise,  in  the  lateral  rotary  movements,  and  in  some  cases  there 
is  a  slight  side  movement,  within  certain  limits,  without  any 
percei^tible  rotary  movement. 

The  lateral  path  register  has  attached  to  each  extremity 
a  glass  plate  ground  on  the  under  side,  on  which  the  perpen- 
dicular pencil  of  the  condyle  path  register  records  the  lateral 
movements  of  the  mandible. 

By  use  of  the  lateral  condyle  path  register,  these  side 
movements  in  individual  cases  may  be  recorded,  and  the  artic- 
ulator set  to  reproduce  them  to  a  fairly  accurate  degree.  The 
steps  are  carried  out  as  follows : 

The  condyle  ]3ath  register  is  attached  to  the  occlusion 
models  as  in  taking  condyle  registration,  the  perpendicular 
pencils  being  turned  so  that  they  come  opposite  the  outer  ends 
of  the  condyles. 

The  operator  stands  back  of  the  patient  and  applies  the 
register',  holding  it  at  approximately  the  same  inclination  as 
tlie  pitch  of  the  condyle  paths,  previously  registered.  The 
ground  glass  plates  should  rest  on  the  upturned  pencil  points, 
and  the  arms  be  pressed  in  until  the  edges  of  the  plates  rest 
firmly  against  the  sides  of  the  face.  The  patient  is  instructed 
to  move  the  mandible  sidewise  as  before,  which  movement 
marks  on  the  under  side  of  the  glass,  the  line  or  arc  described 
by  the  moving  condyle  in  its  forward  excursion. 

To  translate  the  lines  recorded  on  the  glass  plates  into 
degrees,  the  following  plan  is  adopted : 

On  a  sheet  of  white  paper  as  wide  as  the  register  bow,  a 
base  line  A  B  is  drawn  from  side  to  side.     A  perpendicular 


VULCANITE 


REGISTEUING   THE   LATERAL   CONDYLE  I'ATIIS 


DETEIIMINING    THE    DEGREE   OP    INWARD    INCLINATION    ol'     TTIE 
LATERAL    CONDYLE   PATHS 


474  VULCANITK 

C  D  is  erected  on  the  base  line,  near  one  edge  of  the  sheet. 
The  lateral  condyle  path  register  is  laid  on  the  sheet,  the 
points  on  the  ground  glass  plate  which  indicate  the  beginning 
of  forward  movement  of  the  condyle  being  placed  at  the  junc- 
tion of  base  with  perpendicular  line  C,  the  base  line.  The 
points  should  also  be  directly  over  the  perpendicular  lines. 
AVith  a  straight  edge  placed  beneath  the  ground  glass,  and 
resting  on  the  paper,  its  edge  is  brought  in  line  with  the 
lateral   path  marked  on  the  ground   glass,   and  which   can 


L    17'  .   16°  K 


A   BECORD   OF    SIXTKK- 

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nXDYLE    PATHS.      AVERAGE 
II'    LEFT  CONDVLE  PATHS. 
1  .    SIXTEEN'  DEGREES 


readily  be  seen  tiirough  the  transparent  plate.  If  properly 
placed,  its  edge  should  coincide  with  the  .junction  of  the  per- 
pendicular with  the  base  line. 

The  register  is  removed  and  a  line  drawn  along  the 
straight  edge  on  the  paper  C  E.  This  line  usually  forms  an 
angle  with  the  perpendicular  line,  the  apex  of  which  is  on  the 
base  line.  By  applying  the  protractor  to  the  angle,  the  num- 
ber of  degrees  included  may  be  read,  and  the  lateral  path 
recorded  accordingly  on  the  articulator. 


VULCANITE  475 

THE    ANGULAR    INCLINATION    OF    THE    LATERAL 
CONDYLE   PATH 

Dr.  Gysi  states  that  tlu-  average  angular  inclination  in- 
ward, of  sixteen  pairs  of  condyles  recorded,  sliows  17  de- 
grees for  the  left  and  16  degrees  for  the  right  condyle. 

This  lateral  movement  of  the  mandible  is  evidently  the 
result  of  an  unconscious  or  involuntary  effort  of  the  organism 
to  increase  the  occlusal  function  of  the  molars  on  the  working 
side,  as  well  as  to  develop  more  effective  balancing  contact  on 
the  protruded  side.  That  it  is  less  important  than  the  for- 
ward and  downward  condylar  movement  is  self-evident,  yet 
both  should  ])o  rockoiiod  with  in  denture  construction. 

SUBSEQUENT    STEPS    OF    DENTURE    CONSTRUCTION 

When  the  registrations  have  been  determined  as  outlined, 
and  the  articulator  adjusted  accordingly,  the  subsequent  steps 
of  denture  construction  are  carried  out  in  practically  the  same 
manner  as  detailed  in  the  previous  chapter. 

Because  of  the  liability  of  errors  occurring,  in  carrying 
out  the  various  steps,  the  completed  dentures  should  be  tested 
with  carbon  paper,  to  correct  any  c-nsp  interference  that  may 
exist  and  remove  high  points  that,  without  such  means  of  dis- 
closing them,  are  not  discernible  to  either  prosthetist  or 
patient. 


CHAP  T  K  R     XXIII 

CONSTRUCTION  OF  PARTIAL  DENTURES 

VARIOUS   TYPES 

A  substitute  wliicli  replaces  one  or  more,  but  not  all  of  the 
natural  teeth  in  either  arch,  is  commonly  termed  a  partial  den- 
ture. This  name  is  usually  applied  to  a  removable  substitute 
having  a  base  plate  which  rests  upon  and  is  principally  sup- 
ported by  the  mucous  tissues  covering  the  bony  substructure 
of  the  dental  arches,  in  contra-distinction  of  bridge  work, 
which  fulfills  essentially  the  same  purpose  but  is  attached  to, 
and  mainly  supported  by  some  of  the  remaining  natural 
teeth  or  roots.  A  piece  of  bridge  work,  however,  in  the 
broadest  sense,  is  a  partial  denture,  since  it  replaces  a  miss- 
ing portion  of  the  natural  denture.  The  term  bridge  relates 
to  the  manner  of  replacement,  the  bridging  over  of  spaces 
caused  by  loss  of  some  of  the  natural  teeth. 

PLANNING  A  PARTIAL  DENTURE 

In  planning  a  partial  denture,  aside  from  the  general 
routine  steps  involved,  several  factors  of  importance  must  be 
determined,  the  dominant  ones  of  which  are  as  follows : 

First — The  materials  of  which  the  substitute  is  to  be 
constructed. 

Second — The  general  outline  form  of  the  base  plate. 

Third — The  means  of  retention  to  be  employed. 

Fourth — The  class  of  teeth  to  be  used  and  the  manner  of 
their  attachment. 

BASEPLATES  FOR  PARTIAL   DENTURES 

The  base  plate  is  the  foundation  of  a  denture  which  rests 
upon  the  oral  tissues,  and  to  which  the  substitute  teeth  are 
attached.  Through  it,  under  normal  conditions,  the  force  of 
masticatory  effort  is  equalized  and  distributed  to  the  mucous 
tissues  overlying  the  bony  sub-structure  in  such  manner  as  to 
cause  no  injury  to  the  tissues  themselves  and  no  inconveni- 
ence to  the  patient. 

Gold  and  vulcanite,  either  alone  or  in  cojnbination,  are 
the  materials  most  commonly*  employed  for  partial  denture 
bases,  preference  in  most  cases  being  given  the  former  be- 

476 


CONSTRUCTION    OK    PARTIAL    JJKNTURES  477 

cause  of  its  better  appearauce,  couduetivity  auil  greater 
strength  with  least  bulk  as  compared  with  vulcanite.  How- 
ever, there  are  many  cases  where  vulcanite  alone  can  be  used 
to  good  advantage,  and  other  cases  in  which  its  use  with  gold 
is  indispensable,  particularly  where  much  restoration  of  bor- 
der contour  is  required. 

PARTIAL  DENTURES  OF  VULCANITE 

The  outline  form  and  size  of  a  partial  denture  is  governed 
to  a  great  extent  at  least  by  the  position  of  the  teeth  to  be 
replaced.  The  manner  of  retention,  however,  has  an  impor- 
tant bearing  on  the  linear  dimensions  of  the  base  plate.  When 
clasps  or  retaining  appliances  of  similar  character  are  used, 
the  terminals  of  the  base  plate  should  be  extended  beyond 
these  means  of  attachment  when  necessary,  so  as  to  develop 
denture  balance,  as  explained  under  the  heading,  "Indica- 
tions and  Contra-Indieations  Governing  the  Application  of 
Clasps." 

By  drawing  a  line  or  laying  a  straight  edge  from  one 
clasp  or  attachment  to  the  other,  the  linear  extension,  both 
mesially  and  distally,  necessary  to  secure  correct  denture  bal- 
ance, can  readily  be  determined. 

In  upper  partial  dontui'es,  when  retention  depends  upon 
atmospheric  pressure  and  adhesion,  the  base  ijlate  should 
cover  a  considerable  portion  of  the  palatine  vault,  but  seldom 
to  such  an  extent  as  in  a  full  deuture. 

With  the  great  variety  of  frictional  appliances  available 
and  improved  methods  of  their  construction  the  retention 
of  partial  dentures  is  very  much  simplified,  and  the  form 
of  upper  dentures  can  be  materially  reduced  in  size  over  those 
in  which  atmospheric  pressure  is  employed. 

In  width,  the  base  plate  of  an  upper  partial  denture  need 
seldom  exceed  from  one-fourth  to  five-sixteenths  of  an  inch, 
where  it  passes  along  the  lingual  surface  of  the  natural  teeth, 
when  retained  in  place  by  frictional  appliances. 

The  base  plate  need  only  be  considered  as  a  frame-work 
or  splint  for  holding  the  teeth  in  position,  the  saddle,  which 
rests  upon  the  border  and  supports  the  tooth.,  coupled  with 
but  slight  bearing,  of  the  base  plate  proper  upon  the  tissues, 
u.sually  affords  ample  resistance  to  masticatory  stress. 

The  thickness  of  a  base  plate  of  vulcanite  is,  of  course, 
governed  somewhat  by  its  width,  but  not  altogether,  since  a 
thin,  wide  base  plate  will,  under  use,  fracture  more  quickly 
than  a  thicker  but  narrower  one  containing  an  equal  or  even 


478  CONSTRUCTION    OK    PARTIAh    DKNTURES 

less  bulk  of  material.  By  actual  measuremeut,  a  very  nar- 
row base  plate,  if  constructed  of  a  good  quality  of  vulcanite, 
need  not  exceed  from  one-sixteenth  to  one-twelfth  of  an  inch 
in  thickness  except  when  absorption  of  tissues  requires  a 
greater  amount  for  restoration  of  lost  border  contour. 

TECHNIC  OF  CONSTRUCTION  OF  PARTIAL  UPPER  VULCANITE 
DENTURES  WITHOUT  CLASPS 

In  all  cases  an  accurate  plaster  impression  of  the  teeth 
and  tissues  involved  should  be  secured  in  plaster.  From  this 
impression  a  cast  should  be  developed  in  magnesium  oxy- 
chlorid,  or  Spence's  plaster,  because  of  the  greater  hardness 
of  these  materials. 

When  loss  of  but  few  teeth  have  occurred,  these  not  being 
contiguous,  a  mash  bite  of  sufficient  bulk  to  take  an  impres- 
sion of  the  lower  teeth  and  project  labially  so  that  the  bite 
stem  of  the  face  bow  may  be  firmly  imbedded  in  it,  will  usu- 
ally jjrove  satisfactory  for  mounting  the  upper  cast  in  correct 
position  on  the  occluding  frame,  and  for  developing  the  lower 
cast  as  well.  Or  an  impression  of  the  lower  arch  can  be 
secured,  a  cast  developed  from  it  and  the  special  bite  fork, 
designed  for  partial  cases,  can  be  used  for  securing  the  cor- 
rect relation  between  the  mandible  and  maxilla,  after  which 
the  two  casts  can  be  mounted  on  the  frame  in  a  similar  man- 
ner to  an  edentulous  case. 

TAKING   THE    PROTRUSIVE    BITE 

Should  it  be  deemed  advisable  to  take  a  protrusive  bite, 
it  is  accomiilished  as  follows :  Place  two  rolls  of  wax  between 
the  bicuspids  and  molars,  one  on  either  side ;  have  the  patient 
l^rotrude  and  bite  as  in  full  cases  where  this  step  of  condyle 
registration  is  carried  out.  The  two  bites  are  removed  from 
the  mouth  and  placed  in  position  on  the  lower  casts,  the  con- 
dyle slots  of  the  frame  loosened  and  the  back  spring  unhooked. 
The  upper  cast  is  then  moved  backward  and  pressed  down- 
ward until  the  teeth  take  their  proper  position  in  the  bite. 
It  is  usually  necessary  to  trim  away  the  buccal  and  lingual 
margins  of  wax  before  seating  the  casts,  so  that  it  may  readily 
be  seen  when  they  are  in  exact  position.  Care  should  be 
taken  not  to  distort  the  wax  during  the  trimming  process. 
The  condyle  slots  are  now  set  tirmly  as  the  wax  bites  indicate, 
the  wax  removed,  and  the  back  spring  again  connected,  when 
the  ease  is  ready  for  the  selection  of  the  teeth. 


CONSTRUCTION    OF    PARTIAL    DENTURES  47'J 

SELECTING  AND   GRINDING   THE   TEETH 

When  only  a  few  teeth  are  missing,  it  is  seldom  necessary 
to  try  the  wax  model  denture  in  the  mouth,  therefore  the  use 
of  a  hard,  unyielding  base  jjlate,  such  as  is  used  in  full  cases, 
is  uncalled  for.  A  good  quality  of  sheet  base  plate  wax  will 
answer  the  purpose. 

Teeth  of  suitable  size  and  color  are  selected  to  fill  the 
spaces.    When  possible  to  do  so,  plain  teeth  should  be  selected 


KEDUCTIOX     Oi.-      I'ltOXIJIATE     Sirp.FACF.S 
TEETH   WHERE   RT'ArE   HAS   BECOME 
CONSTKICTEB 


and  ground  to  accurately  tit  the  border,  thus  obviating  the 
application  of  artificial  gum  restoration.  They  should  be  of 
sufficient  length  not  to  require  tipping  inward  at  their  cervical 
ends  to  meet  the  border  and  thereby  be  thrown  out  of 
alignment. 

When  teeth  adjoining  a  space  have  moved  toward  each 
other,  for  example,  a  central  and  opposite  lateral  incisor,  thus 
reducing  the  space  occupied  by  the  lost  central,  it  is  often 
advisable  to  disc  away  their  proximating  surfaces.     This  in- 


ri.ATE     TEETH     BACKED.     WITH    LINGUAL    EX- 

TEXSIOX  ADDED.   FOB   CLOSE 

BITE  CASE 


creases  the  width  of  space  and  decreases  the  width  of  the 
immediately  adjoining  teeth  so  that  the  replacement  will  more 
nearly  harmonize  in  form  and  proportion  with  the  other  in- 
cisor than  woujd  be  the  case  were  such  change  not  made. 

By  highl}-  polishing  the  surfaces  reduced,  no  injury  to 
the  natural  teeth  is  liable  to  result. 

There  is,  however,  a  limit  to  the  aiJplication  of  plain 
teeth  in  partial  cases.    "Wlien  gum  restoration  is  required  and 


■ISO  CONSTRUCTION    OF    PARTIAL    DENTURES 

the  line  of  junction  of  tlie  artiticial  with  the  natural  gum  tissue 
is  visible,  a  gum  section  tooth,  or  if  two  or  more  contiguous 
teeth  are  missing,  a  gum  section  block  which  includes  the 
teeth  required  should  be  selected  and  ground  to  neatly  fill 
the  space  and  restore  the  lost  tissues  with  porcelain.     When 


such  a  block  is  not  procurable,  plain  teeth  may  be  selected  and 
a  porcelain  gum  attached  by  baking  as  described  under  the 
heading,  "Special  Uses  of  Porcelain." 

In  some  cases  it  may  be  possible  to  apply  "Protesyn"  in 
partial  restorations,  but  since  this  material  depends  entirely 
upon  undercut  spaces  for  its  retention,  it  will  be  difficult  to 
develop  the  necessary  anchorage  in  limited  spaces.  Pink  or 
granular  gum  restorations  are  the  least  desirable  of  any  of 


rini 


the  materials  mentioned  and  when  possible  their  use  should 
be  avoided. 

When  two  or  more  plain  teeth,  not  requiring  gum  restora- 
tion, approximate,  "Fogg's  Interstitial  Gum  Blocks"  can  be 
used  to  advantage  in  filling  the  embrasures,  thus  avoiding  the 
display  of  vulcanite   in   these   spaces.     These  also,  together 


CONSTRUCTION    OF    PARTIAL    UKNTURKS 


with  the  method  of  application,  ave  deserilied  under  tht 
of  "Special  Uses  of  Porcelain." 


head 


WAXING  THE  CASE 

The  teeth  haviui;-  been  ground  and  waxed  in  position,  the 
base  plate  is  applied  to  the  lingual  surfaces  of  the  teeth  and 
given  its  desired  outline  form.  The  wax  sliould  be  allowed 
to  extend  occlusally  on  the  lingual  surfaces  of  tiie  natural 
teeth  sufficiently  to  furnish  a  reasonably  broad  liearing  for 
tlie  base  plate,  for  retention  i)urposes.  A  single  thickness  of 
ordinary  sheet  wax  will  not  afford  enough  Imlk  of  material 
for  the  base  plate  and  foi-  loss  of  material  as  a  result  of  fin- 
ishing the  vulcanite.  Two  sheets  will  reiuhM'  the  case  too 
I'ulkv.  therefore  the  first  sheet  can  be  thickened  scuiiewhat  l)v 


111  I    or   DL\TLRr    IX  \MIILII   JIM  (    ' 

TrnsTiTi  vr   gim  f\iings    \k] 
iM>r(  \Ti  n 


hurnishing  a  sliglit  addition  of  wax  to  it  over  all  surfaces 
and  more  where  deficient  contour  requires.  The  wax  should 
extend  well  above  the  offset  slioulder  on  tlie  lingual  surfaces 
of  the  porcelain  teeth  so  as  to  insure  ample  material  for  de- 
veloping smooth  surfaces  in  the  final  finishing. 


FLASKING  THE  CASE 

When  plain  teeth  have  been  ground  to  the  border,  no 
gum  restoration  having  been  required,  the  teeth  may  I)e  im- 
bedded in  the  tirst  section  of  the  flask  with  the  cast  of  the 
mouth.  Frequently,  in  spaces  where  gum  sections  have  been 
fitted  and  absorption  of  the  border  is  marked,  so  that  con- 
siderable space  exists  between  the  border  side  of  the  block 
and  the  cast,  gum  sections  may  also  be  invested  the  same  as 
plain  teeth.  Special  care  must  be  taken  in  packing  the  case  to 
fill  the  space  between  tlie  block  and  cast  with  rubber  before 
closing  the  flask,  otherwise  the  vulcanite  is  lialile  to  lie  de- 
ficient from  failure  of  surplus  rubber  being  force<l  intd  the 


482  CONSTRUt'TION    OK    PARTIAL    DENTURKS 

space.  When,  however,  tlie  space  between  cast  and  block  is 
constricted,  so  that  it  will  bo  difficult  to  introduce  the  rubber, 
the  case  should  be  invested  so  that  the  block  will  be  cauglit 
and  hold  by  the  plaster  investment  in  the  second  half  of  the 
flask.     Tliis   sini])liiios  the  ])ackin.n'  of  the  case   so   that   tlie 


SECTIONAL    VIEW 


xn    WITIIOl'T    Gl'.M 


vulcanite  will  flow  freely  back  of  and  surround  tlie  block  as 
desired  in  the  final  closing  of  the  flask. 

Sometimes  both  methods  of  investing  the  teeth  are  adopt- 
ed in  the  same  case.  .  When  the  replaced  teeth  are  on  opposite 
sides  of  the  cast,  the  latter  can  be  set  more  deeply  in  the 
flask  on  that  side  occupied  by  the  plain  teeth  without  restora- 
tion than  on  the  other  side  where  gum  restoration  has  been 
applied.  This  gives  maximum  strength  with  minimum  bulk  to 
the  plaster  which  supports  the  plain  teeth. 


Projecting  plaster  teeth  should  be  trimmed  even  with  the 
lingual  mai'gin  of  wax,  and  the  outer  surfaces  of  the  cast 
backed  up  with  plaster  and  rounded  down  to  the  line  of  sep- 
aration of  the  flask  in  such  manner  as  to  obliterate  all  under- 
cuts. 


CONSTKUCTION     OK    PARTIAL    DKNTIKIOS  l.s:i 

The  points  iiixohcd  in  Hiiskiui;  aii.\'  case  are,  lirst,  to  8Ui)- 
port  the  east  under  its  base,  so  tliat  it  will  not  fracture  under 
the  stress  of  closing;  second,  to  construct  a  matrix  in  which 
to  mold  the  basic  material  which  will  not  yield  in  forcing  out 
the  excess  rubber,  not  permit  the  teetli  to  become  dislodged, 
and.  third,  to  so  shape  the  invested  case  in  the  tirst  half  of  the 
flask  that  the  second  will  readily  separate  from  it  without  pro- 
ducing fracture  of  the  investment. 

PARTIAL  DENTURES   OF   VULCANITE  WITH   CLASPS 
GENERAL   CONSIDERATIONS 

Wlien  a  partial  denture  of  vulcanite  is  to  l)e  retained  in 
position  with  clasps,  the  order  of  procedure  is  as  follows: 

Take  impressions  of  the  teeth  to  be  embraced  by  the 
clasps,  and  from  these  develop  metal  dies.  C'onstriict  the 
clasps  as  described  under  the  heading,  "Technic  of  Clasp  Con- 
struction." Attach  the  anchorage  lugs  to  the  clasps  in  such 
position  that  they  will  neither  interfere  with  correct  align- 
ment of  the  i^orcelain  teeth  nor  require  extra  bulk  of  vulcan- 
ite to  cover  them. 

The  clasps  are  now  placed  in  position  on  the  teetli  in  the 
mouth  and  a  mash  bite  secured,  using  the  face  bow  if  the 
case  calls  for  such  procedure.  Should  the  clasps  come  away 
with  the  bite,  they  are  returned  to  proper  position  on  the 
teeth. 

An  impression  in  plaster  is  now  taken  which  should  in- 
clude all  of  the  teeth  involved  in  developing  correct  occlusion, 
and  all  of  the  liorder  surfaces  to  be  covered  by  the  substi- 
tute. 

On  removal  from  tlie  month,  the  broken  parts  of  the  im- 
pression, if  fractured,  are  replaced  and  firmly  luted  together, 
the  clasps  adjnsted  in  correct  position  in  their  respective 
matrices  and  wedged  apart  so  that  each  wing  rests  in  con- 
tact with  the  matrix  wall  of  the  impression.  Should  any  of  the 
plaster  which  flowed  under  the  anchorage  lug,  next  the  border, 
have  become  broken  and  lost  in  removal  of  the  impression,  a 
little  wax  should  be  flowed  over  the  lug  and  the  general  con- 
tour of  the  impression  be  restored  in  this  manner.  When  the 
loss  of  impression  in  this  area  is  extensive  and  cannot  be  re- 
stored wdth  comparative  accuracy,  a  new  impression  should  be 
secured. 

A  cast  is  now  develo]ied  in  the  usual  manner,  using  pref- 
erably some  of  the  harder  materials  for  this  i)nr]iose.    When 


iSI  COXSTKICTIOX     ()!•'     I'Airi'lAI,     1 IIONTI '  It  KS 

liartleiietl,  lln'  iiii|ircssi(iiL  is  cjii'i'l'iillx    I'ciiKixcd   lo  iUdid  ilis- 
placing  the  clasps  or  ri'ac1iiriii,<;  the  tcctli. 

The  wax  bite  is  now  trinuned  freely  on  that  side  that  re 
ceivcs  tlie  working  cast,  so  that  hotli  teetli  aii<l  chisps  iiia\ 
occupy  the  same  i)osition  in  the  bite  that  the  natural  teeth 
and  clasps  sustained  to  it,  when  in  the  moutii. 

The  steps  from  this  point  on  are  essentially  the  same  as 
those  concerned  in  the  i)rodnction  of  a  partial  vulcanite  case 
without  clasps. 

In  case  it  is  considered  necessary  to  try  the  wax  model 
dentures  in  the  mouth,  which  is  sometimes  done  for  the  pur- 
pose of  testing  occlusion,  the  base  plate  should  be  formed 
around  the  clasp  lugs  in  such  manner  that  the  denture  may  lie 
released  without  disturbing  the  clasps  from  their  position  on 
the  teeth.  Under  no  circumstances  should  the  clasps  be  dis- 
turbed from  the  time  the  impression  is  filled  until  the  case 
is  vulcanized,  in  the  class  of  dentures  under  consideration. 

When,  however,  the  base  plate  consists  of  metal,  the 
clasps  are  usually  permanently  attached  to  it  in  the  prelim- 
inary constructive  stages,  as  will  be  explained  later.  In  such 
case  they  will  come  away  from  tlie  cast  with  the  l)ase  plate. 

In  flasking  the  case,  special  care  should  be  taken  to  cover 
the  exposed  ends  of  the  clasps  with  the  plaster  investment  in 
the  first  section  of  the  flask,  so  as  to  hold  them  firmly  in  posi- 
tion after  the  wax  is  removed  and  during  the  packing  and  clos- 
ing of  the  case. 

It  is  also  frequently  advisable,  before  ])acklng  the  matrix, 
to  jilace  between  the  anchorage  lug  and  the  cast  a  small  wedge 
of  vulcanite,  of  similar  color  to  the  basic  rubber  being  used, 
to  prevent  displacement  of  the  clasp  liy  the  rubber  in  the 
matrix  in  the  closing  of  the  flask. 

The  wedge  can  be  cut  from  an  old  base  plate,  should  be 
clean,  and  all  surfaces  freshened  so  as  to  insure  close  imion 
of  the  new  rubber  with  it.  When  neatly  applied,  no  difference 
in  color  will  be  noticealile,  and  practically  all  danger  of  clasp 
dis])]acement  will  lie  ol)viate(l. 

PARTIAL  LOWER  DENTURES  OF  VULCANITE 

The  construction  of  i)artial  lower  dentures  of  vulcanite, 
either  with  or  without  clasps,  is  much  the  same  as  for  similar 
upper  cases.  Attention  should  be  given  one  important  detail 
which  differs  from  upper  partials,  particularly  in  those  cases 
where  the  anterior  teeth  are  px'esent,  and  the  replacements 
occur  along  the  posterior  borders. 


CONSTKICTIUN    OK    I^ARTIAL    DKNTrUKS  485 

While  in  upper  partial  cases  the  stress  i)f  mastication  is 
resisted  directly  by  the  saddle  under  the  replaced  tooth  or 
teeth,  yet  the  comparatively  flat  or  somewhat  flaring  sur- 
faces of  the  lingual  border  base  ])late,  which  rests  upon  the 
mucous  tissues,  receives  some  of  the  stress  also  and  imparts 
general  stability  to  the  denture. 


In  lower  cases  but  little  if  any  suppoi-t  is  afforded  the  den- 
ture by  the  lingual  border  surfaces  of  the  base  plate  next  the 
teeth,  because  of  the  generally  perpendicular  relation  of  these 
surfaces  of  the  natural  tissues.  It  is  therefore  necessary  to 
extend  the  base  plate  well  up  on  the  cingula?  of  the  anterior 


OCn.USAT,  VIEW   OF   LOWEK   PARTIAL  MLCAMTH    liASK   PLATE, 

SIIOWINC    FINMSHING  SHOI'LDERS  FOR  TilE   SFCCOMI 

AD111T10N   OF    RPliliER 

teeth,  otherwise  if  this  is  not  done,  irritation  and  absorption 
of  the  lingual  gingival  tissues  will  occur  in  a  very  short  time. 
The  application  of  stop  clasps  to  the  first  bicuspids,  or  even  the 
second  bicusiiids,  when  the  replaced  teeth  are  situated  to  the 
distal  of  the  clasps,  will  practically  overcome  the  tendency  of 
lower  partials  to  tip  anteriorly.    The  use  of  clasps  without 


lai;  CONS'I'IU'C'I'ION     Ol''     I'Airi'lAI,    1  )K.\TI '  ItKS 

.stoi)s  in  the  s;iiiir  Im-jil  imi  .-iiid  iiiiilci-  llic  same  (•(iiiditidiis 
usually  iiuii'iiiciil    the  uiiilcsiralilc  couditious  lucntioiiL'd. 

Frequently,  in  differenl  cases,  it  is  advisable  to  construct 
the  base  of  vulcanite  tn  wliich,  a1  the  s;une  time,  clasp  may 
be  attached.  This  base  plate  is  tiicn  littrd  in  the  mouth  the 
same  as  a  gold  base  denture,  a  mash  liite  takeji  and  the  teeth 
selected,  waxed,  ground  to  meet  requirements  and  vulcanized 
to  the  ])reviously  constructed  base. 

By  forming  finishing  shoulders  on  the  l)ase  against  which 
the  second  addition  of  vulcanite  will  finish  and  using  a  slightly 
different  shade  of  rubber,  very  artistic  results  can  be  realized. 

The  introduction  of  the  lingual  bar  of  metal  for  lower  and 
the  over-arch  bar  for  upper  cases  combined  with  improved 
forms  of  frictional  retention  a])pliances,  have  proven  so  satis- 
factory that  the  teclmic  of  partial  denture  construction  has 
been  practically  revolutionized  within  the  last  few  years. 

MOUNTING  THE   CASTS   ON  THE   OCCLUDING  FRAME 

When  a  mash  bite  has  been  taken,  in  conjunction  with  the 
face  bow,  it  is  advisable  in  these,  as  in  njany  other  similar 
cases,  to  attach  the  face  bow  to  the  occluding  frame  and  de- 
velop the  occlusion  cast  before  adjusting  the  working  cast  or 
that  one  to  which  the  artificial  teeth  are  to  be  fitted,  in 
the  bite.  The  reason  for  so  doing  is  that  the  bite  which  re- 
ceives the  working  cast  must  be  trimmed  away  freely  so  that 
the  occlusal  surfaces  of  the  teeth  may  rest  perfectly  on  the 
wax  surfaces  impressed  by  the  natural  teeth.  This  cannot  be 
determined  accurately  unless  practically  all  of  the  buccal, 
labial  and  lingual  surfaces  of  the  bite  are  ciit  away  sufficiently 
to  expose  these  occlusal  areas  to  view,  as  has  been  pre\'iously 
stated.  Now,  if  an  attempt  is  made  to  force  the  working  cast 
into  the  bite,  or  if  the  bite  is  trimmed  before  the  occlusion  cast 
is  developed,  distortion  of  the  wax  will  most  certainly  occur, 
and  later  on,  when  the  occlusion  cast  is  developed,  the  rela- 
tion between  the  two  will  be  incorrect. 

Summarized,  the  steps  are  as  follows : 

Apply  face  bow,  with  mash  bite  attached,  to  the  occluding 
frame.  Fill  the  occlusion  side  of  the  bite  with  plaster,  attach- 
ing it  to  the  bow  of  the  frame.  Trim  wax  bite  to  receive  the 
working  cast,  being  careful  not  to  injure  the  plaster  teeth  of 
the  occlusion  cast  while  doing  so.  Adjust  working  cast  in 
trimmed  wax  bite  and  attach  to  occluding  frame.  When  the 
plaster  has  set  warm  the  wax,  open  the  fi-ame  and  remove  the 
wax  from  the  occlusion  cast. 


CONSTRUCTION    OF    PARTIAL    DENTURES  4S7 

REGISTERING   THE    CONDYLE    PATHS   IN    PARTIAL    CASES 

Au  ordinary  protrusive  mash  l)itt',  wlieu  properly  triminetl 
so  that  the  teeth  of  both  oasts  may  correctly  enter  their 
impressions,  will  serve  to  set  the  condyle  paths  of  the  oc- 
cluding frame  to  coincide  with  tiiose  of  the  patient. 

ARRANGING  THE  TEETH 

Teeth  of  suitable  foi-m  and  color  are  selected  and  ar- 
ranged as  in  full  cases,  the  plaster  teeth  on  the  occlusion  cast 
serving  as  a  guide  in  developing  correct  alignment  and  oc- 
clusion. (*are  must  be  taken,  therefore,  not  to  mutilate  the 
occlusion  model  by  attempting  to  force  the  porcelain  teeth 
into  imperfectly  softened  wax  l)y  closing  the  frame  as  in  full 
cases.  Such  procedure  nearly  always  fractures  the  occluding 
plaster  teeth  and  destroys  the  only  means  of  testing  the  ac- 
curacy of  occlusion  in  the  constructive  stages  of  the  case. 

When  the  very  slight  connection  between  the  wax  saddles 
and  anchorage  spurs  is  considered  it  will  readily  be  seen  that 
trial  of  the  wax  model  denture  in  the  mouth  is  impracticable. 
Even  when  saddles  of  Ideal  Base  Plate  are  formed  and  firmly 
luted  to  the  anchor  spurs,  to  serve  as  a  foundation  on  which 
to  arrange  the  teeth,  the  benefits  of  a  "try  in"  of  the  case  is 
questionable,  because  of  the  general  distui'bance  of  relation 
of  the  several  parts  to  each  otlier,  wliicli  coiiunonly  occurs 
during  such  procedure. 

The  points  of  interference  between  porcelain  teeth  and 
those  on  the  occluding  cast  should  be  noted  and  correction 
made  by  grinding  as  each  tooth  is  set  in  position..  When 
the  protrusive  bite  is  taken,  as  outlined,  the  relation  of  the 
lower  and  upper  te"eth  to  each  other  in  lateral  movements 
shoiild  be  tested  and  corrections  made  accordingly.  The  neces- 
sity of  developing  perfect  teeth  on  the  occlusion  cast  and  of 
avoiding  their  fracture  during  the  arrangement  of  the  sub- 
stitutes is,  therefore,  of  extreme  im|)t)rtance. 

The  case  is  waxed  to  the  re(|uired  outline  form  and  given, 
the  desired  surface  develoiiment  of  th(>  finislied  denture,  when 
it  is  ready  for  flasking. 

-FLASKING  THE  CASE 

Partial  cases  of  the  type  here  described  are  flasked  the 
same  as  ordinary  vulcanite  dentures,  except  that  the  anterior 
lingual  surface  of  the  cast  should  be  filled  with  plaster  in  the 
first  investment  of  the  case,  so  as  to  enclost'  the  exposed  yior- 


488  CONSTRUCTION    OK    PARTIAI-    DKNTURES 

tioii  of  the  lingual  bar  aud  hold  it  rigidly  duriug  subsequent 
procedures  of  flask  separation,  reinoval  of  wax,  packing  the 
rubber,  final  flask  closing  and  vulcanizing. 

Since  these  steps,  as  well  as  finishing  the  case,  are  similar 
to  those  of  ordinary  cases,  the  details  need  not  be  repeated. 

LOWER  PARTIAL  GOLD  BASE  DENTURES 

In  replacing  lower  ])osterior  teeth  it  is  frec^uently  advis- 
able, and  a  common  method  of  practice,  to  construct  a  gold 
base  and  attach  the  substitute  teeth  to  it  with  vulcanite,  or 
other  means,  as  conditions  require. 

One  of  the  older  methods,  which  in  favorable  cases,  has 
I^roven  very  satisfactory,  is  carried  out  as  follows : 

A  die  and  counterdie  of  the  case  are  developed  in  the  usual 
manner,  on  which  a  gold  base,  usually  of  28  or  29  g.  and  20  k. 


LOWER    PARTIAL.  SWAGED    GOLD   BASE    WITH 
DOUBLER      A,    BASE  B.    DOUBLER 

DETAIL   OF   VULCANITE    RIM 

C.  WIRE    BEFORE    SOLDERING 

D.  WIRE    AFTER    SOLDERING    AND 
SQUARING 


is  swaged.  The  lingual  l)and  of  gold  which  connects  the  two 
saddles  should  extend  well  up  on  the  cingute  of  the  anterior 
teeth  to  prevent  settling  of  the  denture  under  stress  as  previ- 
ously mentioned.  The  principal  base  should  be  reinforced  with 
a  doubler,  anteriorly,  aud  extending  back  of  the  teeth  clasped 
on  either  side,  about  one-half  inch.  This  doubler  may  be  of 
29  or  30  gauge  gold.  The  base  plate  and  doubler  are  pickled, 
polished  and  united  with  solder,  trimmed  to  correct  outline 
and  reswaged.  Clasps  are  developed  on  independent  metal 
dies  constructed   for  the  purpose.     Th.ese  are  fitted  to   the 


CONSTKICTIU.N    l)K     I'AKTIAI-    I  )K.\T  I '  H  K8  4S'J 

teeth  ill  the  mouth.  The  hase  plate  is  triumiecl  to  take  its 
proper  position  on  the  border  without  interfering  witli  the 
clasps.  An  impression  is  tlien  taken  of  the  teeth  clasped, 
preferably  of  one  tooth  at  a  time,  with  clasp  in  position, 
and  including  the  contiguous  part  of  the  base  plate.  The 
base  plate  can  thus  be  held  in  position  while  the  plaster  can 
be  applied  in  a  small  hinged  tray.  When  set,  the  impression 
is  removed,  the  clasp  and  base  plate  adjusted  in  position,  luted 
firmly  with  wax  and  a  small  cast  developed,  which  holds  the 
clasp  and  base  plate  in  correct  relation  during  soldering. 

When  united,  the  base  plate  is  returned  to  the  mouth  and 
an  impression  of  the  other  tooth  and  clasp  secured  in  like 
manner.  This  clasp  and  the  base  plate  are  united  as  just 
outlined.  The  metal  structure  is  now  i)ickeled,  polished  and 
I'cturned  to  the  mouth  for  final  bite  and  iinjiression. 

FORMING  THE  FINISHING  SHOULDER  FOR  VULCANITE  WITH 
GOLD  PLATE 

In  these,  as  in  practically  all  cases  of  gold  base  dentures, 
to  which  the  teeth  are  attached  with  vulcanite,  a  shoulder 
should  be  formed  against  which  to  finish  the  latter.  This 
may  be  done  by  cutting  narrow,  2>arallel-sided  strips  of  gold 
plate  of  whatever  curvature  is  required  and  applying  and 
soldering  the  same  along  the  line  on  the  base  plate  where  the 
\ulcanite  should  terminate.  These  strips  are  applied  and 
soldered  neither  at  right  angles  to  nor  flatly  against  the  base 
plate,  but  usually  somewhat  slanting  so  as  to  form  a  ^"-shaped 
groove  interiorly,  while  the  outer  surfaces  form  a  continuous 
curve  with  the  gold  base  and  vulcanite.  This  method  is  not  only 
])ractical  and  economical,  but  artistic  as  well.  It  is  particu- 
lai'ly  applicable  to  those  cases  where  border  absorption  has 
progressed  unequally  and  where,  if  correct  contour  be  given 
the  case,  the  vulcanite  will  be  disposed  in  unsymmetrical  out- 
line on  the  base.  In  such  ease  a  strip  of  suitable  width  and 
curvature  can  be  cut,  contoured,  applied  and  soldered  to  the 
iiase  in  such  manner  as  to  develop  normal  contour  to  the  den- 
ture, and  symmetrical  exposure  of  the  vulcanite  as  well. 

FORMING  THE   SHOULDER  WITH   WIRE 

The  most  common  method  of  developing  the  finishing 
shoulder  for  the  vulcanite  is  by  soldering  a  wire  along  the 
line  on  the  base  plate  as  indicated  by  the  terminal  margin  of 
the  previously-contoured  wax.    That  surface  of  the  wire  pre- 


■l!t(l  CONS'l'UrC'I'ION     Oh'     I'AirriAL     KKN'TlliKS 

sciiliiig  low.-inl  llic  \  iilr;iiii1r  ;ui';i  is  s(|Uiin'il  out  with  stones 
and  plu.n'  liiiisliiiiii'  Inii's,  wiiiic  liir  oiitci-  siirrarcs  of  wive  ami 
solder  arc  ,i;i\cii  llic  aii|ii'nxiiiiii1i'  curxjiturc  of  tlic  rniislic<l 
case. 

The  wire  not  oiil>'  atl'oi-ds  a  linisliiug  slioultlcr  for  tlio 
\'iilcaiiite,  bvit  when  united  to  the  gold  base  imparts  rigidity  to 
the  latter  to  almost  any  degree  desinnl,  de] lending  on  the 
gauge  used  and  the  nniouiit  of  solder  applied. 

EXTENT  TO  WHICH  THE  WIRE  IS  APPLIED  PERIPHERALLY 

A  shoulder  wire  is  apjilied  along  those  areas  on  a  base 
plate  where  loss  of  contour  of  the  border  becomes  plainly 
noticeable.  This  applies  not  only  to  lines  parallel  with  the 
border  crest  l)ut  to  the  end  or  perpendicular  lines  as  well. 
In  lower  partial  cases,  of  the  type  under  consideration,  the 
wire  wliicl)  forms  the  anterior  terminal  shoulder  will  usually 
be  laid  ])ai'allel  with  (lie  distodingnnl  line  angle  of  the  tooth 
clasped,  or  at  such  point  that  when  the  vulcanite  is  applied 
and  the  case  finished,  the  general  lingual  contour  of  the  case 
is  continuous  witli  that  of  the  I)ase  iilate  along  the  lingual 
surfaces  of  the  natural  teeth. 

The  wire  should  extend  from  the  anterior  lingual 
shoulder  margin,  distally,  along  the  Ungual  border,  curve  over 
the  crest  of  the  latter  to  the  Iniccal  side  and  pass  forward  along 
the  margin  to  near  the  anterior  terminal  of  the  base  plate. 
It  should  not  rise  perpendicularly  as  on  the  lingual  side  be- 
cause the  presentation  of  a  line  of  gold  in  this  area  is  un- 
sightly and  unnecessary  as  well.  By  trimming  the  base  plate 
a  little  scant  at  the  anterior  buccal  terminal  the  artificial  gum 
.naterial  can  overrun  the  latter  and  thus  oI)viate  the  display 
of  any  gold.  The  ability  to  recognize  lost  border  surfaces  and 
contours  and  lay  the  shoulder  wires  in  correct  ])osition 
to  restore  them  is  an  art  that  should  be  acqii.ired  by  every 
prosthetist  and  one  which,  when  developed,  stamps  him  a 
master  of  his  calling. 

LINGUAL  BAR  DENTURES 

A  very  common  and  satisfactory  method  of  replacing  the 
lower  posterior  teeth  is  by  means  of  saddles  either  of  gold  or 
of  vvilcanite,  combined  with  the  lingual  bar  to  serve  as  a 
foundation  for  carrying  the  substitute  teetli.  Various  methods 
of  retention  are  employed,  the  most  fref|uent  will  now  be 
mentioned. 


CONSTRUCTION    OF    PARTIAL    DKNTURES  JStl 

RELATION  OF  LINGUAL  BAR  TO  ORAL  TISSUES 

In  constructing  lo^Yel■  lingual  bar  cases  the  assembling 
of  the  several  parts  in  correct  relation  to  each  other  and  to 
the  oral  tissues  must  be  carried  out  in  a  definite,  systematic 
and  orderly  manner.  The  position  of  the  bar  in  reference 
to  the  lingual  border  surfaces  is  particularly  important.  When 
in  the  finished  denture,  if  allowed  to  touch  the  soft  tissues,  or 
to  bear  upon  them  with  any  degree  of  force,  it  will  canse  more 
or  less  discomfort,  sometimes  so  much  so  as  to  recjuire  re- 
construction of  the  case.  On  the  other  hand,  the  bar  cannot 
be  placed  too  far  from  the  border  or  too  near  the  gingival 
luargin  of  the  gums,  or  tnugu(>  movements  will  be  interfered 
with. 

It  is  impossible  to  state  definitely  the  exact  position  of 
the  bar  as  each  case  possesses  peculiarities  of  its  own.  Usually 
when  placed  from  one-fourth  to  three-eighths  of  an  inch  below 
the  gingival  margin,  when   the  lingual  muscles  will  permit. 


and  about  one  twenty-fifth  of  an  inch  from  the  border  tissiies, 
neither  tongue  movements  will  be  interfered  with  nor  will  the 
border  tissues  be  impinged  npon. 

FORMS  OF  LINGUAL  BARS 

It  is  not  possible  to  here  describe  all  of  the  various  forms 
of  bars  used,  nor  the  many  general  methods  of  construction 
followed  in  these  cases,  but  an  outline  of  the  principal  steps 
will  be  given  to  serve  as  a  foundation  in  this  work.  A  case 
of  rei^lacement  of  the  posterior  teeth  involving  a  lingual  bar, 
stop  clasps  and  \-ulcanite  saddles  will  be  described. 

TECHNICAL'  STEPS    IN    LINGUAL   BAR   CASES 

F'irst,  impressions  of  the  teeth  for  clasp  construction 
should  be  secured,  and  these  appliances  developed  in  accord- 
ance with  steps  previously  described. 

The  clasps  are  placed  in  position   on  the  teeth   and  a 


ty2  CONSTKlUrKJiN     OK     PAU'IMAI-     OKN'I'l   ItlOS 

plaster  impressidii  secured  of  the  liii.niial  ai'ciiK  oi'  tlie  l)ortlei' 
next  which  the  bar  will  rest,  and  of  suflicieiil  liorder  areas  hack 
of  the  teeth  clasped  to  indicate  the  iiiaiiiier  in  which  the 
terminal  ends  of  the  hnr  can  be  bent  to  best  advantage  for 
anchorage  puriioses.  The  clasped  teeth  innst  also  be  em- 
hraced  by  the  ini])ression. 

To  prevent  marring  of  the  cast  while  adapting  the  lingual 
bar  it  should  be  formed  fi-oni  some  of  the  harder  materials, 
as  Spence's  plaster  or  oxy-cliloride  of  magnesia. 

The  cast  having  been  formed  a  measurement  of  the  length 
of  wire  to  be  used  in  making  the  bar  is  secured,  usually 
with  a  smaller  wire  which  can  be  readily  bent,  or  preferably 
with  a  piece  of  12  gauge  electric  fuse  wire.  The  latter  wire 
is  very  pliable  and  can  be  formed  to  the  exact  shape  of  the 
permanent  bar,  its  ends  flattened  for  retention  purposes  and 
any  peculiar  bends  which  the  case  calls  for  can  be  discovered 
before  attempting  to  confonn  the  very  rigid  wire  of  precious 
metal.  This  step  will  not  be  considered  necessary  by  the 
experienced  wire  liender,  but  will  prove  most  useful  to  the 
beginner. 

High-grade  clasp  metal  wire,  or  iridio-platinum,  from  12 
-tQ-34-gange~thickness.  is  usually  used  for  the  bar  in  orderTEat 
it  may  stand  the  various  stresses  to  which  sulijected  in  the 
constructive  stages  and  in  subsequent  use,  without  bend- 
ing. 

Two  pieces  of  16-gauge  wire  are  sometimes  bent  sep- 
arately to  the  form  desired  and  afterward  united  with  solder. 
This  plan  is  followed  by  those  who  find  difficulty  in  conform- 
ing the  heavier  gauge  wire.  Care  should  be  taken  to  fill  the 
V-shaped  spaces  between  the  two  wires  with  solder.  When 
imperfectly  filled,  food  lodges  in  them  and  the  doubled  wire 
feels  uncomfortable  to  the  tongue. 

To  develop  good  anchorage  in  vulcanite  saddles,  it  is 
necessary  to  extend  the  bar  back  of  the  clasped  teeth  from 
one-half  to  five-eighths  of  an  inch.  The  bar  should  be  bent 
outward  and  upward,  to  the  crest  of  the  border,  each  terminal 
end  flattened  broadly  and  a  hole  drilled  through  it,  or  a  short 
cross-head  soldered  on  to  prevent  the  gradual  loosening  of 
the  saddle  imder  stress. 

The  flattened  ends  of  the  bar  should  be  warped  to  lie 
parallel,  but  not  quite  in  contact,  with  the  border  surfaces. 
The  ideal  position  for  the  terminal  ends  of  the  wire  in  the 
finished  case  is  in  the  center  of  the  saddles. 


CONSTRUCTION    OF    PARTIAI.    UKNTl'UKS  41t:! 

VARIATION  IN  FORM  OF  CONNECTION  BETWEEN   LINGUAL 
BAR  AND  CLASP 

A  conunuii  and  very  ]>ractical  lucthdil  itf  construt'ting  tht^ 
skeletou  frame  work  for  a  lingual  bar  case  is  as  follows: 

The  bar  is  coiiformecl  anteriorly  to  the  east,  as  previously 
deseribed,  but  instead  of  being  carried  back  of  the  teeth  em- 
braced by  the  clasps  and  terminating  in  the  vulcanite  saddle 
it  is  bent  upward  and  outward  at  the  disto  lingual  angle  of 
each  of  the  clasped  teeth,  in  such  position  as  not  to  render  the 
'lingual  side  of  the  ease  bulky  nor  interfere  with  arrangement 
of  the  substitute  teeth. 

This  manner  of  connection  of  clasp  and  bar  affords  no 
anchorage  of  metal  framework  to  saddles.  To  supply  such 
attachment,  a  piece  of  clasp  wire  of  the  same  gauge  as  the  bar, 
about  one-half  inch  long,  is  flattened  throughout  about  two- 
thirds  of  its  length,  bent  to  conform  to  the  curvature  of  the 
border  crest  and  distal  surface  of  the  tooth  and  clasp  and 
soldered  to  the  latter.  The  better  plan  is  to  fit  the  anchor 
spur  in  the  angle  between  the  turned-up  end  of  the  lingual 
bar  and  clasp  and  form  the  connection  principally  between  the 
two  wires,  thus  obviating  too  broad  an  attachment  to  the 
clasp.  Another  method  of  anchoring  the  lingual  bar  to  vul 
canite  saddles  is  as  follows: 

The  bar  is  adapted  to  correct  lingual  curxature,  as  de- 
scribed. The  terminals,  instead  of  being  bent  outward  and 
over  the  crest  of  the  border,  pass  backward,  ]mrallel  with  the 
lingual  periphery  of  the  saddle  on  either  side,  or  it  may  lie 
somewhat  above  the  peripheral  margin  of  th(>  saddle,  so  as 
to  be  entirely  enclosed  with  the  vulcanite. 

Two  ribs  of  rigid  metal  are  bent  to  the  l)uceo-lingual  con- 
tour of  the  boi'ders  and  soldered  to  the  lingual  bar,  one  at  the 
distal  extremity  of  the  latter,  the  other  midway  between  that 
point  and  the  clasped  tooth.  These  ribs,  as  well  as  the  Itar, 
should  be  enclosed  within  the  vulcanite. 

SOLDERING   THE   CLASPS   AND    BAR    IN    CORRECT    RELATION 
TO  EACH  OTHER 

The  bar,  when.jjroperly  conformed,  is  blocked  in  position 
on  the  cast  by  interposing  a  small  pellet  of  wax  under  each 
terminal  end  and  one  anteriorly.  While  the  wax  is  soft  the 
bar  is  pressed  to  the  exact  position  desired  and  luted  by  melt- 
ing a  portion  of  the  wax  lo  both  bar  and  cast.  The  excess 
wax  is  then   trinnncd   awav.   a   small   ainnunl    of  investment 


494  CONSTRUCTION    OF    PARTIAL    DENTURKS 

mixed  and  Howcd  over  the  bar  at  these  three  points,  leaving 
the  greater  portion  of  metal  exposed. 

A  strip  of  20-gauge  clasp  metal,  about  one-eighth  inch 
wide,  is  titted  between  each  clasp  and  the  bar,  the  lower 
end  of  the  strip  resting  between  the  bar  and  east,  the  I'tpper 
end  extending  above  the  gingival  margin  of  tlie  clasp  so  that 
the  solder  may  develop  a  broad  attachment  between  the  two. 
No  eifort  need  be  made  to  fit  the  strip  accurately  to  the  cast, 
since  any  slight  space  that  may  exist  between  the  two  will 
later  on  fill  with  vulcanite. 

Flux  is  now  applied  and  the  bar  and  clasj*  on  each  side 
are  connected  with  solder,  flowing  it  not  only  in  the  joints 
but  over  the  strip  as  well,  to  stiffen  it  and  form  a  rigid  con- 
nection. This  method,  it  will  be  seen,  does  not  require  the 
removal  of  the  clasps  from  their  position  on  the  cast,  and 
therefore  the  relation  between  them  and  the  teeth  they  em- 
brace is  the  same  as  when  in  the  mouth.  When  soldered  the 
case  is  removed  from  the  cast,  picketed,  polished  and  washed 
and  is  now  ready  for  the  final  bite  and  impression. 

A  sliglit  variation  from  the  above  method  is  sometimes 
carried  out  whereby  the  attachment  of  clasps  and  l)ar  may  be 
made  as  described  and  stops  developed  on  the  clasps  at  the 
same  time.  This  refers  to  cases  in  which  stops  were  not  de- 
veloped on  the  clasps  or  soldered  to  them  during  the  con- 
structive stages  or  before  the  impression  was  taken. 

The  strip  which  forms  the  connection  between  bar  and 
clasps,  either  of  clasp  ]ilate  or  half-round  wire,  is  cut  of  suf- 
ficient length  to  reach  from  the  bar  across  the  clasp  and  to  the 
point  where  the  occlusal  rest  or  stop  should  terminate.  It  is 
then  annealed  and  with  pliers  shaped  to  meet  the  recpiire- 
ments  of  both  standard  and  stop,  when  it  is  attached  with 
solder,  as  described. 

Sometimes  the  location  of  the  stop  will  be  out  of  normal 
alignment  with  position  of  the  clasp  and  bar  connection.  In 
such  case  the  stop  can  be  formed  separately  and  soldered  at 
the  time  of  connecting  the  bar  and  clasp.  It  will  be  found 
most  convenient,  and  accurate  as  well,  to  form  the  stops  on 
the  clasps  and  unite  them  during  the  constructive  stages,  at 
which  time  more  ])erfect  adaptation  can  be  secured  while  the 
clasps  are  on  the  metal  dies. 

TAKING  THE  WAX  BITE 

The  bar,  with  clasps  attached,  is  now  introduced  in  the 
mouth  and  its  relation  and  that  of  the  clasps  to  the  tissues 


CONSTRUCTION    OK     PARTIAL    DKNTCRKS  495 

and  Ici'tli  xcrilicd.  If  (•(HTcct  a  wax  iiiasli  ))il('  is  lakt'ii  with 
the  api»liaiic('  in  iiusitiuii,  caiv  l)(_'iiig  takeu  to  iiichule  all  nec- 
essary tooth,  and  the  l)()vdor  areas  as  well.  In  this,  as  in 
practically  all  classes  of  extensive  re])lacements,  the  face  bow 
shouid  he  a)ii)lied  and  the  hite  cavefuUy  removed  without  dis- 
tortion. 

TAKING   THE   IMPRESSION 

The  final  impression  in  all  cases  should  he  in  plaster.  In 
cases  of  the  class  iinder  consideration  a  full  impression  of  the 
border  surfaces  to  be  covered  by  the  saddles,  the  teeth  clasped 
and  the  anterior  teeth  to  slightly  below'  the  gingival  line  is 
essential.  Lingually  the  impression  should  extend  deeply 
enougli  to  embrace  the  bar  opposite  the  teeth  clasped,  but  not 
necessarily  anterior  to  these  locations. 

Special  care  must  be  observed  in  taking  hoth  bite  and 
impression  that  undue  stress  is  not  brought  upon  the  anchor 
spurs  posteriorly,  or  the  lingual  bar  anteriorly  of  the  teeth 
clasped,  otherwise  the  framework  will  l)e  tipped  and  thrown 
in  an  abnormal  relation  to  the  teeth  and  oral  tissues.  By  en- 
closing the  terminal  ends  of  each  anchor  spur  in  a  small  mass 
of  soft  modeling  compound,  then  pressing  the  bar  down  until 
the  clasps  take  their  proper  position  on  the  teeth  and  the 
bar  its  correct  relation  to  the  border,  the  framework  can  be 
balanced  and  steadied  while  taking  the  impression.  The  com- 
pound serves  the  i)urpose  of  temporary  saddles  and  when 
properly  ap])lied  to  the  border  becomes  a  part  of  tlie  im- 
pression. 

The  impression  usually  fractures  and  comes  away  in 
pieces.  These  should  he  cleared  of  debris,  reassembled  and 
luted  tirmly  together,  varnished  and  a  cast  of  hard  material 
constructed  on  which  to  vulcanize  the  case. 

ARTIFICIAL  STONE 

Recently  there  has  l)een  jilaced  on  the  market  an  artificial 
stone  product  which  can  be  mixed  with  water  and  which  will 
harden  in  about  four  hours.  It  is  dense  and  hard  and  will 
stand  rough  usage.  It  softens  somewhat  during  vulcanization 
and  is  more  readily  removed  from  the  vulcanite  than  is  oxy- 
chlorid  of  magiiesia.  This  ])roduct  is  specially  useful  in  the 
construction  of  partial,  and,  in  fact,  all  cases  where  the 
preservation  of  relations  of  several  parts  in  constructive 
stages  is  essential.  The  material  referred  to  is  "Weinstein's 
Artificial  Stone,"  prepared  by  C.  A.  Nielsen  Co.,  New  York. 


i:m;  cons'I'1U'c"|'1(».\   oi''   i'aktial   dkntukks 

THE  LINGUAL  BAR  COMBINED   WITH   GOLD  SADDLES 

In  cases  of  this  type,  one  of  I  he  coniindii  methods  of  con- 
strnction  is  as  follows: 

Fii'st — Impressions  of  the  teeth  to  be  ehvsped  are  secured 
and  clasps  constructed  by  methods  previously  oiitlined. 

Second — A  full  impi-ession,  in  plaster,  is  secured  of  the 
lower  arch,  including  all  of  the  ])arts  concerned  in  the  forma- 
tion of  saddles  and  lingual  bar.  In  most  cases  the  impression 
should  be  scraped  along  the  border  crests  slight  1\-,  but  the 
r<'iier  so  afl'orded  should  iu)t  extend  to  anterior  or  posterior 
terminals. 

The  derived  cast  is  trimmed  and  converted  into  a  model, 
so  as  to  readily  withdraw  from  the  sand  mati'ix,  and  a  die 
and  counterdie  formed. 

Third — Saddles  are  swaged  to  the  border  surfaces  and 
trimmed  to  approximately  correct  peripheral  outline. 

Fourth — The  lingual  bar  is  adapted  to  the  required  con- 
t(mr  of  the  case,  using  the  die  as  a  model  on  whicli  to  do  tlie 
lifting.  Tlae  Benson  Plier  is  particularly  well  adapted  to  the 
work  of  bar  bending,  the  wire  being  held  in  the  concave  de- 
pression back  of  the  beak  contact. 

In  gold  saddle  cases,  the  terminals  of  the  bar  should  lie 
parallel  with  and  rest  against  the  lingual  margin  of  the  sad- 
dles to  which  they  are  afterward  soldered.  By  proper  trim- 
ming, the  upper  margin  of  the  bar  may  lie  formed  into  a  finish- 
ing shoulder  for  the  vulcanite  attachment  of  the  teeth. 

If  any  doubt  exists  as  to  the  depth  to  which  the  lingual 
border  of  the  saddles  can  extend  without  impingement  on  the 
tissues  the  safest  plan  will  be  to  test  the  saddles  in  the  montli 
before  uniting  them  to  the  bar. 

Fiftli,  after  the  saddles  are  trimmed  to  correct  lingual 
width  they  are  returned  to  the  die,  the  lingual  bar  adjusted  as 
described  under  the  preceding  heading,  ''Lingual  Bar  Den- 
tures," page  490. 

The  terminal  ends  of  the  bar  are  now  firmly  waxed  to  the 
saddle  margins,  care  being  taken  while  adjusting  it  to  avoid 
springing  the  bar.  It  is  frequently  a  good  plan,  after  the  bar 
is  perfectly  adjusted  to  the  two  saddles,  to  unite  one  end 
only  with  its  saddle,  remove  from  the  die,  invest  and  solder 
the  two  together.  The  partially  constructed  frame  is  returned 
to  the  die  and  careful  adjustment  secured  between  it  and  the 
opposite  saddle,  after  which  they  are  invested  and  united  as 
in  the  first  instance. 


CUN'STKrCTlOX    oK     I'AIM'IAI-    HKiNTIKKS  497 

Sixth,  tlic  slvL'lctuii  (Iciilui'c  is  ijicklcd.  clraiiscd  and  in- 
troduced iu  the  mouth  for  llual  ii('ri])licrnl  triiniiiiiiii  and  gen- 
eral adjustment. 

Seventh,  the  chisps  having  been  formed  are  adjusted  to 
the  teeth,  the  denture  base  introduced,  trinnned  wliere  inter- 
ference witli  clasps  occur  and  the  relation  Ijetween  clasps, 
teeth  and  baseplate  secured  as  ordinarily  accomj^lished  or  by 
the  compression  method  describe<l,  when  sucli  procedure  is 
indicated. 

Eighth,  when  clasps  and  baseplate  are  united  and  the  den 
ture  base  cleansed;  it  is  returned  to  the  mouth  for  final  im- 
pression and  bite.  By  usual  methods,  casts  are  ]iroduced  and 
mounted  on  the  occluding  frame. 

Ninth,  the  teeth  are  occluded,  and  when  deemed  advisable, 
cases  of  this  type  can  lie  removed  from  the  cast  for  final  trial 
in  the  mouth. 

Tenth,  after  flasking  and  separating  the  case,  if  the  sad- 
dles have  not  previously  been  spurred  with  a  graver,  this 
step  should  be  carried  out  before  final  closing  of  the  packed 
flask.  In  addition  to  this  method  of  anchorage,  small  loops  of 
wire  should  lie  soldered  on  the  saddles  and  the  latter  coated 
with  a  film  of  thin  chloro-rubber  to  act  as  a  cementing  me- 
dium between  gold  and  vulcanite. 

SETTLING  OF  DENTURES  FROM  USE 

When  a  denture  of  any  type  is  introduced  in  the  mouth 
and  worn  foi'  even  a  sliort  time  the  mucous  tissiies  on  which 
it  rests  will,  under  pressure,  yield  slightly,  and  as  a  result 
the  denture  will  settle,  as  it  is  commonly  termed.  The  amount 
of  such  settling  varies  in  different  individual  mouths  and  fre- 
quently in  different  areas  of  the  same  mouth,  depending  on 
the  thickness  and  condition  of  mucous  tissues. 

It  is  apparent,  as  a  result  of  such  settling,  particularly  in 
partial  dentures,  that  two  and  possibly  three  conditions  ad- 
versely affecting  the  usefulness  of  the  denture  may  develop. 

First,  the  maximum  service  of  the  denature  will  be  im- 
paired by  the  greater  or  less  loss  of  occlusal  contact  which  in- 
variably occurs.  SjBcond,  when  the  substitute  is  fitted  with 
retention  appliances,  and  no  provision  is  made  for  settling  of 
the  denture,  undue  stress  may  be  brought  upon  the  anchor 
teeth.  Third,  as  a  result  of  the  preceding  condition  peri- 
dental inflammation  of  the  roots  of  the  teeth  embraced  by  the 
clasps,  or  to  which  the  denture  may  lie  anchored  by  other 


i'.iS  CONS'rUICTKlX    (>!•"     I'AlfriAl,     DKN'I'l'RKS 

iiicaiis.  is  li;ililc'  Id  ciisiic.  \',\  till'  ilispliiy  (if  i-arcl'iil  Jiidg- 
nu!iit  as  1(1  tlic  iinilialilf  aiiitMiiil  llic  tissues  will  yield  under 
workiu.n'  conditidiis.  and  ran-yiui;'  nut  certain  stej)S  to  c'()ni))(']i- 
sate  for  sueli  settlin.i;',  the  dil'liculties  mentioned  nui>'  ho 
ax'oided.      Tliese   stejis    will    now    he    hrietiy   (letaile(l: 

In  tlie  eonstniction  ol'  a  part  iai  vulcanite  denture  to  wliit'li 
stop  clasps  are  adjuste(l.  a  piece  ol'  cardboard  should  be  i)laeed 
lietween  the  stop  and  the  occlusal  area  of  the  tooth  on  which 
it  rests,  at  the  time  of  placing'  the  clasp  on  the  tooth  for  final 
impression.  The  area  of  the  cardboard  need  not  exceed  that 
of  the  occlusal  area  of  the  sto]).  Its  thickness  should  be 
gauged  by  the  extent  it  is  estimated  the  denture  will  settle; 
it  may  range  from  the  thickness  of  a  sheet  of  medium  weight 
writing  ])a])er  to  that  of  a  heavy  visiting  card.  The  piece  of 
card  can  be  attach(>d  to  the  sto})  l)y  flowing  between  the  two  a 
thin  film  of  wax.  After  the  impression  is  removed,  and  before 
constrncting  the  cast,  the  cardboard  should  be  removed  from 
the  sto}).  As  a  i-esnlt  of  interposing  the  cardboard  as  de- 
scribed, the  clas])  occupies  a  position  on  the  tooth  slightly 
nearer  the  plane  of  occlnsion  than  it  did  on  the  die,  during  its 
construction,  or  would  occnpy  if  ])laced  on  the  natural  tooth, 
without  the  inter])osition  of  the  cardboard. 

The  final  I'esnlt  of  snch  proc(>dnre  is  that  when  the  com- 
pleted denture  is  i)laced  in  the  nioutli  the  stop  may  project 
slightly  above  the  occlnsal  snrface  ui'  the  tooth  it  embraces. 
After  a  short  period  of  use,  oftentiiues  within  twenty-four 
lionrs,  the  settling  of  the  denture  will  bring  the  stop  in  con- 
tact with  the  tooth. 

In  occluding  the  teeth,  in  partial  cases,  it  is  advisable  to 
set  the  substitute  teeth  so  that  they  strike  strongly  against  the 
opposite  occlnding  teeth  to  insure  strong  contact  occlusally 
when  introduced  in  the  mouth. 

To  further  insure  good  contact  l)etween  the  replaced 
teeth  and  those  in  the  opposite  arch,  after  settling  of  the  den- 
ture has  occurred,  the  teeth  on  the  substitute  should  not  be 
ground  to  perfect  occlusion  on  first  introduction  of  the  finished 
denture  in  the  mouth.  This  should  be  done,  however,  after  a 
lapse  of  twenty-four  to  forty-eight  hours,  provided  the  pa- 
tient has  Avorn  the  denture  in   th(»  meantime. 

COMPENSATING  FOR  SETTLING   OF  GOLD   BASE  SADDLES 

The  preceding  method  is  also  applicable  to  the  adjust- 
ment of  clasps  to  a  gold  base  denture,  but  the  following  plan, 
when  it  can  be  carried  out  with  accuracy,  is  to  be  preferred : 


CONSTRUCTION  OF  PARTIAL  DENTURES         im 

The  clasps  are  placed  in  ))ositioii  on  their  respective  teeth, 
without  interposing  the  cardboard,  as  described,  and  the 
denture  l)ase  introduced  and  seated  on  the  border. 

.A  suitable  tray  is  selected  and  softened  modeling  com- 
pound placed  within,  on  each  side,  but  not  anteriorly,  so  as  to 
embrace  a  portion  of  the  central  area  of  each  saddle  Neither 
the  anterior  teeth  nor  clasjis  should  l)e  embraced  by  the  com- 
pound. Pressure  is  brought  upon  the  tray  to  force  the  im- 
pression material,  not  only  on  the  border  crests,  but  over  the 
buccal  and  lingual  areas  of  the  saddles  as  well.  There  should 
be  sufficient  bulk  to  the  compound  so  that  the  impressions  of 
the  two  sides  may  be  secured  without  depressing  the  tray 
below  the  level  it  should  occupy  in  taking  the  final  impression. 
When  chilled  the  impression  may  usually  be  removed  withcmt 
disturbing  the  ]JOsition  of  either  baseplate  or  clasps. 

Both  anterior  and  posterior  terminals  oi  each  impression 
are  removed,  by  cutting,  leaving  a  ridge  al)out  one-fourth  inch 
wide  extending  from  Iniccal  to  lingual,  across  the  tray.  These 
transverse  ridges  of  compound,  one  on  either  side  of  the  tray, 
are  actual  cross-sections  of  the  impressions  and  are  designed 
to  force  the  saddles  firmly  in  contact  with  tlie  tissues  while  the 
plaster  impressions  arc  secured  of  the  bas(>  plate,  the  teeth 
and  the  unattached  clasps. 

Each  side  of  the  tray  is  now  filled  with  sufficient  plaster, 
of  suitable  consistency,  to  secure  impressions  of  the  desired 
parts.  When  introduced  and  properly  centered,  pressure  is 
applied  and  the  tray  forced  borderward  until  the  ridges  of 
compound  come  in  contact  with  the  saddles.  The  pressure  is 
now  increased  to  a  very  considerable  extent,  the  idea  being 
to  compress  the  mucous  tissues  to  nearly  the  full  extent  of 
their  yielding  capacity,  after  which  casts  are  developed  and 
the  clasps  soldeued. 

When  the  clasps  are  permanently  attached  to  the  base 
plate  and  the  latter  is  returned  to  the  mouth,  it  will  be  seen 
that  the  stops  of  the  clasps  usually  stand  slightly  above  the 
occlusal  surfaces  of  the  teeth  embraced. 

By  repeating  the  same  steps  for  producing  pressure  on 
the  base,  in  taking  the  final  impression,  the  t>eeth,  when  ground 
and  adjusted  to  the  base  plate  as  usual  and  later  are  perma- 
nently attached' CO  the  denture,  will  strike  the  occluding  teeth 
strongly  in  occlusion.  They  should  not,  however,  be  ground 
to  perfect  occlusion  at  first  sitting,  but  time  be  given  for  the 
tissues  to  yield  before  making  final  correction. 

Dr.  G-oslee  suggests  placing  a  small  post  of  wood  between 


sou  CUNSTIUTTION    OK     l\\l{'l"IAI.    DKNTliRIOS 

the  s;hI(II('  and  occlusal  surl'accs  of  llic  oijpositc  teeth,  the 
montli  being  open  snt'ficiently  tor  the  introduction  of  tray. 
By  means  of  this  post  the  patient  can  coni])ress  tlie  tissnes 
under  the  saddk'  dnrinn'  tlie  hardening  of  the  im])ression.  A 
lialf  tray,  sneli  as  is  nsed  in  ])artial  cases,  by  having  its  tloor 
sU:)tted  to  aeconnnodate  the  post,  is  nsed  foi'  carrying  tlie  im- 
in-ession  material  to  place. 

To  relieve  strain  on  anchor  teeth,  elliptical  s])rings  unit- 
ing the  clasps  with  base  plate  have  been  demonstrated  by  Dr. 
L.  J.  Weinstein  of  New  York,  who  ascribes  the  suggestion  to 
a   Connecticut   |)rac1itioner. 


\NI)    Fi.AT    JIANI).    OI'EN 


With  the  se\eral  fundamental  iirinciples  of  partial  den- 
ture construction  outlined,  of  both  vulcanite  and  gold  bases  in 
conjunction  with  stop  clasps,  the  application  of  various  other 
forms  of  retention  appliances  will  l)e  outlined. 


THE  ROACH  CONTINUOUS  LOOP  CLASP 

TECHNIC  OF  CLASP  CONSTRUCTION 

An  impression  of  the  tooth  which  the  clasp  is  to  embrace, 
and  the  proximating  tooth  also,  is  secured  which  should  be 
tilled  with  modelite,  a  very  hard  cement-like  substance,  w^iich 
sets  quickly  and  will  withstand  rough  usage  without  marring 
readily;  or  a  die  may  be  formed  of  Melotte's  metal.  A  piece 
of  18,  19  or  20  gauge,  sixteen  per  cent  platinized  clasp  metal 
wire,  about  2  inches  long,  is  required  for  each  clasp.      The 


CONSTRUCTION    OF    PAKTIAI.    UENTUKKS  5Ul 

gauge  dei)eiuls  on  tlie  length  of  the  h)()|i  and  hows  and  the 
stress  to  whieli  it  will  he  snhjected. 

The  wire  is  annealed  and  hent  in  the  middle  to  form  a 
close,  i)arallel  staple,  after  which  it  is  opened  slightly  and 
pressed  down  lietween  the  two  proximatiug  teeth,  the  ends 
hent  ontwavd  and  around  the  liuccal  and  lingual  surfaces  of 


ROACH    OPEN"    COXTINUOUS    LOOP    CLASP.       CLASP    APPLIED    TO     LDWEH    LINGUAL 

BAR,      GOLD     SADDLE     CAiSE.        NOTICE     FINISHING     SIlOULDEIt     FOH     VULCANITE 

FOBJIED   liY  SOLDERED  WIRE  TO  SADDLE.      ALSO  BIB  EXTENDING  PROM  LINGUAL 

BAR.   ONER  BORDER  CREST.  FOR  STRENGTHENING  PURPOSES 


I.dWKIi    l'.\ltTl.\ 


the  tooth  to  form  the  hucoal  and  lingual  spans  so  as  to  em- 
hrace  it  closely.  It  must  clear  the  gingival  tissue  at  all  points. 
The  adaptation  is  comjileted  hy  Ijeuding  the  buccal  and 
lingual  terminals  so  as  to  form  a  projecting  lug  for  attach- 
ment to  the  baseplate,  or  by  uniting  with  solder  and  turning 
the  extreme  outer  ends  slightly  apai't,  they  will  serve  for  an 
anchorage  in  vulcanite. 


502  CONSTRUCTION    OK    PARTIAL    DENTURES 

111  most  eases,  wlicii  the  cuilirasiirfs  between  tlic  prox- 
iiiiatiiig-  teeth,  in  wliieli  tlie  vertical  loop  of  the  bow  will  rest, 
are  free  from  ,i<iii,iiival  tissue,  the  wire  on  both  buccal  and 
lingual  sides  sliould  be  ean-ied  well  iido  these  spaces  and 
comparatively  chjse  to  the  gingiva  before  turning  it  to  form 
the  horizontal  sjaans.  By  so  doing  the  tendency  of  the  dis- 
tal end  of  the  denture  to  leave  its  border  is  overcome. 


li'i'iAr,   I  I'l'i.it   AMI    iiiwi.i:   (.(11,11   i:\si,    iu.nti  iii.s      'iiii.   i  rri  is    inN'iii'.r    is   riTTi;i) 
WITH  sti;i;l  facinc.    v\ii  i-'Lat  iiaxd  ci^vsrs     Tin:  i.ciwi.it  ulnti  hi.  with 
itiucii  I'liXTiNi  oi  s  i.dor  Axr>  flat  ijand  ci.a.sp 


i.ixni'AT.   \ii:w  OF  Tin-:   riiFCEiiixT;   cases 


APPLICATION   OF  THE   CONTINUOUS  LOOP  CLASP 

The  application  of  clasps  of  this  type  to  a  lingual  liar  gold 
saddle  ease  is  as  follows : 

The  saddles  and  bar  having  lieen  formed  as  previously 
described,  the  baseplate  is  introduced  and  the  clasps  adjusted 
to  their  respective  teeth.  The  lugs  of  the  clasps  are  bent  so 
as  to  rest  on  the  saddles.  An  impression  is  now  taken,  using 
the  pressure  method  when  advisable,  when  on  removal  and 


CONSTKl'CTIOX    OV    PAKTIAl.    DKNTVUIOS  50:; 

reassembling-  ol'  the  parts  a  east  of  investment  is  developed 

ami  tlie  clasps  soldel'ed   to  the  hase]ilate. 

THE  ROACH  OPEN  LOOP  CLASP 

The  open  loop  clasp  is  constructed  and  applied  in  mncli 
the  same  manner  as  the  continuous  loop  clasp.  When  clasps 
of  this  type  are  to  be  formed  a  heavier  wire  should  be  used, 
since,  not  being  continuous,  as  is  the  preceding  clasp,  it  is 
liable  to  be  bent  with  use  unless  the  wire  is  comiiaratively 
riffid. 


THE  KOAfTT  OPEX  T.nOP   CI-ASP 


The  outer  end  may  he  returned  liack  npon  itself  or  be  bent 
in  any  manner  to  take  advantage  of  a  depressed  area  on  the 
tooth,  thus  adding  to  its  stability. 

The  open  loop  clasp  may  lie  formed,  tirst,  as  a  doul)le  bow 
clasp,  the  two  terminals  united  with  solder  to  form  a  rigid  lug 
for  attachment  and  the  outer  loop  severed  and  bent  as  condi- 
tions indicate  or  they  may  merely  be  severed  without  bending. 

The  advantages  of  this  type  of  clasp  are  manifold.  The 
long,  linear  contact  of  the  wire,  with  varying  surfaces  of  the 
tooth  insuring  great  clasping  proi^erty,  together  with  but  lit- 
tle superficial  area  of  tooth  surface  covered,  is  tlie  ]irincipal 
one. 

No  provision  need  be  made,  as  with  stop  clasps,  for  the 
settling  of  the  denture,  since,  with  slight  effort,  the  vertical 
loop  can  be  raised  by  bending  the  horizontal  bows  occlusally 
when  occasion  requires. 


,",Ut  CONSTIilC'I'IO.N     OK     I'AKTIAI,     I  )l':.\'l'l '  K ICS 

Dciituri's  littcd  witli  Inop  clasps  do  not  I'l'cl  rigid  and  iiu- 
yieldiiig,  as  is  often  the  case  wiien  non-resilient  clasps  are 
used,  yet  they  are  retained  and  rest  firmly  in  position. 

The  loop  clasp,  by  its  form,  obviates  the  necessity  for  a 
stop  in  most  instances,  excepting  when  no  proximating  tooth 
is  present. 

THE  BALKWILL  CLASP 

A  clasp  similar  in  form  to  the  open  loop  has  been  in  use 
in  England  for  many  years.    A  loo]i  clasp,  together  with  one 


THE   BAI.KWII.I,    (II'EN    7. 


of  modified  form,  was  described  and  illustrated  by  Balkwill 
in  his  book  on  Mechanical  Dentistry,  edition  of  1880. 

The  modified  form  of  clasp  referred  to  consisted  in  adapt- 
ing a  strip  of  clasp  metal  to  the  buccal  surfaces  of  two  prox- 
imating teeth  and  connecting  it  with  denture  base  on  the  lin- 
gual side  with  a  wire  looj). 

Still  another  form  of  retaining  appliance  is  shown  in  the 
Dental  Cosmos,  Vol.  56,  page  1194,  by  Dr.  Heinrickseu. 

This  appliance  consists  of  a  loop  of  clasp  metal  bent  to 
the  curved  contour  of  the  gingival  tissues,  and  having  a  ball 
terminal  which  rests  in  the  embrasure  against  the  tooth  on 


CONSTRUCTION    OF    PARTIAL    DENTURKS  5U5 

tilt'  opposite  side  from  the  replacement.  The  wire  is  beut  so 
as  not  to  impinge  on  the  soft  tissues  nor  does  it  touch  the 
tooth  except  at  its  terminal  end. 

To   render   the   appliance   effective   there   must   he  good 
contact,  in  iioi-nial  position,  between  the  natural  and  prox- 


TIIE  JlEl.ViiUKSEX   rAUTIAI.    I.OOl'   BAI.L-POIXTKIl 


imating  porcelain  tooth  on  the  denture,  and  the  ball  must  be 
placed  close  to  the  gingiva.  If  in  the  case  illustrated  the  con- 
tact of  the  ball  was  near  the  occlusal  or  incisal  area  and  con- 
tact between  the  teeth  was  defective  or  close  to  the  gingiva 
the  action  of  the  lnop  would  Ix'  to  unseat  the  denture  at  its 
distal  terminal. 

THE  ROACH  BALL  AND  TUBE  ATTACHMENT 

This  appliance  consists  of  a  ball  with  projecting  spur  for 
anchorage  purposes  and  a  tube  of  lieavy  clasp  metal  which  re- 


ceives the  ball.     The  tube  is  slotted  throughout  one  side  to 
accommodate  the  passage  of  the  spur. 


APPLICATION    OF    THE    ROACH    ATTACHMENT 

The  usual  method  of  applying  the  ball  and  open  tube  at- 
tachment is  as  follows : 

The  crown,  inlay,  Carmichael  attachment,  or  whatever 
means  may  be  em])loyed,  for  securing  anchorage  to  the  natural 


5U6  CONSTRUCTION  OK  I'ARTIAI-  UKNTURES 

tooth  or  root  is  first  constructi'd  and  tciiiiiorarilx  set  in  place. 
For  c'onve'uiciice  of  des('ri])tioii,  a  ci-owii  will  he  considered  as 
the  means  of  attachment. 

The  position  of  tiic  l)all.  which  should  he  close  to  tlie  .2,'in- 
giva",  yet  not  touchin.i;'  it,  is  mai'ked.  To  consci'V'c  si)ac('  i'or 
adjusting  tlie  suhstitutc  teeth  to  the  saddle,  the  ball  should 
be  set  somewhat  to  the  lingual  of  the  border  crest,  yet  not  so 
far  as  to  produce  unnecessary  hulk  on  the  lingual  side  of  the 
finished  denture. 

Eemove  crown  from  the  mouth  and  drill  a  hole  at  point 
marked  for  the  reception  of  the  ball  stem.  When  applied  to  a 
shell  crown,  the  stem  should  be  cut  short,  so  as  not  to  interfere 
seriously  with  the  inner  periphery  of  the  crown,  '^riie  shoulder 
of  the  stem  should  rest  fiat  against  the  surface  of  the  crown. 

When  soldered,  the  surph;s,  if  any  is  present,  is  removed 
and  the  crown  is  returned  to  position  on  the  root.  A  slot  is 
made  in  tlie  saddle,  directly  beneath  the  location  of  the  ball 
to  permit  the  free  passage  of  the  denture  base  to  and  from 
position  without  interference.  The  denture  is  now  seated  on 
its  border. 

An  impression  in  plaster  is  taken,  by  the  pressure  method, 
if  indicated  and  when  set,  is  removed,  the  crown  usually  com- 
ing away  with  it.  If  not,  the  crown  is  remo\ed  and  ])laced 
in  the  impression.  The  latter  is  now  prepared,  and  partially 
filled  in  with  Modelite,  into  which  one  or  two  small  wood 
screws  are  inserted  so  as  to  leave  the  heads  freely  exposed 
and  projecting.  The  remainder  of  the  impression  is  filled 
with  plaster  or  investment  compound,  and  when  hardened  the 
impression  is  removed. 

The  case  now  consists  of  a  cast  representing  a  portion 
of  the  mouth  carrying  crowns  with  attached  balls  and  saddles, 
all  in  correct  relation  to  each  other.  The  next  step  is  to  at- 
tach the  tubes  to  the  saddles  in  the  correct  relation  to  the  balls. 
The  tube  may  be  attached  to  the  saddle  by  various  means,  but 
the  following  method,  suggested  by  Dr.  Roach,  is,  for  several 
reasons,  the  most  practical : 

A  piece  of  15-gauge  clasp  metal  wire,  from  one-half  to 
three-fourths  inch  long,  is  bent  at  right  angles,  flattened  slight- 
Ij^  on  one  side,  the  tube  laid  and  soldered  on  the  flattened  sur- 
face parallel  with  the  vertical  arm.  This  wire  is  called  the 
contact  bar,  because  it  not  only  affords  attachment  of  the  tube 
to  saddle,  lint  tlie  vertical  portion  at  its  u])y)e]-  extremity  is 


CONSTKITTION    OK    1'ART1AI>    DKNTURKS  50? 

In-lit  t(i  lie  ill  ('(intact  with  tlic  aiiclidr  ci-dwii.  a1  iionnal  con- 
tact  point. 

The  bar  is  now  bent  so  as  to  briiii;'  the  liihc  to  a  vertical 
position  snfliciently  liigli  so  that  the  ball  rests  in  its  lower  end. 

The  parts  now  sustain  tiiis  relation  to  each  other:  the 
horizontal  arm  of  tlie  liar  rests  on  and  lies  in  contact  with 


I 


niAGRAilMATIC   CUT.    SHO\VIN(i    ItEI-ATIOX   OF   THE    SEV- 
ERAL PACTOKS  OF  ROACH  APPLIANCE 


TilE   lUIACH   ATT.' 


lMlir.\Eli    WITH    STOP  <'I,AS1' 


saddle;  the  vertical  arm,  at  its  npper  extremity,  rests  at  point 
of  contact  with  the  anclior  crown;  the  tube,  vertically  placed, 
contains  the  ball  near  its  lower  extremity. 

When  this  adjustment  has  been  perfected,  the  horizontal 
arm  is  waxed  tirmly  to  the  saddle.  A  mix  of  investment  is 
applied  around  the  tube,  vertical  arm,  and  anchor  crown,  a 


508  {'ONSTIU'CTIUN    UK    I'AKTIAI-    IJKNTl'HRS 

very  small  ainoiuit  bciiii;-  suliHcient  to  hold  the  |)art  in  correct 
relation.  The  horizontal  arm  is  now  soldered  tirmly  to  the 
saddle.  A  similar  adjustment  and  attachment  is  now  made 
Ix'tween  tube,  contact  bar  and  saddle  on  tlie  ojiposite  side. 


These  a]>]>iianc('s,  in  favorable  cases,  when  properly  ad- 
justed, afford  most  efticient  means  for  retention.  In  addition, 
slionld  the  denture  settle,  the  tube  follows  without  restriction 
l)y  the  ball.  The  necessity  for  iixing  the  tube  hii>h  on  the  ver- 
tical arm  in  the  constmctive  stage  is  apparent 


RP 

SM 

W'lr 

^^V^^^l 

^Vi       -0^ 

^4,.              ^^H 

^m.         *■  1 

A^  y  ■ 

AXTERIOIt    RESTdRATlDX    WITH    ROACH    ATTACHMENT  ArPMED 

When  the  denture  is  subjected  to  masticatory  stress  the 
tube  rotates  on  the  ball,  without  subjecting  the  anchor  tooth 
to  side  stresses  or  strains.  The  contact  bar,  resting  as  it  does 
on  the  contact  ])oint  of  the  tooth,  prevents  the  raising  of  the 


CONSTUrCTIUN    OF    I'AUTIAI.    DKXTUKKS  509 

distal  ciiil  (>r  the  (lenturc,  \ct    in  im  \va\'  resists  compressive 
force. 

By  the  exercise  of  a  lilllc  ingemuty,  the  ball  and  tube 
attachments  may  be  applied  to  advantage  in  many  ways  for 
the  retention  of  partial  dentures  in  both  arches.  They  may 
also  be  combined  with  clasps  of  various  types,  or  with  the  Gil- 
more  or  other  standard  attachments  in  such  manner  as  to  re- 
duce to  the  mininuun  danger  of  injury  to  the  remaining 
natural  tcetli. 

THE   MORGAN   ATTACHMENT 

This  attachment  consists  of  two  parts,  one  of  which  tele- 
scopes within  the  other.  The  outer  consists  of  a  flattened,  open 
loo])  or  partial  band,  called  the  "keeper,"  and  is  attached  to 


the  ci-owii  or  inlay  of  the  anchor  tooth.  The  other  part,  which 
fits  within  the  keeper,  is  termed  the  "anchor"'  and  is  attache(l 
to  the  substitute  or  denture  base. 

Tn  api)lying  these  attachments  to  a  denture  it  is  necessary 
thai  they  should  be  as  nearly  jiarallel  as  possible,  so  that  the 


WITH    .M(lT!(!AX    KETCPKIl     ATTAI'llKll 


appliance    may.  be    introduced    and    i-emoved    without    diffi- 
culty. 

An  appliance  called  a  "soldering  jack"  is  used  for  para- 
lelling  the  keepers  and  for  holding  them  in  )iositi<ui  against 
the  crown   while  soldering. 


•Ml)  CONSTIU'C'riON     OK     I'AKTIAL    I  >l';\"r( '  ItlOS 

TECHNIC    OF    APPLICATION 

jVii  iiui)rcssu)ii,  with  crowns  in  |Hisitii>n,  is  taken  and  re- 
moved, the  crowns  cominc,'  away  willi  i1.  From  this  a  cast  of 
investment  material  is  formed  ol'  usnal  size  and  yivoportions. 


Mill       Mill  (    \X 


UPIIWLI  S 


Tliis  is  set  npon  and  clamped  to  tlie  base  of  the  soldering  jack. 
A  keeper  is  adjusted  to  the  peri)endicular  arm  of  the  jack. 

The  latter  is  moved  so  as  to  Itriiiii'  tlic  attaclmiont  against  the 


crown  surface  at  the  correct  angle  and  in  proper  itosition, 
where  it  is  united  w^ith  solder  to  the  crown.  Without  changing 
the  perpendiculai-  relation  of  the  main  post  which  governs  the 
direction  of  the  arm,  the  set  screw  of  the  latter  is  released, 
it  is  raised  from  the  keeper  already  soldered:  the  other  keeper 


CONSTRUCTION    OP    PARTIAL    DENTURES  ill 

is  adjusted  to  the  arm.  when  it  is  rotated  against  the  other 
crowu  and  attached  in  a  simihir  manner. 

The  crowns  may  now  be  permanently  set.     The  anchors 
are  next  placed  in  position  in  the  keei)ers  for  the  final  impres- 


sion. When  allowance  is  to  he  made  for  settling  of  the  den- 
ture a  U-shaped  piece  of  cardboard  can  be  interposed  between 
the  flange  of  the  anchor  and  the  occlusal  end  of  the  keeper. 
The  impression  is  now  taken  and  removed,  the  anchors  com- 


ing away  with  it  or,  if  dislotlged,  an-  remo\ed  from  the  keep- 
ers and  returned  to  place  in  the  impression. 

A  piece  of  heavy  German  silver  plate,  bent  to  resemble 
the  keeper  l)ut  about  one-half  incli  long,  is  passed  over  each 
anchor  and  the  impression   lilhMl   with   plaster  or  hard   cast 


512  CONWTKIH'TION    ()l<'    l\\UTIAI.    DKNTUKKS 

material.  'I'hc  (Tcniian  >il\('r  posts  wliicli  I'cccivc  the  Hauges 
of  the  Ufeper  prevent  the  distiirbaiicc  of  relation  ot  the  hitter 
to  the  cast.  Loops  siiould  be  sokh'i-cil  on  lhc  extension  of  the 
anchor  for  attachment  in  vulcanite  work. 

In  case  of  a  gold  base  denture,  when  tlie  pi-ojeelion  does 
not  tonch  the  base,  a  ])iece  of  heav.y  plate  mav  l)e  adjnsted  be- 
tween Ihe  two  and  all  united  with  solder.  'I'lie  steps  from 
now  on  are  can-ied  ont  as  in  an  ordinarx-  xuh-anite  ease. 

THE    CONDIT   ATTACHMENT 

"^rhe  Coiidil  attachment  consists  of  two  ])ieees.  the  inner, 
a  chisp  metal   tube,  o])en  at  the  side  and  ends,   which   is  at- 


tached to  the  anchor  crown,  the  ojien  side  toward  the  space  to 
be  tilled.  The  outer  part  is  a  telescoping  tube,  open  at  the 
side  and  one  eud.  To  the  other,  or  occlusal,  end  is  attached  a 
floor,  in  the  center  of  which  is  fixed  a  rigid  post,  the  same 
diameter  as  that  of  the  inside  of  the  inner  tube.  It  will  be 
seen  that  tliis  appliance  possesses  greater  grasping  property 
than  any  of  the  other  standard  types  descriljcd,  since  the  inner 
tube  grasps  the  center  post  of  the  outer  appliance,  while  the 
latter  grasps  the  outer  surfaces  of  the  inner  tube. 

The  application  of  these  appliances  is  similar  to  that  of 
the  Morgan,  just  described,  a  paralleling  device  being  neces- 
sary for  the  proper  adjustment  of  the  inner  tubes  to  their 
respective  crowns. 


CONSTRUCTION  OF  PARTIAL  DENTURES 


SMAl.I.    IlESTORATIOXS    SHOWINO    VARIAa»IONS    IN    APPLICA- 
TION  OF   CONDIT    ATTACHMENT 


CONSTRUCTION    OK    PARTIAL    DENTURES 


Wlieu  amplo  oecluso-gingival  space  exists,  these  appli- 
ances, when  properly  balanced  and  adjusted,  serve  a  most 
useful  purpose. 

THE   GILMORE  ATTACHMENT 

This  appliance  consists  of  a  U-shaped  clip  or  clasp  of 
rig-id  yet  resilient  metal,  the  tlauges  of  which  receive  a  14-gauge 
wire.  No  paralleling  device  is  needed  other  than  the  eye  in 
adjusting  this  attachment  to  a  case,  but  at  the  same  time  when 


E3 


ENLARGED     VIEW     OF     GILMORE 

ATTACHMENT  DESIGNED  FOR 

METAL  OK  VULCANITE 

WORK 


ENLARGED     VIEW     OF     GILMORE 

ATTACHMENT  DESIGNED  FOR 

VULCANITE  WORK 


two  or  more  are  used  in  a  denture  they  should  be  placed  with 
tianges  as  nearly  parallel  as  possible  with  the  line  of  direc- 
tion of  introduction  to  and  removal  from  the  mouth. 


APPLICATION  OF  THE  GILMORE  ATTACHMENT 

The  application  of  the  Gilmore  attachment  varies  in  dif- 
ferent eases  according  to  tlie  position  of  the  anchor  teetli  and 
the  spaces  to  be  filled. 


CONSTRUCTION    OP    PARTIAL    DENTURES  515 

For  example,  in  a  lower  partial  denture  in  which  the 
posterior  teeth,  back  of  the  cuspids  or  bicuspids,  are  to 
be  replaced,  it  is  necessary  to  provide  against  the  movement 
of  the  denture  away  from  the  anchor  teeth.     The  necessity 


BARS     BENT.     AIM'LIEI) 


FOR    GILMORE 


for  this  is  apparent,  since  the  attachment  itself  cannot  resist 
horizontal  movement,  under  stress,  of  the  denture  along  the 
ridge.    When  the  space  to  be  filled  is  bounded  anteriorly  and 


ANGLE  B.Ul  BENT  TO  SET 

AGAINST       CROWN       AND 

.\I,\EOI.AR  BORDER 


posteriorly  by  natural  teeth,  these  prevent  such  movement 
and  the  application  of  the  appliance  is  simple. 

The  technic  of  application  of  the  Gilmore  appliance  in 


[-  ,::^  ^_^\ 


CROWN  WITH  BAR  Al'I'LIED  FOR 
GILMORE  ATTACHMENT.  THE 
VERTICAL  ARM  LIES  TOO  CLOSE 
TO  GINGIVAL  jVHEA  OF  THE 
CROWN,  ALSO  SHOULD  fiXTEND 
NEARLY  TO  OCCLUSAL  SURFACE 


CROWN  WITH  BAR  APPLIED  FOB 
GILMORE  ATTACHMENT.  THE 
BAB  SHOULD  NOT  ENCROACH 
TOO  CLOSELY  ON  GINGIVAL 
TISSUES    NEXT    TO    CROWN 


the  first  case  mentioned,  all  of  the  teeth  posterior  to  the  sec- 
ond bicuspids  having  been  lost,  is  as  follows : 

Crowns   are  constructed  for  the  second   bicuspids   and 
placed  in  position,  but  not  cemented  to  their  respective  roots. 


516  CONST'RIH'TIOX    OF     PARTIAI.    DENTl'KKS 

All  imiJri's.sioii  is  secured  and  iciiiox cd,  the  ciowiis  usu- 
ally coining  away  witli  it.  Fruiii  the  impression,  a  east,  com- 
posed of  investment  material,  is  secured.  To  the  distal  sur- 
face of  each  crown  a  piece  of  14-gauge  wire  of  iridio -phitinuni 
or  highly  platinized  clasp  metal    is  adapte<l. 

The  wire  should  be  bent  so  as  to  lie  in  contact  with  the 
occlusal  two-thirds  of  the  crown;  at  the  gingival  third  it 
should  leave  the  crown  surface  at  a  gradually  increasing  slant 
to  form  a  clearance  sj^ace  for  the  protection  of  gingival  tis- 
sue. The  horizontal  portion  of  the  wire  should  conform  to  and 
rest  lightly  upon  the  border,  its  position  lieing  usually  slightly 
to  the  lingual  of  the  crest.  At  a  distance  not  exceeding  three- 
eighths  of  an  inch  from  the  crown  the  distal  end  should  be 
turned  up  sharply  at  a  right  angle.  The  direction  of  this 
vertical  portion  of  the  wire  should  be  parallel  with  the  line  of 
direction  of  introduction  and  removal  of  the  denture.  Its 
height  may  vary  from  one-sixteenth  to  three  thirty-seconds  of 
an  inch.  When  the  wire  is  properly  conformed  it  is  waxed 
in  position  against  the  distal  crown  wall,  and  a  mix  of  in- 
vestment is  made  and  applied  over  the  bar  along  the  ridge, 
being  careful  to  enclose  the  distal,  vertical  end.  This  is  neces-. 
sary  to  obviate  jjossible  lateral  rotation  of  the  end  against  the 
crown  wall  in  soldering.  The  wax  is  removed  from  the  joint 
flux  applied  and  the  bar  is  soldered  to  the  crown. 

It  is  frequently  advisable  to  extend  the  solder  somewhat 
beyond  the  area  of  l)ar  connection  with  the  crown  to  render 
the  latter  rigid.  A  l)etter  ])lan  is  to  adapt  and  solder  a  piece  of 
plate  to  the  distal  wall  of  the  crown  during  the  constructive 
stages.  The  addition  should  be  attached  with  high-grade  sol- 
der, so  that  the  union  may  not  later  be  disturbed  in  soldering 
the  bar. 

When  the  bars  are  attached  the  rough  surfaces  of  both 
crown  and  bar  are  removed  and  given  the  final  finish.  The 
crowns  are  again  returned  to  position  in  the  mouth  and  a  bite 
and  final  impression  secured.  The  teeth  are  occluded,  the 
case  carved,  flasked  and  separated,  and  the  matrix  packed  as 
usual. 

ADJUSTMENT   OF   CLASPS   TO   BARS 

A  strip  of  cardboard,  cut  to  fit  between  the  flanges  of  the 
attachment,  is  pressed  in  place  against  the  inner,  curved  sur- 
face of  the  attachment,  and  the  latter  set  in  position  on  the 
bow.     This  is  to  allow  for  sul)sequent  settling  of  the  denture. 

The  clasp  should  occupy  a  position  about  midway  between 
the  crown  and  terminal  end  of  the  bar.    It  should  be  ranged 


CONSTRUCTION    OF    PARTIAL    DENTURES  517 

with  Haiige.s  parallel  or  as  nearly  so  as  possible,  with  those  of 
the  opposite  attaclunent ;  tliat  is,  l)oth  attachments  shouhl  ))(■ 
placed  so  that  the  flanges  stand  ])eri)endicular.    Furthermore, 


REIATION   OF  GILMORE   ATTACHMENT 
TO   BAR  AND  CAST.  IN  VULCANITE    WORK 

A. 14  G    BAR 

B.  GILMORE  ATTACHMENT 

C. CARDBOARD 

D.  FILM    OF    PLASTER 

DlACiUAMMATlL-     CVT     SHOWING     DELA- 
TION   OF  THE   SEVERAL  PARTS    OP 
A  GILMORE  ATTACHMENT 


they  should  be  forced  as  closely  to  the  liar  as  the  interposed 
cardboard  will  permit. 

The  last  step  before  closing  the  flask  consists  in  obliter- 
ating the  s])aces  between  bars  and  borders  so  as  to  exclude 
file  lubber  in  closing  tlie  flask.    This  is  necessary  so  that  the 


CASE  IN   WHICH   IT   IS  L'NNECESSARY    TO  BEND   TERMINAL 

END    OK    4SARS    VERTICALLY     FROM    THE    BORDER, 

GILMORE    ATTACHMENTS 

bars  and  crowns  may  later  be  removed  from  the  vulcanite 
without  mutilation.  A  thin  mix  of  plaster  is  applied  in  the 
space  between  the  borders  and  bars,  and  along  the  outer  sides 
of  the  flanges  as  well,  so  that  the  surfaces  are  free  from  under- 


518 


CONSTRUCTION    OF    PARTIAL    DKNTUHBS 


cuts.      Tlie   plastoi'   should    init    ciitci-   the   (i]icniiios   beneath 
anchor  lugs,  nor  surround  the  hitter. 

Wlien  the  plaster  has  hardened,  the  tlask  is  closed  and  the 
case  vnleanized.     On  o])ening-  and  ch'ansiiiii-  the  denture,  the 


surplus  vulcanite  is  removed.  A  thin  t)lade  instrument  is 
passed  along  on  either  side  of  the  bar  and  flanges,  to  remove 
as  much  as  possible  of  the  plaster  which  was  built  in  under 
the  bar.  With  a  little  careful  pressure  and  manipulation,  the 
bars  will  part  from  the  vulcanite  without  difficulty,  after  which 
the  ease  is  finished.    The  margins  of  the  groove  which  receives 


LINGUAL    \1E\V    OF    I'RECEDING    CASES 


the  bar  should  be  smoothed  and  a  round  bur  of  approximately 
the  diameter  of  the  bar  should  be  applied  in  the  groove  to 
deepen  it  slightly  and  also  to  deepen  the  opening  into  which 
the  terminal  end  of  the  bar  enters.  This  step  is  carried  out 
to  provide  for  future  settling  of  the  denture. 


CONSTRUCTION    OP    PARTIAL    DENTURES  519 

Oftentimes  two  or  three  widely  separated  roots  or  teeth 
can  be  utilized  for  supporting  a  denture.  Roots  should  be 
filled  and  post  inlays,  whieh  extend  neatly  to  the  peripheral 


ALVEOLAR    BAK    Sfl'PORTED    BY    TWO    ROOTS    ANll    TWO    IXLAT    AT- 

TA1-IIME\TS.      THREE  OR  MORE  (ilLMORES  MAY  BE  AT- 

TACIIEO    AS   REOrlREI) 

margins,  constructed  for  anchorage  purposes.  Such  attach- 
ments may  be  combined  with  crowns  set  on  roots  of  teeth  or 
with  inlays  set  within  tootli  crowns  and  all  connected  by  a 


border  bar.  It  is  frequently  advisable,  when  only  two  or 
three  teeth  remain,  to  remove  the  crowns  and  inlay  the  roots 
as  described.    By  this  procedure  there  will  be  no  break  in  the 


CONSTRUCTION    OK    I'AKTIAl.    DKNTl'HKS 


FULL  DENTl'RE,   I'ALATAL  VIEW,  SHOWING  (iK()(>\  E 
FOR  AL\EOLAR  BAR  WITH  (ilLMORE  AP- 
PLIANCE NEAR   EXTREMITIES 


ALVEOLAR  BAR   SIPPIIRTEH   HV   TWO  CISPII)  ROOTS. 

A  GILMORE  ATTACHMIINT  SHOULD   BE  PLACED 

BACK     OF      IvACII      lUlOT     AND     ONE     IN 

TIIK    .\1  EI  II  AX    LINE 


SECTIONAL  \  I  E  W  OF 
ROOT  WITH  DOWEL  AND 
INLAY  TO  WHICH  ALVE- 
OLAR BAR   IS  TO  ATTACH 


OCCLUSAL  VIEW  OF  INLAY 
IN  POSITION  ON  ROOT.  WITH 
ALVEOLAR  BAR  ATTACHED 


CONSTRt^CTION    OF    PARTIAL    DENTURES  521 

aitilicial  i>iini  rt'stdvatioii,  nor  in  tlic  aliniinicnt  of  the  sub- 
stitute teeth. 

Tins  system,  as  well  as  the  others  previously  deseribed, 
are  capable  of  a  wide  range  of  ap])lieation.  Tn  fact,  they  seem 
limited  only  by  the  skill  of  the  prosthetist. 


GILMORE    ATTACHMENT     MOVEMENT 

OF  DENTURE  DISTALLY  PREVENTED 

BT    LOCKING    AGAINST    MESIAL    OF 

FIRST  BICUSPID 


522  CONSTIUU'TION    OF    PARTIAL    DKNTIIRES 

THE    PALATAL    ARCH    BAR 

The  palatal  arch  Ijar  luliills  a  similar  purpose  in  upper 
partial  dentures  as  the  lingual  bar  in  lower  cases.  The  idea 
of  a  bar  is  not  to  afford  support  by  its  bcarino-  against  the 


LINGDAL   BAB,   GILMOBE   APPLIANCES 


tissues,  but  to  unite  widely  divergent  points  of  support  by 
means  of  a  light  yet  rigid  structure,  and  convert  them  into 
what  has  been  termed  inuliiple  anchoyage.  This  may  be  ac- 
complished quite  as  efficiently  in  the  upper  as  in  lower  arch. 
Briefly  stated,  the  system  of  partial  denture  construe- 


CONSTRUCTION    OF    PARTIAL    DENTURES  523 

tion  as  practiced  to-day  consists  in  developing  light,  rigid 
structures,  supported  in  tlie  mouth  in  such  manner  as  to  cause 
no  injury  to  the  remaining  natural  teeth,  nor  subject  the 
anchor  teeth  to  undue  strain  or  injury. 

THE   KELLY  ATTACHMENT 

The  Kelly  attachment  consists  of  two  small  thimbles,  each 
closed  at  one  end,  which  telescope  one  within  the  other,  with 
reasonably  tight  contact. 

Retention  of  a  denture,  however,  in  which  these  appli- 
ances are  utilized,  is  not   depended  upon  the  closeness   of 


adaptation  of  tlic  thimlile  walls,  but  upon  diverging  or  con- 
verging the  appliances  in  setting  them  upon  the  anchor  teeth. 

APPLICATION   OF  THE   KELLY  ATTACHMENT  IN   VULCANITE 
WORK 

Caps  are  formed  and  titted  with  dowels  to  prepared  roots. 
To  these  caps  the  inner  thimbles  are  adjusted  and  soldered 
so  as  to  present  from  one-sixteenth  to  one- sixty-fourth  inch 
divergence  from,  or  convergence  to,  each  other. 

The  outer  are  set  in  position  on  the  inner  thimbles  and  an 
impression  secured.  The  cast  produced  from  the  impression 
carries  the  two  outer  thimbles  as  projections  above  the  border 
surfaces.  Freqneiitly  a  shell  crown  is  constructed  to  telescope 
loosely  over  the  outer  thimble,  as  its  presence  on  the  cast  pre- 
vents placing  an  ordinary  vulcanite  tooth  in  this  location. 
The  vulcanite  fills  the  space  and  forms  the  bond  of  union  be- 
tween the  thimble  ajid  crown.  The  case  is  carried  through  in 
the  usual  mani>er,  the  thimbles  remaining  with  the  cast  in 
flask  separation,  but  they  become  a  component  part  of  the 
denture. 

Wlieu  tinished,  the  margins  around  the  opening  of  the 
thimbles  are  slightly  beveled  and  smoothly  polished. 


524  CONSTRTK'TION    OH     PARTIAL    DENTURES 

In  introducing-  the  denture,  the  yield  of  the  peridental 
membranes  of  the  roots  involved,  together  with  some  slight 
spring  in  the  dentui'c  itself,  ))ermits  the  inner  thimbles  to 
enter  the  outer,  altliongli  not  in  perfect  alignment.  When 
seated,  however,  no  strain  upon  the  anchor  roots  is  noticcal)I('. 


KELLY     COMBINED    WITH     GILMORE    ATTACHMENT 

A.  KELLY    THIMBLE 

B .  14    GAUGE   BAR 

C.  GILMORE  ATTACHMENT 


These  attachments,  slightly  modified,  are  frequently  com- 
bined with  others,  as,  for  instance,  the  Grilmore.  They  can 
be  applied  in  gold  base  dentures  with  even  greater  ease  than 
in  vulcanite  work,  the  outer  thimlile  being  soldered  to  the  base- 
plate. The  thimbles  vary  in  size  from  three  thirty-seconds 
to  one-fourth  of  an  inch  in  diameter,  or  even  larger. 


THE  GRISWOLD  ATTACHMENT 

This  attachment  consists  of  two  triangular- shaped  tele- 
scoping tubes,  the  outer  one  open  along  the  angle,  the  other, 
or  inner,  being  slotted  through  the  middle  of  one  side. 


ENLABGED       VIEW 
OF     GRISWOLD 
ATTACHMENT 


SKETCH    OF  GRISWOLD    INNER   TUBES   IN   POSITION 


CONSTRUCTION    OF    PARTIAL    DENTURES 


ll  l.rAMI  K  AH  I  III.  lit  .Mil  II   lull 

OR    STRIP.      DEXTIRE  HVV- 

PORTED  I)Y  FOUR  CKIS- 

WOLD  .\TT.\1'HMEXTS 


ri'PER     ANTEBIOr.     RESTORATION     SADDLE 

DEXTURE  STIPP0R1E1J  BY  GRISWOLD'S 

ON  FIRST   BICUSPIDS 


The  smaller  is  attached  hy  its  a^ex  to  a  crdwii  or  inlay, 
while  the  other  is  soldered  to  the  gold  hase  or  enclosed  within 
the  vulcanite. 

FORMS   OF  PORCELAIN   TEETH 

Porcelain  teeth  as  siip]ilied  by  the  manufacturers  are 
divided  into  two  classes,  known  as  plai)i  and  giDii  teeth.  Each 
of  these  classes  can  again  be  sulidivided  into  two  classes,  vul- 
canife  and  phifc  teeth. 

PLAIN   TEETH 

A  plain  tooth  represents  the  crown,  or  a  portion  of  the 
crown,  of  a  natural  tooth  in  porcelain.  Since  teeth  of  this 
type  are  designed  to  take  the  place  of  lost  natural  teeth,  they 
represent,  more  or  less  jDerfectly,  the  anatomic  forms  of  the 
natural  organs  in  general  outline.  The  linguo-gingival  areas 
of  most  porcelain  teeth  are  deticient,  or  lacking  in  contour,  to 
afford  means  for  attachment  to  the  metal  or  vegetable  mate- 
rial which  forms  the  structure  of  the  substitute. 


MEANS  OF  ANCHORAGE 

Metallic  pins  are  most  conuuonly  used  f^r  anchorage  pur- 
poses, one  end  of  each  pin  being  enclosed  and  tixed  in  the 
porcelain  by  fusion  of  the  latter  around  it,  the  other  end 
projecting  for  attachment  within  the  substitute  material.  A 
plain  tooth  is  usually  supplied  with  two  pins,  vulcanite  teeth 
having  headed  pins  while  in  plate  teeth  the  pins  are  straight. 


526  CONSTRUCTION    OF    PARTIAL    DENTUKKS 

Another  means  of  anchorage  consists  in  (Ievelo])iug 
within  the  porcelain  some  mechanical  form  of  attatihment,  as 
dovetailed  projections,  or  countersunk,  depressed  areas,  with 
small  openings  extending  through  the  proximate  surfaces,  as 
in  diatoric  and  similar  forms  of  teeth. 

PLAIN  TEETH  FOR  VULCANITE  WORK 

Teeth  of  this  type  are  designed  for  use  with  plastic  bases, 
of  vulcanite  and  celluloid,  headed  pin,  and  diatoric  teeth  being 
the  most  common  forms  used.     These  are  manufactured  in 


f^f\f%^ 


SET  OP  NO.    28,   PLAIN  TKETH.    \Tn,CANITB    (S.    S,    W.) 

great  variety  as  to  length,  width  and  color,  some  in  no  wise 
resembling  natural  tooth  forms,  while  others  approach  very 
closely  to  anatomic  types. 

Both  platinum  and  alloys  of  base  metal,  usually  nickel, 
are  used  for  pins  of  vulcanite  teeth,  the  latter  being  employed 
because  of  its  cheapness.    Unless  protected  by  a  film  of  non- 


SET    OP  NO.    28,    PLAIN   TEETH,    VULCANITE    (JUSTI) 

oxidizable  metal  as  an  electro-deposit  of    gold,    base    metal 
pins  are  liable  to  disintegration  with  use  in  the  mouth. 

The  oxidation  of  base  metal  pins  during  fusion  of  the 
porcelain  frequently  causes  discoloration  of  the  latter,  some- 
times to  such  an  extent  as  to  render  the  product  unfit  for  use. 
This  occurs  most  frequently  in  anterior  teeth,  where  the  bulk 
of  porcelain  is  limited.  To  overcome  this  difficult^^  thin 
platinum  tubes,  the  inner  ends  flanged,  are  baked  in  the  teeth, 


CONSTRUCTION    OF    PARTIAL    DENTURES  527 

in  the  locatioii  of  the  pius,  aud  the  base  metal  plus  are  after- 
ward soldered  within  the  tubes. 

ADVANTAGES  OF  PLAIN  TEETH  IN  VULCANITE  WORK 

There  are  two  principal  advantages  in  the  use  of  plain 
teeth  in  vulcanite  work  as  compared  with  gum  teeth. 

First,  they  are  more  easily  arranged  in  anatomic  align- 
ment, and,  if  necessary,  can  be  readily  modified  to  meet  usual 
and  unusual  occlusal  requirements. 

Second,  they  can  be  placed  in  restricted  locations  and 
spaces  where  gum  teeth  cannot  be  used. 


V  LJJJ 


^  R 


VARIOUS    SIZES    OF    rL.lIX    TEETH.    FOR    \TI.C.i>.ITE   OR    CELLULOID.    COXSTRICTED   CERVICES 


PL.ilX       TEETH,        VULCANITE. 

TRANSVERSE  CORRUGATIONS. 

CONSTRICTED  CERVICES 


OBJECTIONS 

The  iirincipal  objection  to  the  use  of  plain  teeth,  where 
gum  restoration  is  necessary,  is  on  account  of  the  gum  mate- 
rial at  present  available.  Pink  vulcanite  is  oi)aque,  and  under 
most  favorable  conditions  affords  but  little  resemblance  to 
living,  healthy  gum  tissue. 

The  silicate  cements  are  being  tested,  as  to  durability, 
as  a  substitute  for  gum  restorations.  This  material  fulfills 
esthetic  requirements  quite  as  well  as  porcelain. 


.      DIATORIC  TEETH 

Diatoric  or  pinless  teeth  are  so  formed  as  to  afford 
anchorage  for  plastic  materials  around  and  within  the  porce- 
lain. Teeth  of  this  type,  when  bulk  of  material  is  not  too  re- 
stricted, and  the  mechanical  retention  forms  are  well  propor- 


528  CONSTRUCTION    OF    PARTIAL    DENTUHKS 

tioiied,  are  cajiablc  of  witlistaiidiiig  iiiasticatdry  sifcss  (inite 
as  well  as  pin  teeth.  In  addition,  they  are  much  h'ss  ex])en- 
sive,  a  factor  of  some  importance  at  times. 

Diatoric  molar  and  bicuspid  teeth,  when  sliiihlly  m(i<lilicd 
by  griiidiiis',  ;ire  fi-e(|iieiitl>-  used  iu  cdnjunctidii  with  .yold,  in 


the  construction  of  bridge  work,  the  technic  lieing  similar  to 
that  employed  in  the  application  of  full  or  i^artial  liorcelain 
crowns,  for  such  purposes. 


COUNTERSUNK   PIN  TEETH 


A  countersunk  pin  tooth  consists  of  a  fully  contoured 
porcelain  crown,  in  the  base  or  cervical  portion  of  which  is  a 
depression  from  which  projects  a  headed  pin  for  anchorage 


o  mMi 


COUNTERSUNK  PIX  TEETH.    BISCUSPIDS 


^ 


m 


no 


COUNTERSUNK    PIN    TEETH,    ANTERIORS 


purposes.  The  advantage  of  this  type  of  tooth  in  denture  con- 
struction is  due  to  the  fact  that  the  full  lingual  contour  of  each 
tooth,  which  the  basic  material  need  not  envelope  to  any  ex- 
tent, feels  more  comfortable,  and  enables  the  patient  to  speak 
more  distinctlv  than  when  such  contour  is  deficient. 


CONSTRUCTION    OP    PART1AI>    DENTURES  529 

ASH'S    TUBE    TEETH 

A  tube  tooth  consists  oH  a  fully  contoured  porcelain  crown, 
having  an  opening  extending  entirely  through  it  from  cervical 
base  to  occlusal  surface  or  just  to  the  lingual  of  the  incisal 


TUBE  TEETH.  BISCUSPIDS  AND  MO- 
LARS (ASH'SI.  SET  ON  GOLD  CASTING, 
JX  WHICH  IRIDU)  I'LATINl  M  PINS 
ABE  ENCLOSED.  SHOWING  AI'IT.ICATION 
IN   BRIDGE    WORK 


edge.  Teeth  of  this  ty])e  are  occasionally  used  in  conjunction 
with  vulcanite,  a  headed  pin  or  wire,  slightly  smaller  than  the 
opening,  and  longer  than  the  crown  being  titted  to  each  before 


A                   B 

B 

D 

E 

4  1 

F               G 

H 

1 

1 

J 

V.iRlOlS   FORMS   OK   ASUS    MINEUAE  TEETH 
A — Porcelain    Tip   with    Pins    for    Anterior    Restorations 
B — Flat  Back   Repair  Facing 
C.    D.    E— Very   Short    Bite   Molars.    Dialorir 
F.    G— Dimelon-  Faciiigs 
H.    I.  .1— Tulie  Teeth 

packing  the  case.  The  head  of  the  pin  projects  slightly 
beyond  the  cervical  end  of  crown.  In  closing  the  packed 
flask,  the  rubber  is  forced  into  the  vacant  space  in  the  tube 
and  around  the  pin  head  and  thus  firmly  anchors  the  tooth 


530  CONSTRTTCTION    OF    PARTIAL    DKNTURES 

ill  ])lac('.  These  teeth  are  capable  of  a  wide  range  of  applica- 
tion ill  crown  and  bridge  restorations  as  well  as  in  metal  base 
denture  construction,  but  unfortunately  are  not  easily  pro- 
cured or  extensively  used  in  this  country. 


I'ARTIAl,     DEXTDBE.      GOLD     BASE.     Tl'BE     TEETH 

(ASH'S) 
PLAIN   PLATE  TEETH 

A  plain  plate  tootli  consists  of  a  veneer  or  partial  crown 
of  porcelain.  It  is  usually  supplied  with  two  straight,  head- 
less pins  which  project  from  the  flattened  lingual  surface. 
Teeth  of  this  type  are  designed  for  use  with  metal,  in  crown, 
bridge  and  denture  work.  Because  of  the  liability  of  fracture 
occurring  in  these  teeth  during  soldering  operations,  and  the 
further  difficulty  of  replacement,  when  fractured  from  any 
cause,  facings  of  the  replacable  type  are  gradually  coming 
into  general  use  for  the  purposes  mentioned. 

VARIOUS   FORMS  OF  PLAIN   TEETH 

There  are  various  forms  of  ])lain  teeth  designed  for  spe- 
cial purposes,  among  which  may  l)e  mentioned  the  Dimelow 


BACKING     WITH      STAPLE     PINS 

ADAPTED  FOR   DIMEI^flW 

FACING 


facing,  consisting  of  a  flat  back  veneer,  having  two  holes  in 
the  location  usually  occupied  by  the  ]iins,  and  which  slant 
slightly,  from  lingual  to  labial,  incisally.    These  holes  receive 


CONSTRUCTION    OP    PARTIAL    DENTURES  531 

two  pins,  projeftiug  at  a  corresponding  angle  from  the  substi- 
tute. Mechanical  anchorage  is  thus  aftorded  by  the  slant  of 
the  pins  as  well  as  by  the  cement  which  serves  as  a  bond  of 


OOOXD 


SHORT  AND   LONG  BITE  BICUSPIDS   AND  MOLARS.   DIMBLOW  TEETH 

union  between  the  two  factors.    Tliis  tooth  is  used  principally 
in  repair  work  for  crowns  and  1)ridges. 

ASH'S  FLAT  BACK  REPAIR  FACING 

This  tooth  consists  of  a  flat  back  veneer,  having  a  trans- 
verse, oblong,  dovetailed  opening  in  its  lingual  surface,  for  the 


FLAT       BACK       KlOl'AII!       FACING 

USED    PRLNCIPALLY    IN    CROWN 

AND  BRIDGE  KEPAIHS 


reception  of  a  metal  projection  on  the  substitute  and  for  the 
cementing  medium.  It  is  used  principally  in  repair  work  on 
crowns  and  bridges. 


ASH'S  HELIX  TOOTH 


This  tooth  consists  of  a  flat  back  veneer,  having  a  cylin- 
drical, threaded  opening  in  its  lingual  surface,  in  the  center 


of  which  is  a  threaded  metal  pin.  A  slight  collar  surrounds 
the  opening,  which  may  or  may  not  be  ground  away  as  con- 
ditions  of  adjustment  demand. 


CONSTRUCTION    OK    I'AKTIAI.    UKNTUKKS 


Teeth  of  this  lyi)c 
where  the  .ilvoohir   I'id 


SADDLE   BACK  TEETH 

;nc   iiitciuk'd  for  use  in  those  cases 
(■  is  prouiinent,    and    space    is    con- 


SIKIKT    lUTE    SADDLE    llAl'K    HllTSl'lD.S 


strieted.  Tliey  arc  intended  principally  for  vulcanite  work, 
altiiough  tliose  sup])lied  witli  plain  or  headless  pins  are  often 
used  in  crown  and  ])rid"('  work. 


CONTINUOUS   GUM   TEETH 

The  teeth  used  in  continuous  gum  cases  are  of  the  plain 
type,  but  differ  from  those  described  in  having  cervical  ex- 
tensions which  resemble  the  outer  surfaces  of  the  roots. 

These  extensions  serve  two  purposes.  First,  they  afford 
support  to  the  tooth  in  its  attachment  to  the  iilatinum  liase, 


CONTlNIlOrS    GUM    TEETH 


during  fusion  of  the  added  i)orcelain,  and  second,  being  com- 
l)0sed  of  high  fusing  porcelain,  they  supply  a  portion  of  the 
recjuired  Inilk  or  contoui'  of  the  denture  proper,  thereby  pro- 
portionately reducing  contraction  in  the  bulk  of  continuous 
gum  body,  due  to  fusion. 

GUM  TEETH  FOR  VULCANITE  WORK 

Gum  teeth,  as  their  name  implies,  have  an  extension  root- 
ward,  which  in  contour  and  color  represents  the  natural  gum 
tissue.  They  are  made  in  single  tooth  sections  and  in  blocks 
of  twos  and  threes  for  full  dentures.  Special  sections  of  two, 
three,  and  even  four  teeth  are  procurable,  for  use  in  partial 
denture  construction.     Sections  of  this  type  are  indicated  in 


CONSTRIirTION    OF    PARTIAL    DENTIRKS 


SKT  OF  -NO.    :;S   GIM  SECTION   TEETH    (S.    S.    W 


THE    IM    \l      Itl  I    \Tlo\    in      VDIOIN 

IXG       BI.OIKS      OF      GUM       SECTION' 

TEETH     BEFORE    GRINDING 


VAKIOCS   FORMS   OF    ANTERIOR    BLOCKS.     NOTICE    THE    FESTOONS    AND    UNDULATING    SUR- 
FACES OF  GUMS 


534  CONSTRUCTION    OF    PARTIAL    DENTURES 

cases  where  gum  restoration  is  recniircd,  and  the  joint  be- 
tween natural  and  artiticial  gum  is  visible. 

Because  of  the  difficulty  in  developing  anatomic  occlusal 
requirements  in  full  dentures,  gum  section  teeth  arc  not  used 
in  such  cases  to  any  extent. 


SPECIAL  FORMS  OF  GUM  KLOCKS   FOR  ANTERIOR  REPLACEMENTS 

GUM  TEETH  FOR  METAL  WORK 

Since  there  is  a  wide  range  of  ditference  in  contraction 
and  expansion  of  metal  and  porcelain  the  use  of  gum  teeth  in 
conjunction  with  gold  or  other  metals  is  contined  to  single 
teeth  or  blocks. 

Gum  teeth  designed  for  metal  work  have  flat  backs,  and 
straight  or  plain  pins.  Special  care  must  be  used  in  solder- 
ing operations  to  avoid  fracture  of  the  porcelain,  which  occurs 
from  unequal  distribution  of  heat,  sudden  changes  of  tem- 
perature and  ditference  in  expansion  between  teeth  and  metal. 


PROPORTIONATE  PARTS  OF  TEETH 

In  selecting  a  tooth  for  any  given  case  attention  should 
be  given  to  the  shape  and  angle  of  its  cervical  end  or  "ridge 
lap,"  the  "shut"  and  the  "bite." 

RIDGE   LAP 

This  term  refers  to  the  beveled  surface  of  a  tooth  which 
slopes  lingually  from  its  cervical  portion  to  the  lingual  side. 
The  ridge  lap  varies  in  its  length  and  angular  inclination  in 
different  teeth,  although  the  shut  and  bite  in  the  same  teeth 


CONSTRUCTION    OF    PARTIAL    DENTURES  535 

may  be  alike.    Likewise,  either  the  shut,  or  bite,  or  both,  may 
vary,  while  the  ridge  lap  will  be  the  same. 

When  the  alveolar  ridge  is  prominent,  liut  little  absorp- 
tion having  occurred,  and  the  lip  line  is  high,  teeth  with  long 


ridge  lap  are  indicated.  When  much  absorption  has  occurred 
and  but  little,  if  any,  of  the  ridge  shows,  when  the  lip  is 
raised,  teeth  with  short  ridge  lap  are  indicated. 


THE  SHUT 


The  sliut  refers  to  the  space  between  the  upper  and  lower 
alveolar  processes,  or  between  the  teeth  of  one  arch  and  the 
alveolar  process  of  the  opposite  arch.     The  shut  of  an  arti- 


ficial tooth  is  indicated  bj'  the  distance  between  its  lingual 
shoulder  and  the  angle  formed  by  its  ridge  lap  with  its  lingual 
surface. 

THE   BITE 

The  bite,  or  overhife,  in  artificial  teeth  refers  to  the  dis- 
tance between  the  incisal  end  of  a  tooth  and  its  lingual 
shoulder. 


In  selecting  teeth,  special  care  must  be  given  this  point. 
When  teeth  with  short  bite  are  selected,  and  the  case  demands 
considerable  overbite  of  tlie  upper  over  the  lower  teeth,  the 
lingual  shoulders  must  be  ground  away  to  a  greater  or  less 


536  CONSTRUCTION    OF    PARTIAI>    DENTURES 

extent,    to    secure    the    (icsircil     rdatimi,    wliich     l'rei|iieiitl>' 
weakens  the  porcelain. 

Another  case  in  wliicli  lon^'-liite  teeth  sliouhl  he  used  is 
in  h)wer  anterior  rephicenients.  By  tlie  use  of  long-hite  teetli 
much   less   vulcanite   is   required   to   develop   proper   lingual 


SHORT    RIDGE 
LAP 

Long    Simt.    Mertiuin 
Bite 


MEDIUM  RIDOE 
liAT 

Short    Shut.    Long 
Hite 


EXTRA    LONG 
RIDGE   LAP 

Short   Shut.   Mediiu 
Bite 


contour  than  when  this  ])()rtion  of  the  crown  is  devoid  of  nor- 
mal contour. 

This  portion  of  the  tooth  may  be,  and  usually  is, 
described  as  having  a  }n\iq,  vipdhrm  or  short  bite. 

THE  TOOTH  SHADE  GUIDE 

Most  manufacturers  of  ])orcelain  teetli  j^i'ovide  a  shade 
guide  on  which,  in  some  manner,  are  displayed  the  different 
shades  or  colors  of  teeth  supplied  by  them.  These  guides 
usually  are  composed  of  from  twenty-five  to  forty  sample 
central  incisors  of  average  size,  all  differing  in  shade,  tone 
or  tint.  By  means  of  a  guide  of  this  type,  teeth  of  suitable 
color  may  be  selected  with  a  reasonable  degree  of  accuracy. 

Some  prosthetists  without  a  special  knowledge  of  the 
laws  of  harmony  are  able  to  arrive  at  satisfactory  results  in 
the  selection  of  teeth  of  api)ropriate  shades  for  any  individual 
case. 

How  they  do  it  or  why  the  results  are  satisfactory  they  do 
not  attempt  to  explain  further  than  it  is  by  guesswork  or  in- 
tuition. 

Intuition,  however,  in  color  science  is  not  the  result  of 
guesswork,  but  is  due  to  a  more  or  less  conscious  or  uncon- 
scious development  of  color  function  in  the  visual  organs,  as 
has  been  explained. 


CONSTRUCTION    OF    PARTIAL    DENTURES  537 

APPLICATION   OF  THE  TOOTH  SHADE  GUIDE  IN  PRACTICE 

The  patieut  sliould  hf  seated  facing-  a  direct  liglit.  The 
face,  eyes  and  hair  shouUl  be  scanned  as  a  whole,  to  deter- 
mine the  general  color  scheme  of  the  complexion  and  to  esti- 
mate, as  closely  as  ]5ossible,  the  eomplementaries  of  the  tints 
there  displayed. 

By  carefnl  observation,  with  a  little  experience,  this 
examination  enal)les  the  prosethetist  to  select  from  the  shade 
guide  a  tooth  of  the  general  tints  required.  The  first  selec- 
tion, even  if  possessing  the  fundamental  tints  indicated,  may 
not  meet  requirements.  The  tooth  may  be  too  light,  or  too 
dark,  or  it  may  need  the  addition  of  some  primary  or  sec- 
ondary color  of  greater  or  less  intensity,  to  develop  the 
necessary  harmony.  If  not  pleasing,  other  teeth  are  tested 
until  one  is  found  that,  by  its  presence  in  the  mouth,  creates 
the  impression  of  liarmony  and  is  satisfying  to  the  esthetic 
sense. 

Strong  colors  displayed  in  the  complexion  call  for 
strongly  marked  shades  of  teeth,  within  certain  limits  of 
course,  while  a  person  having  a  complexion  made  up  of  weak 
colors  must  be  supplied  with  teeth  of  neutral  tints,  or  highly 
attenuated  colors  of  a  generally  neutral  tone. 

Porcelain  teeth  are  perceptibly  darkened  by  the  sliadows 
of  the  lips  and  oral  cavity,  some  more  tlian  others,  depending 
on  their  translucency  or  power  of  transmitting-  light. 

In  selecting  teeth,  therefore,  it  is  advisable  to  test  them 
not  only  in  direct  light  but  to  change  the  position  of  the 
patient  so  that  the  teeth  may  be  subjected  to  both  lip  and  oral 
shadows,  and  the  effect  noted.  When  tested  by  direct  light 
only  too  light  a  shade  of  tooth  is  liable  to  be  selected,  with 
the  result  that  in  the  finished  denture  the  teeth  will  appear 
too  dark. 

When  a  suitable  color  of  tooth  has  been  selected  a  record 
should  be  made  of  its  number,  and  from  tliis  teeth  of  a  cor- 
responding color  number  are  yirocureil. 

A  NEW  GUM  FACING 

Protesyn,  a  silicate  cement,  has  been  recommended  and 
is  being  used  to  a  limited  extent,  as  a  substitute  for  pink,  or 
granular  jiink,  sum  facing,  in  vulcanite  dentures. 

It  is  semi-translucent  in  texture  and  compares  favorably 
in  appearance  with  jiorcelain  for  gum  restorations.  The  most 
serious  objection  urged  against  this  material  is  that  a  denture 
to  which  it  is  applied  must  be  kept  moist  at  all  times,,  other- 
wise the  jirotesyn  will  contract  and  fi'acture. 


538  CONSTRUCTION    OP    PARTIAL    DENTURES 

The  following  illustrations,  with  descriptive  text,  have 
been  supplied  by  the  L.  D.  Caulk  Co.,  Philadelphia : 

"There  is  scarcely  a  process  in  the  pi'actice  of  dentistry 
that  is  simpler  than  the  making  of  a  Protesyn  denture.  The 
esthetic  effect  is  striking,  as  it  reproduces  absolutely  the  ap- 
pearance of  the  natural  gum,  giving  a  result  not  approached 
with  any  other  material.  A  package  of  Protesyn  is  sufficient 
to  make  from  six  to  ten  dentures.  The  method  of  manipula- 
tion has  been  carefully  worked  out  l)y  the  manufacturers  and 
experienced  dentists,  and  must  be  followed  absolutely  if  the 
liest  results  are  to  be  secured.  The  successive  steps  in  mak- 
ing a  Protesyn  denture  are  ])i('tnr(Ml  and  described  as  follows: 


I.  One  thickness  of  baseplate  wax  is  placed  on  the  cast 
in  the  usual  manner ;  the  teeth  are  set  up  and  waxed  up  from 
the  palatine  side.  An  undercut  is  left  at  the  labial  cervical 
mai'gin  for  retention  of  the  Piotesyn  between  the  teeth  and 
vulcanite. 


II.     Putting  on  the  rim.    Cut  and  attach  one  or  two  strips 
of  wax  (depending  on  the  labial  fullness  desired),  and  attach 


CONSTRUCTION    OF    PARTIAL    DENTURES  539 

the  strip  or  strips  to  the  top  of  the  plate,  making  an  undercut 
for  Protesyn  retention. 

HI.     A  fully  waxed  u])  east  ready  to  lie  fliasked,  packed 
witli  rubber  and  vulcanized.     The  itolislied  and  finished  den- 


ture will  naturally  be  a  duplicate;  it  is  then  ready  for  the 
Protesyn.    Mix  a  sufficient  quantity  at  one  time  to  complete 


the  denture.  In  making  the  mix,  a  large,  strong  agate  spatula 
is  required.  The  consistency  should  be  about  the  same  as  a 
correct  mix  of  Synthetic  Porcelain.     The  mix,  however,  may 


540  CONSTRUCTION    OK    I'AKTIAL    DRNTURES 

be  made  with  more  dcliheiation  than  a  mix  of  Synthetic,  in- 
asmiieh  as  Protesyn  is  sk)w  setting,  and  therefore  the  operator 
has  ample  time  to  secure  the  proper  consistency  witliont  haste. 
A  period  of  from  twenty  to  twenty-tive  minutes  is  availal)le 
from  the  time  the  mix  is  begun  until  the  Protesyn  is  molded 
and  festooned,  before  the  mass  becomes  too  hard  to  work. 
Wlien  ready  for  the  denture,  tlie  Protesyn  must  be  a  stiff, 
homogeneous  mass. 

IV.  The  method  ol'  putting  Protesyn  on  the  plate.  Small 
successive  quantities  are  taken  on  the  spatula  and  forced  into 
the  space  provided  for  it.  drawing  the  spatula  across  the  front 
rim  of  the  denture,  continuing  until  the  whole  space  is  filled 
slightlv  to  excess. 


V.  Shaping  the  Protesyn.  At  this  stage  the  mass  is 
])atted  and  smoothed  and  forced  fully  into  the  undercuts. 
The  finger  must  be  slightly  anointed  with  the  lubricant.  Avoid 
folds  and  laps  of  Protesyn. 


^'^I.     Coating  lightly  with  Protesyn  lubricant   prelimin- 
irv  to  the  molding. 


CONSTRtTCTION    OF    PARTIAT.    nRNTT'RBS 


VII.     Using  a   tautaliini   iiistnuiu'ut   Id   force   back   the 
Protesvn  and  to  clefino  the  gum  niai'sins. 


VIII.     Finally  smootliin.<i'  and  tinisliing  the  gum  margins 
with  Protesvn  brush  No.  1. 


IX.     Forming   the   festoons,    showing   how     easily     and 
artisticallv  this  mav  be  done  with  Protesvn. 


CONSTRUCTION    OF    PARTIAL    DENTURES 


X.  Stippling  witii  brush  No.  2.  The  area  indicated  at 
the  iJoint  of  the  brush  as  shown  in  the  picture  is  the  only  part 
of  the  natural  gum  that  shows  a  decided  stippled  effect.  Uver- 
stippling  and  excessive  festooning,  besides  being  unnatural, 
render  the  denture  less  sanitary. 


HH£ 

^^"^tJBB 

bI 

Pf^"^^ 

Km 

Hj^ 

t ;      1 

j^nph 

^^Ki.   ,,' 

^tjr^ 

XI.  The  completed  denture  coated  with  Protesyn  Lubri- 
cant. When  the  denture  is  finished  and,  five  or  ten  minutes 
later,  the  Protesyn  sufficiently  hardened,  it  must  be  immedi- 


CONSTRUCTION    OF    PARTIAL    DENTURES  543 

ately  heavily  coated  with  Protesyn  Lubricant,  exercising  care 
in  its  application  not  to  mar  or  obliterate  the  festooning. 

XII.     A  period  of  twenty-four  hours  must  elapse  after 
the  Protesvu  denture  has  been  finished,  coated  with  lubricant 


and  laid  away,  before  it  is  cleaned  and  placed  in  water.     To 
clean,  use  a  brush,  soap  and  water. 

XIII.  Method  of  removing  Protesyn  from  a  denture  in 
case  repair  of  the  vulcanite  becomes  necessary.  This  is  done 
after  the  denture  has  l)een  repaired  and  otherwise  finished. 
We  do  not  recommend  the  old  Pi'otesvn  to  remain  after  it  has 


been  through  the  vulcanizer.  Use  a  knife-edge  carborundum 
wheel.  Cut  a  longitudinal  groove  and  chip  the  Protesyn  away 
with  chisels  or  scalers.  Then  thoroughly  remove  all  of  the 
old  Protesyn  and  apply  new. 


544  CONSTRUCTION    OF    PARTIAL    DENTURES 

XIV.  An  upper  and  a  lower  Protesyn  gold  denture  ai'tic- 
ulated.  In  these  cases  the  Protesyn  is  extended  to  tlie  under- 
cut of  the  turned-up  or  wire-soldered  rim,  the  teeth  l)eing 
anchored  by  the  usual  cleats  and  vulcanite  attachment  pala- 


tally.     Spurring  on  the  labial  face  may  also  be  resorted  to 
for  added  attachment,  as  in  the  case  of  vulcanite. 

X^^.  Here  are  shown  a  removable  bridge  and  a  lower 
Protesyn  denture.  This  suggests  the  wide  use  of  Protesyn  in 
bridge-work.    In  tiiis  lower  denture  (as  also  in  No.  12,  shown 


in  the  bowl  of  water)  the  Protesyn  is  used  conservatively,  al- 
lowing ample  body  of  vulcanite  margins  for  rim-titting,  with- 
out destroying  the  undercut  for  Protesyn.  These  cases  also 
show  the  Protesyn  extended  beyond  the  high  lip-line. 


CONSTRUCTION    OF    PARTIAL    DENTURES  545 

In  the  making-  of  Protesyn  dentures  these  requirements 
must  be  observed.  The  mass  must  be  mixed  to  the  proper  con- 
sistency. The  i^late  when  finished  must  be  heavily  coated  with 
lubricant  and  laid  aside  for  twenty-four  hours,  when  it  is 
cleaned  and  placed  in  water.  Henceforth,  it  must  always  re- 
main in  water  when  not  in  the  mouth  of  the  patient.  The 
patient  must  be  instructed  on  this  point. 


NATURAL  DENTURES  REPRODUCED  IN  PORCELAIN 
TEETH  AND  WAX 

The  following  series  of  cuts  has  been  introduced  to  show 
some  of  the  commonly  occurring  variations  in  arrangement 
of  the  natural  teeth.  These  eases  represent  as  nearly  as  pos- 
sible, by  means  of  porcelain  teeth  arranged  in  wax,  the  con- 
ditions found  in  the  mouths  of  living  subjects.  Most  of  these 
illustrations  have  appeared  in  the  past  in  the  Dental  Cosmos 
and  several  of  them  appear  in  the  American  System  of  Den- 
tistrv,  18SS,  in  an  article  on  celluloid  and  zvlonite  l)v  Dr. 
W.  W.  T<]vans. 


I.     Ai)pearance  of  teeth  of  person  i)ast  middle  life,  gum 
recession,  strongly  mai'l^cd  meciianical  alirasioii. 


II.     Teeth  of  a  woman  of  thirty  to  tliirty-flve.     There  is 
ratlier  long  overbite,  and  the  chamferiiisi-  of  tlie  edges  of  the 


546  CONSTRUCTION    OF    PARTIAL    DENTURES 

lower  incisors  is  i)lainl.v  seen.  Tlie  right  central  overlaps 
the  left.  Two  teeth  are  lost  from  these  arches,  the  right 
upper  first  bicuspid  and  the  left  lower  first  molar.  The  upper 
denture  is  provided  with  ])lnmp('rs  to  restore  disturl)ed  facial 
contour. 


III.  The  denture  of  a  man  past  fifty  years  of  fige.  The 
teeth  are  inclined  well  forward,  with  end  to  end  occlusion. 
The  effect  of  wear  is  seen  on  the  incisal  edges  of  the  lower 
incisors,  and  indicated  by  the  squaring  of  those  of  the  upper 
lower  incisors  separated,  as  is  often  seen;  gums  receded. 


IV.  The  denture  of  a  girl  of  twelve  or  thirteen  years  of 
age.  The  cuspids  are  not  yet  fully  erupted,  and  the  incisors 
show  a  ver}^  marked  example  of  the  cusplets  which  adorn 
them  when  first  erupted. 

V.  The  denture  of  a  man  between  twenty-five  and  thirty 
years  of  age.  Teeth  are  fully  developed,  large,  with  a  long 
overbite.  The  upper  cuspids  are  elongate  and  incline  slightly 
inward.  The  lower  incisors  are  considerably  crowded  and 
inclined.     The  upper  right  first  bicuspid  and  lower  left  first 


CONSTRUCTION    OK    PARTIAL    DENTURES  547 

molar  have  been  lost.     Two  tillings  are  shown  in  tlie  upper 
central  incisors. 


VI.     The  denture  of  a  young  woman  between  eighteen 
and  twenty  years  of  age.    All  of  the  teeth  are  fully  eruiited, 


and  the  little' cusps  of  the  incisors  are  nearly  effaced.    Every 
tooth  is  in  a  healthv  condition. 


VII.  The  denture  of  a  man  between  forty  and  fifty 
years  of  age.  Occlusion  almost  end  to  end.  Some  recession 
of  the  gums.    Plumpers  to  restore  disturbed  facial  contour. 


CONSTKIU'TION    OF    PARTIAI-    niONTUUES 


VIII.     Denture  of  a  man  between  fift.\-  and  sixty  years 
of  age.     The  teeth  show  wear  from  use. 


IX.  Teetli  of  a  man  ahont  fifty  years  old.  Left  npper 
lirst  bicuspid  lost.  Teeth  show  incchanical  abrasion. 
l'lum|)('i-s. 


X.     Overlap])ino'  lateral  ineisors.    Gnms  are  prominently 
ridged,  indicating  position  of  roots. 


CONSTRUCTION  OF  PARTIAL  DENTURES 


XI.     T(>eth  arrangod  with  close  bite,  considerable  over- 
lap, lateral  rotated. 


XII.     Central  incisors  rotated  outward  distally.    Laterals 
rotated  inward  distallv  and  slislitlv  within  the  arch. 


XIII.      Centrals    inclined    inward,    hiterals   overlapping, 
cuspids  i^rominent. 


XIV.     Centrals     V-shaped.        All      incisors     diverging 
strongly  from  incisal  edges  apically. 


CONSTRUCTION    ()K     PAKTIAI.    DENTURKS 


XV.     Incisors  (mt  of  ;ili,n'iiincnt. 


XVI.'  Plain  teeth  a,ronnd  to  liorder.     Gmn  restoration 
from  cuspids  backward. 


C  If  AFTER     XXI  \^ 

CELLULOID    DENTURES 

Of  the  plastic  vegetable  bases  used  in  dentiare  construc- 
tion, celluloid  presents  the  most  natural  appearance,  closely 
approaching  porcelain  in  the  translucent,  live-tissue  color  of 
the  gums  and  mucous  membrane. 

It  is  not  generally  as  durable  as  vulcanite,  freciuently 
discoloring  and  rapidly  disintegrating  in  some  mouths,  while 
again  it  ]iroves  satisfactory  in  other  cases.  Its  value  as  a 
denture  base  is  largely  dependent  upon  the  manner  of  manip- 
ulation of  the  material  during  construction,  as  well  as  on 
the  care  bestowed  upon  it  by  its  possessor. 

DISCOVERY  OF  CELLULOID 

In  1855  an  Englishman  by  the  name  of  Parks  invented 
the  material  now  known  as  celluloid,  and  which  he  named 
parksite  or  zylonite.  In  1859  a  man  by  the  name  of  Mack- 
intosh, also  in  England,  patented  the  material  called  collo- 
dion, from  which  he  constructed  denture  bases.  This  sub- 
stance was  improved  upon  by  Dr.  McClelland  of  Louisville, 
Ky.,  in  1860,  who  gave  it  the  name  of  rose  pearl.  The  denture 
base  was  made  from  sheet  collodion,  moistened  in  alcohol  and 
ether  sufficiently  to  render  it  plastic  for  securing  adaptation 
to  the  cast.  The  teeth  also  were  attached  with  additions  of 
the  same  material,  similarly  softened.  Dentures  so  con- 
structed showed  a  decided  tendency  to  warp  in  drying  out. 

The  Newark  Manufacturing  Company,  organized  in  this 
country  in  1869,  began,  and  for  a  number  of  years  conducted, 
a  series  of  experiments  to  determine  the  possibilities  and 
limitations  of  this  material.  After  the  lapse  of  a  number  of 
years  and  the  expenditure  of  large  sums  of  money,  during 
which  time  many  almost  insurmountable  difficulties  were  met 
and  overcome,  a  product  of  stable  character  was  finally 
evolved,  capable  of  application  to  innumerable  purposes. 

COMPOSITION   OF   CELLULOID 

Celluloid  is  made  from  pi/ru.rijlin,  or  the  woody  filler  of 
plants.     This  material  is  treated  with  nitric  and  sulphuric 

.551 


552  CELLULOID    DENTURES 

acids,  after  which  it  is  known  as  nitro-ceUulose,  or  (pincotton, 
a  highly  explosive  substance. 

The  proportions  of  this  material  with  other  substances, 
as  used  for  dental  purposes,  are  about  as  follows :  Guncotton, 
100  parts;  camphor,  40  parts;  white  oxide  of  zinc,  2  parts; 
vermilion,  .06  part. 

Zylonite  is  made  by  first  dissolving  the  guncotton  in 
ether,  or  methyl  alcohol,  and  then  combining  it  with  the  other 
ingredients.  Celluloid  is  made  by  effecting  the  union  of  the 
several  ingredients  by  means  of  heat  and  pressure,  without 
first  dissolving  the  guncotton. 

MANUFACTURE   OF   CELLULOID 

The  following  abbreviated  description  of  the  manufac- 
ture of  celluloid  appeared  in  the  Dental  Cosmos,  January, 
1875,  being  a  reprint  from  an  article  in  the  American  Ar- 
tisan: 

"After  the  pulp  is  ground  in  the  beater  engine,  and  the 
camphor  and  whatever  coloring  matter  may  be  desired  are 
thoroughly  incorporated  with  it,  the  substance  being  kept, 
meanwhile,  at  the  proper  temperature,  the  superfluous  water 
is  removed  by  pressure  and  absorption,  a  peculiar  porous 
material,  made  especially  for  the  latter  purpose,  being  em- 
ployed. 

"During  the  process  of  drying  under  pressure  and  ab- 
sorption, the  material  becomes  nearly  converted,  so  that  it 
is  no  longer  nitro-cellulose,  but  imperfect  celluloid.  In  so 
far  as  conversion  has  taken  place,  its  properties  have  under- 
gone a  total  change.  All  that  remains  to  convert  it  into  the 
various  articles  referred  to  is  manipulation  under  heat  and 
pressure,  during  which  the  chemical  combination  is  com- 
pleted. 

"For  some  qualities  of  the  material  desired  to  be  pro- 
duced, a  small  percentage  of  alcohol  is  added  in  the  subse- 
quent manipulation.  As  evidence  that  there  is  a  perfect 
chemical  combination,  and  not  a  mere  mechanical  mixture 
of  the  materials,  the  fact  may  be  stated  that  camphor  in  its 
uncombined  state  is  an  extremely  volatile  substance  when 
exposed  to  the  air;  in  its  combination  with  nitro-cellulose  it 
loses  this  property  altogether.  An  enumeration  of  the  prop- 
erties of  the  material,  which  we  shall  give  anon,  will  be  fur- 
ther proof  of  the  chemical  combination. 

"When  the  material  is  properly  converted,  comparatively 
no  shrinkage  takes  place.     There  is  no  escape  of  the  cam- 


CELLULOID    DENTURES  553 

phor,  uuless  au  excess  has  been  employed,  and  in  that  case 
the  excess  of  camphor  will  escape  from  the  surface  of  the 
celluloid;  but  whatever  uncombined  camphor  remains  in  the 
interior,  it  is  so  closely  imprisoned  by  the  solid  surfaces  that 
it  cannot  escape.  By  varying  the  proportion  of  the  excess  of 
camphor,  different  degrees  of  solidity  and  flexibility  are  ob- 
tained.    .     .     . 

ADVANTAGES    CLAIMED    FOR    CELLULOID 

"Without  the  admixture  of  coloring  matter  it  has  a  pale 
amber  color.  If  it  is  desired  to  make  the  material  white,  like 
ivory,  oxide  of  zinc  is  used,  and  for  other  colors  various 
mineral  pigments  are  incorporated  with  it,  or  dyes  soluble 
in  alcohol,  or  any  of  the  analine  dyes,  may  be  caused  to  per- 
meate the  matei'ial  to  give  it  any  desired  color.  It  is  hard 
and  elastic,  having  a  hardness  ranging  from  horn  to  that  of 
ivory.  It  is  as  tough  as  whalebone.  In  elasticity  it  greatly 
exceeds  ivory.     .     .     . 

"Celluloid  is  also  a  very  fair  non-conductor  of  heat  and 
electricity,  not  quite  so  much  so  as  hard  rubber,  Init  approxi- 
mating the  latter  very  closely  in  this  particular.     .     .     . 

"While  it  is  so  good  a  non-conductor,  it  is  not  perceptibly 
electric.     .     .     . 

"But  perhaps  the  most  remarkable  property  of  this 
otherwise  very  remarkable  material  is  the  fact  that  it  be- 
comes plastic  at  a  temperature  of  from  250  to  300  deg.  F., 
and  this  property  enables  it  to  be  molded  with  facility  into 
a  great  variety  of  forms  for  ornament  and  utility.  Pure 
celluloid  has  a  specific  gravity  of  about  1.4. 

"A  profitable  and  successful  industry,  based  upon  these 
l)roperties  of  celluloid,  is  the  manufacture  of  dental  plates. 
The  material  can  be  made  precisely  the  color  of  the  palate 
and  gums. 

COMPARATIVE   STRENGTH    OF   CELLULOID   AND    VULCANITE 

"It  is  much  stronger  than  rubber  and  has  a  perfectly 
clean  surface.  It  may  be  more  easily  manipulated  than  rub- 
ber, as  it  does  not  require  to  be  vulcanized.  It  possesses  all 
the  valuable  qualities  of  rubber  for  dental  purposes  with 
none  of  its  defects.  It  requires  only  about  1/60  as  much 
vermilion  to  give  the  proper  color  to  celluloid  as  is  required 
to  impart  the  usual  color  to  rubber.  The  danger  of  saliva- 
tion, which  sometimes  occurs  in  the  use  of  rubber  for  dental 
purposes,   is,  therefore,   obviated.     The   difificulties   encoun- 


554  OBbLULOIl)    DRNTURES 

tered  in  tlio  application  of  celluloid  to  dental  plates  have 
been  very  great,  and  many  failures  were  at  lirst  experienced, 
but  with  untiring  perseverance  the  inventors  have  pursued 
the  subject  until,  during  the  last  year  or  two,  they  claim  to 
have  produced  an  article  possessing  all  the  requirements  de- 
sired, not  a  single  failure  having  been  experienced  through 
any  fault  of  the  material  made  within  a  twelvemonth  past." 
The  foregoing  claims  are  somewhat  exaggerated  in  sev- 
eral respects,  but,  taken  as  a  whole,  the  description  of  this 
material  is  an  admirable  one.  Just  about  the  time  celluloid 
came  into  use,  much  litigation  was  in  progress  between  the 
Groodyear  Rubber  Company  and  members  of  the  dental  pro- 
fession, who  refused  to  pay  a  royalty  to  the  above-named 
company  for  the  privilege  of  using  vulcanizable  rubber  for 
dental  purposes.  At  that  time  celluloid  was  welcomed  and 
widely  used,  but  owing  to  the  fact  that  its  properties  were 
not  fully  understood,  and  that  the  methods  of  manipulation 
were  not  perfected,  many  failures  have  been  recorded  against 
it.  These  failures  will  now  be  mentioned  and  the  causes  ex- 
plained. 

DISADVANTAGES   OF   CELLULOID   AS   A   DENTURE   BASE 

First. — In  some  cases  these  seems  to  be  a  gradual  solu 
tion  of  the  substance  by  the  fluids  of  the  mouth.  Such  action 
results  in  thinning  and  the  consequent  weakening  of  the 
baseplate.  The  material  around  the  pins  of  the  teeth  is 
gradually  worn  or  dissolved  away,  thus  allowing  the  latter 
to  become  displaced  under  the  stress  of  mastication. 

Second. — When  used  for  some  time,  in  many  instances  a 
very  disagreeable  odor  develops,  so  objectionable  that  the 
denture  cannot  be  worn  with  comfort. 

Third. — ^The  baseplate  often  becomes  badly  discolored, 
assuming  a  dirty,  brown  appearance,  and,  in  the  case  of 
smokers,  a  black  film,  extremely  difficult  to  remove,  forms  on 
the  surface. 

Fourth. — Liability  of  the  cast  to  become  distorted  in 
molding  the  celluloid  blank  over  it.  When  this  occurs,  failure 
to  secure  adaptation  to  the  oral  tissues  results. 

Most  of  these  objectionable  features  mentioned  are 
largely  due  to  faulty  technic,  and  can  be  obviated  to  a  great 
extent  by  exercising  care.  When  the  blank  is  molded  over 
the  cast  in  the  presence  of  oil,  steam  or  glycerine,  the  vola- 
tile constituents  are  not  eliminated  as  they  should  be,  but. 
on  the  contrary,  the  celluloid  seems  to  take  up  some  of  the 


CELLITLOID    DENTURES  555 

liqi^ids  and  becomes  reduced  in  density  and  less  resistant  to 
the  action  of  the  finids  of  the  montli. 

GENERAL    METHODS    OF    MANIPULATION 

The  best  results  are  attained  by  pressing  celluloid  in  a 
dry  chamber,  at  high  temperature,  continuing  the  process 
as  long  as  may  be  consistent  with  the  work  in  hand.  By 
this  method  the  volatile  constituents  are  driven  off,  the  ma- 
terial rendered  more  dense  and  compact,  while  its  elasticity 
will  be  increased  and  its  color  improved  over  the  product 
resulting  from  the  moist  process. 

Steam,  oil  or  glycerine  softens  the  plaster  cast  and  flask 
investment  as  well,  rendering  them  more  susceptible  to  com- 
pressive force  and  consequent  distortion  in  closing  the  flask. 
When  dry  heat  is  employed,  the  flask  contents  become  hard- 
ened by  the  evaporation  of  the  moisture  before  the  com- 
pression force  is  applied,  and  consequently  there  is  less  lia- 
bility of  warpage  or  distortion  occurring  than  by  the  moist 
method. 

The  chief  objection  to  the  dry  method  is  due  to  the  dan- 
ger of  burning  tlie  blank  during  the  process  of  pressing. 
By  cutting  ample  waste  gates  in  the  plaster  investment  sur- 
rounding the  matrix,  so  that  no  surplus  material  comes  in 
contact  with  the  metal  flask,  this  danger  is  largely  overcome. 
An  extra  large  sized  flask  for  investment  purposes  is  neces- 
sary in  order  to  afford  the  needed  space  for  deep  and  wide 
gates. 

The  flask  should  be  of  the  same  general  form  as  a  vul- 
canite flask,  but  larger  and  hea^'ier  throughout.  The  gTiide- 
pins  should  be  strong  and  long  enough  to  hold  the  two  halves 
of  the  flask  in  proper  relation  to  each  other  when  separated 
by  the  introduction  of  the  unpressed  blank. 

CONSTRUCTION   OF   THE   WAX    MODEL   DENTURE 

The  construction  of  the  wax  model  denture  for  a  cellu- 
loid case  differs  in  no  essential  particulars  from  that  for  a 
vulcanite  case.  The  wax  contour  model  is  constructed  and 
fitted  in  the  mouth  to  establish  the  bite  and  the  direction  of 
the  condyle  paths. '  On  this  the  teeth  are  occluded  and  tried 
in  the  mouth  for  appearance,  alignment,  occlusion  and  bal- 
ancing contact,  after  which  it  is  returned  to  the  cast,  the  lat- 
ter detached  from  the  occluding  frame,  and  the  case  is  ready 
for  investment  in  the  flask. 


CELLULOID  DENTURES 


FLASKING 


Upper  eases  should  he  invested  iu  the  shallow  half  of 
tlie  flask;  lower  cases  in  tlie  deeper  portion,  in  order  to  con- 
sei've  space.  In  upper  cases  the  anterior  part  of  the  cast  is 
elevated,  more  or  less,  to  insure  a  parallel  relation  between 
the  several  surfaces  of  the  east  and  the  guide-pins,  or  the 
line  of  direction  in  which  the  two  halves  of  the  flask  must 
travel  in  closing.  Sliould  undercuts  be  present,  the  material 
may  fail  to  find  its  way  into  them  on  account  of  the  matrix 


rEI.LUI.dID    FLASK    1  IK.SICNEll    1!V    1>I1.    H     C     MIM.ER    c  IF   FORTLAND,    ORB. 

margins  preventing;  hence  the  necessity  for  elevating  the 
cast,  as  suggested. 

Coarse  plaster  should  be  used  for  investment  purposes, 
as  it  withstands  high  pressure,  without  perceptible  yielding, 
much  better  than  impression  plaster. 


CUTTING   THE   WASTE   GATES 

Deep  and  wide  waste  gates  should  extend  entirely 
around  the  matrix,  these  being  cut  in  the  side  of  the  flask 
containing  the  cast,  for  if  cut  in  the  opposite,  or  matrix,  side, 
the  walls  of  the  latter  would  be  weakened  and  probably 
crushed  under  the  pressure  required  to  force  out  the  excess 
material.  The  outer  margin  of  the  gate  should  be  at  least 
an  eighth  of  an  inch  from  the  inner  margin  of  the  flask  to 


CELLULOID    DENTURES  557 

prevent  any  possibility  of  the  surplus  celluloid  coming  in 
contact  with  the  heated  metal.  It  is  a  peculiar  fact  that  com- 
bustion of  celluloid  almost  invariably  occurs  when  brought 
in  contact  with  metal  lieated  to  300''  F.  or  above,  while  if 
enclosed  entirely  in  plaster  the  temperature  may  be  raised 
fifteen  to  twenty  degrees  higher  before  the  material  will  burn. 
The  inner  margin  of  the  gate  should  approach  very  close  to 
the  matrix  margin,  so  that  the  surjilus  material  may  flow 
out  readily  after  it  once  passes  the  matrix  periphery.  The 
plaster  between  the  two  margins  of  the  gate  outline  is  cut 
out  in  V-shaped  form,  sufficiently  deep  to  afford  ample  space" 
for  any  surplus  present. 

CLEARING  THE   MATRIX   OF   WAX   AND  DEBRIS 

The  gates  having  been  formed,  the  wax  is  removed  from 
the  interior  of  the  flask,  the  latter  cleansed  with  boiling  water, 
the  sharp,  angular  margins  of  the  matrix  are  trimmed  off 
to  prevent  them  fracturing  and  mixing  with  the  celluloid  in 
closing  the  flask. 

The  face  of  the  cast  should  be  covered  with  a  tilm  of 
collodion  to  give  smoothness  to  the  surface  of  the  denture 
pressed  against  it. 

SELECTION   OF  THE  BLANK 

Celluloid,  as  prepared  for  dental  purposes,  comes  in 
the  form  of  blanks,  blocks  having  the  general  form  of  a 
denture  baseplate,  but  considerably  thicker  than  the  finished 
denture  will  be,  so  as  to  suj:)ply  the  necessary  surplus  to  fill 
the  matrix  under  pressure. 

The  blanks  come  in  various  sizes  and  are  numbered  as 
follows,  beginning  with  the  smallest:  No.  21/2,  3,  31/0,  4,  41/2, 
5,  5^^,  6,  6I/0.  These  are  sufficiently  thick  to  insure  a  sur- 
plus of  material  for  ordinary  cases.  Wben  a  large  amount  of 
absorption  has  occurred,  it  is  sometimes  necessary  to  use  a 
thicker  blank  than  those  mentioned.  For  such  purposes  a 
series  of  extra-thick  blanks  are  supplied  and  numbered  as 
follows:   2i/,a,  3a,  Sy.a,  4a,  4i/.a,  etc.,  up  to  ev^a. 

When  using  upper  blanks  of  this  variety  it  will  invaria- 
bly be  necessary  to  reduce  the  palatine  portion  to  a  reason- 
able thickness  with  a  lathe  burr,  shown  elsewhere.  If  not 
I'educed,  the  matrix,  and  frequenth^  the  cast,  is  distorted  in 
forcing  out  the  excessive  surplus,  oftentimes  to  such  an  ex- 
tent as  to  destroy  denture  adaptation. 

Frequently  it  will  be  necessary  to  modify  the  form  of  a 


558  CELLULOID    DKNTURES 

blank  before  introducing  and  pressing,  so  that,  in  a  general 
way,  it  will  conform  to  the  face  of  the  cast.  This  is  done 
by  placing  it  in  boiling  water  until  thoroughly  heated,  and 
with  pliers  bending  the  outer  rim  to  the  required  form,  or  if 
the  vault  portion,  as  in  flat-arch  cases,  needs  modifying,  lay 
the  blank  on  a  flat  surface,  and  with  a  round-end  wood  handle 
depress  the  central  area  until  the  outer  rim  settles  down 
over  and  encloses  the  labial  and  buccal  surfaces  of  the  cast. 
It  may  be  necessary  to  heat  the  blank  three  or  four  times  in 
order  to  give  it  the  proper  form,  but  time  devoted  to  this 
preliminary  adaptation  is  well  spent,  as  it  reduces  the  lia- 
bility of  the  celluloid  folding  on  itself,  of  the  matrix  failing 
to  fill,  and  also  of  the  latter  becoming  distorted  from  the 
application  of  unequal  pressure. 

Usually  during  this  preliminary  adaptation  the  blank 
will  become  more  or  less  soiled.  This  may  be  corrected  by 
scraping  the  soiled  surfaces  and  also  rubbing  the  blank  with 
a  clean  piece  of  muslin  moistened  with  spirits  of  camphor. 
The  application  of  the  latter  will  also  prevent  the  tendency 
of  the  celluloid  to  flake  or  crack  during  the  pressing  process. 
The  blank  is  now  set  upon  the  cast,  and  the  upper  half  of 
the  flask  set  in  position  to  engage  with  the  guide-pins  of  the 
opi^osite  side,  then  carefully  let  down  until  the  matrix  mar- 
gins are  in  contact  with  the  blank.  Care  should  be  taken  to 
see  that  the  latter  is  not  displaced  during  this  step. 

PRESSING  THE  CASE 

A  dry-chamber  press  should  be  used,  for  reasons  pre- 
viously mentioned.  The  flask  is  set  on  the  bedplate  of  the 
press,  matrix  side  down,  so  that  in  ease  any  of  the  teeth  be- 
come loosened  in  the  dry  heat,  gravity  will  retain  them  in 
position.  The  three  screws  which  draw  the  bedplate  up 
against  the  lid  of  the  press  should  be  tightened  evenly,  so 
that  the  guide-pins  may  at  all  times  travel  in  a  perpendicu- 
lar direction  and  parallel  with  the  screws.  No  jiressure 
should  be  put  upon  the  blank  until  the  latter  is  thoroughly 
heated  to  a  tem]ierature  of  at  least  300°  F.,  at  which  point 
it  should  be  maintained  during  the  pressing  process.  At 
least  twent.y-five  minutes  should  be  allowed  for  raising  the 
temperature  in  the  interior  of  the  press  up  to  tliis  point. 

When  the  proiDer  temperature  has  been  attained,  the 
bolts  are  gradually  tightened,  and,  as  before  suggested,  care 
should  be  taken  to  kee]i  the  bedplates  iiarallel  at  all  times 
with  the  top  of  the  press,  so  that  the  guide-pins  will  not  be 


CELLULOID    DENTURES  559 

bent.  The  case  should  be  lifted  out  of  the  press  from  time 
to  time  for  examination,  to  determine  the  progress  of  the 
closure,  but  should  be  returned  to  the  chamber  as  quickly  as 
possible  to  prevent  cooling. 

Too  much  pressure  should  be  avoided.  Celluloid,  even 
when  plastic,  is  rather  sluggish  and  flows  slowly  If  forced 
too  rapidly,  or  faster  than  the  normal  flow  the  matei'ial  will 
warrant,  distortion  of  the  matrix  and  face  of  the  cast  will 
occur,  and  a  misfit  will  result. 

When  the  flask  is  closed,  the  source  of  heat  is  cut  off  and 
the  case  allowed  to  cool  for  ten  or  fifteen  minutes  or  longer, 
if  time  permits.  This  permits  the  molecules  of  the  material, 
under  the  continued  heat  and  pressure,  to  adjust  themselves 
to  each  other,  and  lessens  the  danger  of  warpage  which  some- 
times occurs  when  pressure  is  relieved  too  suddenly.  In  every 
case  the  flask  and  contents,  whether  suddenly  or  quickly 
chilled,  must  he  perfectly  cold  before  the  press  bolts  are 
loosened,  otherwise  distortion  may  result. 

REMOVAL  OF  THE  CASE  FROM  THE  FLASK 

In  removing  a  case  from  the  flask  it  will  be  found  that 
the  plaster  is  extremely  hard  and  difficult  to  cut.  The  desire 
to  pry  the  flask  apart  suddenly,  or  use  a  hammer  to  knock 
the  investment  out  of  the  flask,  is  great,  but  if  these  methods 
are  emploj^ed  some  of  the  teeth  will  very  likely  be  fractured. 
It  is,  therefore,  best,  even  though  more  tedious,  to  saturate 
the  case  in  water,  pry  off  tlie  top  and  bottom  plates,  and  re- 
move the  content  of  the  flask  by  cutting  close  to  the  inner 
periphery  of  the  flask. 

FINISHING 

No  special  directions  are  necessary  for  finishing  cellu- 
loid cases,  as  this  material  is  susceptible  to  the  same  methods 
of  polishing  as  vulcanite.  Should  there  be  a  decided  odor  of 
camphor  present  when  the  case  is  finished,  it  may  be  re- 
moved by  immersing  the  denture  in  a  10  per  cent  solution 
of  sulphuric  acid  for  a  few  minutes.  If  allowed  to  remain 
in  the  acid  for  a  long  time,  or  in  a  strong  solution  for  a  short 
time,  solution  of  the  celluloid  will  occur. 

GENERAL  REMARKS 

As  before  stated,  celluloid  is  not  as  durable  a  material 
as  vulcanite,  but  it  certainly  deserves  some  consideration 
as  a  serviceable  and  inexpensive  base  for  dentures,  as  well 


560  CELLULOID    DENTURES 

as  for  its  beauty  and  dost'  rfsciiihlaiicc  to  the  natural  gum 
tissues. 

Celluloid  is  peculiar,  aud  its  physical  properties  must 
be  well  understood  in  order  to  derive  the  best  results  from 
its  use  in  denture  construction.  It  forms  an  admirable  base 
for  temporary,  and  under  favorable  conditions  for  perma- 
nent dentures  also.  Celluloid  does  not  serve  well  as  a  base 
for  partial  dentures,  for  the  reason  that  single  or  isolated 
teeth  are  more  readily  displaced  from  a  base  of  this  material 
than  from  one  of  vulcanite. 

CASTS  FOR  CELLULOID  CASES 

Since  the  principal  source  of  error  in  celluloid  denture 
adaptation  is  due  to  compression  and  consequent  distortion 
of  the  cast  in  pressing  the  material,  and  since  the  pressure 
applied  cannot  well  be  reduced  imder  that  usually  employed, 
on  account  of  the  sluggishness  of  the  material,  even  under 
high  temperature  and  pressure,  the  remedy  lies  in  the  use 
of  a  harder  substance  than  plaster  for  casts.  Any  of  the 
three  materials  previously  mentioned  in  connection  with  cast 
construction  are  applicable  for  this  purpose,  viz.,  oxy- 
chloride  of  magnesium,  Spence's  plaster,  and  tin,  although 
when  the  latter  is  used  great  care  must  be  exercised  to  avoid 
overheating  and  consequent  burning  of  the  celluloid. 


CIIAPTKR     XXV 

REPAIRING  VULCANITE    DENTURES 

The  materials  of  whieli  vulcauite  deuturew  are  composed 
are  susceptible  to  wear  and  breakage  under  stress,  and  since 
dentures  of  this,  as  well  as  of  all  types,  are  subjected  to 
more  or  less  heavy  masticatory  effort,  accidents  of  various 
kinds  frequently  occur  to  both  the  vulcanite  base  and  the 
porcelain  teeth.  The  accidents  which  are  of  most  frequent 
occurrence,  with  methods  for  repairing  such  cases,  will  now 
be  outlined. 

FRACTURE  OF  THE  VULCANITE  BASE 

Fracture  of  the  baseplate  may  be  caused  by  the  appli- 
cation of  sudden  or  undue  stress  in  handling  while  cleans- 
ing, or  from  a  fall ;  or,  in  case  unequal  absorption  of  the 
alveolar  process  occurs  after  the  denture  is  introduced,  under 
heavy  masticatory  stress  the  baseplate  breaks  from  the  re- 
sulting imdue  torsional  strain,  due  to  lack  of  support  over  the 
absorbed  areas. 

Under  such  conditions  a  fissure  usually  makes  its  ap- 
pearance at  some  point  along  the  margin  of  the  baseplate, 
and,  unless  corrected,  extends  more  deeply  into  the  vulcanite, 
finally  resulting  in  fracture  of  the  denture  into  two  or  more 
pieces.  Occasionally  complete  fracture  of  the  baseplate  will 
occur  suddenly  from  undue  strain,  as  from  the  sudden  crush- 
ing of  a  hard  morsel  of  food,  as  well  as  from  some  of  the 
causes  previously  mentioned. 

Usually  the  plan  of  repair  of  a  denture  is  easily  deter- 
mined. Occasionally,  however,  the  natiire  of  the  accident 
and  the  causes  leading  up  to  it  clearly  indicate  that  recon- 
struction, instead  of  repair,  will  prove  most  serviceable. 

It  should  be  noted  that  the  preceding  outline  covers  a 
common  class  of  accidents,  due  to  two  different  causes — 
first,  those  resulting  from  sudden  undue  stress,  as  in  care- 
less handling  or  from  a  fall ;  and,  second,  those  resulting  from 
torsional  or  bending  strain  in  masticatory  effort. 

In  all  cases  where,  up  to  the  time  of  the  accident,  the 
adaptation  of  the  denture  to  the  tissues  has  proven  satis- 
factory,  repairs   are   generally  indicated.     In   those    cases 

561 


562  REPAIRING    VULCANITE    DENTURES 

wliere  the  primary  cause  of  the  fracture  is  due  to  imperfect 
adaptation  of  denture  to  oral  tissues,  reconstruction  of  the 
case  is,  in  most  instances,  indicated,  since  by  the  usual  meth- 
ods of  repair  tlie  g-reatest  efficiency  cannot  be  realized. 

REASSEMBLING  A  FRACTURED  BASEPLATE 

In  repairing  a  fractured  denture,  the  first  consideration 
is  to  assemble  and  hold  the  several  i^arts  of  the  baseplate  in 
correct  relation  to  each  other  while  preparing  the  joints  and 
splicing  the  fractured  pieces  together  with  new  material.  This 
is  best  accomi^lished  by  constructing  a  cast,  not  in  the  usual 
way,  by  taking  an  impression  of  the  mouth,  but  by  reassem- 
bling the  broken  pieces  of  the  denture  and  filling  in  the 
maxillary  or  border  side  with  plaster  to  serve  as  a  cast. 

TECHNIC  OF  SECURING  A  CAST  FROM  THE  BASEPLATE 

The  broken  parts  of  the  baseplate  are  pressed  together 
until  the  fractured  surfaces  show  perfect  contact,  and,  while 
in  this  relation,  sticky  wax  is  applied  to  the  lingual  surfaces 
on  either  side  of  and  across  the  fracture  line,  but,  for  ob- 
vious reasons,  not  on  the  border  or  palatine  areas.  The 
wax  should  be  applied  in  sufficient  bulk,  so  that  when  chilled 
it  will  hold  the  several  broken  pieces  firmly  and  accurately 
while  the  cast  is  being  formed. 

The  border  and  palatine  sides  of  the  denture  are  now 
coated  with  a  thin  film  of  oil,  and  the  material  of  which  the 
cast  is  to  be  constructed  is  aijplied  in  the  same  manner  as 
in  an  impression  and  allowed  to  harden. 

Sometimes  the  relation  of  the  several  parts  of  the  den- 
ture can  be  best  maintained,  while  securing  the  cast,  by  im- 
bedding them  to  a  slight  extent  in  modeling  compound,  care 
being  taken  to  maintain  the  correct  relationship  of  the  frac- 
tured surfaces  until  the  compound  has  hardened  somewhat. 
This  method  is  especially  applicable  to  holding  in  correct 
relation  the  two  halves  of  a  full  lower  denture,  fractured  in 
the  incisor  region.  When  sticky  wax  alone  is  used  in  such 
cases,  slight  pressure  on  the  outer  sides  of  the  denture  while 
handling  is  liable  to  disturb  the  correct  relation  of  the  frac- 
tured surfaces  before  the  cast  is  secured.  This  danger  can 
be  obviated,  in  most  cases,  by  laying  a  small  piece  of  wood, 
as  a  match  or  a  rigid  wire,  between  the  distal  ends  of  the 


REPAIRING    VULCANITE    DENTURES  563 

baseplate  and  attaching  each  end  tirraly  to  the  ]3late  with  wax 
before  forming  the  cast. 

The  method  frequently  followed  of  assembling  the  frac- 
tured parts  of  a  baseplate  on  a  cast  derived  directly  from 
an  impression  of  the  month  is  objectionable,  because  it  is 
inaccurate.  The  cast,  being  hard  and  unyielding,  will  not 
permit  the  baseplate  to  settle  to  position,  as  it  does  on  the 
soft  and  yielding  areas  of  the  mouth,  and  when  the  repair  is 
accomplished  with  the  several  parts  thus  sustaining  an  in- 
correct  relation   to   each   other,   even   though   the   distortion 


may  be  slight,  a  misfit  usually  results,  or  the  occlusion  of  the 
teeth  is  impaired. 

Repairs  occasionally  present,  usually  in  partial  dentures, 
however,  where  the  broken  pieces  can  be  placed  in  the  mouth 
and  an  impression  secured  which  will  give  a  more  accurate 
relation  of  the  parts  to  each  other  than  is  possible  to  obtain 
by  adjusting  the  fractured  surfaces  together  and  applying 
wax,  as  outlined. 

METHODS  OF  JOINING  THE  FRACTURED  PIECES 

A  long  bevel  joint,  if  properly  formed,  will  present  the 
best  appearance  and  prove  the  strongest  and  most  satisfac- 
tory manner  of  repairing  a  fractured  vulcanite  base  of  any 
of  the  methods  in  vogue.  The  practice  of  cutting  a  series  of 
dovetailed  spaces  on  either  side  of  the  fracture  line  for  the 
reception  of  the  new  material,  in  most  cases,  tends  to  weaken 
the  old  \^ilcanite,  and  when  the  base  is  composed  of  other 


564  REPAIRING    VULCANITE    DENTURES 

than  black,  basic  material,  the  repair,  when  completed,  will 
present  a  very  unsightly — or,  at  least,  noticeable — appear- 
ance, because  of  the  variation  in  the  color  of  new  and  old 
vulcanite,  as  well  as  on  account  of  the  irregular  outline 
margins  of  the  patch. 

A  cabinetmaker  who  desires  to  produce  the  strongest 
possible  union  between  two  pieces  of  wood — a  joint  that  will 
resist  both  torsional  strain  and  end  pull — will  make  a  long 


bevel  joint  instead  of  halving  each  piece  and  abutting  the 
halved  ends  against  the  corresponding  shoulder  of  the  oppo- 
site piece.  Tests  show  that  the  bevel  joint  is  the  strongest  of 
the  two  methods  outlined,  not  only  in  wood,  but  in  vulcanite 
as  well. 

The  dovetailed  method  of  repairing  a  simple  fracture  is 
based  upon  the  principle  that  some  positive  form  of  mechani- 
cal anchorage  is  essential,  even  though  it  be  gained  at  the 
expense  of  weakening  the  old  vulcanite,  and  in  areas  not 
previously  involved  in  the  break;  it  accords  too  much  value 
to  the  dovetail,  a  joint  calculated  to  resist  end  pull  and  not 
torsional  strain,  and  not  enough  in  the  lap  joint,  which,  with 
practically  perfect  union  of  surfaces  between  new  and  old 
vulcanite,  will  resist  both  torsional  strain  as  well  as  end 
pull.  The  fact  does  not  seem  to  be  generally  well  under- 
stood that  under  proper  conditions  new  rubber  will  unite 
tirmly  and  permanently  with  old  vulcanite.  The  necessary 
requisites  for  serviceable  union  between  the  old  and  new 
vulcanite  are  as  follows :  Fresh,  clean  surfaces  to  the  old 
base,  produced  by  tiling,  scraping  or  burring;  the  covering 
of  these  surfaces  with  a  thin  tilm  of  rubber  cement  before 
adding  the  new  rubber,  and  the  maintenance  of  pressure 
upon  the  newly  added  material  during  vulcanization ;  also 
freedom  of  the  joint  from  wax,  grease  or  dirt. 

The  rubber  cement  should  correspond  in  color  with  the 
vulcanite  or  the  fresh  rubber  between  the  surfaces  of  which 
it  is  interposed,  to  avoid  imjiarting  a  variegated  appearance 
to  the  joint. 

The  commercial  rubbei'-tire  cement,  which  is  nearly  in- 
visible when  applied  to,  or  used  in  connection  with,  any  color 


REPAIRING    VULCANITE    DENTURES  565 

of  vulcanite,  may  be  used,  or  a  cement  maj^  be  made  by  dis- 
solving red,  pink  or  black  rubber  in  any  solvent,  such  as 
benzine,  bisulphide  of  carbon  or  chloroform.  When  the  lat- 
ter is  used  the  solution  is  called  "chloro-rubber. "  The  three 
colors  should  bo  kejit  in  stock,  in  the  laboratory,  in  tightly- 


stoppered  bottles,  for  use  as  occasion  requires.  Excessive 
application  of  cement  to  a  joint,  without  removal  of  the  sur- 
plus, will  result  in  jjorosity  of  the  newly-added  material. 

FORMING  THE  BEVEL  JOINT 

Two  shallow  grooves,  about  one-sixth  the  thickness  of 
the  baseplate  in  depth,  are  cut,  one  on  either  side  of  the  frac- 


SECTIONAL  VIEW  OP  BASEPLATE, 
SHOWING  OUTLINE  OP  BEVEL  OF 
OLD  VULCANITE.  THE  CENTRAL 
BEVELED  PORTION  IS  TO  BE  RE- 
MOVED 


ture  line,  and  approximately  parallel  with  it  on  the  lingual 
side  of  the  baseplate.  These  grooves  limit  the  area  of  the 
old  base  to  be  covered  by  the  new  vulcanite  and  determine 
the  outline  of  the  patch,  as  it  might  be  called.  When  the 
fracture  line  is  very  irregular,  the  position  of  the  limiting 


566  REPAIRING    VULCANITE    DENTURES 

marginal  Hues  may  be  varied,  if  by  so  doing  a  more  sym- 
metrical balancing  of  the  new  witli  the  old  vulcanite  can  be  se- 
sured. 

The  relative  position  of  these  lines  to  the  fracture  line 
may  be  modified  by  inci'easiug  or  dimiuisliing  their  distance 
from  the  latter  uniformly;  or,  if  the  conditions  of  the  case 
re(}uire,  the.y  may  be  laid  in  curved  or  diagonal  directions. 
The  result  of  varying  the  position  of  the  marginal  lines  will 
be  to  vary  the  length  and  pitch  of  the  bevel,  but  this  will  in 
no  way  interfere  with  the  strength  of  the  repair.  The  main 
object  of  varying  the  outline  margins  of  the  freshened  area, 
as  before  stated,  is  to  give  a  symmetrical  form  to  the  newly- 
added  vulcanite,  and  when  good  judgment  is  displayed  in 
planning  the  repair,  very  presentable,  and  at  times  quite 
artistic,  results  are  realized.  In  most  instances  the  average  re- 
pair is  an  unsightly,  and  often  an  unsatisfactory,  operation, 
when  in  practically  every  instance  where  a  repair  is  indi- 
cated, both  satisfactory  and  esthetic  results  are  possible  when 
proper  steps  are  taken. 

SUMMARY  OF  THE  TECHNICAL  STEPS  FOLLOWED  IN 

REPAIRING  A  MEDIAN  LINE  FRACTURE, 

FULL  DENTURE 

Assemble  and  unite  the  fractured  pieces  firmly,  as  pre- 
viously outlined;  secure  tlie  cast;  with  a  pencil,  sketch  on  the 


DENTURE     WITH     COMPLETE     PRACTUIIE.     EX- 
TENDING  ENTIRELY   THUOnGH   PALATINE    AND 
LABIAL    GUM   PORTIONS 

lingual  surface  of  the  baseplate,  as  symmetrically  as  possi- 
ble, the  position  of  the  marginal  lines  which  limit  the  area 
to  be  covered  by  the  new  vulcanite;  cut  the  grooves  along 
these  lines  to  the  depth  previously  indicated;  bevel  off  the 


REPAIRING    VULCANITE    DENTURES  567 

old  vulcanite  from  the  bottom  of  these  grooves  to  the  oppo- 
site or  palatal  surface  of  the  baseplate,  terminating  the  bevel 
in  feather-edge  along  the  fracture  line.  This  entirely  re- 
moves the  inner  wall  of  each  groove  and  converts  the  outer 
wall  into  a  shoulder  against  which  the  new  vulcanite  tinishes. 

When  the  break  extends  through  the  labial  portion  of 
the  denture,  the  outer  surface  of  the  pink  gum  should  be 
beveled  in  a  similar  manner  to  the  alveolar  border  joint 
surface.  In  all  cases  of  pink  vulcanite  gum  repairs,  where 
the  fracture  occurs  anteriorly,  or  anywhere  between  the  cus- 
pids, the  marginal  lines  of  the  repair  sliould  be  laid  back 
of  the  cuspids,  so  as  to  render  invisible,  if  possible,  the  line 
of  junction  of  the  old  with  the  new  vulcanite.  This  is  impera- 
tive on  account  of  the  unsightly  discoloration  noticeable  in 
joint  areas  on  pink  gum  after  vulcanization. 

In  preparing  the  joint,  the  beveling  is  most  easily  ac- 
complished by  applying  those  areas  of  the  baseplate  to  be 


LAIUAI.    VIEW    OF    I'ltKCKIllNCj 


reduced  against  the  emery  band  on  the  lathe  mandrel.  Con- 
stricted areas  that  cannot  be  reached  by  this  means  can  be 
reduced  with  large  fissure  or  round  burs  in  the  engine. 

After  beveling,  the  fractured  pieces  are  returned  to  the 
cast,  a  piece  of  sheet  wax  is  applied  to  the  freshened  areas 
on  the  lingual  surface  of  the  denture",  and  with  a  hot  spatula 
burnished,  but  not  melted,  down  to  the  required  contour  of 
the  finished  ease. 

METHOD  OF  FLASKING  A  REPAIR  CASE 

It  is  seldom  possible  to  flask  a  full  denture  so  that  the 
matrix  side  of  the  flask  can  be  withdrawn  from  that  con- 
taining the  baseplate,  to  which  the  teeth  have  previously  been 
permanently  attached,  without  injuring  the  matrix,  especially 
those  portions  of  it  which  fill  the  embrasures.  Therefore,  in 
repairs  involving  the  labial  or  buccal  gum  surfaces,  as  well 
as  lingual  portions  of  a  denture,  provision  must  be  made  for 


5«S  REPAIRING    VULCANITK    DKNTURES 

plrU'iiin-  the  iuMk'i-  on  the  gum  surfaces  in  such  manner  as  not 
to  he  disturhed  in  the  tinal  eloshig  of  the  flask. 

'I'his  may  be  accomplished  in  two  ways.  First,  by  cover- 
ing tlie  prepared  and  waxed  portion  of  gum  repair  with  the 
plaster  in  the  first,  half  of  the  flask,  and  by  means  of  one  or 
more  suitably  located  connecting  gates  removing  the  wax  from 
the  gum  surface,  packing  the  matrix  through  these  openings, 
and  with  an  excess  of  rubber  in  the  gates  condense  that  form- 
ing the  gum  rejjair  in  the  partially  enclosed  matrix  in  the 
final  closing  of  the  flask. 

Second,  the  following  method,  when  carefully  carried  out, 
involves  less  time  and  is  (juite  as  effective  as  the  first  and 
can,  in  most  cases,  be  followed.  The  details  are  as  here  out- 
lined : 

When  the  beveling  of  the  several  surfaces  involved  in 
the  repair  is  completed  and  the  parts  are  adjusted  to  the  cast, 
the  lingual  surface  is  waxed  as  before  described.  Instead  of 
waxing  the  gum  areas  they  are  coated  with  a  thin  film  of  rub- 
ber cement,  well  rubbed  into  the  freshened  surfaces  with  a 
pellet  of  cotton. 

A  strip  of  pink,  or  granular,  rubber,  large  enough  to 
neatly  cover  the  entire  area  of  removed  old  gum,  is  applied, 
and  with  a  large,  hot  burnishing  spatula  is  pressed  firmly 
against  the  freshened  areas  until  perfect  contact  and  firm  ad- 
hesion is  develojjed.  Smaller  pieces  are  added  and  burnished 
against  that  already  placed  until  the  required  g-um  contour 
is  developed  and  a  compact  homogeneous  mass  results. 

When  the  pink  gum  restoration  has  been  liuilt  up  as  de- 
scribed, the  case  is  ready  for  flasking,  and  herein  lies  the 


ODM  FACING  APPLIED  TO  FRESHENED  I.AIilAI,  AREAS 


advantage  of  packing  the  gum  repair  as  outlined,  since  com- 
plications in  flasking  and  subsequent  packing  are  avoided. 

A  mix  of  plaster  is  made  and  the  case  invested  in  the 
lower  half  of  the  flask  just  as  though  no  gum  surfaces  were 
involved ;  that  is  to  say,  the  entire  labial  and  buccal  portions, 


REPAIRING    VULCANITE    DENTURES  5,69 

including  the  gum  surfaces  just  packed,  the  teeth  and  the 
lingual  surface  of  the  baseplate  not  included  in  the  repair 
area  in  this  location,  are  covered  or  entirely  enclosed  within 
the  plaster  investment  in  the  first  half  of  the  flask.  The  pink 
gum,  packed  as  above  described,  is  thus  entirely  enclosed 
within  a  matrix.  No  provision  need  be  made  for  producing 
pressure  on  the  pink  rubber,  for,  if  properly  packed,  the  ex- 
pansion of  the  mass  of  pink  rubber  in  vulcanizing  is  sufficient 
to  hold  it  firmly  in  contact  with  the  old  vulcanite  and  cause  it 
to  unite  firmly  with  the  latter. 

When  the  plaster  in  the  lower  half  of  the  flask  is 
smoothed  up  and  varnished,  the  upjter  half  of  the  flask  is  ad- 
justed, filled,  and  when  hardened,  separated,  the  wax  removed 
with  hot  water,  the  surfaces  of  freshened  rubber  covered  with 
a  film  of  rubber  cement,  well  rubbed  in,  some  l)asic  ruliber  of 
appropriate  shade  is  applied  to  the  cut-out  area,  slightly  in 
excess  of  the  actual  bulk  required,  so  as  to  insure  pressure 
in  vulcanizing,  the  two  halves  of  the  flask  are  adjusted,  and 
while  cold  the  bolts  are  tightened  with  finger  power  only,  the 
case  is  warmed  with  dry  heat  and  finally  closed  in  the  usual 
manner.     Vulcanization  is  carried  out  as  for  ordinary  cases. 

REPLACING   A   DISPLACED   TOOTH 

When  a  tooth  has  been  forced  from  the  denture  base,  its 
pins  having  itulled  out  of  the  vulcanite,  or  as  sometimes  oc- 
curs, when  a  small  section  of  vulcanite  enclosing  the  pins 
fractures  and  comes  away  with  the  tooth  without  injuring  or 
in  any  way  impairing  the  usefulness  of  the  latter,  replace- 
ment of  the  same  tooth  can  in  most  cases  be  effected  liy  very 
simple  methods.  The  following  means  for  replacing  bicus- 
pids and  molars  are  both  simple  and  serviceable. 

First,  adjust  and  wax  the  tooth  in  its  correct  position  in 
the  vulcanite  base,  enlarging  the  old  pin  holes  if  necessary, 
to  let  the  tooth  in  place.  The  periphery  of  the  vulcanite 
socket  in  which  the  tooth  rested  before  displacement  should 
be  disturbed  to  the  least  possible  extent  at  this  time,  as  it 
guides  the  tooth  to  proper  place. 

Second,  oil  the  labial  or  buccal  surfaces  of  the  teeth  and 
gums,  including,  the  displaced  tooth  and  extending  a  short  dis- 
tance mesially  and  distally  from  it. 

Third,  make  a  matrix  of  plaster  by  building  it  against 
these  oiled  surfaces.  This  is  necessary  in  order  that  the  dis- 
placed tooth  can  be  returned  to  correct  position  after  the  sup- 


570  REPAIRING    VULCANITE    DENTURES 

porting  vulcanite  on  the  lingual  side  is  removed  preparatory 
to  adding  new  vulcanite  for  the  repair. 

Fourth,  remove  the  matrix  and  the  tooth,  and  with  a  vul- 
canite tile  or  a  large  engine  bur  form  a  dovetail  space  in  the 
basei^late,  to  the  lingTial  of  the  tooth  displaced,  as  wide  as  the 
latter  and  deep  enough  to  entirely  obliterate  the  old  pin  holes. 

Fifth,  return  and  hold  the  tooth  in  correct  position  on  the 
baseplate  by  means  of  the  matrix,  and  apply  wax  in  the  dove- 
tailed space  around  the  pins  and  against  the  i^orcelain,  build- 
ing it  out  to  the  required  contour  of  the  finished  denture. 

Sixth,  remove  the  matrix,  invest  the  case  in  the  lower 
half  of  the  flask,  entirely  enclosing  the  denture  in  plaster  ex- 


DENTUKE     BASE     PREPAKED     FOR     REPLACEiMEXT     OF 

ONE   TOOTH.    SHOWING    FOBMjVTION    OF 

DOVETAIL    SPACE 

cept  a  small  surface  immediateh'  surrounding  and  including 
the  waxed  repair  area.  The  tooth  itself  should  remain  in 
position  in  the  baseplate,  and  be  covered  sufificiently  with 
plaster  to  obviate  its  being  raised  on  forcing  the  rubber  into 
the  dovetailed  space  and  vinderneath  the  tooth  in  closing  the 
flask.  Smooth  the  upper  surfaces  of  plaster,  tapering  the 
margin  around  the  repair  area  so  that  the  plaster  in  the  upper 
section  maj'  separate  readily,  varnish,  complete  the  invest- 
ment in  the  upper  half  of  the  flask,  and  allow  time  for  plaster 
to  set. 

Seventh,  separate  flask ;  pick  out  as  much  wax  as  possible 
and  use  hot  water  for  the  removal  of  the  last  traces  of  it. 

Eighth,  apply  a  thin  film  of  rubber  cement,  being  very 
careful  to  avoid  excess,  since  as  before  stated  a  surplus  will 


REPAIRING    VULCANITE    DENTURES  571 

cause  porosity  iu  the  uewly  added  rul)lier  in  vulcanizing-.  Cut 
and  apply  some  small  jiieces  of  basic  rubber  of  appropriate 
shade,  usually  slightly  darker  than  the  denture  base,  as  the 
latter  will  darken  somewhat  with  each  vulcanization.  With  a 
warm,  round  end  rubber  packing  instrument  the  pieces  should 
be  fairly  well  condensed  in  the  dovetailed  space  and  around 
the  pins,  and  a  little  surplus  added  to  insure  slight  pressiire 
on  the  mass  when  the  flask  is  closed  and  during  vulcanization. 
Ninth,  close  the  flask,  vulcanize  and  finish  in  the  usual 
manner.  When  the  pink  gum  margin  has  been  fractured  and 
requires  restoration,  the  surfaces  are  freshened  and  small 
pieces  of  pink  rubber  are  built  up  to  the  required  contour, 
condensing  them  with  a  hot  instrument.  This  should  be  done 
before  flasking  the  case,  the  pink  rubber  being  enclosed  in  the 
first  half  of  the  investment  as  previoush'  outlined  in  repair- 
ing a  fractured  baseplate.  Usually,  however,  on  account  of 
the  unsightly  discoloration  at  the  line  of  junction  of  the  new 
with  the  old  pink  vulcanite,  visible  areas  needing  repairs 
should  be  extended  to  such  point  that  the  discolored  joints  are 
invisible,  and  only  new  pink  vulcanite  will  show.  This  often 
necessitates  carrying  the  beveling  back  as  far  as  the  second 
bicuspid  on  each  side. 

REPLACING  A  DISPLACED  TOOTH  BY  THE  CASTING 
METHOD 

When  the  displaced  tooth  is  situated  between  two  proxi- 
mating  teeth  as  in  a  full  denture,  and  rests  in  a  vulcanite 
socket  or  matrix  having  a  complete  periphery,  attachment  of 
a  new  tooth  may  be  made  by  casting.  The  advantage  of  this 
method  is  that  vulcanization  is  obviated,  a  process  wLich, 
when  resorted  to  as  is  usual  in  repair  cases,  while  the  plaster 
is  "green,"  soft  and  yielding,  often  results  in  warpage  and 
consequent  loss  of  adaptation  of  the  denture  to  the  oral 
tissues. 

The  steps  are  as  follows : 

The  vulcanite  which  enclosed  the  pins  is  freely  cut  away 
and  in  addition  a  cavity,  having  a  decided  undercut,  is  formed 
in  the  sides  and  battom  of  the  vulcanite  matrix  in  which  the 
tooth  rests.  Care  must  be  taken  not  to  disturb  the  peripheral 
outline  of  the  matrix,  or  if  unavoidably  disturbed,  of  restor- 
ing in  wax  the  lost  portion  after  the  tooth  is  finally  set  in 
place.  A  positive  connection  of  the  wax  so  applied  with  the 
interior  of  the  matrix  is  essential  so  that  the  metal,  when  cast. 


572  KKFAIIUNG    VULCANITIO    DENTURES 

will  flow  t'rniii  1lic  interior  outwardly  and  talcc  the  place  ol' 
the  wax. 

Now  at  a  point  well  within  one  of  the  lingual  embrasures 
drill  a  hole  connecting  with  the  undercut  cavity,  as  nearly 
parallel  with  the  long  axis  of  the  tooth  as  possible.  A  broken 
engine  bur  converted  into  a  drill  of  the  full  diameter  of  the 
shank  produces  a  hole  of  convenient  size.  Later  on  the  bur, 
l)y  reversing,  will  assist  in  forming  the  sprue. 

The  tooth  is  now  returned  to  position  in  its  matrix  and 
waxed  externally,  if  necessary,  to  hold  it  in  place,  thus  leaving 
the  undercut  space  free  from  wax  or  debris. 

A  .093  wire  (the  diameter  of  an  engine  bur  shank)  is  now 
passed  into  the  sprue  previously  drilled  in  the  baseplate,  or 


KEPLACING    A    TOOTH    BV    THE    CASTING    METHOD 

the  drill  may  be  reversed  and  used  for  this  purpose,  a  mix  of 
investment  or  plaster  is  made,  tilled  in  the  palatine  or  border 
side  of  the  denture,  to  form  a  base  to  prevent  the  denture 
tipping,  carried  out  against  the  buccal  or  labial  surface,  over 
the  occlusal  or  incisal  surfaces,  and  down  on  the  lingual  sur- 
face of  the  denture  surrounding  the  sprue  wire. 

While  the  plaster  is  yet  soft,  a  small  cup,  similar  to  or 
made  from  a  common  thimble,  having  a  hole  drilled  in  the 
bottom,  is  slipped  over  the  sprue  wire  and  pressed  down  into 
the  plaster  sufficiently  deep  to  support  it  when  the  wire  is 
withdrawn,  and  to  insure  its  stability  under  the  pressure  of 
casting. 

When  the  plaster  has  hardened,  the  sprue  wire  is  with- 
drawn, thus  forming  a  sprue  connecting  the  thimble  with  the 


REPAIRING    VULCANITE    DENTURES 


573 


iiiuiercut  space  under  the  tooth.  Fiisi})k'  metal  is  melted  and 
])oured  into  the  thimble,  from  which  it  is  forced  into  the  space 
by  means  of  Melotte's  moldiue,  contined  within  a  ring  or  cup 
somewhat  larger  than  the  diameter  of  the  thimble.  Forcing 
the  metal  in  the  undercut  under  pressure  causes  it  to  fill  the 


MOLDINE 

SPRUE 
FORMER 


ri'*~~-~ 

) 

— ^'^ 

~^DOVE 
SP 

TAILED 
^CE 

]>1AG1!AMMAT1C    VIEW   OF   THE    INVESTED  I'AKE.    THIMBLE 

IN  rOSITION.  AND  MOEDINE  rARKIER.      SPUUE 

FORMER   NOT    YET    REMOVED 

entire  s))ace  and  enclose  the  heads  of  the  pins  perfectly,  thus 
making  a  very  serviceable  repair.  When  finished,  the  only 
metal  showing -is  that  which  tills  the  sprue,  which,  when 
dressed  down  and  polished,  is  scarcely  noticeable. 

Dr.  A.  C.  Alexander  of  Kahoka,  Mo.,  first  called  the  writ- 
er's attention  to  this  method  of  repair  two  years  ago,  and 
since  that  time  it  has  been  applied  satisfactorily  in  many 


574  KEI'AIKING    VULCANITK    DENTURES 

practical  eases.  In  geiipval,  the  principle  is  similar  to  the 
metliod  suggested  by  Dr.  J.  P>.  P)('an  in  ISdl)  foi'  attaching  gum 
sections  to  east  ahimiiiiini   Imscs  l)\-  roruiin,^-  an  undercut  in 


the  baseplate  and  casting  tin  into  the  space  so  formed  and 
around  the  pins  of  the  section ;  described  in  Harris,  Ed.  1870. 

ANOTHER  METHOD  OF  REPAIR  BY  MEANS  OF 
FUSIBLE  METAL 

Cut  a  decided  dovetail  in  the  lingual  surface  of  the  den- 
ture, as  for  an  ordinary  vulcanite  repair,  but  greater  care 
must  be  exercised  in  developing  positive  mechanical  anchor- 
age in  the  space  in  repairs  of  this  type  than  where  vulcanite 
is  employed,  since  in  the  latter  case  the  union  is  an  adhesion 
of  molecular  material  and  not  merely  a  mechaiucal  anchor- 
age, while  in  the  repair  under  consideration  the  union  of  the 
metal  with  the  base  is  mechanical. 

Fill  the  palatine  or  border  surface  of  the  denture  with 
plaster  to  form  a  base,  extending  it  out  over  the  outer  sur- 
faces of  the  gums  and  teeth  to  serve  as  a  matrix  for  holding 
the  displaced  tooth  in  position. 

The  ease  should  be  set  at  such  an  angle  in  the  investment 
that  gravity  will  assist  in  tilling  the  undercut  space  when  the 
molten  metal  is  poured. 

The  case  being  properly  invested  as  described,  some  Mel- 
lotte's  or  other  easily  fusible  metal  is  melted  in  a  small  ladle 
and  poured  into  the  dovetailed  space.    As  it  begins  to  congeal, 


REPAIRING    VULCANITE    DENTURES  575 

a  little  surplus  is  added,  and  with  a  pad  of  blotting  paper 
folded  three  or  four  times,  pressure  is  made  on  the  mushy  or 
semi-hardened  metal  to  force  it  into  all  parts  of  the  space  and 
around  the  pins  of  the  tooth.  AVheu  hardened,  the  excess  is 
trimmed  off  and  the  surface  polished  to  proper  contour. 

REPAIRING  BY  MEANS  OF  AMALGAM 

A  very  common  method  of  attaching  a  displaced  tooth  is 
to  form  the  dovetailed  space  as  just  described,  adjust  the 
tooth  in  position  and  form  a  matrix  in  such  manner  that  it 
will  not  become  displaced  nor  allow  the  tooth  to  be  forced  out 
of  position  imder  the  pressure  of  i^acking  the  amalgam.  A 
mix  of  amalgam  of  moderate  consistency  is  made  and  quickly 
forced  into  the  space  prepared  for  it  and  around  the  tooth 
23ins,  using  small-pointed  pluggers  to  pack  it  into  the  deeper 
portions  of  the  dovetail. 

Repairs  made  in  this  manner,  although  at  times  quite 
satisfactory,  are  ixsually  temijorary  in  character,  the  amal- 
gam around  the  pins  fracturing  under  masticatory  stress  and 
allowing  the  tooth  to  be  dislodged. 

By  forming  a  loop  of  fine  tinned  iron  wire,  such  as  is 
used  for  root  measurement,  twisting  it  around  the  pins  and 
weaving  it  back  and  forth  between  the  two,  three  or  four 
times,  additional  anchorage  of  the  tooth  to  the  denture  will 
be  gained  over  that  afforded  by  the  pin  heads  alone.  This 
method  is  very  applicable  in  amalgam  or  fusible  metal  re- 
pairs, where  the  tendency'  of  the  pin  heads  to  pull  out  or  the 
amalgam  to  readily  fracture  under  stress  is  very  marked. 
The  loojj  should  be  well  embedded  in  the  amalgam.  It  can 
readily  be  seen  that  if  a  little  tension  is  placed  on  the  loop 
to  take  up  the  slack,  and  it  is  well  surrounded  with  metal,  that 
the  tooth  or  pins  will  most  likely  fracture  before  displace- 
ment will  occur.     (See  wire  loop  on  tootJi  pins,  i^age  572.) 

Still  another  method  of  increasing  anchorage  is  by  sold- 
ering to  the  pins  a  smalUloop  of  wire  of  suitable  form  to  fit 
within  the  dovetailed  space  and  be  entirely  enclosed  within 
the  metal. 

REPAIR    INVOLVING   THE    SUBSTITUTION    OF 
ANOTHER  TOOTH 

When  in  addition  to  being  forced  from  the  baseplate  the 
tooth  is  fractured  and  rendered  useless  as  well,  another  tooth 
must  be  selected  for  the  repair.     Since  the  chance  is  slight 


576  REPAIRING    VULCANITE    DENTURES 

of  finding  a  substitute  of  tlie  same  size,  mold  and  occlusal 
form  as  the  fractured  tooth,  the  steps  just  outlined,  although 
in  the  main  applicable,  must  be  varied  somewhat  to  insure 
correct  alignment  and  satisfactory  occlusal  conditions  in  the 
completed  repair. 

In  the  methods  previously  outlined,  the  position  for  and 
occlusion  of  the  displaced  tooth  was  found  by  returning  it 
to  the  vulcanite  socket  in  which  it  rested  before  displacement 
and  of  holding  it  there  with  wax,  if  necessary,  while  a  satis- 
factory matrix  was  secured.  This  plan  is  not  applicable  in 
case  a  new  tooth  is  used,  because  it  will  seldom  fit  in  the  old 
socket.  In  full  denture  cases,  and  in  some  partials  as  well, 
the  denture  is  returned  to  the  patient's  mouth  and  a  wax  or 
modeling  compound  mash  bite  is  secured,  involving  the  space 
to  be  filled,  the  proximating  and  occluding  teeth. 

In  case  of  complicated  occlusion,  the  denture  and  bite 
should  be  transferred  from  the  mouth  to  the  occluding  frame 
with  the  face  bow,  mounted,  and  the  bite  filled  with  plaster  to 
develop  the  occluding  teeth,  after  which  the  bite  material  is 
removed. 

In  uncomplicated  cases  the  bite  may  be  filled  in  with 
plaster  and  an  extension  at  the  same  time  be  made  ligually 
so  as  to  cover  definite  areas  on  the  lingual  surface  of  the  den- 
ture, or  it  may  even  extend  across  the  entire  baseplate,  the 
point  of  importance  being  to  have  a  sufficient  number  of 
guides  to  bring  the  occluding  plaster  teeth  into  normal  rela- 
tion with  those  of  the  denture  when  the  bite  material  is  re- 
moved. 

The  old  socket  is  now  burred  out  in  its  interior,  and  the 
lingual  side  cut  away  to  receive  the  new  tooth.  Care  should 
be  taken  not  to  disturb  the  gum  margin  and  further  compli- 
cate the  repair.  In  fitting  the  substitute  tooth  in  place  the 
porcelain  itself  can,  in  many  cases,  be  ground  to  fit  the  socket 
on  the  gum  side  of  the  denture.  Usually,  however,  a  little 
careful  trimming  of  the  vulcanite  socket,  together  with  a  little 
grinding  of  the  tooth,  will  develop  a  satisfactory  joint,  that 
will  not  recjuire  the  addition  of  new  gum  material. 

PRELIMINARY   DOVETAILING  OF  A   DENTURE  BASE 

In  partial  dentures,  where  an  isolated  tooth  is  to  be  re- 
l)laced,  it  is  frequently  advisable  to  prepare  the  dovetail  form 
on  the  baseplate  for  the  reception  of  the  new  rubber  before 
taking  the  bite.     By  so  doing  the  danger  of  mutilating  or 


REPAIRING    VULCANITE    DENTURES  577 

breaking  the  proximating  plaster  teeth  when  the  cast  is  run 
up  will  be  obviated. 

A  small  wax  bite  is  now  taken,  involving  the  space  to  be 
filled,  the  proximating  teeth  and  the  opposite  occluding  teeth. 
The  denture  and  bite  should  be  removed,  if  possible,  to  ob- 
viate danger  of  distorting  the  latter.  If  for  any  reason  the 
bite  and  denture  are  separated  in  removal,  they  should  be 
carefully  fitted  together  and  held  firmly  by  melting  some  of 
the  bite  wax  at  various  points  against  tlie  denture. 

The  cast  is  now  formed  in  tlie  united  denture  and  wax, 
and  when  hardened,  the  opposite  side  is  run  up.  The  occlu- 
sion cast  should  extend  over  onto  the  palatal  surfaces  of  the 
denture  so  that  it  may  be  guided  to  place  when  the  wax  bite 
is  removed. 

On  removal  of  the  wax  a  suitable  tooth  is  selected,  waxed 
in  place,  and  the  case  flasked,  packed  and  vulcanized  in  the 
usual  manner. 

Sometimes  the  neck  or  vulcanite  connecting  an  isolated 
tooth  with  the  denture  base  must,  on  account  of  the  occluding 
teeth,  be  so  reduced  in  thickness  as  to  invite  ready  fracture 


A  PLATE  TOOTH  BACKED 
WITH  GOLD.  TO  \VHICH  A 
CLASP  METAL  EXTENSION 
IS  APPLIED  FOB  ENCLOS- 
URE WITHIN  THE  VULCAN- 
ITE 


under  stress — an  accident  which  frequently  occurs — in  partial 
dentures  carrying  upper  anterior  teeth.  To  repair  such  a 
case,  one  of  two  methods  must  be  adopted,  either  the  opposing 
tooth  must  be  shortened  to  make  room  for  greater  bulk  of 
vulcanite,  or  a  plate  tooth  must  be  selected,  ground  to  posi- 
tion, backed  with  gold  and  a  strip  of  heavy  clasp  metal 
abutted  against  the  backing  to  which  it  is  attached  with  solder. 
This  strip  should  lie  close  against  the  maxillary  surface,  yet 
not  quite  in  contact  with  it,  and  extend  lingually  so  as  to  be 
enclosed  in  the  vulcanite.  Two  or  three  holes  should  be 
punched  in  the  extension,  or  its  edges  should  be  notched  with 


578  REPAIRING    VULCANITE    DENTURES 

a  file  to  afford  anchorage  in  the  vulcanite  whioli  encloses  it. 
The  clasp  metal  strip  must  be  sufficiently  broad  and  thick  to 
withstand  heavy  masticatory  stress  without  bending,  or,  if  of 
light  gauge,  it  may  be  stiffened  by  flowing  solder  over  it. 

This  plan  of  backing  a  tootli  with  metal  and  attaching 
to  it  a  lingual  extension  in  close  bite  cases  is  often  resorted 
to  in  the  initial  construction  of  the  denture  when  the  bite  is 
exceptionally  close. 

SUBSTITUTING    ARTIFICIAL    FOR    LOST    NATURAL 
TEETH  IN  PARTIAL  CASES 

It  frequently  occurs  that  when  a  partial  denture  has  been 
worn  for  some  time,  one  or  more  of  the  remaining  natural 
teeth,  through  accident  or  as  the  result  of  disease,  are  lost. 

If  the  adaptation  and  general  requirements  of  the  den- 
ture are  satisfactory,  aside  from  the  conditions  noted,  re- 


placement of  the  lost  with  artificial  teeth  may  be  readily  ac- 
complished by  the  following  method: 

With  a  file  or  engine  burs  form  a  dovetail  in  the  base- 
plate to  the  lingual  of  the  space  to  be  filled.  In  case  the  bor- 
der in  which  the  natural  teeth  were  situated  has  absorbed, 
the  baseplate  should  be  cut  back  to  a  i^oint  where  its  maxillary 
surface  rests  upon  the  mucous  tissues,  thus  permitting  the 
new  vulcanite  to  join  the  old  baseplate  and  form  a  continuous 
bearing  surface  over  the  absorbed  area.    In  such  cases  a  long 


REPAIRING    VULCANITE    DENTURES  579 

bevel  splice  will  prove  more  serviceable  than  the  dovetail 
method. 

The  denture,  having  been  cut  out  as  described,  is  re- 
turned to  the  mouth  and  a  mash  bite  is  taken,  being  careful 
to  press  the  wax  or  compound  firmly  against  the  labial  or 
buccal  absorbed  areas,  and  to  secure  an  accurate  impression 
of  the  occluding  teeth. 

On  removal  of  the  bite  and  denture  they  should  be  care- 
fully adjusted  and  luted  together,  and  the  subsequent  steps 
carried  out  as  described  under  the  "repair  of  partial  den- 
tures." 

REPAIRING  GUM  SECTION  CASES 

When  one  of  the  sections  of  a  gum  section  denture  has 
been  fractured  beyond  the  possibility  of  further  usefulness, 
a  new  block  must  be  selected  that  will  conform  as  perfectly 
as  possible  to  the  broken  section  in  form,  size,  color,  length  of 
bite  and  curvature  of  the  labial  or  buccal  surface. 

Usually  this  is  a  difficult  matter  unless  the  prosthetist  is 
fortunate  in  securing  a  block  of  the  same  manufacture,  mold 
and  shade.  In  repairs  of  this  class  the  vulcanite  in  which 
the  old  pins  are  enclosed  should  be  freely  cut  away,  the  den- 
ture introduced  in  the  mouth  and  a  bite  taken.  The  case  is 
then  mounted  on  the  occluding  frame  and  the  block  selected 
and  ground  to  fit  the  ends  of  the  proximating  sections.  The 
block,  if  thick,  may  need  grinding  or  dressing  down  on  the 
surface  that  approximates  the  baseplate,  or  the  vulcanite  it- 
self, if  of  sufficient  thickness,  can  be  reduced  with  burs  to 
permit  the  block  to  settle  into  correct  labial  or  buccal 
contour  position.  Special  care  should  be  taken  in  grinding 
the  joints  to  hold  the  block  in  correct  alignment  when  testing. 

Subsequent  steps  are  carried  out  as  outlined  in  the  re- 
pair of  a  single  tooth. 

SUBSTITUTION  OF  A  BASEPLATE 

Although  the  adaptation  of  a  denture  may  be  satisfac- 
tory, and  its  occlusion  correct,  yet,  because  of  frequent  re- 
pairs which  have  detei'iorated  the  quality  of  the  vulcanite,  or 
because  of  some  peculiar  fracture  which  renders  impossible 
a  satisfactory  repair,  a  new  baseplate  may  be  substituted  for 
the  old  vulcanite  In-  tlie  matrix  method  in  much  shorter  time 
than  is  required  to  reconstruct  the  case  in  the  usual  way. 
The  procedure  is  as  follows : 


580  REPAIRING    VULCANITE    DENTURES 

CONSTRUCTION  OF  THE  MATRIX 

The  baseplate,  if  fractured,  should  he  reassembled  and 
the  several  parts  held  in  proper  relation  by  means  previously 
described,  "Eei^airing  a  Fractured  Baseplate." 

Oil  the  denture  with  a  thin  him  of  vaseline  and  develop 
a  cast  sufficiently  deep  to  raise  the  peripheral  margin  of  the 
denture  about  three-eighths  of  an  inch  above  the  base  bottom 
and  smooth  its  outer  surfaces. 

Countersink  the  buccal  walls  of  the  cast  at  two  points  on 
each  side  so  that  the  matrix,  when  formed  and  removed,  may 
be  returned  to  projjer  position  again.  Varnish  the  outer  sur- 
faces with  separating  medium. 

Oil  the  outer  surfaces  of  the  teeth  and  gum  restoration; 
make  a  mix  of  and  aj^ply  plaster  to  the  buccal  and  anterior 
walls  of  the  cast  and  denture  surfaces,  extending  from  the 
median  line  to  the  tuberosity  on  one  side  and  from  the  base 
up  over  the  incisal  and  occlusal  surfaces  of  the  teeth.  This 
addition,  which,  when  completed,  forms  one-half  of  the  matrix, 
should  be  about  three-eighths  of  an  inch  in  thickness. 

When  the  plaster  forming  this  portion  has  set,  the  me- 
dian end  is  squared  up,  a  countersunk  depression  made  in  the 
planed  surface,  the  latter  varnished,  and  a  second  application 
of  plaster  is  applied  in  a  similar  manner  extending  back  to 
the  tuberosit}^  on  the  opposite  side. 

When  hardened,  the  outer  surfaces  of  plaster  are 
smoothed  up,  and  with  a  few  light  taps  of  the  hammer  on  the 
sides  and  base  of  the  matrix,  it  will  come  away  in  two  pieces. 

REMOVAL  OF  THE  TEETH  FROM  OLD  BASEPLATE 

The  teeth  are  now  removed  from  the  old  vulcanite,  one  at 
a  time,  being  careful  to  card  them  on  wax  in  regular  order 
so  as  to  avoid  confusion  in  their  arrangement. 

Each  tooth  is  now  thoroughly  cleaned,  the  old  vulcanite, 
if  any  remains,  is  removed  from  around  the  pins  and  returned 
to  its  position  in  the  matrix. 

Should  any  tooth  become  disturbed  or  fall  out  of  place  in 
raising  the  matrix  to  an  upright  position,  a  little  liquid  silex 
touched  to  the  labial  or  buccal  surfaces  will,  on  returning  the 
tooth,  under  pressure,  retain  it  firmly  in  place. 

FORMING  THE  WAX  BASEPLATE 

A  sheet  of  wax  is  now  applied  to  the  cast  surfaces  and 
trimmed  peripherally  so  as  not  to  interefere  with  the  matrix 
being  carried  to  exact  position  against  the  cast  surfaces. 


REPAIRING    VULCANITE    DENTURES  581 

Each  half  matrix  is  tlien  returned  to  position  against 
the  sides  of  the  cast  and  brouglit  in  contact  anteriorly,  being 
guided  and  lield  in  place  by  the  projections  of  the  matrix  fit- 
ting into  the  countersunk  holes  of  the  cast.  Usually  a  string 
is  woimd  several  times  around  the  matrix  and  cast  and  tied 
tightly  to  hold  all  firmly  together,  or  a  heavy  rubber  band  ap- 
plied peripherally  will  be  more  convenient  to  a]3ply  and  serve 
the  purpose  equally  well. 

The  teeth,  each  one  in  its  individual  matrix,  and  the  two 
halves  of  the  matrix  in  correct  position  against  the  cast,  now 
bear  the  exact  relation  to  the  cast  surfaces  that  they  did  be- 
fore removal  of  the  vulcanite. 

Softened  wax  is  pressed  into  the  space  between  the  teeth 
and  cast  to,  and  the  general  contour  of  the  case  developed  as 
it  was  before  the  removal  of  the  old  base. 

A  heated  spatula  is  now  passed  under  the  pins  and  along 
the  ridge  lap  of  each  tooth,  as  well  as  into  the  interproximal 
spaces  and  embrasures,  to  firmly  cement  the  teeth  to  the  wax 
base,  so  that  they  will  not  be  disturbed  or  come  away  with  the 
matrix  when  the  latter  is  removed. 

Care  should  be  taken  not  to  touch  the  matrix  walls  with 
the  heated  spatula,  or  in  any  manner  melt  the  wax  against 
these  surfaces.  Should  this  occur  not  only  the  adherent  wax, 
but  some  of  the  teeth  are  liable  to  come  away  with  the 
matrix. 

To  obviate  the  union  of  the  wax  with  the  matrix,  the  lat- 
ter can  be  coated  with  a  thin  film  of  oil  after  the  teeth  are  in 
place  and  just  before  assembling  the  parts  of  the  matrix  to 
the  cast.  Care  should  be  taken  not  to  apply  any  oil  to  the 
teeth. 

The  string  or  band  is  now  removed  and  the  matrix  is 
gradually  and  carefully  worked  free,  so  as  not  to  disturb  the 
position  of  the  teeth  in  the  wax.  Each  tooth  should  now  be 
tested  to  see  that  it  is  still  firmly  adherent  to  the  wax.  A 
further  test  can  be  applied  by  returning  the  matrix  to  its 
former  position. 

The  wax  model  denture  is  now  smoothly  finished,  flasked, 
l^acked,  vulcanized  and  finished  in  the  usual  manner. 

In  planning  the  reconstruction  of  the  case,  should  it  hv 
deemed  advisable  to  test  the  denture  in  the  mouth,  ideal  or 
some  unyielding  baseplate  should  be  applied  to  the  cast  in- 
stead of  the  ordinarv  wax. 


582  UKPAIRING    VULCANITE    DENTURES 

MODIFIED  METHODS  OF  RECONSTRUCTION 

A  somewhat  simpler,  but  less  accurate,  method  of  sub- 
stituting a  new  for  an  old  baseplate  frequently  resorted  to  is 
as  follows: 

Thoroughly  clean  the  denture,  oil  the  palatine  surface 
aTid  secure  a  cast. 

MOUNTING  CAST  AND  OLD  DENTURE  ON  THE  OCCLUDING 
FRAME 

Mount  the  cast  and  denture  on  the  occluding  frame  in  as 
nearly  the  normal  position  as  possible  without  the  use  of  the 


Url'ER  DENTURE  MOUNTED  ON  OCCLUDINU  FRAME.     TEETH  EMBEDDED  IN  PEASTER  MATRIX 

face-bow.  An  occluding  frame  with  an  incisor  guide  pin  is 
preferable,  as  such  an  appliance  obviates  springing  of  the 
bows  in  the  subsequent  steps. 

FORMING  THE   MATRIX 

Turn  back  the  upper  bow  on  which  the  case  is  mounted 
and  apply  a  mix  of  plaster  to  the  lower  Iww,  building  it  up 
sufficiently  high  for  the  teeth  of  the  denture  to  enter. 


REPAIRING    VULCANITE    DENTURES  583 

Drop  tlie  upper  bow  down  and  press  the  teeth  into  the 
plaster  so  that  all  exposed  portions  of  porcelain  are  covered. 
It  may  be  further  extended  against  the  labial  and  buccal  gum 
svirfaces,  although  this  is  not  usuallv  necessarv.     The   set 


PRECEDING  CASE  WITH  OLD  BASEPLATE  KEMOVED  AND  TEETH  RETURNED  TO  THEIR 
RESPECTIVE  MATRICES 

screw  at  the  back  of  the  frame,  or  the  incisor  guide,  should 
l)e  firmly  tixed  so  as  to  hold  the  upper  and  lower  bows  a 
fixed  distance  ajjart  after  removal  of  old  baso]jlate. 


FORMING  THE  WAX   BASEPLATE 

When  the  plaster  has  set,  carefully  separate,  remove  the 
teeth  from  the  old  baseplate  and  return  them  to  their  respec- 
tive positions  in  the  matrix. 

A  baseplate  with  roll  of  wax  is  adapted  to  the  cast,  the 
wax  warmed  slightly,  and  the  upper  bow  of  the  frame  closed 
so  as  to  force  the  wax  against  the  teeth  in  the  matrix. 

That  portion  of  the  matrix  enveloping  the  outer  surfaces 
of  the  teeth  is  cut  away,  so  as  to  allow  the  teeth  now  attached 
to  the  baseplate  to  part  from  the  matrix  without  interfer- 


584  REPAIRING    VULCANITE    DENTURES 

ence,  after  which  the  case  is  waxed  and  the  suhsccjucnt  steps 
are  carried  out  as  usual. 

The  weak  point  of  this  method  is  in  the  lialulity  of  tlie 
frame  springinti'   in  pressing  the  teeth  into  the  wax  and  thus 


shortening  the  bite.     Such  an  error  cannot  well  occur  when 
the  incisor  guide  pin  is  used. 

CORRECTING  IMPERFECT   ADAPTATION   BY    SUBSTI- 
TUTION OF  A  NEW  BASE 

When  the  adaptation  of  a  denture  has  become  impaired, 
but  the  teeth  which  it  carries  occlude  and  interlock  well  with 
those  in  the  opposite  arch,  adaptation  may  be  restored  by  sev- 
eral methods,  the  first  of  which  is  as  follows : 

Thoroughly  clean  the  denture  with  a  stiff  brush  wheel 
and  pumice  stone.  Remove  from  the  entire  palatine  and  bor- 
der surfaces  a  thin  layer  of  the  old  vulcanite  by  means  of  a 
small  lathe  bur  or  a  large  surgical  bur  in  the  engine. 

Apply  a  thin  laj^er  of  well-mixed,  but  rather  thin,  im- 


REPAIRING    VULCANITE    DENTURES  585 

pression  plaster  over  the  entire  interior  of  the  vault  and  bor- 
der surfaces. 

Introduce  in  the  inoutii  and  instruet  patient  to  bite 
intermittently  at  tirst,  then  with  steady,  maintained  pressure 
to  compress  the  tissues,  bring  the  denture  into  correct  occlu- 
sion and  force  out  all  excess  plaster. 

When  hardened,  trim  off  perijiheral  excess,  relieve  pres- 
sure over  hard  areas  by  scraping,  coat  impression  with  sepa- 
rating medium,  secure  a  cast  and  mount  it  on  the  occluding 
frame  in  the  usual  manner. 

P^ither  one  of  the  methods  previously  described  may  be 
adoi^ted  for  securing  the  correct  relation  between  the  teeth 
and  cast,  so  that  on  removal  of  the  old  vulcanite  the  aligii- 
ment  and  occlusion  of  the  teeth  in  the  wax  model  may  be  cor- 
rectly established. 

When  the  matrix  for  the  teeth  is  formed,  the  denture  is 
tirst  removed  from  the  latter,  then  from  the  cast,  the  surfaces 
of  which  are  then  cleared  from  any  remaining  jiortious  of  the 
plaster  impression. 

The  steps  from  this  point  forward  are  the  same  as  those 
already  outlined  under  the  head  of  "Substitution." 

CORRECTING  ADAPTATION  BY  ADDITION  OF  NEW 
RUBBER  TO  OLD  BASE 

When  the  impression  has  been  secured  in  the  manner  de- 
scribed aliove  and  the  cast  secured,  the  case  may  be  flasked 
immediately ;  when  the  investment  plaster  has  set,  the  flask  is 
separated,  the  plaster  is  removed  from  the  impressed  areas, 
and  the  exposed  palatine  and  border  surfaces  of  the  denture 
thoroughh'  freed  from  all  debris. 

All  exjjosed  areas  of  the  baseplate  not  previously  already 
freshened,  and  to  which  new  vulcanite  is  to  be  added,  should 
be  renewed  by  scraping,  these  areas  covered  with  a  thin  film 
of  rubber  cement ;  a  sheet  of  new  rubber  is  cut  to  correct  size 
and  carefully  pressed  against  the  old  baseplate,  being  careful 
not  to  confine  the  air  between  the  two  surfaces. 

The  two  halves  of  the  flask  are  now  adjusted,  the  screws 
tightened  slightly  and  the  flask  contents  heated  to  about  200 
degrees  F.,  dry.  heat,  when  gradual,  but  not  excessive  pres- 
sure is  applied  to  force  out  the  excess  rubber. 

When  closed  the  flask  is  separated,  the  muslin  removed 
and  the  result  of  the  work  so  far  accomplished  noted.  Should 
there  be  an  insufScient  amount  of  rubber,  more  is  added  and 


586  REPAIRING    VULCANITE    DENTURES 

the  flask  finally  closed  and  vnleanizcd  and  the  case  finished 
as  usual. 

Previous  to  the  ajjplication  oi'  the  rubber  cement,  an  am- 
ple waste  gate  should  be  cut  close  to  and  around  the  entire 
periphery  of  the  denture,  but  not  connected  with  the  margin 
of  the  matrix  at  any  point,  to  receive  the  excess  rubber. 

CORRECTING  ADAPTATION  BY  MEANS  OF  RUBBER 
PASTE 

Bur  out  and  freshen  the  surfaces  of  the  baseplate  as 
above  outlined  and  apply  a  film  of  Bridgeford's  rubber  paste, 
a  solution  of  rubber  heavily  loaded  with  powdered  aluminum. 
Thickness  of  the  film  applied  varies,  depending  on  the  amount 
of  old  vulcanite  removed  and  the  extent  of  absorption  of  the 
border  that  has  occurred,  but  usually  from  one  to  one  and  a 
half  millimeters  will  be  sufficient. 

The  denture  with  paste  applied  is  immersed  in  cold  water 
for  an  instant  to  chill  it  slightly  and  also  to  prevent  it  adher- 
ing to  the  oral  tissues. 

On  introduction  into  the  mouth,  the  denture  is  pressed  to 
place  for  a  moment,  removed,  the  excess  around  the  margins 
brushed  otf,  the  case  dipped  in  cold  water  and  again  returned 
to  the  mouth  for  further  adaptation  bj^  closure  on  the  part 
of  the  patient,  as  well  as  reapijlied  pressure  on  the  palatine 
areas  by  the  operator. 

These  steps  are  repeated  three  or  four  times,  or  until 
satisfactory  adaptation  is  secured,  when  the  denture  is  re- 
moved, freed  from  excess  and  set  aside  for  a  short  time  to  al- 
low the  volatile  constituents  time  to  evaporate,  when  the  ease 
is  flasked  in  a  single  investment  and  vulcanized. 

TO  RENEW  THE  ADAPTATION  OF  A  DENTURE  BY 
MEANS  OF  FURLONG'S  PLASTIC  RUBBER 

Prepare  the  palatine  and  border  surfaces  of  the  denture 
by  freshening  as  outlined  in  the  first  method  described. 

Apply  to  these  surfaces  a  sheet  of  Furlong's  Plastic  Im- 
pression Rubber,  pressing  it  well  against  the  old  vulcanite, 
being  careful  not  to  confine  any  air  between  the  surfaces. 

The  plasticity  of  this  rubber  is  increased  and  its  impres- 
sion quality  improved  by  immersing  it  in  warm  water  for  an 
instant  before  introducing  in  the  mouth.  Apply  pressure  as 
when  using  Bridgeford's  paste.    When  satisfactory  adhesion 


REPAIRING    VULCANITE    DENTURES  587. 

has  beeu  developed,  the  excess  is  removed  and  the  denture  is 
flasked  in  a  single  investment,  vulcanized  and  finished  in  the 
usual  manner. 

TO    CORRECT    OCCLUSION    WHEN    DENTURE    ADAPTA- 
TION IS  SATISFACTORY 

It  sometimes  occurs  that  a  patient  may  persistently  main- 
tain an  incorrect  bite  in  trial  of  the  contour  models  and  of  the 
wax  model  denture  in  the  mouth,  and  the  error  only  be  dis- 
covered when  the  cases  are  tinished. 

The  result  is  that  the  occlusion  is  incorrect,  the  teeth  of 
one  of  the  dentures  occupying  a  position  a  little  forward  in 
iipper  and  backward  in  lower  cases,  or  to  one  side  of  the  nor- 
mal alignment. 

The  best  plan,  as  a  rule,  is  to  reconstruct  one  or  both 
dentures,  beginning  with  a  new  impression  and  carrying  out 
the  usual  steps  in  such  cases. 

When,  however,  the  adaptation  of  the  denture  to  be  re- 
constructed is  in  every  way  satisfactory,  equally  good  results 
may  be  attained,  with  minimum  inconvenience  to  both  patient 
and  operator  by  adopting  the  following  method : 

With  a  small  engine  bur  cut  the  vulcanite  from  around 
the  pins  and  remove  the  teeth. 

By  means  of  a  vulcanite  file  and  the  emery  cloth  band  on 
the  lathe,  sufficient  vulcanite  is  removed  to  permit  the  shift- 
ing of  the  teeth  to  proper  position  without  interference.  The 
entire  outer  gum  surfaces  should  be  removed  so  that  in  the 
completed  case  no  joints  or  lines  of  junction  will  be  visible, 
a  layer  of  new  material  having  replaced  the  old. 

The  case  now  presents  the  same  conditions  as  does  the 
one  in  which  the  double  vulcanization  method  is  followed,  the 
old  base,  denuded  of  teeth  and  surrounding  vulcanite,  serving 
as  a  foundation  on  which  to  construct  the  wax  contour  model. 
On  this  base  the  teeth  are  waxed  and  occluded  and  the  subse- 
quent steps  carried  out  in  the  usual  manner. 


C  II  A  I"!'  \']  \l     \  X  \'  1 

CONTINUOUS    GUM   DENTURES 

From  an  esthetic,  as  well  as  Jiygienic  standpoiut,  coii- 
tiuuous  gum  dentures  fulfill  most  perfectly  the  requirements 
of  substitutes  for  the  lost  natural  teeth.  They  are  most 
strongly  indicated  in  full  cases,  although  at  times  partial  den- 
tures of  this  type  will  prove  very  serviceable. 

ADVANTAGES 

Continuous  gum  dentures  possess  two  important  ad- 
vantages over  dentures  of  any  other  type. 

First,  they  are  absolutely  impervious  to  moisture,  exempt 
from  chemical  action  to  which  they  are  ordinarily  subjected 
in  use,  and  afford  but  little  opportunity  for  the  lodgment  and 
retention  of  food;  consequently  they  are  easily  kept  clean 
and  free  from  decomposing  food  and  from  the  odors  of  ptyalin 
of  retained  saliva. 

Second,  the  gum  surfaces,  being  composed  of  glazed  por- 
celain enamel  tinged  with  pink,  present  an  unbroken  or  con- 
tinuous gum  surface  free  from  joints,  tissures,  or  cracks  of 
any  character,  and  which  is  united  to  the  underlying  vitrified 
porcelain,  the  teeth,  and  to  the  peripheral  margins  of  the 
baseplate  by  fusion. 

When  the  denture  is  proijerly  constructed  and  the  gum 
enamel  artistically  a]>plied,  it  is  impossible  in  most  cases  to 
detect  the  fact  that  the  substitute  is  artificial. 

DISADVANTAGES 

The  principal  objections  urged  against  dentures  of  this 
type  are  as  follows: 

First,  excessive  weight,  particularly  in  upper  cases  where 
much  absorption  of  the  border  has  occurred. 

Second,  difficulty  in  construction,  from  warpage  of  the 
entire  denture  due  to  shrinkage  of  mass  in  fusing  the  silicious 
material  around  the  teeth  and  to  the  base;  to  the  formation 
of  fissures  in  the  underlying  body  and  in  the  enamel  in  the 
final  baking;  to  the  tendency  of  the  mass  of  porcelain  to  be- 
come porous  at  any  stage  of  fusion  after  the  first  baking. 

Third,  dentures  of  this  type  are  liable  to  fracture  if  care- 

588 


CONTINUOUS    GUM    DENTURES  589 

lessly  handled,  because  of  their  excessive  weiglit  and  tlie  fria- 
bility of  the  materials  of  which  composed. 

Fourth,  the  expense  of  time  and  material  involved  place 
them  beyond  the  reach  of  persons  of  limited  means. 

In  regard  to  the  first  objection,  when  good  adaptation  of 
the  dentures  is  secured  and  the  teeth  are  arranged  anatomi- 
call}^,  the  weight  of  the  denture  is  seldom  noticeable  to  the 
patient. 

The  second  objection  can  be  overcome  by  patient  attention 
to  details  on  the  part  of  the  prosthetist. 

The  third  objection  more  especially  concerns  the  patient, 
who,  however,  if  ]n"operly  instructed,  can  usually  avoid  acci- 
dent. 

The  fourth  disadvantage  is  an  important  one  to  both  pa- 
tient and  prosthetist.  The  patient  must  of  course  decide 
whether  a  denture  of  this  type  is  within  his  means.  The 
prosthetist,  on  the  other  hand,  must  exact  such  fee  as  will 
cover  the  cost  of  the  materials  and  recompense  him  well  for 
all  possible  time  involved  in  constructing  the  case.  Oversight 
in  this  ]iarticular  is  responsible  for  many  failures  in  the  class 
of  work  under  consideration,  the  tendency  being  to  rush  the 
constructive  details  to  their  detriment,  or  turn  the  case  over  to 
someone  who  may  prove  incompetent. 

In  no  department  of  prosthetics  is  there  an  opportunity 
for  the  display  of  greater  skill,  or  the  realization  of  finer 
esthetic  results,  than  in  the  planning  and  construction  of 
dentures  of  this  type.  There  is  first,  the  development  of  a 
well  trussed,  yet  light,  platinum  baseplate;  second,  the  ar- 
rangement of  the  teeth  anatomically,  as  well  as  esthetically ; 
third,  their  attachment  to  the  baseplate  by  soldering,  and 
bracing  when  necessary,  in  such  manner  as  to  remain  un- 
changed during  the  contraction  of  the  porcelain  in  fusing;  and 
finally,  the  application  of  the  porcelain  body,  and  subse- 
quently, the  enamel  so  disposed  as  to  represent  nature's  best 
efforts  in  contour  gum  effects  and  vault  irregailarities. 

Formerly  dentiires  of  porcelain  were  constructed  without 
metallic  bases,  but  on  account  of  the  shrinkage  which  invari- 
ably occurred  in  baking,  adaptation  was  seriously  interfered 
with,  or  entirely  destroyed.  As  a  result  corrections  had  to  be 
made  by  the  method  mentioned  elsewhere  of  securing  a  new 
cast  of  the  mouth,  pigmenting  its  surface,  and  by  repeated 
trials  of  the  denture  to  the  cast,  locating  the  high  points,  which 
were  then  ground  away  imtil  close  adaptation  was  secured. 
The  grinding  of  the  glazed  surfaces  exposed  many  minute 
spaces,  and  left  the  porcelain  more  or  less  rough  and  porous. 


590  CONTINUOUS    GUM    DENTURES 

A  further  objection  to  the  all-porcelain  denture  was  that 
unless  formed  thick  and  somewhat  bulky,  it  was  lial)le  to  frac- 
ture under  usage  in  the  mouth. 

About  1855  Dr.  John  Allen  of  New  York,  introduced  tlie 
method  of  attaching-  the  teeth  to  a  platinum  base  and  fusing 
the  porcelain  around  them.  By  this  means  warpage  of  the 
denture  during  baking  was  to  a  large  extent  obviated.  This 
is  essentially  the  method  in  vogue  today,  the  constructive  de- 
tails of  which  are  as  follows : 

FORMING  THE   PLATINUM   BASEPLATE 

From  an  impression  of  the  mouth  a  model  is  secured.  A 
die  and  counterdie  are  formed  in  the  manner  elsewhere  de- 


PLATINtlM    BASEPLATE.    SWAGED    AND    TRIMMED    TO 

APPROXIMATELY     CORRECT     PERIPHERAL 

OUTLINE 

scribed,  and  a  pattern  of  the  baseplate  obtained.  Usually  pure 
platinum  No.  28  gauge,  is  used,  since  a  thinner  plate  unless 
heavily  reinforced,  will  not  furnish  a  sufficiently  rigid  founda- 
tion to  prevent  warpage  of  the  porcelain  during  baking,  or 
obviate  fracture  of  the  finished  denture  under  stress. 

In  the  swaging  of  a  platinum  baseplate  special  care  should 
be  taken  to  avoid  the  formation  of  folds  in  any  location,  since 
if  subsequently  corrected  by  flowing  solder  into  them,  and  re- 
ducing the  excess  by  grinding,  an  unsightly  area  is  left  due  to 
difference  in  color  of  solder  and  baseplate. 

FITTING  THE  BASEPLATE  IN  THE  MOUTH 

When  swaged  and  trimmed  peripherally,  the  base  should 
be  introduced  in  the  mouth  and  tested  as  to  general  adaptation 


CONTINUOUS    GUM    DENTURES  591 

aud  stability.  All  margins  which  impinge  on  the  muscles  or 
frenum  should  be  corrected,  and  the  peripheral  outline  of  the 
baseplate  trimmed  to  as  nearly  the  exact  outline  of  the  finished 
denture  as  possible.  This  is  necessary  in  order  to  avoid  the 
unsightly  appearance  caused  by  grinding  away  the  metal  rim, 
often  into  the  porcelain,  to  relieve  impingement  when  the  fin- 
ished denture  is  introduced — a  condition  frequently  seen  in 
cases  where  proper  care  has  not  been  exercised  in  pei'ipheral 
trimniing  of  the  baseplate. 

REINFORCING  THE   BASEPLATE 

Since  porcelain  in  thin  layers  is  easily  fractured,  the 
metal  framework  of  dentures  and  bridges  which  are  to  be 
overlaid  with  this  material  should  have  sufficient  inherent 


DISTAL     SHOULDER    WIRE     AD.U>TED     TO     PLATINUM 

JiASEPLATE.      THIS   WIRE   SHOULD   BE    iu   TO    22 

GAUGE,     AND     TERMINATE    ABOUT    THE 

CENTER   OF  EACH  TUBEROSITY 

strengtii,  exclusive  of  the  added  porcelain,  to  withstand  all 
stress  to  which  they  may  be  subjected. 

A  platinum  base  may  be  strengthened  in  several  ways,  the 
most  common  methods  of  which  will  now  be  given : 

First,  to  strengthen  an  upper  baseplate,  a  platinum  wire 
of  22  to  2-t  gauge  is  adapted  and  soldered  to  the  lingual  side 
of  the  baseplate  near  its  distal  margin.  It  should  be  laid  in  a 
symmetrical  curve,  and  advanced  further  forward  in  the  vault 
portion  than  at  either  side.  The  object  in  placing  the  two  ends 
near  the  margins  at  their  terminal  points  on  the  tuberosities 
is  to  afford  some  space  for  a  graceful  curve  to  the  porcelain 
in  its  extension  distally  from  the  second  molars. 

Over  this  wire  a  second  strip  of  platinum,  usually  31  or 
32  gauge,  is  swaged  to  the  plate.    The  anterior  margin  of  this 


CONTINUOUS    GUM    DENTURES 


strip  should  overlap  the  wire  anteriorly,  and  the  posterior 
margin  extend  slightly  beyond  the  distal  margin  of  the  base- 
plate, to  afford  a  shoulder  on  whioh  to  lay  the  solder.    When 


I'l.ATE    AMI     UIRK 


swaged,  the  anterior  margin  of  tlie  strip  is  trimmed  to  the  an- 
terior surface  of  the  wire  and  the  two  ends  cut  so  as  to  termi- 
nate on  the  tuberosities  and  even  with  the  underlying  wire. 


In  addition  to  the  doubler  just  described,  a  second  doubler 
is  sometimes  swaged  and  trimmed  as  illustrated,  to  overlay 
the  border  and  extend  into  the  palatine  area.    It  should  not 


CONTINUOUS    GUM    DENTURES  593 

extend  much  beyond  tlic  crest  of  the  border  either  labially  or 
incisally;  first,  because  it  is  not  necessary  for  strength;  sec- 
ond, the  space  it  would  occupy  if  extended  can  be  best  con- 
served for  increasing  bulk  of  poi'celain ;  third,  unnecessary 
metal  adds  to  the  weight  of  the  denture. 

Instead  of  the  doubler  just  described,  some  prefer  to 
adapt  and  solder  a  piece  of  1(i  or  14-gauge  iridio-platiniun 


I)Orm,EB    TltlMMEII    AND    SOLUEBBD    TO    BASEl'LATE 

wire  along  the  crest  of  the  border  in  such  position  as  not  to  in- 
terfere with  correct  tooth  alignment. 

The  doubters,  of  whatever  form,  should  l)e  firmly  attached 
to  the  baseplate  with  high-grade  platinum  solder,  and  the  base 
reswaged  to  correct  any  warpage  that  may  have  occurred. 

FORMING  THE   FINISHING  SHOULDER   FOR  THE   PORCELAIN 

It  is  necessary  in  order  to  avoid  fracture,  to  form  a  right- 
angle  shoulder  around  the  entire  periphery  of  the  base, 
against  which  the  porcelain  may  settle  in  fusing.  The  anterior 
margin  of  the  doubler  and  underlying  wire,  when  squared  out 
with  small  stones  and  burs,  constitute  tlie  distal  shoulder, 
while  that  on  the  labial  and  liuccal  periphery  is  formed  on 
these  surfaces  by  soldering  a  wire  of  about  18  gauge  to  the 
baseplate. 

One  end  of  the  peripheral  wire  should  abut  the  doubler 
and  wire  on  oilo  tuberosity,  and  be  bent  to  lie  in  contact  with 
the  baseplate  rim  for  a  distance  of  about  an  inch  anteriorly. 
It  is  then  clamped  in  position  and  attached  with  solder 
throughout  a  portion  of  this  distance,  and  the  plate  cooled. 
The  adaptation  of  the  wire  and  attachment  with  solder  should 


594  CONTINUOUS    GUM    DENTURES 

proceed  in  sections,  rather  than  to  attempt  to  adapt  and  elanip 
it  around  the  entire  periphery  at  the  start. 

The  wire  should  be  parallel  with  the  periphery  of  the 
baseplate  rim,  but  be  placed  about  one-sixteenth  of  an  inch 
from  it,  so  that  subsequent  trimming,  if  necessary  to  relieve 
muscular  'impingement,  may  be  accomplished  witliout  en- 
croaching on  the  porcelain. 

Extensive  contouring  of  the  solder  in  the  space  on  tiie 
l)eripheral  side  of  the  wire  should  not  be  attempted,  as  pits 
are  liable  to  develop  in  bulky  masses  of  platinum  solder  dur- 
ing the  fusing  of  the  porcelain.    The  angle,  however,  should 


BASEPLATE     WITH     PERIPHERAL     WIRE     ATTACHED. 

ALSO    A    STRENGTHENEK   ADAPTED    TO 

BORDER    AREAS 


be  filled  in  to  develo})  a  uniform,  but  slightly  tapering  or  con- 
cave surface. 

The  angle  between  wire  and  baseplate  presenting  toward 
tlie  crest  of  the  border  should  not  be  filled  to  any  extent  with 
solder,  since  this  surface  of  the  wire  must  subsequently  be 
squared  out  in  forming  the  shoulder. 

Small  square-edged  carborundum  stones  are  now  applied 
to  the  wire  to  develop  a  square  shoulder  against  which  the 
porcelain  may  be  fused.  Plug-finishing  burs  are  also  useful 
for  this  purpose.  The  shoulder  should  jjresent  a  definite  angle 
around  the  entire  periphery  of  the  base,  for  if  left  round  at 
any  point  a  crease  may  form  by  the  contraction  of  the  porce- 
lain, or  the  latter  may  overlap  the  rounded  surface  as  a  thin 
edge  and  the  latter  be  fractured  in  handling. 

The  soldering  is  best  accomplished  by  means  of  nitrous 
oxid  and  gas  blow-pipe,  or  when  pure  gold  is  used  as  a  solder 


CONTINUOUS    GUM    DENTURES 


595 


the  ordinary  gas  blow-pipe  may  be  employed.  Platinum  solder 
is  preferable  to  pure  gold,  as  it  is  not  dissipated  during  the 
several  bakings  of  the  porcelain  as  is  pure  gold,  the  latter 
being  absorbed  by  the  platinum  at  high  temperatures.     Fre- 


THE  TURNER  ALCOHOL  liLOWPrPE.  ^\^TICH 

DEA'ELOPS    AN   INTEN.SB    PLAJIE    SUITjVBLE 

FOR  FU.SINr,  PLATINUM  SOLDER 


([uently  joints  united  with  pure  gold  as  a  solder  pull  apart 
during  baking,  or  under  slight  stress  when  the  finished  piece 
is  introduced  in  the  mouth. 

RESWAGING  AND   CLEANSING  THE  BASEPLATE 

The  doubter  and  peri]iheral  shoulder  wire  having  been 
attached  by  soldering,  the  baseplate  should  be  reswaged  to 
correct  the  warpage  that  may  have  occurred  during  this  op- 
eration. 

To  prevent  the  baseplate  from  becoming  lodged  in  the 
counterdie  in  swaging,  due  to  the  peripheral  shoulder  wire 
being  driven  into  the  sides  of  the  latter,  a  few  layers  of  damp 
newspaper  can  be  interposed  between  the  two.  The  die  and 
counterdie  sliould  at  all  times  be  kept  oiled  to  prevent  con- 
tamination of  the  platinum  by  the  base  metals.  In  addition 
to  this  precautionary  measure  the  baseplate  should  be  boiled 
in  dilute  acid  and  .thoroughly  polished  on  the  lathe  with  a 
stiff  brush  wheel  and  pumice  stone,  to  prevent  any  possible 
danger  from  this  source. 


DEVELOPING    THE    OCCLUSION    AND    CONTOUR    MODEL 

The  baseplate  is  now  in  condition  to  receive  the  rim  of 
wax,  by  means  of  which  the  occlusion  and  facial  contour  is 


596  CONTINUOUS    GUM    DENTURES 

established.  The  steps  from  now  on  are  exactly  similar  to 
those  described  under  the  head  of  J-^iill  Denture  Construction 
np  to  that  of  permanently  attaching  the  teeth  to  the  baseplate, 
with  the  exceptions  resulting-  fi'oni  the  use  of  a  special  type  of 
tooth  for  these  cases. 

CONTINUOUS    GUM    TEETH 

Teeth  intended   for   continuous   gum  woi*k   differ  from 
vulcanite  teeth  in  having  gingival  extensions  resembling  roots. 


A    SKT    IIF    NO. 


rONTixuors  r:uM  teetti. 


These  extensions  are  flattened  somewliat  on  their  lingual  sur- 
faces to  obviate  excessive  grinding  in  aligning  the  teeth  on 
the  baseplate. 

These  root  extensions  serve  two  very  useful  purposes ; 
first,  being  composed  of  high-fusing  porcelain  which  is  unaf- 


tMiUiiiiimui 


I'ENTRAL.    AND    BICUSPID.    TURNED 


fected  by  contractile  changes  dui-ing  vitrification  of  the  con- 
tinuous gum  body,  the  bulk  of  the  latter  required  for  the  case 
is  materially  lessened,  and  shrinkage  of  the  denture  mass  is 
proportionately  reduced ;  second,  in  addition  to  the  long  pin 
attachment  of  the  tooth  to  the  baseplate,  the  extension  serves 
to  increase  stability  by  resting  upon  the  baseplate,  thus  ob- 


CONTINUOUS    GUM    DENTURES  59T 

viatiug-  the  danger  of  displacement  due  to  contraction  of  tlie 
body  during  baking. 

When  but  slight  absorption  of  the  I'idge  has  occurred, 
it  is  frequently  necessary  to  grind  away  a  portion  or  all  of 
the  extension,  thus  bringing  the  body  of  the  tooth  directly  in 
contact  with  the  baseplate,  mucb  as  the  ridge  lap  of  an  ordi- 
nary vulcanite  tooth  is  frequently  set  in  contact  with  its  base- 
plate, or  sometimes  upon  the  cast  itself. 

In  other  cases  when  excessive  absorption  of  the  ridge 
has  occurred  and  the  correct  labial,  buccal  and  occlusal  align- 
ment of  the  teeth  have  been  secured,  these  extensions  may 
fail  to  touch  the  baseplate  at  any  point.  It  then  becomes  nec- 
essary to  interpose  blocks  of  high-fusing  porcelain,  as  pieces 


CASE  KEQUIRING   CONSIDER 
ABLE     BEDnCTION     OF     LIN- 
GUAL   SIDE    OF    BOOT 


t'ASE      REQUIRING      ADJUST- 
MENT    OF     BROKEN     PIECES 
OF       PORCELAIN       BETWEEN 
TEETH  AND  BASEPLATE 


of  broken  teeth,  between  the  baseplate  and  the  extensions  not 
in  contact,  or  to  truss  them  in  proper  position  with  platinum 
wire  or  plate.  In  addition  to  the  difference  noted,  continuous 
gum  teeth  are  supplied  with  a  single  platinum  pin,  larger  and 
longer  than  those  ordinarily  used  in  other  types  of  teeth. 


SELECTION   AND  ARRANGEMENT  OF  TEETH 

Teeth  of  suitable  form,  size  and  shade  to  meet  the  recjuire- 
ments  of  the  case  having  been  selected,  they  are  let  within 
the  wax  rim  by  successively  cutting  out  sections  of  the  latter 
of  sufficient  depth- to  permit  each  tooth,  with  its  extension, 
to  assume  propVr  alignment.  No  attention  need  be  given  the 
relation  of  the  extension  end  of  the  tooth  to  the  baseplate 
during  arrangement,  except  when  its  length  or  lingual  surface 
interferes  with  correct  placing  of  the  tooth,  when  it  may  be 
reduced  by  grinding,  or  entirely  excised,  as  conditions  require. 


598  CONTINUOUS    GUM    DENTURES 

The  steps  of  arrangement  and  occlusion  of  full  upper  and 
lower  cases  of  this  type  are  carried  out  in  other  respects  the 
same  as  for  full  dentures  in  general.  When  the  teeth  are 
occluded  the  denture  should  be  waxed  up  labially  and  buccally 
to  represent  the  natural  gums,  with  such  added  contour  as 
may  be  required  for  facial  restoration.  This  step  is  seldom 
carried  out,  but  more  esthetic  results  can  be  produced  by 
following  this  plan  than  by  developing  the  contour  without 
definite  guidance. 

TRIAL  OF  THE  WAX  MODEL  DENTURE  IN  THE  MOUTH 

When  properly  contoured,  the  denture  is  tested  in  the 
mouth,  first  as  to  normal  occlusion;  second,  as  to  clearance 
]iaths  in  lateral  movements;  thii'd,  balancing  contact;  and 
fourth,  general  esthetic  results.  When  corrections  have  been 
made,  if  necessary,  and  the  prosthetist  is  satisfied  that  all  re- 
quired conditions  have  been  fulfilled  up  to  this  stage  of  con- 
struction, the  next  step  is  to  prepare  a  guide  for  testing  the 
labial  and  buccal  contour  of  the  case  at  various  stages  of 
construction. 

DEVELOPING  THE  CONTOUR  MATRIX 

The  entire  labial,  buccal  and  palatine  surfaces  of  the 
wax  model  denture  are  now  coated  with  a  thin  film  of  oil,  a 
mix  of  plaster  made,  and  a  cast  of  ordinary  form  developed 


l^'^J 

■^^^^H 

FOUR  PIECE    MATRIX,    AM.    I'AIiTS     IN    CURRENT    Ar'l'OSrriON 

l)y  filling  in  the  palatine  and  border  svirfaces  of  the  baseplate. 
This  cast  should  be  about  %-inch  thick  in  the  vault  region, 
or  sufficiently  deep  to  raise  the  peripheral  margins  of  the 
baseplate  about  one-fourtli  inch  above  the  base  of  the  cast. 
The  sides  of  the  cast  should  he  trimmed  smooth,  converging 
slightly  from  the  base  upward,  to  the  outer  peripheral  line  of 
the  wax.  At  several  points  on  the  labial  and  buccal  surfaces 
of  the   cast   shallow  countersunk  depressions   are  made   to 


CONTINUOUS    GUM    DENTURES  599 

develop  pro.jcctiinis  on  the  several  sections  of  the  labial  and 
buccal  matrix.  This  is  necessary  in  order  that  any  section  of 
the  matrix  may  be  returned  to  position  independently  of  the 
other  pieces.  The  side  of  the  base  is  varnished  with  shellac, 
which,  when  dry,  is  coated  with  a  thin  film  of  oil. 

Plaster  is  now  applied  to  one  of  the  buccal  surfaces  and 
built  against  the  base  of  the  cast,  the  wax  and  outer  surfaces 
of  the  teeth.  It  should  not  extend  over  the  buccal  marginal 
ridges  or  incisal  edges  of  the  teeth.  This  first  section  includes 
the  area  from  the  tuberosity  back  of  the  second  molar  to  the 
middle  of  the  cuspid  tooth.     It  should  be  about  three-eights 


FOUn-riECE    MATRIX    FOB    LOWER    CASE.    USED    FOB    TESTING    CONTOUU    Of    CASE 
DURING   CONSTBUCTION   STAGES.    PARTIALLY   SEPABATED 

of  an  inch  in  thickness,  its  outer  surface  parallel  with  the  buc- 
cal surface  of  the  cast  base  and  denture.  When  hardened  the 
anterior  end  of  this  first  section  is  squared  up,  varnished  and 
oiled. 

Another  mix  of  plaster  is  now  applied  to  the  incisor  area, 
building  against  the  squared  end  of  the  first  section  and 
extending  to  the  opposite  cuspid  tooth.  When  set,  this  section 
of  plaster  is  trimmed,  varnished,  oiled,  and  the  third  piece  cor- 
responding to  the  first  on  the  opposite  side  is  constructed. 

When  the  plaster  has  set  the  three  sections  are  tapped 
slightly  to  loosen,  then  removed,  and  the  wax  model  denture 
is  detached  from  the  cast.  These  are  now  set  aside  until  after 
the  ai)plication  of  the  body  in  the  second  baking,  when  the 
baseplate  is  returned  to  the  cast  and  the  several  labial  and 
buccal  areas  are  tested  as  to  required  fullness,  or  excess  of 
apiilied  body,  by  returning  each  section  to  position  against 
the  cast  base.  By  sawing  partly  through  any  section  at  one  or 
more  points,  cutting  from  without  inward,  it  may  be  cleanly 
fractured  into  any  numl)er  of  required  pieces,  any  one  of 
which  may  be  used  for  test  purposes  over  its  own  particular 
area. 


600  CONTINUOUS    GUM    DENTURES 

It  is  possible  by  caliperiiig  a  number  of  prominent  areas 
of  the  waxed  case,  and  recording  the  same,  to  arrive  at  com- 
paratively accurate  results  in  the  disposition  of  the  gum  body. 
The  time  required  for  measuring,  recording,  and  later  for 
reference,  usually  aggregates  more  than  that  required  for 
forming  a  matrix,  while  the  latter  when  suitably  fractured  will 
determine  quickly  the  accuracy  of  many  gingivo-peripheral 
surface  contour  lines. 

These  various  steps  having  been  completed,  the  case  is 
now  ready  for  investment,  ]iroparatovy  to  attaching  tlie  teeth 
to  the  baseplate. 

INVESTMENT  OF  THE  WAX  MODEL  DENTURE 

In  continuous  gum  cases  the  teeth  must  be  rigidly  at- 
tached to  the  baseplate  by  soldei'ing  and  trusting  to  prevent 
their  relation,  as  established  in  the  wax  rim  and  by  trial 
in  the  mouth,  from  becoming  distorted  by  the  contraction  of 
the  porcelain  while  fusing  the  latter.  The  steps  are  carried 
out  as  follows: 

The  wax  representing  the  labial  and  buccal  surfaces  of 
the  gums  is  removed  from  these  areas  and  from  between  the 
embrasures  and  root  extensions  as  well,  so  as  to  permit  the 
investment  to  partially  surround  and  hold  the  teeth  when 
lingual  support  is  removed.  A  mix  is  made  of  some  standard 
investment  material  which  possesses  considerable  hardness 
when  set.    A  portion  of  the  investment,  about  one-lialf  inch 


IIM       TKETH       ARRANGED       ON 
\sn-I.ATE.        WAX     REMOVED 
l;\srltES      TO      ALLOW      IN- 
r      MATERIAL      TO      ENTER 
THESE  SPACES 


thick  and  a  little  larger  than  the  area  of  the  baseplate,  is 
placed  on  a  sheet  of  paper  on  the  bench.  Another  portion  is 
filled  in  the  palatine  side  of  the  platinum  base  and  the  latter 
pressed  down  upon  that  resting  on  the  paper,  until  it  ap- 
proaches within  three-eighths  of  an  inch  of  the  bench.  The 
investment  is  then  worked  into  the  embrasures  and  over  the 


CONTINUOUS    GUM    DENTURES  601 

occlusal  and  incisal  surfaces  of  the  teeth.  .  To  resist  the  more 
or  less  rough  usage  it  will  receive  in  applying  the  truss  bars 
and  soldering,  the  investment  should  be  about  three-eighths 
of  an  inch  thick  througli  the  side  walls.  All  overhanging  por- 
tions should  be  removed  from  the  occlusal  and  incisal  surfaces, 


FROM    I.INCIAI. 


to  permit  of  ready  access  in  bending  the  i)ins  and  soldering 
them  to  the  truss  or  baseplate. 

When  hai'deued  the  rough  excess  of  investment  is  trimmed 
away,  the  wax  surrounding  the  lingual  surfaces  of  the 
teeth  in  which  the  pins  are  imbedded  is  thoroughly  warmed 
and  removed — care  being  taken  not  to  dislodge  the  teeth — 
the  final  trimming  of  all  excess  investment  accomplished  and 
the  case  thoroughly  cleansed  with  a  stream  of  hot  water. 

FITTING    AND    APPLICATION    OF    THE    METAL    SUPPORT    TO 
THE  TEETH 

Occasionally  cases  present  where  the  long  pins  of  the 
continuous  gum  teeth  can  be  directly  applied  and  soldered  to 
the  platinum  baseplate  in  such  manner  as  to  give  all  necessary 
support  to  the  t_eeth.  More  frequently,  when  much  absorption 
of  the  border  has  occurred,  it  is  necessary  to  extend  some  kind 
of  metal  support  from  the  border  crest  to  the  angle  of  junction 
of  the  pins  with  the  porcelain.  The  Allen  method,  although 
not  the  best,  is  most  frequently  resorted  to,  and  is  as  follows: 


G02  CONTINUOUS    GUM    DENTURES 

The  platiniiiii  pins  are  straightened  ont  at  I'ight  angles 
to  the  long  axes  of  the  teeth.  A  strip  of  cardlioard  abont  four 
inches  long  is  cut  like  the  illustrated  pattern,  subject  of 
course,  to  such  modifications  of  form  as  tlie  slant  from  the 


SUri'ORTIXC    TRfSS    MAY 


border  to  the  iiins  and  to  the  varying  width  of  the  space  be- 
tween the  same  at  different  points.     (See  cut  on  page  603.) 

This  cardboard  pattern  is  corrected  by  trial,  and  recon- 
structed if  necessary,  until  when  finally  fitted  it  exactly  repre- 


SECTMINAI,    VIKW  OF   TOOTH. 
BASEPI.ATE       JIBTAI.       SUP- 
PORT   AND    INVESTMENT 


sents  the  form  of  metal  strip  to  cut  for  the  proper  support  of 
the  teeth.  The  pattern  as  shown  usually  represents  the  seg- 
ment of  an  ellipse.  A  metal  duplicate  of  30  or  31  gauge  iridio- 
platinum  plate  is  now  made  and  bent  to  place.  Marks  are  now 
made  at  various  points  on  its  lingual  surface  between  the  teeth, 


CONTINUOUS    GUM    DENTURKS 


to  indicate  the  position  for  punching  the  holes,  the  idea  lieing 
to  so  place  the  holes  that  the  pins  when  bent  and  soldered  to 
the  strip  will  not  close  them.  The  holes,  usually  about  ten 
or  twelve  in  number,  should  be  located  about  midway  lietween 
tlie  border  crest  and  the  pin  margin  of  the  strip  and  should 


rAI'ER    I'ATTKUX    UF    METAL   Siri'OliT    KOU   THE  TEETH 

be  about  cue-sixteenth  of  an  inch  in  diameter.  At  various 
l)oints  along  the  margin  which  rests  on  the  border,  crescent- 
shaped  notches  are  cut  in  the  strip.  Through  these  various 
openings  the  labial  and  buccal  ]iortions  of  porcelain  become 
more  or  less  firmlv  united  and  under  stress  of  mastication 


METAL    SLl'lMJUT, 


splitting  of  the  denture  is  not  so  liable  to  occur  as  is  the  case 
when  the  openings  are  omitted. 

It  will  readily  be  seen  that  a  support  so  formed  mechani- 
cally divides  the  denture  into  two  portions,  and  is  therefore 
a  source  of  weakness,  which  after  consti'uction  of  the  case,  can- 


CONTINUOUS    GUM    DRNTURRS 


not  be  overcome.     More  recent  and  bettei-  methods  will  be 
shown  for  trussing  and  holding  tiie  teeth  in  position. 

The  holes  having  been  punclied  and  the  notches  cut  as 
described,  the  striji  is  returned  to  position  and  the  pins  bent 


down  in  contact  with  it,  and  the  baseiilate  also  if  the  space  is 
not  too  wide. 

The  invested  case  is  now  placed  on  a  Bunsen  stove  to 
thoroughly  dry  and  become  heated.    Medium  fusing  platinum 


SECTION  SHOWING  PIN 

ADAPTED     TO     METAL     SOP- 
PORT.    AND.     IN    THIS    CASE. 
TO       THE       BASEPLATE       AS 
WELL 


solder  is  cut  in  small  pieces  preparatory  to  the  final  union 
of  the  many  parts.  When  thoroughly  heated,  the  invested 
case  is  placed  on  a  solder  block  in  such  position  that  gravity 
will  retain  the  solder  in  jjcsition  in  certain  areas  to  wliieh 


CONTINUOUS    GUM    DENTURES  605 

it  is  now  applied.  The  nitrous  oxid  and  gas  blow-pipe  previ- 
ously mentioned  is  now  directed  on  the  solder  placed,  and 
when  fused  the  position  of  the  case  is  changed.  The  process 
is  repeated  until  all  of  the  teeth  are  firmly  united  to  the  strip 
and  the  latter  to  the  baseplate.  The  use  of  excessive  amounts 
of  solder  should  be  avoided,  as  it  only  increases  the  weight 
of  the  denture  without  materially  adding  strength. 

Pure  gold  is  often  used  as  a  solder  in  this  class  of  work, 
and  while  commonly  safe,  there  is  danger  of  it  being  absorbed 
b}'  the  platinum  and  the  joints  becoming  disconnected. 

In  all  soldering  operations  of  the  class  under  considera- 
tion, certain  essentials  should  be  kept  in  mind.  These  may 
be  summarized  as  follows : 

Close,  clean  joints. 

Strong,  yet  not  too  bulky,  investment. 

Plenty  of  preliminary,  as  well  as  blow-pipe,  heat. 

Small  pieces  of  platinum  solder  laid  just  where 
they  are  needed. 

Avoid  the  use  of  too  concentrated  or  long-con- 
tinued flame  on  any  one  tooth. 

Depend  on  gravity  for  retaining  and  carrying 
the  solder  in  position  when  fused. 

Avoid  the  use  of  flux,  since  the  metals  do  not 
oxidize  and  its  presence,  if  allowed  to  come  in  contact 
with  the  porcelain  at  high  temperatures,  is  certain 
to  check  the  latter. 

SUPPORTING  THE  TEETH  WITH  WIRE 

When  the  distance  between  the  border  crest  and  the  pin- 
porcelain  junction  of  the  teeth  does  not  exceed  one-fourth  of 
an  inch,  a  No.  18  gauge  iridio-platinum  wire  can  be  bent  as 
shown  in  the  illustration,  to  afford  a  comparatively  rigid  sup- 
port for  the  teeth,  while  the  tendency  to  divide  the  porcelain 
into  an  outer  and  inner  portion  is  obviated,  or  at  least  greatly 
reduced.  The  technic  of  application-fitting  and  trying  is  so 
simple  that  it  need  not  be  here  detailed. 

When  the  amount  of  absorption  is  excessive  and  the  teeth 
must  of  necessity  be  raised  a  considerable  distance  from  the 
baseplate,  the  foll6wing  plan  can  be  adopted. 

Two  wires  of  16  gauge  iridio-platinum  are  bent  to  con- 
form to  the  arch.  One  is  laid  on  the  border  crest,  not  neces- 
sarily in  close  contact,  but  touching,  the  baseplate  at  the  distal 
extremities  and  at  several  intermediate  ]ioints.     The  other 


606  CONTINITOUS    GUM    DENTURES 

wire  is  bent  to  lie  in  close  contact  witli  the  pins  and  porcelain 
at  their  junction.  The  extremities  of  this  wire  are  carried 
from  the  pins  of  the  second  molar  in  a  sloping  direction,  down 
alongside  of,  and  in  contact  with,  the  wire  on  the  border 
crest. 


WIRE     TRUSS. 


Five  or  six  iridio-platinnm  posts  are  now  cut  and  fitted 
so  as  to  reach  from  the  baseplate  to  the  wire  under  the  pins. 
They  should  also  touch  the  wire  on  the  border  crest.  The 
pins  are  now  bent  around  the  upper  wire  and  the  frame-work 
when  soldered  forms  a  rigid  truss,  capalile  of  withstanding 
all  ordinary  strains. 


In  these  cases  of  excessive  absorption,  the  teeth  are  fre- 
quently so  placed  that  their  cervical  extensions  do  not  touch 
the  baseplate,  nor  can  the  border  wire  of  the  truss  at  all  times 
be  bent  in  such  manner  as  to  afford  them  necessary  support 
without  reducing  the  efficiencv  of  the  truss. 


CONTINUOUS    GUM    DENTURES 


By  blocking  in  tlie  space  between  the  baseplate  and  the 
porcelain  roots  with  broken  pieces  of  old  porcelain  teeth,  or 
even  whole  teeth,  so  placed  as  not  to  interfere  with  proper 
contouring  of  the  gum  body,  the  danger  of  distortion  in  fusing 
is  ol)viated.    The  presence  of  tlie  blocks  of  liigh-fusing  porce- 


lain is  not  in  the  least  objectionable,  biit  rather  an  advantage, 
since  the  bulk  of  gum  body  required  will  be  proportionally 
reduced.  The  soldering  of  the  wires  is  carried  out  in  a  man- 
ner similar  to  that  followed  in  attaching  the  teeth  by  means 
of  the  metal  strip. 

When  the  teeth,  by  whatever  method  adopted,   are   at- 
tached to  the  baseplate,  the  investment  is  allowed  to  cool.    It 


is  then  placed  in  \yater  to  soften  and  finally  carefully  removed 
so  as  not  to  disturb  the  position  of  the  teeth.  The  latter,  al- 
though firmly  fixed  to  the  truss  bar  or  strip  by  the  pins,  can 
be  rotated  or  bent  under  stress  until  rigidly  fixed  by  fusion 
of  the  first  application  of  body. 


608  CONTINUOUS    GUM    DENTURES 

In  some  cases  it  may  be  advisable  after  soldering  to  try 
the  skeleton  denture  in  the  month  to  test  the  occlusal  relations 
of  the  teeth.  Frequently  some  slight  change,  as  rotating  a 
tooth  or  modifying  its  axial  alignment  at  this  time  will  ob- 
viate what  might  later  on  prove  a  glaring  defect. 

The  skeleton  denture  is  now  boiled  in  dilute  HCl,  thor- 
oughly washed  and  the  palatine  and  outer  surfaces  of  the 
platinum  base  roughened  by  passing  a  sharp-pointed  blade 
over  them  in  various  directions  to  afford  some  slight  hold 
for  the  porcelain.  The  case  is  now  ready  for  the  application 
of  the  continuous  gum  body. 

CONTINUOUS  GUM  BODY  AND  ENAMEL 

Under  the  description  of  porcelain  will  ))e  found  the  gen- 
eral formula'  of  confimious  gum  body,  and  giDii  etiawel.  These 
materials,  supplied  hy  the  manufacturers  for  denture  con- 
struction, come  in  powder  form,  usually  in  one-ounce  pack- 
ages. They  are  commonly  referred  to  as  hodij  and  enamel. 
The  body  is  almost  white  in  powder  form;  during  fusion  it 
assumes  a  yellowish  tint  much  resembling  dentin. 

The  enamel  is  a  delicate  pink,  which  on  fusing  assumes 
varying  shades  ranging  from  almost  imperceptible  pink  to 
a  pinkish  purple,  depending  on  the  thickness  of  the  layer  and 
the  amount  of  heat  applied. 

The  body  supplies  the  necessary  bulk  and  contour  to  the 
case,  and  is  usually  applied  and  fused  two  times.  The  enamel 
supplies  the  color  and  is  fused  once,  although  at  times  two 
applications  are  necessary. 

PREPARATION   OF   THE   BODY 

As  a  preliminary  requirement  in  successful  porcelain 
work  the  strictest  care  as  to  cleanliness  must  be  observed. 
This  includes  clean  hands,  instruments,  materials  and  a  room 
free  from  dust. 

About  one-half  the  contents  of  the  box  of  body  is  placed 
upon  a  flat  glass  or  porcelain  slab  four  inches  square,  or  even 
larger.  With  a  drop  tube  sufficient  distilled  water  is  added 
to  the  powder  to  make  a  medium  plastic  mass. 

The  specific  gravity  of  titanium  oxid  is  4.2;  of  silex,  2.66; 
and  of  kaolin,  2.6.  It  is  apparent  that  in  a  thinly-fluid  mix 
of  body  the  coloring  matter  will  gravitate  below  the  other 
ingredients  if  much  time  elapses  before  taking  up  the  surplus 
moisture.  While  the  quality  of  such  mass  when  fused  may  not 


CONTINUOUS    GUM    DENTURES  609 

be  impaired  it  will  not  be  of  exactly  uniform  color.  To  avoid 
separation  of  the  constituents  mentioned  the  pasty  mass 
should  be  thoroughly  spatulated  and  the  excess  moisture  ab- 
sorbed by  immediately  pressing  a  clean  linen  towel  or  napkin 
over  it. 

APPLICATION  OF  THE  BODY  TO  THE  TEETH  AND  BASEPLATE 

With  a  moderately  broad  spatula  the  body  is  applied  to 
the  lingual  surfaces  of  the  teeth,  and  vibrated  to  i)osition  by 


drawing  a  knurled   instrument   against  the   side   or  back  of 
the  baseplate. 

The  skeh>ton  denture  should  be  held  l)y  i)iacing  the  tinnnli 
against  the  iieripheral  rim  or  within  the  maxillary  portion  of 
the  basei^late  and  the  index  linger  on  the  occlusal  surfaces 
of  the  teeth.  Now,  by  applying  the  middle  finger  against  the 
buccal  surfaces  of  the  teeth  and  extensions  and  holding  the 
baseplate  edgewise  the  body  will  be  prevented  from  dropping 
through  the  open  spaces.  The  excess  moisture  which  is  forced 
out  by  the  settling  of  the  granules  together  is  taken  up  with 


610  CONTINUOUS    GUM    DENTURES 

tlie  napkin  and  anotlicr  mass  oi"  ))ody  applied  in  liko  manner 
until  the  greater  bulk  of  lingual  contour  re(piired  is  developed. 
It  will  l)e  found  most  convenient  to  apply  tlie  bulk  of 
body  to  the  lingual  space  in  three  sections;  first,  from  the 
cusjjid  to  the  tuberosity  on  one  side,  vil)rating  and  absorbing 
the  moisture;  second,  from  cuspid  to  cuspid  ineisally;  third, 
from  cuspid  to  tuberosity  on  the  opposite  side.  Each  addi- 
tion as  it  is  applied  and  vibrated  to  place  should  be  relieved 
of  the  surface  moisture.  In  dentures  requiring  excessive 
restoration,    it    sometimes    becomes    necessarv    to    further 


CONBEXSING    THE   BODY   WITH   CARVING   TOOL 

eliminate  the  moisture  by  passing  the  case  a  few  times 
rai3idly  through  the  Bunsen  flame,  to  prevent  the  flowing  of 
the  adapted  body  while  vibrating  subsequent  additions  to 
place.  Should  further  additions  of  body  to  areas  which  have 
been  rendered  comparatively  dry,  be  necessary,  such  areas 
should  be  moistened  before  making  the  adBitiou,  so  that  the 
two  will  intimately  unite.  When  this  precaution  is  neglected 
the  comparatively  dry  body  will  absorb  the  moisture  from 
the  mass  last  added  so  rapidly  that  the  latter  cannot  be  vi- 
brated into  a  dense,  compact  state. 

The  lingual  contour  is  developed  roughly  to  approximately 
the  required  thickness  of  the  finished  case,  as  are  the  laliial 


CONTINUOUS    GUM    DENTURES 


and  buccal  surfaces  also.  C*are  should  be  taken  to  avoid  ex- 
cess of  material  in  any  area,  for  if  present  in  excess,  removal 
by  grinding  would  be  necessary,  while  any  deficiency  may  be 
corrected  in  the  second  application  of  the  body. 


[<)X   BEFORE   BAKING 


Tlic  denture  should  be  brushed  free  from  all  particles  of 
the  body  that  may  be  lodged  upon  the  platinum  baseplate  or 
the  teeth  where  not  actually  required,  as  during  fusion  they 
will  become  firmly  attached  to  either  platinum  or  teeth  and 
must  subsequently  be  removed  with  discs. 

Special  care  should  be  given  to  the  exposed  jiortion  of 
the  teeth  to  see  that  proper  gum  curvature  is  outlined.     Dr. 


THE     CASE     READY     FOR     FIRST     BAKIXd.         CON- 

TIXIIOCS    GUM    BODY    DIVIDED    WITH    THIN 

BL.VDE   INSTRUMENT 

L.  P.  Haskell  recommends  for  this  purpose  an  ordinary  quill 
toothpick  sharpened  to  a  neat,  smooth  blade-like  point.  A 
delicate  spatula  will  answer  the  same  purpose.  This  step  is 
followed  by  applying  a  delicately-pointed  camel 's-hair  brush. 


612  CONTINUOUS    GUM    DENTURKS 

moistened  first,  afterward  drying  and  removing  every  particle 
of  body  not  required  from  the  gingival  curvatures. 

Since  porcelain  contracts  from  one-sixth  to  one-fifth  its 
bulk  in  vitrifying  when  applied  in  the  manner  described,  unless 
preventive  measures  are  used  the  teeth  are  liable  to  be 
warped  out  of  i)osition  from  the  contraction  of  the  material 
between  and  around  the  root  extensions.  To  obviate  this  diffi- 
culty a  thin  spatula  should  be  passed  through  the  body  to  the 
baseplate  on  both  external  and  vault  surfaces.  Each  tooth 
previously  fixed  by  its  pin  to  the  truss  or  stay  wire  thus  be- 
comes a  fixed  center  toward  which  the  body  composing  that 
section  will  contract. 

The  case  should  finally  he  inspected  to  see  that  all  sur- 
faces are  free  from  excess  material  before  introducing  in  the 
furnace. 

SUPPORTING   CONTINUOUS   GUM   CASES   WHILE   FUSING 

To  obviate  danger  of  war})age  of  the  denture  during 
baking,  it  must  be  supported  at  widely  divergent  points.  One 
of  the  most  convenient  methods  consists  in  bending  a  16-gauge 
platinum  wire  in  the  form  of  a  V,  bending  the  angled  end  and 


the  two  terminals  upward  so  as  to  form  three  legs  of  sufficient 
height  to  raise  the  denture  clear  of  the  muifle  slab.  The  two 
terminals  support  the  case  at  the  tuberosities,  and  the  angular 
•  leg  anteriorly.  These  three  points  of  contact  give  uniform 
support  to  the  case  at  all  times  and  effectually  prevent  warp- 
age. 

This  form  of  support  is  also  of  advantage  because  it  does 
not  absorb  the  radiated  heat  as  does  a  support  composed  of 
fibre  asbestos  and  investment  material  commonly  employed. 
In  case  a  support  of  the  latter  class  is  used  it  should  be  re- 
duced to  the  smallest  possible  dimensions  consistent  with 
strength. 


CONTINUOUS    GUM     DENTURES 

PORCELAIN  FURNACES 


Electric  furnaces  of  various  types  are  almost  universally 
used  at  the  jn-esent  time  for  the  fusing  of  porcelain  in  pros- 
thetic procedures.     The  Custer  and  the  Hammond  represent 


DENTURE    IX   rOSITIOX.      ELECTRIC    FURNACE    (CUSTER   TYPE) 

two  of  the  most  serviceable  forms,  although  there  are  others 
almost,  if  not  quite,  equally  as  dependable. 

The  principle  involved  in  the  generation  of  heat  depends 
upon  the  resistance  offered  by  a  fine  platinum  wire  to  the 
passage  of  a  current  of  electricity.  When  a  110-v.  current  of 
low  amperage  is  passed  through  a  28-gauge  wire  the  resist- 


614  CONTINUOUS    GUM     DIONTUKKS 

ance  ofiVrcd  to  the  passage  ol'  the  current  is  manifested  by 
the  wire  becoming  heated  to  high  temperature  of  varying  de- 
gi'ees,  depending  on  the  length  of  wire  and  the  time  of  current 
flow. 

When  a  <'(in(Uictor  oft'ers  resistance  to  the  passage  of  a 
current  to  such  an  extent  that  lieat  is  manifested  the  voltage 
of  the  current  is  reduced.  By  interposing  outside  resistance, 
as  a  rlieostat  in  wliicli  the  resistance  can  he  graduallv  reduced 


or  entirely  cut  out,  the  amount  of  heat  generated  within  the 
furnace  is  easily  controlled.  This  is  an  important  advantage 
in  the  fusing  of  porcelain,  for  if  heated  too  rapidly,  bulky 
pieces  contract  unevenly,  while  the  quality  of  the  fused  product 
is  impaired. 

Time  is  a  most  important  factor  in  the  fusing  of  porce- 
lain. Practically  all  of  the  high-fusing  bodies,  with  the  excep- 
tion of  tooth  bodies,  can  be  fused  under  2,000  deg.  F.  if  srab- 
jected  to  long  continued  heat.  The  quality  of  porcelain  so 
fused  is  denser  and  its  color  better  than  when  subjected  to 


CONTINUOUS    GUM    DENTURES  615 

rapid  fnsiou.  However,  very  satisfactory  results  may  be 
secured  hy  adoi:)ting'  the  plan  of  fusing  at  a  temperature  about 
midway  l)etween  the  lowest  possible  point  of  vitrification  and 
that  required  for  the  shortest  time  for  the  particular  body 
used. 

FIRST  BAKING  OF  THE  CONTINUOUS  GUM  CASE 

The  case  is  now  introduced  into  the  furnace,  teeth  upward, 
and  placed  on  its  sup])ort.  The  latter,  whether  of  wire,  as 
suggested,  or  composed  of  investment  materials,  should  rest 
on  a  fire-clay  slab  to  afford  protection  to  the  slightly  imbedded 
fiirnace  wires.  This  is  necessary  to  obviate  short  circuiting  of 
the  current,  and  also  to  prevent  any  small  flakes  of  porcelain 
which  might  become  detached  from  falling  to  the  furnace  floor 
and  there  fusing  to  the  fire-clay  lining,  or  over  the  nearly- 
exposed  wires. 

The  muffle  is  closed,  the  rheostat  arm  set  on  the  first  but- 
ton and  allowed  to  remain  there  a  sufficient  time  to  expel  all 
moisture.  This  usually  requires  from  8  to  10  minutes.  If 
this  step  is  crowded  too  rapidly,  the  body  will  flake  off  as  a 
result  of  the  sudden  generation  of  steam  within  the  mass. 

Several  methods  are  in  vogue  in  the  baking  of  porcelain, 
any  one  of  which  will  give  good  results  if  carefully  carried 
out.  The  following  method,  and  one  preferred  by  the  writer, 
is  to  gradually  increase  the  temperature  in  uniform  steps  as 
follows : 

When  the  moisture  has  lieen  expelled,  which  can  readily 
be  seen  by  the  chalk.v  appearance  of  the  case,  the  rheostat  arm 
is  moved  from  first  to  second  button,  where  it  is  allowed  to 
remain  until  the  maximum  heat  of  that  section  is  developed. 
This  usually  retpiires  from  15  to  20  minutes.  The  arm  is  now 
moved  on,  allowing  five-minute  interval  between  each  change. 
In  extra-lmlky  cases  the  interval  may  be  safely  extended  one 
or  two  minutes  longer. 

With  a  new  or  strange  furnace,  preliminary  tests  should 
always  be  made  to  determine  the  length  of  time  required,  and 
the  particular  button  at  which  fusion  will  occur.  The  time 
of  fusion  will  vary  somewhat  with  the  intensity  of  the  current 
and  various  other  conditions.  If  in  a  position  where  a  strong 
di'aft  of  air  strikes  the  furnace  fusion  is  retarded. 

The  liody  should  not  l)e  glazed  during  the  first  leaking,  but 
carried  to  the  point  of  fusing  the  most  fusible  ingredients,  yet 
stopped  before  the  granular  surface  is  entirely  lost.  This 
stage  is  called  "biscuit  bake."    It  presents  a  semi-granular, 


616  CONTINUOUS    GUiM    UFINTURKS 

yet  partially  ulazcd  aiii)paran('e,  while  the  ])(iicclain  is  dense 
and  darkened. 

When  tlie  fusing  stage  is  reached  the  interior  of  the  fur- 
nace and  contents  present  a  bright  red  appearance,  so  that  it 
is  sometimes  difficult  at  first  to  distinguish  the  outlines  of 
the  case.  By  carefully  viewing  the  Imccal  surfaces  of  the 
denture  in  line  with  the  back  of  the  furnace,  the  roughly 
granular  surface  can  be  seen  to  gradually  disappear.  The 
fusion  should  be  stopped  at  this  stage  by  reversing  the  rheo- 
stat arm,  opening  the  switch  and  the  case  allowed  to  cool.  If 
removed  and  cooled  suddeul}%  fracture  of  the  porcelain  is 
almost  certain  to  occur. 

SECOND  BAKING 

The  gum  body  should  now  be  freshly  spatulated,  adding 
water  and  absorbing  it  as  previously  described.  The  case 
is  dipped  in  cold  water,  the  surplus  shaken  out,  fresh  body  ap- 
plied to  the  fissures  purposely  formed  before  the  first  baking 
and  all  others  that  may  have  developed  in  any  location  from 
contraction  in  baking.  The  body  should  be  actiially  com- 
pressed in  these  fissures  when  possible  to  reduce  to  the  mini- 
mum the  slightly  greater  contraction  that  must  occur  over 
these  areas  than  will  be  noticeable  where  the  freshly  added 
material  is  thinner. 

The  case  should  now  be  developed  to  full  contour  on  all 
surfaces  and  the  labial  and  buccal  areas  tested  with  the  con- 
tour matrix  previously  formed.  If  deficient,  more  body  should 
be  added,  and  if  too  full  the  amount  reduced  as  required. 

Palatine  rug,-?  should  be  developed  somewhat  stronger 
than  the  natural  marking,  as  some  detail  will  be  lost  in  fusing. 

Again,  all  surplus  body  must  be  carefully  brushed  from 
the  teeth  and  baseplate,  the  moisture  expelled,  and  the  case 
returned  to  the  furnace  for  the  second  baking.  This  step 
is  carried  out  as  before,  except  that  less  time  is  required 
on  first  button — usually  about  10  minutes,  and  the  fusion 
stopped  at  the  semi-granular  stage.  Since  time  of  exposure 
to  heat  is  an  important  factor  in  fusing  porcelain  care  must 
be  taken  not  to  over-fuse  the  case. 

In  the  second  baking  the  body  last  applied  is  not  alone 
affected.  That  first  fused  is  also  advanced  from  the  biscuit 
to  the  glazed  stage.  It  also  contracts  to  a  very  slight  extent, 
although  the  greatest  contraction  has  previously  occurred  in 
the  first  fusing. 


CONTINUOUS    GUM     DENTURES  617 

\\'Ir'11  the  seeuud  appliccitioii  of  body  lias  been  biscuited, 
fusion  is  stopped  as  in  the  first  halving  and  the  case  allowed 
to  cool,  when  it  is  ready  for  the  tliird  bake. 

PREPARATION   OF  THE   CASE   FOR  THE   THIRD   BAKING 

The  case  should  now  be  thoroughly  inspected  for  fissures 
that  may  have  formed  during  the  last  baking.  These  usually 
are  found  at  the  junction  of  the  body  with  the  lingual  surfaces 
of  the  teeth,  and  around  the  periphery  of  the  base,  although 
they  may  occur  in  any  location.  When  not  extensive  they  may 
be  filled  with  another  mix  of  the  gum  body  and  the  case  enam- 
eled. The  overlying  enamel,  although  not  requiring  a  tem- 
l)erature  for  fusion  sufficiently  high  to  fuse  the  body  last 
added,  will  intermingle  and  unite  with  it  to  form  a  compact 
mass. 

APPLICATION  OF  THE  GUM  ENAMEL 

The  gum  enamel  is  now  mixed  with  water,  spatulated, 
and  the  surplus  moisture  absorbed  as  in  the  preparation  of 
the  body.  It  is  applied  to  the  case  in  a  thin  uniform  layer 
about  1-32  of  an  inch  thick.  Since  slight  variation  in  shade 
of  the  pink  enamel  is  desirable  in  the  finished  case  this  et¥ect 
may  be  produced  by  varying  the  thickness  of  the  layer  of 
enamel  as  it  is  api^iied.  Care  sliould  be  taken  to  distribute 
it  uniformly  over  the  rngje  and  avoid  tilling  in  the  depressions 
between  the  ridges,  the  tendency  being  for  it  to  settle  into 
depressed  areas.  By  pressure  and  burnishing,  the  gum 
settle  into  depressed  areas.  By  pressure  and  burnishing,  the 
gum  enamel  while  slightly  moist  can  be  distrilnited  and  con- 
densed so  that  when  fused  it  will  display  a  very  lif elite  color. 
Since  it  is  almost  transparent  if  not  applied  in  sufficient  thick- 
ness, the  enamel  when  fused  will  frequently  present  an  an- 
ipmic  and  uusiglitly  appearance.  On  the  other  hand,  if  applied 
too  tliickly,  the  color  will  be  abnormally  dark. 

Particular  attention  should  be  given  the  gum  festoons  to 
have  them  of  proi)er  curvature  and  distinctly  developed. 
Every  particle  of  surplus  should  be  swept  clear  of  exposed 
tooth  surfaces,  the  baseplate,  and  from  the  lingual,  labial  and 
buccal  embrasures,  where  its  presence  as  a  pigment  would 
prove  unsightly. 

Briefly  summed  up,  the  teeth  should  stand  out  clean  and 
prominent,  the  gum  festoons  and  other  surface  markings 
should  be  sharply,  or  at  least  plainly,  defined,  and  the  base- 
plate free  from  all  adherent  particles. 


618  CONTINUOI'S    (!I'M     DIONTL'KRS 

The  moi.sluic  is  now  giadually  evaporated  by  passing 
the  case  througli  a  current  of  heated  air  above  a  Bunsen 
flame,  in  preference  to  placing  in  the  furnace  to  dry,  so  that 
if  any  of  the  gum  enamel  Hakes  off  in  drying  it  may  l)e  cor- 
rected before  halving. 

FUSING  THE   ENAMEL 

The  denture  is  now  introduced  into  the  furnace  and  lieat 
applied  as  before.  Gum  enamel  fuses  at  a  considerahly  lower 
temperature  than  gum  hody,  so  wlien  the  furnace  becomes 
well  heated  the  case  shoiild  lie  watched  very  closely  to  avoid 
overfusing  and  bleaching  the  color. 

The  enamel  should  be  perfectly  glazed  so  that  it  may 
easily  be  kept  clean,  will  look  well,  and  not  prove  irritating 
to  the  mucous  tissues  as  a  result  of  roughened  surfaces. 

Being  able  to  distinguish  the  outlines  of  the  denture  when 
in  the  furnace  and  highly  heated,  and  to  determine  the  in- 
stant when  the  enamel  is  perfectly  glazed,  is  one  of  the  es- 


sential points  in  porcelain  technic,  and  comes  only  with  ex- 
l^erience  and  careful  observation. 

When  fused,  the  current  is  shut  otT,  the  furnace  opened, 
and  the  case  examined  to  see  that  glazing  has  been  accom- 
plished. If  satisfactory,  the  furnace  is  closed  and  the  denture 
allowed  to  remain  within  until  perfectly  cold.  Sudden  chill- 
ing or  drafts  of  cold  air  striking  the  porcelain  when  heated 
will  almost  certainly  check  it,  sometimes  in  a  very  unsightly 
manner. 


CONTINUOUS    GUM    DENTURES  619 

FINISHING  THE  DENTURE 

The  enamel  surfaces,  if  properly  fused,  require  no  fin- 
ishing. The  peripheral  margins,  palatine  vault  of  the  platinum 
base,  and  the  lingual  surface  of  the  doubler  are  first  polished 
as  in  gold  denture  construction  with  felt  wheels  and  pumice 
stone,  following  with  the  finer  j^owders. 

The  fact  sliould  be  kept  in  mind  that  when  porcelain  bod- 
ies are  brought  to  a  state  of  fusion,  continued  heat,  even 
though  the  tem]X'rature  is  not  elevated,  will  gradually  rendei- 


LAlllAI.    VIEW    OK    FIN'ISHEI)    IlEXTrRE 


them  glasslike,  friable,  porous,  l)leach  the  color,  and  render 
them  weak  and  devoid  of  usefulness  for  prosthetic  restora- 
tions. Much  better  and  more  certain  results,  therefore,  can  be 
attained  by  subjecting  the  case  to  only  three  bakings — two 
for  the  body  and  one  for  the  enamel — than  are  possible  when 
a  greater  numl^er  of  bakings  are  required. 

SPECIAL  USES  OF  PORCELAIN 

Oftentimes  in  the  construction  of  dentures  for  partial 
cases  some  of  the  spaces  to  be  supplied  with  teeth  are  in  a 
conspicuous  position.  When  but  slight  absorption  of  the 
ridge  has  occurred,  plain  teeth  may  be  neatly  fitted  against 
the  natural  tissues  in  such  manner  as  to  escape  detection. 
This  may  be  done  by  first  grinding  the  ridge  lap  of  each  tooth 
to  conform  to  the  irregularities  of  the  ridge,  and  afterward 
paring  away  on  the  cast  the  area  on  which  it  rests.  This  step 
advances  the  teeth  slightly  beyond  the  palatine  and  border 
surfaces  of  the  baseplate,  so  that  with  use  they  become 
slightly  imbedded  in  the  tissues  and  thus  present  about  the 
same  appearance  as  do  natural  teeth  surrounded  with  their 
gingivae. 

INTERSTITIAL  BLOCKS   OF   PORCELAIN 

When  two  or  more  contiguous  teeth  are  missing  and  they 
are  replaced  by  plain  teeth  without  giim  restoration,  it  is  fre- 


020  CONTINUOUS    GUM    DENTURES 

queiitl}  (lifliciilt  to  obviate  tlie  display  of  vulcanite  in  the  em- 
brasures of  the  artiticial  teeth. 

Recently  there  has  been  placed  on  the  market  Fogg's  in- 
terstitial porcelain  blocks,  which,  when  properly  applied,  over- 
come the  difficnlty  mentioned.     These  pieces  of  porcelain  are 


i  k  k  k  k  i  k 


UkkkU. 


wedge-shape  in  form  and  slightly  concaved  on  their  mesial 
and  distal  areas  to  embrace  the  proximating  surfaces  of  the 
teeth.  Their  exposed  surfaces  are  overlaid  with  pink  gum 
enamel. 

By  selecting  blocks  of  suitable  length  and  grinding  their 
proximating  surfaces,  as  well  as  those  of  the  teeth,  these 
points  may  be  so  nicely  adjusted  that  they  have  the  appear- 


^i^^P 


ance  of  natural  gum  tissue  in  the  embrasures.  They  are 
ground  and  fitted  in  position  before  flasking  the  ease,  invested 
as  though  a  part  of  the  teeth,  and  become  firmly  attached  by 
means  of  the  flowing  of  the  vulcanite  in  closing  the  packed 
flask. 

GUM   SECTIONS 

Gum  section  teetli,  either  single  or  in  blocks,  can  often  be 
used  to  advantage  in  partial  cases,  particularly  when  border 
absorption  is  marked. 

By  grinding  the  margins  of  the  block  to  a  thin  edge  where 
it  joins  the  gum  tissue,  very  natural  restoration  of  the  lost 
gum  tissue  can  be  accomplished.  The  block  should  be  reduced 
at  the  expense  of  the  lingual  or  border  side,  since  if  reduced 
from  the  labial  or  buccal  margins  the  pink  enameled  surface 


CONTINUOUS    GUM    DENTURES 


is  destroyed  and  a  liglit  colored  line  of  demarcation  shows  at 
the  junction  of  the  block  with  the  soft  tissues. 

Gum  section  teeth  are  used  to  a  limited  extent  only,  at  the 
present  time,  in  full  cases  because  of  the  difficulty  in  develop- 


ilM  BLOrK  OF  THREE  TEETH 


iug  anatomic  relations.  Oftentimes  when  care  is  used  in  con- 
structive steps  and  the  condyle  path  pitch  is  not  excessively 
steep,  most  esthetic  results  may  be  secured  with  gum  section 
teeth  combined   with   vulcanite  or  irold  and  vulcanite  bases. 


.IDINTS    CROUND 


622  CONTINUOUS    OVM    DKNTUUES 

They  are  very  useful  in  i)artial  cases  in  tlie  repliiccineiit  of 
teeth  in  conspicuous  positions. 

It  is  sometimes  difificult  to  secure  porcelain  sections  Tor 
special  cases  other  than  the  usual  three-tootli  anterior  and 
two-tootli  posterior  stoclv  blocks.  Stoclv  blocks  are  frequently 
applicable  when  the  number  of  teeth  thej'  include  corresponds 
to,  or  is  greater  than,  the  number  of  teeth  to  lie  replaced  in 
the  space,  the  extra  teeth  being  easily  cut  away,  hut  unfortu- 
nately the  loss  of  teeth  does  not  occur  with  regularity.  V\n- 
example,  two  centrals  and  a  lateral  may  be  missing,  or  a 
cuspid  and  two  bicuspids.  In  these  and  many  other  cases, 
stock  blocks  will  not  fulfill  the  requirements  without  the  use 
of  two  l)Iocks  and  the  grinding  of  a  joint. 

CONSTRUCTION  OF  GUM  BLOCKS  FOR  SPECIAL  CASES 

Various  methods  have  been  suggested  for  baking  single 
blocks  to  meet  the  requirements  of  unusual  cases,  but  because 
of  the  friability  of  blocks  so  formed,  few  undertake  their  con- 
struction. Dr.  Walter  M.  Bartlett  of  St.  Louis  has  produced 
some  very  artistic  work  in  this  line,  and  by  a  comparatively 
simple  method  of  teclmic.  TTis  method  is  practically  as  fol- 
lows: 

An  impression  is  secured  from  which  a  plaster  cast  is 
derived.     Plain  vulcanite  or  ordinary  long  pin  facings  are 


TWO  ri.Aix  Ti:i:i'ii  ahapteh  to 

PLATINUM    FOIL  ru\  EitED    CAST 

BEADY     FOB     AI'PLICATION      OF 

GUM   BODY 


selected  and  ground,  when  necessary,  to  bring  them  in  proper 
alignment  in  the  usual  manner.  The  teeth  are  now  removed 
and  a  piece  of  platinum  foil  is  burnished  to  the  cast  over  the 
area  to  be  covered  by  the  block.  The  foil  base  should  be  so 
formed  as  to  be  easily  released  without  distortion.  When 
properly  adapted  and  trimmed  to  suitable  outline,  it  is  re- 
tained on  the  cast  uniil  the  model  block  is  formed. 


CONTINUOUS    GUM    DENTURES  623 

The  teeth  are  now  roturueil  to  the  cast  aud  wax  flowed 
between  them  and  the  foil  to  hold  them  in  position.  The 
future  block  is  now  modeled  in  wax  to  the  exact  outline  de- 
sired, and  when  hardened,  the  teeth,  wax  and  foil  are  removed 
as  one  piece.  Care  should  be  taken  to  avoid  covering  the 
pins  of  the  teeth  with  the  wax,  since  in  introducing  the  porce- 
lain paste  it  will  fill  all  spaces  caused  by  the  removal  of  the 
wax,  and  the  pins  would  thus  be  obscured. 

The  block  is  now  invested,  pins  and  border  side  down,  in 
tenax.  The  investment  should  be  as  small  as  possible  to  be 
consistent  with  strength.  When  set,  the  wax  is  thoroughlj' 
removed  with  hot  water,  and  continuous  gum  body,  or  the 
regular  high  fusing  crown  and  bridge  porcelain,  is  filled  into 
the  space  between  the  foil  aud  the  teeth.  The  gum  is  now 
carved  to  tlie  desired  contour  and  the  entire  case  carefully 
dried,  when  it  is  ready  for  fusing. 

In  simple  cases  one  application  and  baking  of  the  body 
will  be  all  that  is  required,  the  slight  shrinkage  which  occurs 
being  compensated  for  and  covered  over  by  the  layer  of 
enamel  which  follows. 

When  fused,  if  much  contraction  of  tlie  l)ody  has  oc- 
curred, a  second  application  should  be  made  and  fused,  fol- 
lowed by  the  application  and  fusing  of  the  gum  enamel. 

By  scraiaing  the  cast  slightly  around  the  periphery  of  the 
gum  block,  so  that  the  latter  may  fit  the  tissues  closely,  and 


CASE        BAKED.  LABIAL       VIEW. 

BLOCK    CONSTRUCTED  FOR    SPECIAL 

CASE.       (DR.     G.     W.     SCHWARTZ) 


l)y  l)riiiging  the  body  and  enamel  to  a  gradual  rather  than  an 
abrupt  termination  around  the  margins,  the  block  when  fitted 
in  place  in  the  molith  can  be  scarcely  distinguished  from  the 
natural  teeth  aiid  tissues. 

The  platinum  foil  is  now  peeled  off  and  the  sharp  margins 
of  the  periphery  removed  with  fine  discs,  when  the  l)lock  is 
readv  for  iise. 


CONTINUOUS    GUM    DENTURES 


Another  luctliod  cuiisists  in  swaging  a  thin  phite  of  plat- 
inum in  the  form  of  a  saddle,  to  cover  the  ridge  and  serve  as 
a  foundation  for  the  liaek  of  the  gum  portion.  To  this  saddle, 
long   pin   facings    are   soldered    and    addilional    attachments 


I-LATINLM     BASE     WITH     UlNli     PIN 

TEETH    ATTACHED    FOIt    BE<:EI'TIOX 

OP    PORCELAIN    BODY 


added  for  vulcanite  anchorage,  when  advisable.  The  porce- 
lain is  applied  and  baked  as  in  the  ]n-evious  ease.  By  this 
method  the  platinum  is  not  removed,  liut  becomes  a  part  of 
the  section. 


C  H  A  P  T  E  I{     X  X  ^'  1 1 

CROWN  WORK 
PRELIMINARY  CONSIDERATIONS 

When  tlirongh  accident,  or  as  the  result  of  caries,  the 
crown  of  a  natural  tooth  has  been  impaired  so  that  operative 
procedures  will  not  fully  restore  it  to  usefulness,  an  artificial 
crown,  when  conditions  are  favorable,  can  be  constructed  to 
replace  it.  Oftentimes  the  perfectly  formed  natural  crown 
of  a  healthy  tooth  is  reduced  in  size,  or  entirely  removed,  and 
an  artificial  siibstitutr"  placed  over  it  or  on  the  root,  to  serve  as 
an  abutment  or  jjier  for  a  bridge. 

Such  a  i)rocedure,  when  necessary,  is  considered  good 
practice  and  justitiable  in  well-selected  cases,  the  benefits  in 
improved  masticatory  function  and  esthetic  appearance  re- 
sulting from  the  replacement  of  missing  teeth,  more  than  com- 
pensating for  the  sacrifice  of  the  natural  tooth  crown. 

The  successful  crowning  of  teeth  requires  a  thorough 
knowledge  of  several  correlated  subjects,  viz.,  histological 
and  physiological  structures  of  the  teeth  and  tissues  involved; 
oral  pathological  conditions;  therapeutic  methods  of  treat- 
ment of  diseased  conditions ;  anatomatic  and  esthetic  forms  of 
the  teeth;  hygienic  requirements  of  crowns;  technical  pro- 
cedures. 

STRUCTURES   OF  THE  TEETH   AND   INVESTING 
TISSUES 

The  grosser  structures  of  wliicli  a  tooth  is  composed  are 
as  follows: 

Dentine,  whicli  constitutes  the  larger  portion  of  both 
crown  and  root,  and  within  which  the  pulp  chamber  is  sit- 
uated. 

Enamel,  which  envelops  the  crown  portion  of  dentine,  and 
gives  the  crown  its  anatomatic  form. 

Cementum,  which  covers  the  root  portion  of  dentine,  and 
furnishes  attaclmient  to  the  fibres  of  the  peridental  membrane. 
The  cementum  at  the  cervix  of  a  tooth  comes  to  the  enamel 
margin  and,  in  some  cases,  slightly  overlaps  the  latter. 

The  Peridental  Membrane,  composed  of  fibrous  tissue,  is 
interposed  between  the  root  of  a  tooth  and  its  bony  socket  or 

625 


626  CROWN    WORK 

alveohis.  The  fibres  of  this  meinln-aiie  extond  from  the  socket 
walls  to  the  eementum  covering  the  root,  most  of  them  running 
in  an  apical  direction  as  well  as  tangentally.  The  tooth  is  re- 
tained in  position  princiijally  by  the  network  of  fibres  which 
pass  in  various  directions  through  the  gingival  tissue. 

The  attachment  of  the  peridental  fibres  to  the  tooth  termi- 
nates with  the  gingival  termination  of  the  eementum.  They 
do  not,  however,  terminate  at  the  margin  of  the  alveolus,  but 
continue  on  incisally  or  occlusally  into  tlie  glngivus,  forming 
a  sort  of  fibrous  network  or  band  which  liolds  the  gum  tissues 
firmly  in  contact  with  the  axial  surfaces  of  the  tooth.  By 
passing  through  the  interproximate  spaces  and  across  the  em- 
brasures from  tooth  to  tooth,  they  unite  the  lingual  with  the 
laljial  giugivi  and  buccal,  and  form  what  is  termed  the  dental 
ligament. 

Now,  since  the  eementum  comes  to,  or  slightly  overlaps, 
the  gingival  margin  of  enamel,  and  since  the  peridental  fibres 
are  attached  to  the  extreme  gingival  margin  of  the  eementum, 
extending  outward  from  this  point  and  interlacing  to  form 
tlie  dental  ligament,  in  those  cases  where  the  peripheral  ring 
of  enamel  is  entirely  removed  for  the  reception  of  a  crown 
band,  more  or  less  cutting  and  laceration  of  the  peridental 
fibres  in  this  region  occurs  from  the  use  of  the  cleavers,  files, 
discs  and  stones.  These  severed  fibres  may,  or  may  never, 
again  re-unite  with  the  eementum,  depending  on  the  extent  of 
injury  done,  the  general  tonicity  of  the  parts  and  the  character 
of  the  joint  between  the  crown  band  and  the  root  periphery. 

In  line  with  this  idea,  Di'.  F.  B.  Noyes  in  his  Dental  Histi- 
ology, page  189,  says:  "That  the  tissues  (peridental  mem- 
brane) may  be  re-attached  to  the  surface  of  a  root  is  both 
theoretically  possible  and  clinically  demonstrable,  but  for  it 
to  occiir,  biological  laws  must  be  observed  and  the  conditions 
are  very  difficult  to  control,  especially  with  the  old  methods 
involving  the  excessive  use  of  strong  antiseptics.  It  is  well 
to  remember  that  a  dentist  can  never  cure  a  suppurating 
pocket  along  the  side  of  a  tooth  root,  but  if  the  conditions  can 
be  controlled  the  cells  of  the  tissue  may  form  a  new  layer  of 
eementum,  re-attaching  the  tissues,  and  so  close  the  pocket. 
It  is  a  biological  problem,  not  a  matter  of  drugs,  except  as 
they  are  a  means  of  i^roducing  a  cellular  reaction.  In  view 
of  its  function,  therefore,  the  eementum  becomes  not  the  least 
but  the  most  important  of  the  dental  tissues,  for  no  matter 
how  perfect  the  crown  may  be,  without  firm  attachment  the 
tooth  becomes  useless  and  is  soon  lost." 


CROWN    WORK  627 

One  of  the  gravest  dangers  resulting  from  traumatic  in- 
jury to  the  peridental  fibres  and  their  failure  to  again  re- 
attach themselves  to  the  root,  is  in  the  loss  of  tension  of  the 
dental  ligament  at  or  near  the  site  of  injury.  In  such  cases 
the  formation  of  a  pocket  is  almost  certain  to  occur,  and  into 
this  food  finds  its  way,  is  difficult  to  remove,  decomposes,  and 
pathological  conditions  arise,  which  in  many  cases  from  infec- 
tion eventually  result  in  phagedenic  pericemeutitis  or  other 
troubles. 

It  will  thus  1)6  seen  that  while  a  crown  may  restore  the 
function  of  mastication,  accomplish  desired  esthetic  results, 
and,  by  wedging,  maintain  proximate  contact  which  has  been 
lost  i^revious  to  its  application,  yet  pathological  conditions 
may  be  induced  througli  imi)roper  technic  and  an  imperfectly 
adapted  band. 

^lany  prosthetists,  either  through  carelessness  or  to  avoid 
traumatic  injury  to  the  peridental  membrane,  fail  to  remove 
all  of  the  peripheral  enajnel  ring  from  the  root  when  prepar- 
ing it  for  a  band,  with  the  result  that  the  latter,  when  applied, 
presents  a  shoulder  which  not  only  invites  the  lodgment  of 
food,  but  proves  a  constant  mechanical  irritant  to  the  gingival 
tissues  as  well.  The  greatest  care  should  therefore  be  ob- 
served to  remove  all  of  the  enamel  in  cases  where  indicated, 
and  yet  avoid  excessive  injury  to  the  peridental  membrane 
and  gingival  tissues  in  general. 

PHYSIOLOGICAL    RELATIONS 

The  pulp  of  a  tooth  occupies  tlic  central  chamber,  or  what 
is  termed  the  pulp  chamber  and  root  canal.  It  is  largely  com- 
posed of  embryonal  connective  tissue  in  which  very  few  con- 
nective tissue  fibres  are  present.  It  contains  nerve  filaments 
and  minute  blood  vessels  which  enter  through  the  apical  fora- 
men of  the  root. 

The  primary  function  of  the  pulp  is  a  dentine  builder, 
the  outer  layer  of  columnar  cells,  called  odontoblasts,  receiv- 
ing from  the  blood  and  depositing  from  without,  inward,  the 
calcific  materials  of  which  the  dentine  is  composed.  The  den- 
tinal fibrils,  occupying  the  dentinal  tubuli,  are  the  remnants  of 
the  odontoblastic  c^lls  which  have  become  reduced  in  diameter 
and  withdraw  inward  as  calcific  dentinal  deposit  progresses. 

The  secondary  function  of  the  pulp  is  that  of  a  sensory 
organ,  as  it  is  very  responsive  to  thermal  changes,  to  chemical 
action  on,  and  traumatic  injury  to  the  tooth. 


fi28  CROWN     WORK 

111  tilt'  prc|)ar;iti()ii  ol'  u  vital  tooth  I'or  I  lie  r('cc|i1ion  of 
a  crowu,  the  friction  caused  by  engine  stones  and  iliscs  is 
often  exceedingly  painful,  even  though  the  site  of  the  opera- 
tion is  far  removed  from  the  pulp.  Since  the  dentinal  iibrils 
are  devoid  of  nerve  filaments,  external  irritation  when  notice- 
able, is,  without  doubt,  conveyed  to  the  pnlp  by  molecular  vi- 
bration of  the  contents  of  the  tubuli,  and  the  heat  caused  by 
friction  as  well. 

U.sually  it  is  customary  to  devitalize  a  tooth  before  adapt- 
ing a  shell  crown,  for  two  reasons;  first,  so  as  to  reduce  to 
the  minimum  the  pain  resulting  from  the  use  of  stones  and 
cleaners  in  the  root  preparation,  and  second,  to  avert  possible 
]iathological  conditions  subsequently  arising  from  death  of 
the  pulp,  either  from  the  shock  of  denuding  the  crown  of  its 
enamel,  or  from  thermal  variations. 

When  this  practice  is  resorted  to,  the  pulp  removed,  and 
the  root  apices  perfectly  filled,  it  is  a  most  excellent  procedure. 
The  danger  of  following  this  plan  in  every  case  lies  in  the 
fact  that  frequently  teeth  have  multiple  roots  or  multiple 
canals — more  than  the  normal  number — and  some  of  these 
are  liable  to  be  overlooked  in  the  treatment  and  filling.  Again, 
the  roots  of  teeth  may  be  deformed,  and  the  canals  so  tortuous 
and  minute  that  by  the  most  ]iatient  and  conscientious  effort 
it  is  impossible  to  clear  and  fill  them.  These  conditions  are 
frequently  met  with  in  peg-shaped  lateral  incisors,  third 
molars,  and  occasionally  in  the  lower  anterior  as  well  as  other 
teeth.  Should  indications  point  to  abnormalities,  the  X-ray 
will  disclose  their  nature,  and  the  prosthetist  can  then  govern 
himself  accordingly.  When  pathological  conditions  do  not 
require  treatment  or  devitalization,  the  safer  plan  in  these 
abnormal  cases  is  to  crown  the  tooth  without  removing  the 
pulp,  even  though  the  tooth  or  root  preiiaration  may  occasion 
some  pain. 

ORAL  PATHOLOGICAL  CONDITIONS 

The  prosthetist  should  be  able  to  recognize  any  abnormal 
or  pathological  conditions  present  in  the  mouth,  and  be  famil- 
iar with  recognized  and  proven  methods  of  treatment. 

The  most  frequently  occurring  abnormal  conditions  which 
]iresent  in  practice  are  cases  in  which  one  or  more  of  the  teeth 
liave  lost  their  crowns,  or  the  teeth  themselves  are  missing. 
Stieb  loss,  if  of  long  standing — usually  the  result  of  a  substi- 
tute crown  not  having  been  applied — almost  always  entails 
the  loss  of  proximate  contact  of  some,  if  not  all,  of  the  remain- 


CROWN    WORK  629 

iug  natural  teeth.  The  spaces  thus  formed  invite  the  hidg- 
ment  and  retention  of  food.  As  stated  elsewhere,  phagedenic 
troubles  have  their  origin  in  such  mouths  under  these  and 
similar  conditions,  and  unless  corrective  measures  are  resorted 
to,  the  loss  of  all  the  teeth  will  sooner  or  later  occur. 

When  the  axial  surfaces  of  the  teeth  in  general  have  not 
suffered  from  caries,  and  proximal  contact  has  been  lost 
through  loss  of  the  crowns  of  one  or  more  teeth,  the  roots  of 
which  are  in  condition  to  carry  substitute  crowns,  contact  may 
frequently  be  restored  between  teeth  considerably  removed 
from  the  space  to  be  supplied,  by  a  slow  wedging  process. 
The  substitute  crowns  should  be  constructed  of  sufficient  di- 
mensions to  maintain  the  space  gained  in  wedging. 

Hyperaemic  or  putrescent  pulps  should  be  removed,  and 
the  root  canals  of  all  pulpless  teeth  rendered  aseptic  and 
their  apices  filled,  before  attempting  the  preparation  of  roots 
for  crowns.  Pus  pockets  and  alveolar  abscesses  connected 
with,  or  located  near,  the  site  of  operation,  must  be  eradicated. 
Inflammation  of  the  gingival  tissues  and  peridental  mem- 
branes shoiild  be  allayed,  and  when  possible,  restored  to 
health,  before  extensive  crowning  operations  are  undertaken. 
In  some  cases  complete  restoration  to  normal  conditions  may 
not  be  effected,  since  the  irritation  occasioned  by  food  wedg- 
ing on  the  tissues  in  unprotected  locations — as  in  the  em- 
brasures and  interproximal  spaces — may  continue  until  af- 
forded protection  by  suitably  formed  and  well  adapted  crowns. 
Special  care  should  be  given  to  the  removal  of  the  excess  ce- 
ment, which  in  setting  is  forced  out  at  the  periphery  of  a 
crown.  When  this  is  not  entirely  removed  inflammatory  con- 
ditions frequently  develop  which  may  result  not  only  in  im- 
mediate discomfort  to  the  patient,  but  later  on  in  the  forma- 
tion of  a  permanent  gingival  pocket. 

The  prosthetist  should  endeavor  ))y  every  possible  means 
to  temporarily  and  permanently  correct  all  pathological  con- 
ditions present,  and  to  so  form  the  substitutes,  of  whatever 
class,  that  they  may  in  no  way  give  rise  to  a  recurrence  of 
diseased  conditions,  or  initiate  others  of  a  different  character. 

THERAPEUTIC    METHODS    OF    TREATMENT    OF 
DISEASED   CONDITIONS 

It  is  taken  for  granted  that  the  student  is  pursuing  the 
study  of,  and  has  access  to,  textbooks  dealing  with  the  therapy 
of  the  teeth  and  oral  tissues.     Therefore  it  is  unnecessarv  to 


t;;!o  CROWN  work 

recount  the  various  methods  of  trcatiuent  and  tlie  many  gen- 
eral agents  employed,  except  wliore  they  arc  of  s]ieeial  interest 
to  the  prosthetist. 

LOCAL  ANESTHETICS 

Local  anaesthetics  in  some  cases  are  invaluable,  as  for 
instance  in  the  removal  of  pulps,  the  excision  of  hypertro- 
phied  gum  tissue,  the  curetting  of  necrosed  process,  the  scaling 
of  roots  in  deep-seated  alveolar  pockets,  and  at  times  in  the 
preparation  of  roots  of  teeth  for  the  reception  of  crowns. 

Solutions  of  cocaiu,  eucain,  novo-cain  and  various  similar 
agents,  either  alone  or  combined  with  other  drugs,  are  used 
for  this  purpose.  Such  agents  may  be  applied  superficially 
or  injected  at  or  near  the  site  of  operation,  in  which  case  the 
peripheral  nerve  endings  are  influenced  by  the  anaesthetic. 
Novo-cain  and  suprarenin  dissolved  in  Ringer's  solution  are 
frequently  employed,  especially  in  conductive  ana'sthesia. 
By  this  method  the  main  nerve  trunk  back  of  the  site  of  opera- 
tion is  anfesthetized,  the  anjesthesia  being  more  or  less  com- 
plete along  the  peripheral  branches  to  the  nerve  endings,  ex- 
cept where  the  tissues  are  also  supplied  with  other  nerve  fila- 
ments coming  from  some  other  than  the  trunk  anaesthetized. 
In  such  case  an  additional  local  injection  at  the  site  of  opera- 
tion is  sometimes  resorted  to,  to  complete  the  ana?sthesia. 

In  the  use  of  antesthetics  of  any  character,  and  particu- 
larly when  used  by  the  injection  method,  extreme  care  should 
be  exercised  in  the  sterilization  of  the  instruments,  a])pliances 
and  the  agent  itself,  and  in  rendering  aseptic  the  tissues  to 
which  the  aniesthetic  is  applied,  or  through  which  the  needle 
is  inserted. 

Unless  scrupulous  care  is  observed  in  removing  the  peri- 
pheral ring  of  enamel  from  the  root  of  a  tooth,  the  adjacent 
tissues  having  been  anfesthetized,  serious  traumatic  injury 
to  the  dental  ligament  and  gingival  fibres  of  the  peridental 
membrane  is  liable  to  occur,  since  the  nerves  are  imresponsive 
and  can  give  no  warning  of  the  extent  of  injury  being  in- 
flicted. Wlien  possible  to  do  so,  the  use  of  anaesthetics  in 
such  operations  should  be  avoided  for  the  reason  stated. 

Low  per  cent  solutions  of  cocain  or  similar  drugs,  com- 
binded  with  pressure,  usually  produce  effective  anaesthesia  in 
removal  of  pulps,  when  the  solution  and  the  unvulcanized  rub- 
ber, by  means  of  which  pressure  is  usually  applied,  can  be 
confined,  as  within  a  four-walled  cavity,  or  one  that  may  be 
so  formed  by  means  of  a  matrix. 


CROWN    WORK  631 

TREATMENT  AFTER   SETTING  A   CROWN 

After  setting  a  crown,  the  excess  cenient  having  been 
removed,  the  tissues  should  be  massaged,  syringed  witii  warm 
normal  salt  solution,  and  where  pain  is  experienced  an  appli- 
cation of  tincture  of  iodine,  or  a  saturated  solution  of  iodine 
in  beechwood  creosote,  should  be  applied  under  the  free  mar- 
gin of  the  gum  around  the  root  crowned.  This  method  of 
treatment  is  frequently  of  value  as  an  aid  in  relieving  tender- 
ness in  the  jjeridental  tissues. 

Hot  water  alone,  when  properly  applied  and  continued  a 
sufficient  time,  will  very  frequently  reduce  inflammation  or 
abort  an  abscess  in  the  incipient  stage.  The  method  is  as  fol- 
lows: 

A  surgical  tank  used  for  irrigation  purposes,  holding  a 
gallon  or  more,  should  be  filled  with  water  heated  to  about 
135  deg.  F.,  or  even  higher  if  the  patient  can  tolerate  it  with- 
out scalding  the  tissues.  A  nozzle  with  a  very  fine  opening 
should  be  applied  to  the  irritating  tube,  the  nozzle  of  the  bulb 
water  syringe  or  a  glass  dropper  tube  with  curved  point  being 
suitable  for  this  purpose,  the  curvature  permitting  the  water 
to  be  directed  against  the  gingivae  in  the  embrasures  and  in- 
terproximate  spaces  of  the  teeth  affected. 

The  patient  should  sit  with  head  inclined  over  the  foun- 
tain cuspidor,  and  usually  with  a  little  instruction  can,  without 
assistance,  irrigate  the  parts  thoroughly.  The  application 
should  be  continued  for  fifteen  or  twenty  minutes  continu- 
ouslj',  the  efficiencv  of  the  method  depending  upon  contraction 
occasioned  by  heat  of  the  arterioles  and  capillaries,  thus  re- 
ducing the  flow  of  blood  to  the  i)arts  and  enaliling  the  tissues 
to  recover  their  normal  tone. 

The  tank  may  require  refilling  once  or  twice  in  severe 
cases,  and  the  stream  of  water  should  be  directed  not  only 
around  the  gingivae  of  the  tooth  affected,  but  along  the  labial 
or  buccal  and  lingual  surfaces  of  the  border  of  all  of  the  teeth, 
so  as  to  control  the  circulation  of  blood  in  the  entire  arch. 
The  writer  has  in  many  instances  effecti;ally  applied  this 
method  of  treatment  for  the  relief  of  conditions  mentioned, 
and  in  various  other  forms  of  painful  troubles  as  well. 

ANATOMIC   AND    ESTHETIC    FORMS    OF   TEETH 

The  anatomic  form  of  an  artificial  crown  is  governed  by 
its  position  in  the  arch,  and  usually  corresponds  with  the  class 
of  crown  carried  by  the  root  which  will  support  it.    Variations 


632  CROWN    WORK 

from  this  rule  occur  at  times,  exam])les  of  wliicli  aie  seen  in 
tlie  following  instances: 

A  lateral  incisor  has  been  lost  and  the  space  it  occupied 
has  been  nearly,  or  quite,  obliterated  by  the  movement  toward 
each  other  of  the  teeth  on  either  side.  In  case  the  cuspid  root 
requires  crowning,  a  wide  lateral  incisor  placed  upon  its  roots 
would  in  all  jM-obability  fill  the  space  and  be  more  in  harmony 
with  tiie  proxinuiting  teeth  than  would  a  cuspid  crown. 

Sometimes  it  becomes  necessary  to  vary  the  form  and 
Ijroi)ortions  of  an  artificial  crown  for  hygienic  reasons,  to 
raise  or  lower,  omit  or  add.  a  cusp  to  meet  occlusal  require- 
ments, or  to  secure  contact  with  proximating  teeth. 

In  many  instances  a  tooth  has  lost  all  or  a  portion  of  its 
crown  long  before  tlic  patient  presents  for  a  substitute.  Fre- 
quently proximate  contact  of  the  remaining  natural  teeth 
has  been  disturbed  by  such  loss.  Before  crowning  the  root, 
the  lost  space  should,  to  as  great  an  extent  as  possible,  be 
regained  by  wedging,  which  in  turn  will  frequently  restore 
knuckling  contact  at  other  points  where  spaces  have  de- 
veloped from  the  movement  toward  each  other  of  the  teeth 
proximating  the  missing  crown.  In  many  instances  the  wedg- 
ing oi)eration  will  not  only  regain  the  lost  space,  but  may, 
with  benefit  to  the  other  teeth,  tighten  up  all  lost  contacts, 
when  this  can  be  done  without  disturbing  the  occlusion.  The 
crown  when  constructed  to  fill  the  space  may,  therefore,  be 
somewhat  greater  in  its  mesio-distal  diameter  than  was  the 
original  one  it  replaces. 

When  the  root  of  a  tooth,  capable  of  can-ying  a  crown,  is 
slightly  out  of  alignment  labio  or  bucco-lingually,  should 
orthodontic  measures  be  deemed  inadvisable  for  bringing  it 
into  position,  an  offset  crown  may  be  constructed,  and  by  skill- 
ful root  preparation  and  assembling  of  the  several  parts,  the 
crown,  although  not  of  anatomic  form,  will  present  a  good 
appearance  and  fulfill  useful  requirements. 

In  the  construction  of  crowns  of  any  class,  variations  in 
form  from  true  anatomic  types  are  frequently  necessary.  The 
usual  conditions  calling  for  modified  forms  are  exceessively 
wide  or  narrow  spaces,  abnormal  occlusal  surfaces  of  the  op- 
posite teeth,  movement  of  the  remaining  teeth  from  their 
normal  position  with  loss  of  contact,  and  various  other 
causes. 

A  study  of  the  axial  surfaces  of  typical  natural  teeth 
should  be  made,  and  a  reproduction  of  these  surfaces  carried 
out  whenever  possible  in  crown  construction.     The  convexity 


CROWN    WORK  633 

of  tl)e  buccal  and  lingual  axial  surfaces  of  the  bicuspids  and 
molars,  aside  from  the  esthetic  value  of  such  forms,  serves  a 
most  useful  purpose.  The  bulging  mid-crown  forms  of  these 
teeth,  together  with  constricted  crevices,  afford  efficient  pro- 
tection to  the  free  margin  of  the  gums  against  the  excursions 
of  food  tliat  may  be  forced  beyond  the  occlusal  surfaces  of 
the  teeth  in  masticatory  effort. 

As  crowns  are  frequently  constriicted,  their  liuccal  and 
lingual  axial  surfaces  are  either  parallel  with  each  other,  or 
converge  from  the  gingivae  occlusally,  thus  preventing  in- 
clined planes  fin-  directing  food  toward,  instead  of  away  from, 
the  gum  margin.  A  crown  so  formed  invites  the  lodgment 
of  food,  the  formation  of  gingival  pockets,  and  infiammatory 
conditions  which  will  eventually  residt  in  loss  of  the  tooth. 

FLARE  OF  THE  AXIAL  SURFACES  OF  BICUSPIDS  AND  MOLARS 

An  examination  of  many  bicuspids  and  molars  with  a 
view  of  determining  the  average  flare  occlusally  of  their  gin- 
gival cones  was  made  as  follows : 

A  strip  of  No.  60  tin  foil  was  cut  al)()ut  l-'A  of  an  inch 
wide,  slightly  curved  to  more  readily  adai)t  it  to  this  portion 


CROWN  OF  ri'PER  FIRST  MOLAR. 
WITH     TINFOIL     HAND     APPLIED 

TO   (ilNClVAI.   CONE 


of  the  tooth.  It  was  then  bent  around  and  burnished  to  the 
gingival  cone  of  the  tooth,  the  shorter,  or  concave,  margin  of 
the  strip  being  applied  gingivally.  The  ends  were  brought 
squarely  together  and  cut  at  the  angles  of  junction.    The  strip 


634 


CROWN    WORK 


was  then  straightened  ont,  one  cud  laid  parallel  with  tlic 
straight  edge  of  a  cardboard,  and  a  line  drawn  along,  and 
parallel  with,  the  opposite  end,  running  toward  and  intersect- 
ing the  margin  of  the  cardboard.  Tlie  angnlar  divergence 
of  llic  ends  was  read  by  means  of  a  pi'otractor.     From  fifty 


MESI.U-    VIEW    IPF    UI'l'ER    FIRST    MOLAR.      TIN'  HITCAI,    \ii;\\    ii|-    1  iM-ii:    1  HIST    Mill, All       TIX- 

FOIL   STRIP    AISOVE  Foil.  STItir   KH.MOMOIi.      SI  Rl'l.L  S  TRIM.MED 

FROM  ENDS  AND  OCCIA'SAI,  M,UtGIN 

to  one  hundred  teeth  of  eacli  class  were  measured  in  this  man- 
ner, the  reading  of  which  are  as  follows : 

Least  Greatest 

Divergence  Divergence  Average 

Deg.  Deg.  Deg. 

Upper  first  bicuspids 21  33  27 

Upper  second  bicuspids.  ..  .       18  32  27.75 

Upper  first  molars 19.-i  31  25.5 

Upper  second  molars 16  28  24 

Lower  first  molars 28  40  32 

Lower  first  bicuspids 24  43  30 

Lower  second  bicuspids ....        20  35  32 

Valuable  assistance  has  been  received  in  this  work  from 
Dr.  J.  F.  Wallace  of  Canton,  Missouri,  who  made  many 
measurements  of  teeth  by  this  method.  His  work,  while 
varying  slightly  from  that  of  the  writer,  coincides  closely, 
personal  equation  accounting  for  the  difference  in  findings. 


CROWN    WORK  635 

CUTTING  MOLAR   AND   BICUSPID   CROWN    BANDS   BY   THE 
CONIC  SYSTEM 

The  piaotical  application  to  orowu  work  of  the  measure- 
ments seen  in  the  table  will  now  be  shown. 

AVhen  a  molar  or  bicuspid  crown  band  is  cut  to  approxi- 
mately the  form  of  the  tin  foil  pattern  produced  as  above 
described,  it  represents,  when  the  ends  are  united,  a  frustum 
of  a  cone  instead  of  a  cylinder,  as  would  be  the  case  when 
the  ends  of  the  band  are  parallel.  The  small  end  of  the  cone 
represents  the  gingival  margin  of  the  band,  while  the  large 
end,  although  excessive  in  peripheral  outline,  represents  the 
occlusal  margin.  Keproduction  of  the  occlusal  cone  to  cor- 
rect form  can  easily  and  quickly  be  accomplished  with  the 
hawkbill  or  Benson  pliers,  using  the  latter  without  exerting 
excessive  force,  and  when  properly  contoured  the  axial  walls 
of  the  band  will  present  a  similar  appearance  to  those  of  the 
natural  tooth.  The  advantages  of  this  method  are  that  the 
band  walls  are  not  reduced  in  thickness  at  any  point  in  con- 
touring, while  proximate  contact  can  be  secured  without  the 
usual  narrowing  of  the  band  in  its  mid-crown,  bucco-lingual 
diameter. 

The  method  of  diverging  the  ends  of  a  crown  band  from 
gingival  to  occlusal,  has  long  been  followed  by  careful  pros- 
thetists  for  reasons  above  given.  A  few  have  even  cut  the 
band  to  represent  the  section  of  a  cone  instead  of  a  cylinder, 
as  is  most  frequently  the  case,  but  no  definite  rule  has  been 
evolved  capable  of  application  to  the  development  of  bicuspid 
and  molar  bands  in  general. 

By  referring  to  the  table  of  measurements  previously 
shown,  it  will  be  seen  that  the  average  flare  of  a  conic  crown 
band  of  an  upper  first  molar  is  25.5  deg.,  while  the  average 
peripheral  gingival  measurement  of  this  class  of  teeth  is 
29.92  m.  m. 

To  cut  a  conic  crown  band  by  this  system  the  only  ap- 
pliance required  aside  from  the  regular  laboratory  equipment 
is  a  pair  of  ordinary  6-inch  dividers,  a  piece  of  cardboard  and 
a  straight  edge.     The  method  is  as  follows: 

Measure  the  prepared  root  with  wire  in  the  usual  manner 
and  cut  the  loop  opposite  the  twist. 

Draw  a  stlaight  perpendicular  line  on  the  cardlioard 
l)arallel  with  and  near  the  edge,  or  the  edge  of  the  card  can 
be  used. 

Mark  iioints  on  line  A  and  B,  314  inches  apart. 

Mark  width  of  band  B— C. 


(136  CROWN    WORK 

Lay  a  piece  of  gold  plate;  from  wiiidi  the  hand  is  to  be  cut 
on  the  line,  the  upper  corner  at  C. 

Set  divider  points  at  A — B,  radius. 
Hold  plate  firmly  on  card  and  descrilx'  arc  B  D. 
Extend  divider  to  reach  from  A  to  C 
Describe   arc   ('   (}. 


/ 

CARDBOARD 

/ 

Lay  root  measurement  slightly  curved  along  arc  B  D  and 
mark  length  of  band  B  E. 

Lay  ruler  edge  on  points  A  and  E  and  draw  A  F. 

B  C  E  H  represents  the  band  which  is  cut  with  the  shears. 
The  band  when  bent  around  and  the  ends  soldered,  in  the 
usual  manner,  represents  the  section  of  a 'cone  instead  of  a 
cylinder,  the  smaller  being  the  gingival  end. 

In  trimming  the  gingival  end  of  the  band  to  correspond 
to  the  gum  festoon,  the  inner  diameter  of  the  band  is  increased 
as  the  gingival  periphery  is  sheared  away,  and  consequently 


CROWN    WORK  637 

is  larger  than  the  root.  This  may  be  corrected  in  two  ways ; 
first,  by  reducing  the  gingival  periphery  with  the  pliers,  and 
second,  by  cutting  the  band  sliglitly  shorter  than  the  wire 
measurement,  when  laying  it  out. 

By  extending  the  line  along  the  straight  edge  to  the 
center.  A,  and  reading  the  included  angle,  it  will  usually  be 
found  to  range  from  22  deg.  to  28  deg.  This  reading,  how- 
ever, is  unnecessary  for  practical  purposes.  The  variations 
noted  in  a  number  of  readings  are  due  to  variations  in  peri- 
pheral root  measurements,  long  measurements  showing 
greater,  and  short  measurements  less,  divergence  of  the  l)and 
ends. 

In  those  cases  where  for  exami)le,  the  space  in  which  the 
crown  is  to  be  placed  has  become  constricted  by  the  leaning 
toward  each  other  of  the  proximating  teeth,  the  contact  points 
of  the  remaining  teeth  in  the  arch  lieing  good,  this  method, 
for  obvious  reasons,  is  not  applicable. 

In  cases  of  normal  or  excessive  width  of  spaces,  it  is  the 
very  best  method  to  follow  in  the  construction  of  two-piece  or 
band  and  swaged  cus])  crowns.  Its  range  of  application  can 
be  extended  to  include  band  and  cast,  cusp,  and  other  varieties 
of  crowns. 

The  band  of  a  crown  cut  to  represent  a  cone,  when  cut 
gingivally  to  correspond  with  the  festooning  of  the  gums, 
is  enlarged  slightly  since  the  smaller  end  of  the  cone  is  cut 
away.  To  compensate  for  such  enlargement,  the  band  can 
be  cut  from  Vo  to  1  m.  m.  shorter  than  the  root  measure- 
ment. If,  when  festooned,  the  band  is  too  small  to  be  driven 
to  i)lace,  it  can  be  stretched  slightly  by  placing  on  a  round 
numdrel  and  tapping  lightly  with  a  riveting  hammer.  When 
too  large,  it  can  be  reduced  with  contouring  pliers. 

Any  wide  crown  band,  as  for  a  molar  or  bicuspid,  can  be 
tightened  gingivally,  and  its  perfect  peripheral  adaptation 
insured,  the  root  having  been  properly  prepared,  when,  after 
fitting  and  axial  contouring  have  been  accomplished,  its 
gingival  margin  is  reduced  as  above  outlined,  after  which  it 
can  be  finally  driven  to  place.  A  gingival  shoulder  on  the 
natural  tooth  or  root  would  preclude  this  plan  of  final  adapta- 
tion. 

Badly  decayed  teeth,  to  which  shell  crowns  are  to  be 
adapted,  should  in  all  eases  have  their  axial  surfaces  restored 
by  means  of  well  anchored  amalgam  fillings  or  alloy  cast- 
ings, placed  before  the  final  preparation  of  the  tooth  or  root 
is  accomplished,  so  as  to  obliterate  all  gingival  shoulders. 


638  CROWN    WORK 

When  a  tiufoil  envelope  is  adapted  to  any  of  the  twelve 
anterior  teeth,  the  ends  of  the  strip  cut  at  their  junction,  and 
the  strip  flattened,  the  two  ends  will  l)e  approximately  parallel, 
and  when  again  united  in  hand  form  would  form  the  section  of 
a  cylinder.  Anatomically;  the  anterior  teeth  represent  wedges 
or  cylinders  flattened  at  one  end  to  form  incisal  edges. 

STRESS 

The  amount  of  stress  and  the  direction  of  its  ap])lication 
are  of  the  greatest  importance  in  crown,  hridge  and  denture 
construction. 

A  crown,  or  a  prosthetic  appliance  of  any  tyi)e,  may  be 
anatomical  in  form,  yet  when  introduced  into  the  mouth  may 
become  displaced,  or  rendered  useless,  tlirough  some  abnormal 
condition  present,  as  elongated  cusps  of  teeth  in  the  opposite 
arch. 

The  sloping  occlusal  surfaces  of  the  various  cusps  of  a 
tooth,  when  brought  into  contact  with  occhiding  surfaces  of 
opi)osite  teeth,  act  as  inclined  planes,  and  tend  to  force  the 
tooth  of  which  they  are  a  part  forward  or  backward,  or  in  or 
out  of  aligTiment,  unless  such  tendency  is  counterluilanced  by 
proximating  teeth  or  by  contact  planes  of  occluding  teeth 
sloping  in  a  contrary  direction. 

The  greatest  care,  therefore,  should  be  observed  in  the 
development  of  cusps  to  so  form  them  that  displacement  from 
undue  force  on  sloping  planes  cannot  occur.  Oftentimes  the 
occlusal  surfaces  of  the  opposite  teeth  must  be  modified  by 
grinding  to  meet  new  occlusal  requirements  arising  from  the 
introduction  of  ])rosthetic  substitutes.  The  use  of  both  single 
and  double  surface  carbon  paper  will  readily  disclose  points 
of  interference  between  occluding  planes  and  cusps,  and  cor- 
rections can  be  made  accordingly. 

In  constructing  a  crown  with  porcelain  facing,  care  should 
lie  observed  to  so  protect  the  incisal  edge  of  the  facing  from 
direct  stress,  either  by  beveling  and  tipping  it  with  gold,  as 
will  hereafter  be  shown,  or  by  avoiding  contact  with  opposing 
teeth,  under  any  and  all  conditions,  otherwise  the  pins  will  be 
sheared  off,  or  the  porcelain  itself  fractured. 

A  number  of  tests  conducted  by  the  writer,  in  which  the 
facings  of  various  manufacturers  were  employed  in  the  con- 
struction of  porcelain  faced  crowns  with  unprotected,  as  well 
as  protected,  tips,  disclosed  the  following:  That  (>0  pounds' 
.stress  will  fracture  the  strongest  facings,  or  shear  off  the  pins, 
while  others  will  become  dislodged  at  a  pressure  of  12  pounds. 


CROWN    WORK  639 

Protected  facings  were  not  affected  l)y  stress  and  remained 
intact  nntil  snfficient  force  was  apiilied  to  bend  the  metal 
structure  wliicli  constituted  the  metal  tip,  after  wliicli,  with 
slight  additional  stress,  they  were  dislodged. 

Gnatho-d}Tiamometer  tests  show  that  the  masticatory 
muscles  can  deliver  a  stress  of  from  20  to  90  pounds  in  the 
incisor,  and  a  much  greater  amount  in  the  bicuspid  and  molar 
region.  The  necessity  for  protecting  facings  from  stress  in 
some  manner  is  therefore  imperative. 

HYGIENIC  REQUIREMENTS  OF  CROWNS 

In  order  that  the  health  of  the  oral  tissues  may  be  main- 
tained, a  crown  should  be  so  constructed  as  not  to  prove  an 
irritant,  either  by  directing  food  to  and  under  the  free  margin 
of  tlio  gums  and  holding  it  there,  or  by  presenting  rougli,  im- 
iinislied  surfaces  to  the  tissues,  and  by  this  means  setting  up 
mechanical  irritation.  The  first  of  these  conditions  arises 
from  faulty  contour,  the  second  from  too  large  or  too  wide 
a  band. 

In  a  bandless  crown,  imperfect  peripheral  adaptation  of 
the  crown  base  to  the  root  face  will  result  in  shoulders  on 
either  the  root  or  the  crown.  Such  shoulders  may  or  may 
not  prove  mechanical  irritants,  but  in  any  case  they  afford 
lodgment  for  food,  which  through  decomi)osition  will  give  rise 
to  chemical  irritation,  with  recession  of  the  gingivse  and  fre- 
quently recurrent  caries  of  the  root. 

Correct  occlusal  forms  should  be  developed  in  order  that 
the  usefulness  of  substitutes  may  be  realized,  that  undue  side 
stresses  may  be  obviated,  and  that  the  crown  may  not  be  sub- 
jected to  extra  heavy  direct  stress.  When  possible  to  do  so, 
firm  kuuckling  contact  with  the  proximating  teeth  should  be 
established,  and  between  neighboring  teeth  when  such  loss  of 
contact  is  occasioned  by  movement  of  the  teeth  toward  the 
space  which  the  sulistitute  occupies. 

These  several  requirements,  although  previously  men- 
tioned, are  again  in  order  under  this  heading,  since,  if  neg- 
lected, the  hygiene  of  the  mouth  cannot  be  preserved. 

In  introducing  substitutes  of  any  character  into  the  mouth 
the  dominant  idea  should  lie  to  so  form  them  that  with  reason- 
able care  on  the  part  of  the  ])atient  they  may  be  kept  clean; 
that  they  may  not  injure  the  remaining  natural  teeth  or  oral 
tissues;  that  the  function  of  mastication  may  be  restored; 
that  the  esthetic  requirements  may  be  fulfilled;  and  withal, 
that  thev  mav  be  worn  with  comfort. 


(;40  CROWN    WORK 

PORCELAIN-FACED    CROWNS   FOR   THE   ANTERIOR 
TEETH 

By  the  coninioii  iiictliods  in  vogue,  it  is  possible  and  ])i-ac- 
ticable  to  construct  many  classes  and  varieties  of  porcelain- 
faced  crowns  for  the  anterior  teeth.  It  is  not,  however,  ad- 
visable, in  a  work  of  ibis  character,  to  attempt  to  describe 
all  or  even  a  comparatively  limited  number  of  such  substitutes 
in  extensive  detail. 

One  type  of  crown,  in  which  a  hirgc  luimbcr  of  the  con- 
structive steps  are  familiar  and  ai'('('])ted  methods  of  ])rac- 


tice,  and  applicable  to  many  other  similar  types  of  crowns, 
will  therefore  be  described  in  detail.  Consequently,  in  men- 
tioning variations  from  the  type  of  crown  about  to  be  de- 
scribed, rehearsal  of  details  as  hei'e  presented  need  not  be 
repeated. 

The  crown  selected  for  this  description  is  a  left,  upper, 
central  incisor,  this  being  one  of  the  most  prominent  teeth 
in  the  month,  and  one  for  which  a  substitute  crown  is  fre- 
quently required. 

The  same  steps  as  here  detailed  are  applicable  to  the 
crowning  of  all  of  the  upper  anterior  teeth,  and  in  most  in- 
stances, to  the  corresponding  teeth  in  the  lower  arch  as  well. 


CROWN    WORK  641 

The  student,  therefore,  is  advised  to  become  intimately 
familiar  with  every  detail  as  here  presented,  with  the  assur- 
ance that  when  he  has  mastered  the  technic  as  outlined,  he 
has  laid  a  substantial  foundation  for  further  progress,  and 
has  mastered  many  details  appli('al)l('  to  the  construction  of 
various  other  classes  of  crowns. 

TECHNIC  OF  CONSTRUCTION  OF  A  PORCELAIN-FACED 

UPPER,  CENTRAL  INCISOR  CROWN 

GENERAL  STEPS 

Devitalization,  treatment  and  filling  of  root  canal. 

Eemoval  of  remaining  portion  of  natural  crown. 

PreiDaration  of  root — removal  of  enamel. 

Measurement  of  root. 

Cutting  and  soldering  of  baud. 

Scribing  and  fitting  baud  to  root. 

Reducing  root  face. 

Construction  of  root  cap. 

Fitting  cap  to  root,   and  itorfovatiug  for   reception   of 

dowel. 
Adaioting  and  soldering  dowel  to  cap. 
Taking  bite  and  impression. 
Selecting  and  grinding  facing. 
Backing  the  facing. 

Assembling  and  waxing  the  facing  and  cap. 
Removal  and  investment  of  the  assembled  crown. 
Soldering. 
Finishing. 
Setting. 

These  steps  will  now  be  taken  up  in  order  and  the  vari- 
ous details  explained  as  clearly,  yet  briefly,  as  possible. 

DEVITALIZATION,   TREATMENT   AND    FILLING   OF   THE 
ROOT  CANAL 

It  is  assumed  that  the  prostlietist  is  familiar  with  the 
treatment  of  vital  and  non-vital  teetli,  their  peridental  mem- 
branes and  adjacent  tissues.  Therefore,  it  is  unnecessary  to 
dwell  extensively- on  this  subject  further  than  to  emphasize 
the  importance  of  adopting  correct  therapeutic  measures  and 
finally  in  sealing  of  the  apical  end  of  the  root  with  a  pei-ma- 
nent  filling  before  proceeding  with  the  preparation  of  the 
root  for  the  reception  of  the  cap. 


fi42  PROWN    WORK 

REMOVAL   OF   THE   REMAINING   PORTION   OF  THE   NATURAL 
CROWN 

To  avoid  unuecessaiy  injury  to  the  dental  ligament  and 
soft  tissues  which  surround  the  tooth  cervix  while  adapting 


GROOVING     THE    ENAMEL    OF     A 

CROWN      WITH      CARBORUNDUM 

STONE     FOR     APPLICATION     OF 

EXCISING   FORCEPS 


PRELIMINARY    STEP    IN    REMOVING    CROWN.       HOLES    DRILLED 

the  band,  the  remaining  portion  of  the  natural  crown  should 
not  be  reduced  beneath  the  gum  margin  until  after  the 
peripheral  ring  of  enamel  has  been  removed,  the  wire  meas- 


CROWN    WORK 


643 


uremeut  secured,  the  band  scribed  and  trimmed  to  correct 
gingival  outline  and  is  finally  driven  to  place  on  the  root. 

When  a  considerable  portion  of  the  natural  crown   re- 


DIAGRAMMATIC    VIEW    OF 

CROWX     PERFORATED     WITH 

DRILL 


DIAGRAMMATIC    VIEW    OF 
CROWN    PARTIALLY    REMOVED 


mains,  the  excising  forceps  can  be  used  for  its  removal. 
Grooves  should  be  cut  through  the  enamel  and  well  into  the 
dentin  in  the  gingival  third  area,  on  both  labial  and  lingual 
surfaces,   with   a   knife-edge   carborundum   stone.     In   these 


iVrPLICATION  OF  STONE  IN  REIUi 


;IN(;IVAL  SECTION  OF  CROWN 


grooves  the  beaks  or  blades  of  the  forceps  are  set,  when, 
with  the  application  of  a  little  force,  the  crown  can  be  frac- 
tured. 


644  CROWN    WORK 

Auotlicr  mi'tliod,  (luite  as  convenient  as  that  described, 
consists  in  drilling  several  holes  through  the  crown  at  right 
angles  to  the  long  axis  of  the  tooth  and  removing  the  inter- 
vening tooth  structure  between  the  holes  with  cross-cut  fis- 
sure burs.  The  drill  should  be  introduced  in  the  cavity  and 
the  holes  cut  from  within  outward,  when  possible,  or  the 
enamel  surface  can  be  notched  with  a  carborundum  stone  as 
described,  and  the  drill  entered  in  the  groove.  A  bi-bevel 
drill  made  by  flattening  an  inverted  cone  bur  on  two  sides 
and  beveling  the  point  is  most  efficient  for  this  purpose. 

After  the  bulk  of  the  crown  is  thus  removed,  the  remain- 
ing stump  is  reduced  with  engine  stones  to  within  about  one- 
sixteenth  of  an  inch  of  the  gingiva,  after  which  the  enamel 
can  be  removed. 

REMOVAL  OF  THE  ENAMEL 

The  most  effecti\('  instrument  for  removing  the  enamel 
is  the  Case  cleaver,  or  some  modification  of  it  of  which  there 


CASE    ENAMEL    CLEAVEUS 


are  several  on  the  market,  notably  the  Ivory  and  the  Weaver. 
A  selection  of  these  instruments  with  both  straight  and  con- 
tra-angle  shanks  should  be  on  hand  for  this  purpose.    These 


WEAVER    ENAMEL    CLEAVER 


instruments  have  a  side  blade,  terminating  in  a  sharp,  rather 
bulky  point  for  strength,  and  are  tempered  very  hard  so  as 
to  readilv  break  the  enamel. 


CROWN    WORK 


The  point  of  the  iiistriuneiit  is  ai)plie(l  to  the  euamel, 
under  the  gum  margin,  pressure  exerted  and  the  point  drawn 
incisally.    This  step  is  repeated  many  times,  the  position  of 


ENAMEL    CLEA.\'ERS    OF    VARKIUS    FORMS 


the  point  being  shifted  each  time,  until  as  much  of  the  periph- 
eral ring  as  it  is  possible  to  reach  with  the  point  has  been 
so  treated.  The  enamel  will  seldom  come  away  as  a  result 
of  application  of  the  point  in  this  manner,  l)ut  the  cohesion 


BOOT  SHOWING  PERIPHERAL         POSITION  OF  CLEAVER  I'OINT         A  !■  1'  L  I  C  A  T  ION    OF    SIDE 
ENAMEL    RING    TO    HE  IN   FRACTURING   ENAMEL  BLADE  OF  CLEAVER   IN 

REMOVED  SURFACES  REMOVING   ENAMEL 

of  the  rods  will  be  disturbed  by  the  many  fracture  lines  de- 
veloped. 

The  cleaver  is  now  passed  beneath  the  free  margin  of  the 
gum,  the  side  blade  near  the  point  being  laid  in  contact  with 
the  enamel.  The  instrument  should  be  held  with  the  palm 
grasp,  the  thumb  on  the  adjacent  tooth  to  serve  as  a  rest, 
and  with  a  forward  and  outward  movement  incisally,  the 
instrument  is  rotated  from  beneath  the  free  margin  of  the 
gum.  With  the  application  of  moderate  force  applied  to  a 
great  extent  in  a  tangential  direction  the  enamel  can  readily 
be  removed  from  the  labial  and  lingual  surfaces  and  from 
well  into  the  four  embrasures. 

Wlien  the  interproximal  spaces  are  constricted  the 
enamel  must  be  removed  by  other  means,  since  the  cleaver 
points  are  too  Imlky  to  enter  these  spaces  to  any  great  extern. 

A  very  small  tissure  bur  can  frequently  be  passsed  into 
the  embrasure,  and  under  proper  control  will  fracture  the 


646  CROWN    WORK 

remaiiiiug  ouamel  so  that  it  eaii  be  reiuovt'd  with  the  root 
files.  Care  must  be  taken  to  avoid  injuring  the  dental  liga- 
ment, the  peridental  membrane  and   the  proximating  tooth 


CUT     SHOWING     I-11U\1.\1AT1.M,      10(1111     L«tli     AS     A     TIU  MB     BEST     IN 
CLEA\1>."G    ENAMEL 

with  the  bur,  also  to  avoid  notching  the  root  margin  from  the 
bur  working  beneath  the  enamel  and  into  the  dentin. 

SMOOTHING  THE  ROOT  PERIPHERY  WITH   FILES 

A  pair  of  right  and  left  diagonally-cut,  thin-l)laded  files, 
such  as  designed  by  the  writer,  or  others  of  similar  type,  will 
be  found  very  useful  for  i:)laning  and  smoothing  the  periphery 
of  the  root  after  the  cleavers  have  removed  the  Inilk  of 
enamel.  These  files  are  designed  to  be  used  in  a  tangential 
direction,  much  the  same  as  the  cleavers,  and  are  held  with 
the  palm  grasp.  They  pass  without  difficulty  in  constricted 
embrasures. 

The  entire  periphery  of  the  root,  from  its  face  end  to 
as  far  imder  the  free  margin  of  the  gum  as  the  crown  band 
is  to  extend,  must  be  made  smooth  and  free  from  all  irregu- 
larities. 


CROWN    WORK 


ENAMEL  FILES  FOK  SMOOTH- 
ING   ROOT    PERIPHERY. 
(PROTHERO) 


E.NCIM:     KOUT      I'Kl.M.MEIt     Kc  IK 

PERIPHERAL    SMOOTHING 

OF   ROOT 


APPLICATION  OF  THE   liclOT    FILES   IN  PERIPHEISAI,  TltlMMINC   OF   HOOT 


648  CROWN    WORK 

GENERAL  FORM   OF  THE   PREPARED   ROOT 

'l^lic  ])cri[)li('ral  form  of  a  iircpari'il  I'oot  should  he  tliat 
of  the  fri;stnni  of  a  cone,  the  large  end  .situated  under  the 
free  margin  of  the  gum  at  the  terminal  location  of  the  crown 
band,  the  smaller  end  terminating  at  the  face  of  the  root. 
The  flare  of  the  sides  of  the  cone  should  not  be  excessive, 


DIAGRAM    OF    THE    CONIC    FORM 

A      ROOT       SHOULD      BE      GIVEN 

FOR        RECEPTION        OF        BAND. 

LABIAI,  VIEW 


PROXIMATE     VIEW     OF     TOOTH 

SHOWING    GENERAL    REDUCTION 

OF    ROOT    FOB    BAND 


not  more  than  five  degrees  nor  less  than  two  degrees.  A 
root  prepared  with  too  much  flare  affords  but  little  reten- 
tion for  the  band  in  fitting,  while  if  not  flared  at  all,  as  when 
the  periphery  is  not  given  a  cone  shape,  the  band  when 
fitted  will  usually  present  a  gingival  shoulder  under  the  free 
margin  of  the  gnm  of  more  or  less  prominence,  depending  on 


PEUIPHERY 


the  failure  of  the  prosthetist  to  produce  a  true  flare  or  con- 
striction on  all  surfaces,  from  gingival  toward  the  incisal 
area. 

The  exact  fitting  of  the  band  of  a  crown  to  the  root  un- 
der the  free  margin  of  the  gum  is  of  vital  importance,  for 
regardless  of  how  carefully  subsequent  steps  are  carried  out. 


CROWN    WORK  649 

an  imperfect  form  of  I'oot  preparation  will  iuvariably  result 
in  the  production  of  a  shoulder,  either  on  the  root  itself  or 
from  too  large  a  hand. 

TESTING  THE  FLARE  OF  THE  ROOT  SURFACES 

Since  a  considerable  portion  of  the  root  surfaces  to  which 
the  baud  will  be  applied  is  obscured  by  the  gum  tissues,  it 
is  sometimes  difficult  to  determine  with  the  eye  when  proper 
form  is  developed.  One  test  that  may  be  applied  is  to  place 
the  point  of  a  delicate  instrument,  as  an  explorer,  on  the 
side  of  the  root,  near  the  face  end,  and  pass  it  carefully 
toward  the  apex,  observing  closely  the  direction  it  travels, 
or  whether  its  line  of  movement  changes  as  would  be  the  case 
when  it  passes  over  a  ridge  and  gradually  or  suddenly  drops 
into  a  depression. 

By  applying  the  instrument  first  on  one,  then  on  the 
opposite  side  of  the  root,  comjjaring  the  line  of  movement 
each  time  with  the  same  fixed  surface,  as  the  axial  surface 
of  a  proximating  tooth,  it  can  soon  be  determined  whether 
or  not  the  proper  flare  to  the  root  sides  has  been  developed. 

A  second  test  may  be  observed  in  the  wire  root  measure- 
ment, which,  when  tightly  twisted,  if  it  can  be  readily  sep- 
arated from  the  root  without  stretching  or  untwisting,  indi- 
cates that  the  gingival  portion  of  the  root  is  the  largest. 
When  it  becomes  necessary  to  cut  or  untwist  the  wire  meas- 
urement to  effect  its  removal  this  is  positive  proof  that  the 
sides  of  the  root  have  not  been  reduced  to  a  conical  form, 
nor  even  brought  to  a  ijarallel  relation  with  each  other.  Fur- 
ther reduction  of  the  root  becomes  necessary  under  such  con- 
ditions. 

In  general  form,  a  root  should  be  sufficiently  cone-shaped 
so  that  as  the  band  is  forced  apically  it  tightens. 

SECURING  THE   MEASUREMENT   OF   THE   ROOT 

A  piece  of  36-gauge,  annealed  iron  wire,  about  three 
inches  long,  is  bent  in  the  form  of  a  loop,  and  fixed  in  a  denti- 


A    DENTIMETER    FOR    HOLDING    AXD    APPLYIXG    THE    WIRE    MEASUREMENT    TO    ROOT 

meter  or  an  ordinary  broach  holder.  The  loop  is  then  passed 
over  the  projecting  end  of  the  root,  the  handle  turned  until 
the  wire  engages  loosely  with  the  root  surfaces.    Careful  ad- 


CItOWN    WORK 


justnicnl  ol'  the  loop  is  now  iiiade  so  that  it  occupies  a  place 
even  with  or  slightly  under  the  free  mari^iu  of  the  gum.  Un- 
der no  condition  should  it  be  carried  ajiically  to  the  extreme 
limit  of  tlu'  cone  base,  as  such  a  measurement  would  usually 


result  in  a  loose-iitting  band.  The  fundamental  idea  to  keep 
in  mind  is  the  production  of  a  band  slightly  smaller  than  the 
section  of  root  cone  wliere  its  apical  end  will  terminate  when 
finally  fitted.     As  the  metal  is  driven  under  the  free  margin 


il'lM.lEll    TO    HOOT    IN    THE 


of  the  gum,  the  conic  form  of  the  root  will  cause  it  not  only 
to  assume  correct  peripheral  adaptation,  but  stretch  it  sufifi- 
ciently  to  take  its  proper  position.  By  adopting  this  method 
of  fitting  the  band,  together  with  correct  root  preparation, 
gingival  shoulders  are  avoided. 


CROWN    WORK  651 

MEASURING   AND    CUTTING   THE   BAND   FOR   THE   ROOT   CAP 

After  removal  of  the  wire  measurement  from  the  root, 
it  is  cut  opposite  the  twist  and  the  two  halves  are  straightened 
out,  care  being  taken  not  to  \;ntwist  the  wires,  as  such  a  mis- 
hap would  increase  the  length. 


The  straightened  measurement  is  now  laid  on  a  piece  of 
gold  plate,  usually  29  g.  and  22  k.  The  lamina  of  the  gold 
should  run  lengthwise  of  the  band  for  greatest  textile 
strength.  One  end  of  the  measurement  is  placed  exactly  even 
with  the  edge  of  the  plate,  and  with  a  thin,  sharp  blade,  a 


LOOF    JUiASUUEMENT    SE\  EBliD. 

STBAIGHTEXED,    AND    LAID    ON 

GOU)      PLATE      FOR       MAHKINO 

LENGTH    OF    CROWN'    BAND 


mark  is  made  on  the  gold  exactly  even  with  the  other  end  of 
the  wire.    This  indicates  the  length  of  the  band. 

The  width  of  the  band  should  be  slightly  greater  than 
the  apico-incisal  curvature  of  the  gingiva.  Usually  one- 
eightli  of  an  inch  in  width  is  ample,  but  when  the  curvature 
is  very  marked  a  wider  band  will  be  required. 

The  length  and  width  of  the  band  having  Ijeen  marked, 
the  gold  strip  is  cut  with  a  pair  of  plate  shears,  being  specially 
careful  to  cut  it  the  exact  length. 

Another  method  consists  in  making  a  lap  joint  to  the 
band  and  after  soldering  reduce  the  excess  thickness,  the 
idea  being  that  such  a  joint  is  stronger  as  well  as  less  liable 
to  become  unsoldered  in  subsequent  steps. 

When  a  lap  joint  is  to  be  formed  the  measurement  is 
taken  as  described  and  the  gold  marked  accordingly.  An 
amount  equal  to  the  width  of  the  lap  is  now  added  to  the 


652  CROWN    WORK 

original  band  Icii.^lli  as  dcteTniined  by  tlic  wire  nicasurcnR'nt 
and  the  band  cnt  that  much  longer. 

In  forming-  the  band,  one  end  of  the  strip  overlaps  the 
other  an  amount  equal  to  the  excess  length  ])reviousl_y  marked. 

FORMING  AND  SOLDERING  THE  BAND 

The  band  is  now  bent  in  the  form  of  a  ring  or  ferrule 
and  compressed  so  that  the  two  ends  of  the  strip  pass  each 
other  slightly.  When  later  adjusted,  the  ends  will  be  held  in 
contact  by  the  resiliency  of  the  metal. 

The  band  is  now  sprung  a])art  and  the  ends  abutted 
scfuarely  against  each  other  between  which  there  should  be 
absolute  contact,  otherwise  it  will  be  difficult  to  unite  them 
perfectly  with  solder.  Should  either  or  both  ends  have  been 
cut  irregularh'  they  must  be  corrected  by  filing.  By  observ- 
ing care  in  cutting  the  band  the  application  of  the  file  will  be 
unnecessary. 

A  piece  of  36g,  annealed,  untiiuu'd,  iron  wire  is  bent 
around  the  ring  and  t\^isted  to  form  a  loop,  the  twist  opposite 
the  joint.  This  twist  serves  as  a  plier  grasp  for  holding  the 
band  while  soldering,  while  the  loop  itself  prevents  the  ends 
from  springing  apart.  When  tinned  iron  wire  is  used  as  a 
binder,  the  tin  unites  with  the  gold  during  soldering,  to  form 
a  low  fusing  alloy,  and  frequently  as  a  result  the  band  will  be 
partially  melted. 

A  little  flux  (pulverized  borax  and  water,  or  soldering 
flux  paste)  is  applied  on  the  inside  of  the  band  along  the  joint, 
being  careful  to  place  it  oiilii  where  needed,  since  the  solder 
will  spread  imnecessarily  on  the  band  if  the  flux  is  applied 
carelessly  or  in  excess. 

When  the  joint  between  the  two  ends  of  the  band  is  close, 
as  it  should  be,  an  almost  inconceivably  small  amoiint  of  sol- 
der, properly  placed  and  fused,  will  effect  a  perfect  imion. 
An  excess  of  solder,  which,  when  fused,  extends  any  distance 
on  either  side  of  the  joint,  stiffens  the  band  and  renders  its 
perfect  adaptation  to  the  root  difficult  if  not  impossible. 

Usually  a  piece  of  solder  one  m.  m.  long  and  one-half 
m.  m.  wide,  will  prove  ample  for  any  ordinary  band  joint. 

The  piece  of  solder  is  now  laid  on  the  inside  of  the  band 
and  across  the  joint,  each  end  of  the  solder  resting  on  a  dif- 
ferent end  of  the  band,  the  joint  space  being  thus  bridged 
over.  As  the  solder  fuses,  being  already  in  contact  with  the 
two  ends  of  the  band,  gravity  causes  it  to  settle  to  place  in 
the  joint. 


CROWN    WORK  663 

The  twisted  ends  of  tlie  loop  are  grasped  with  a  pair 
of  soldering  pliers  and  the  hand  is  carried  close  to  the  Bun- 
sen  flame,  but  not  into  it,  until  the  moisture  has  all  been 
driven  from  the  borax.  Tlus  should  be  carefully  done  or  the 
evaporation  of  the  moisture  from  the  paste,  and  later  the  driv- 
ing out  of  the  water  of  crystallization  from  the  borax,  during 
which  the  latter  swells,  will  displace  the  solder  before  it  fuses. 


SOLDERING  THE  BAND  JOINT. 
NOTICE  THE  PIEt'E  OF  SOLDEB 
CROSSES  THE  JOINT  jVND  RESTS 
ON    liOTH    ENDS    OF    THE    BAND 


The  band  is  now  carried  into  the  tlanie  and  held  in  the 
reducing  flame  until  the  solder  is  fused,  when  it  must  be  in- 
stantly removed,  as  the  gold  itself  is  liable  to  fuse  at  the  joint 
if  only  slightly  overheated. 

The  wire  is  now  removed  and  tbe  liand  contoured  to  the 
general  form  of  the  root.  "When  the  convexity  of  the  alveolar 
border  is  very  marked,  the  liand  can  be  cut  out  slightly  on 
its  mesial  and  distal  sides  and  from  the  gingival  border,  to 
partially  approximate  the  required  curvature,  after  which 
the  final  fitting  can  best  be  done  on  the  root.  The  joint  of  the 
band  is  usually  placed  to  the  lingual  side  of  the  root,  some- 
times to  the  mesial  or  distal  in  certain  bridge  cases,  but  never 
to  the  labial. 

SWEATING   THE    BAND    (AUTOGENOUS    SOLDERING) 

The  higher  caVats  of  gold  can  readily  be  autngrnouslij 
soldered,  or,  as  it  is  commonly  expressed,  .^ircafed.  This 
process  consists  in  maintaining  the  parts  to  be  united,  as  the 
ends  of  the  band,  in  intimate  contact* and  bringing  the  gold 
along  the  margins  of  the  joint  to  such  a  state  of  fusion  that  the 


654  CROWN    WORK 

molecules  of  the  two  pieces  will  intermingle.  Though  appa- 
rently a  difficult  process,  with  a  keen  vision  and  a  steady 
hand,  it  can  readil.y  be  accomplished. 

The  essentials  to  success  are  a  high  grade  gold  that  will 
not  readily  oxidize,  close  contact  of  the  surfaces  to  be  united, 
a  limited  application  of  clean  flux  along  the  joint,  a  strong 
but  not  large  reducing  flame,  so  that  the  heat  may  be  con- 
centrated along  the  desired  line  of  union,  and  finally  the 
removal  of  the  piece  from  the  flame  the  instant  fusion 
occurs. 

This  method  of  joining  pieces  of  gold  without  the  inter- 
position of  solder  is  applicable,  not  only  to  the  forming  of 
bands,  but  to  the  attacliment  of  discs  to  bands  in  the  produc- 
tion of  root  caps  as  well. 

SCRIBING  THE  BAND  TO  GINGIVAL  OUTLINE 

In  fitting  a  crown  band  of  any  class  to  the  root  or  re- 
maining portion  of  the  crown  of  a  natural  tooth,  its  cervical 
end  should  be  so  shaped  that  as  it  is  passed  into  position  it 
will  touch  the  gingival  gum  margin  at  the  same  time.  When 
trimmed  in  this  manner,  this  will  insure  a  uniform  width  of 
band  under  the  free  margin  of  the  gum,  when  it  is  finally 
driven  to  place. 

The  most  convenient  method  for  marking  this  trimming 
line  on  the  band  is  by  means  of  a  pair  of  jeweler's  spring 
dividers.  In  mechanics,  this  process  is  known  as  scribing. 
The  method  is  carried  out  as  follows : 

The  band  is  passed  over  the  root  until  its  mesial  and 
distal  margins  are  in  contact  with  or  are  carried  slightly 


UNTRIMMED   BAND   APPLIED 
TO    PREPAKED    ROOT 


under  the  gingival  tissues  in  the  interproximate  spaces.  A 
space  usually  shows  on  the  labial  view  of  the  root,  between 
the  gingival  end  of  the  band  and  the  highest  curve  of  the  labial 
gingiva.     This  space  indicates  the  distance  apart  at  which 


CROWN    WORK 


655 


the  points  of  the  dividers  must  be  set,  one  point  being  placed 
in  contact  witli  the  gnm  margin,  the  other  jnst  resting  on  the 
gingival  margin  of  the  band. 

The  dividers  are  now  drawn  along  root  and  gold  band 
from  the  center  of  the  labial  surface,  first  mesially  then  dis- 
tally,  the  point  on  the  plate  marking  a  line  as  the  other  fol- 
lows the  gingival  gnm  curvature. 

The  dividers  should  not  be  rotated  as  in  drawing  an 
arc,  but  be  held  so  that  a  line  extending  from  one  point  to  the 
other  is  at  all  times  parallel  with  the  long  axis  of  the  tooth. 


Since  the  dividers  cannot  conveniently  be  used  within 
the  oral  cavity,  for  marking  the  lingual  trimming  line,  an  ex- 
plorer can  be  used  for  this  purpose,  keeping  its  point  as  far 
removed  from  the  lingual,  gingival  curvature  as  the  divider 
point  which  rested  on  the  gold  was  removed  from  the  labial 
gum  margin  while  marking  the  labial  surface  of  the  band. 

When  both  labial  and  lingual  trimming  lines  are  thus 
marked,  the  band  i's  removed,  and  with  a  pair  of  small,  curved 
beak,  crown  shears,  trimmed  accordingly.  The  margins  are 
now  smoothed  with  a  half  round,  fine  cut  file,  so  that  they 
will  not  irritate  the  soft  tissues  in  the  subsequent  steps  of 
fitting  to  the  root. 


()5U  CROWN     WORK 

FITTING  SCRIBED   BAND  TO   THE  ROOT 

The  band,  with  its  gingival  end  niodihed  as  described,  is 
returned  to  the  root  and  jiressed  cervically  until  al)out  in  con- 
tact with  but  not  quite  l)eneath  the  free  gum  margin.  A  close 
examination  is  now  made  to  see  whether  the  gingival  margin 
of  the  band  is  parallel  with  that  of  the  gum  tissue.  If  not, 
the  band  margin  should  be  corrected  by  reducing  with  a  tile, 
the  points  which  first  touch  the  tissues,  until  the  paralleling 
or  approximation  of  the  two  margins  is  accomplished.  There 
are  cases  where  it  is  necessary  to  carry  the  gingival  band  mar- 
gin farther  beneath  the  gum  at  one  point  than  another,  as 


BAND     SCBIBED.     THIMMED     AM)      liLTJ  I!\EII      TO     ROOT.        NOTICE 

ITS    GINGIVAL    MARGIN    t-OIN<'Il)KS    WITH    CIRVE 

OF    THE    GUMS 

where  the  free  flap  of  the  gum  tissues  varies  in  its  width,  or 
liecause  of  hypertrophy  or  some  previous  injury  it  is  not  of 
normal  curvature  or  depth,  or  where  a  pocket  may  be  present, 
and  it  is  considered  best  to  extend  the  band  to  line  of  attach- 
ment of  the  peridental  fibers  to  the  root.  Such  conditions 
should  be  noted  and  the  band  formed  at  this  time  to  meet  the 
requirements  of  the  case. 

The  band  is  now  carefully  and  lightly  driven  beneath  the 
free  margin  of  the  gum,  usually  to  the  depth  of  one  to  one  and 
one-half  millimeters  when  conditions  are  normal.  The  cer- 
vical margin  of  the  band  should  approach,  but- never  encroach 


CROWN    WORK  657 

Oil  the  attiU'limcnt  of  the  peridoiital  lilicrs  to  the  root,  nor 
should  it  ever  pass  beyond  the  base  of  the  root  cone  developed 
by  the  cleavers  and  files.  Should  this  occur,  the  result  will 
be  the  formation  of  a  shoulder  under  the  free  margin  of  the 
gum,  which  will  prove  a  mechanical  irritant  to  the  soft  tis- 
sues from  the  moment  the  crown  is  permanently  set.  Later, 
when  food  tinds  its  way  beneath  the  tissues  and  lodges  on  the 
shoulder,  as  decomposition  sets  in,  chemical  irritation  aug- 
ments the  nicchauical.  and  loss  of  the  root  will  eventually 
occur.  The  most  painstaking  and  conscientious  effort  should 
be  bestowed  not  only  upon  the  preparation  of  the  root,  but 
in  the  fitting  of  the  band  as  well,  in  order  that  the  sultslitntc 
crown  may  prove  permanent  and  conifortal>le  when  set. 

TRIMMING  BAND  TO  PROPER  WIDTH 

The  band  being  driven  to  place  as  described,  its  cervical 
margin  in  close  contact  with  the  sides  of  the  cone  base  and 
the  proper  distance  under  the  free  margin  of  the  gum,  is  still 


TERVICAL  AND  INCISAJj 
ENDS  OF  BAND  REDUCED 
TO  PROPER  OUTLINE.  BAND 
DRIVEN  TO  PLACE  UNDER 
FREE  GUM   MARCIX 


only  partially  formed  The  opposite  end  of  the  band  or  thai 
portion  which  projects  beyond  the  free  margin  of  the  gum 
must  be  reduced  to  such  length  that  when  the  root  cap,  of 
which  it  forms  a  part,  and  on  which  the  porcelain  facing  rests, 
is  completed,  no  gold  will  be  visible  on  the  labial  surface. 

With  a  sharp  pointed  instrument  a  line  is  marked  on  the 
band  close  to  and  following  the  gingival  curvature  of  the  gums, 
around  its  entire  peri^jhery,  labially,  lingually  and  in  the 
embrasures  as  well. 

The  liaud  is  then  removed  from  the  root  and  with  a  pair 
of  curved  shears  cut  to  the  line  marked  on  labial,  mesial  and 
distal  surfaces,  but  not  necessarily  on  the  lingual  surface, 
since  a  wide  band  in  this  area  is  desirable,  affording  greater 
resistance  to  outward  stress  than  a  narrow  band. 


CROWN    WORK 


CDRVBD    BLADE    CROWN    SHEARS    SUITABLE    FOR    TRIMMING    BAND    MARGINS 


STRAIGHT    BLADE    CROWN    SHEARS    FOR    GENERAL    USE 


CROWN    WORK 


The  baud  is  returned  to  tlie  root,  driveu  to  place,  aud  the 
projecting-  eud  of  the  root  reduced  to  the  gum  margin  on  the 
mesial  and  distal,  slightly  beneath  on  the  labial  and  near  to 
but  not  beneath  on  the  lingual  surface  in  order,  as  before 


STONE  APPLIED  FOR  FINAL  RE- 
DUCTION OF  ROOT  FACE.  ARROW 
INDICATES  DIRECTION  STONE 
SHOULD  REVOLVE  TO  AVOID  IN- 
JURY   TO     FREE     GUM    MARGIN 


stated,  that  the  band  may  be  wider  to  better  resist  the  stress 
of  the  oiDposing  teeth. 

The  general  form  of  the  face  end  of  the  root  should  be 
convex  from  labial  to  lingual  and  straight  or  slightly  con- 
cave from  side  to  side,  depending  on  the  depth  of  the  labiai 
curvature  of  the  gingiva.  The  root  may  also  be  ground  to 
present  two  planes,  one  sloping  from  the  pulp  chamber 
labially,  the  other  from  the  pulp  chamber  lingually.     This 


OTTOLENGUI  ROOT  FACER  AS 

APPLIED  IN  REDUCING  EXCESS 

OF  ROOT " 


form  of  preparation,  which  is  common,  will  usually  require 
less  grinding  of  the  ridge  lap  of  the  facing  than  when  the  root 
face  is  decidedlv  convex. 


66(1  CROWN    WORK 

Tlu'  loot  may  he  raced  willi  an  engine  slune  about  three- 
fourths  of  an  inch  in  diameter  and  one-eighth  inch  face,  or 
witli  the  Ottoleugui  root  facers,  the  various  sizes  of  which 
afford  the  selection  of  one  suitable  to  different  sizes  of  roots. 

The  Roach  root  facer  can  be  used  to  advantage  in  reducing 
the  ])rojecting  end  of  the  root.  This  appliance  has  a  central 
loose  pin  which  keeps  it  within  the  root  periphery. 

In  facing  the  root  with  the  stone  it  should  revolve  from 
the  root  toward  the  free  margin  of  the  gum  to  avoid  laceration 
of  the  soft  tissues. 

The  root  should  be  faced  even  with  but  not  shorter  than 
the  band,  for  when  the  disc  which  forms  the  end  of  the  cap 
is  attached  it  should  rest  directly  upon  the  root  end.     Care 


TlIK  ROACH  BOOT  FACER. 

WITH    MOVABLE    CENTER 

GUIDE  PIN 


should  be  taken,  therefore,  in  facing  the  root,  not  to  reduce  it 
below  the  baud  margin  or  in  driving  the  finished  cap  to  place, 
the  cervical  end  of  the  band  will  be  forced  too  far  apically. 

CONSTRUCTING  THE  ROOT  CAP 

The  root  cap  consists  of  the  band  formed  as  described,  to 
which  is  attached  a  disc  of  metal,  designed  to  rest  upon  the 
root  face  and  which  forms  the  foundation  for  the  crown.  The 
constructive  steps  are  as  follows : 

The  band  is  removed  from  the  root  and  a  disc  of  24  k. 
or  22  k.  30  g.  gold,  slightly  larger  in  diameter  than  the  band, 
is  adapted  to  its  incisal  end.  General  adaptation  may  be 
secured  by  placing  the  cervical  end  of  the  band  on  the  ball  of 
the  thumb,  adjusting  the  disc  correctly  against  the  other  end 
and  with  the  ball  of  the  finger  forcing  it  in  contact  with  the 


CROWN    WORK 


baud  margins.  While  pressure  is  thus  maiutained,  a  tliin 
blade  burnisher  is  applied  between  the  ball  of  the  tinger  and 
the  disc  to  conform  it  accurately  at  all  iioints  to  the  band  edge. 
By  scratching  the  side  of  the  luiiid  and  adjacent  surface  of  the 


KIRST   STEP   IX  ADAI'TING   GOLD 

PLATE  TO  COMPLETED  BAND  IN 

FORMING     BOOT      CAP 


disc  at  two  or  three  points,  the  two  parts  may  later  be  re- 
adjusted in  exact  relation  as  they  must  be  when  soldering. 

When  closely  adapted,  which  means  positive  contact  of 
the  disc  with  the  baud  around  its  entire  periphei'al  edge,  the 
two  are  separated,  a  thin  tilm  of  flux  is  applied  to  the  disc 
surface  on  which  the  band  will  rest,  a  little  to  the  band  edge 
also,  and  the  outer  margin  of  the  disc  is  caught  in  the  beaks 
of  a  pair  of  self -locking  soldering  pliers.    A  very  small  piece 


PLATE    BCRXISHER    FOR    ADAPTIX<;    liACKIXG    TO    FACIXG     (PKl  ITII  ICIil  I 

of  solder  is  cut  and  set  endwise,  one  end  resting  on  the  disc, 
the  other  against  the  outside  of  the  band,  care  being  taken  to 
see  that  the  band  and  disc  are  in  exact  relation  to  each  other, 
as  previously  marked. 

SOLDERING   THE   BAND   TO   THE    DISC 

The  disc  with  band  and  solder  in  i)!ace  is  quickly  passed 
back  and  forth  through  the  flame  a  few  times,  to  gradually 
expel  the  moisture  and  water  of  hydration  from  the  flux  and 
thus  obviate  displacement  of  the  band,  after  which  it  is  held 
in  the  reducing,  flame  until  the  solder  fuses,  when  it  is  quickly 
withdrawn.  When  the  adaptation  between  disc  and  band  is 
perfect,  the  solder  should  flow  around  the  entire  joint  peri- 
]ihery.  Frequently,  however,  the  solder  will  fail  to  flow  along 
the  joint  immediately  in  front  of  the  plier  beaks  because  the 


CROWN    WORK 


conduction  of  heat  l\y  the  latter,  away  from  the  gold  in  tliat 
particular  area,  lowers  the  temperature  below  the  fusing  point 
of  the  solder.     By  grasping  the  opposite  side  of  the  disc  with 


SOLDERING  THE  BAND  AND 
PLATE.  NOTICE  TWO  SMALL 
PIECES  OF  SOLDEK  ON  OPPO- 
SITE SIDE  FROM  PLIER  BEAKS. 
ONE  PIECE  IS  DSnALLY  SUF- 
FICIENT 

the  pliers  and  again  introducing  in  the  flame,  complete  union 
of  band  and  disc  can  usually  be  effected  without  addition  of 
more  solder. 

TRIMMING  OFF   THE   PERIPHERAL   EXCESS   OF   THE   DISC 

The  flat  side  of  the  shear  blade  is  applied  against  the 
side  of  the  band,  and  the  excess  margin  of  the  disc  removed. 
Further  reduction  should  be  made  with  the  file,  care  being 
taken  to  avoid  rounding  the  disc  margin,  but  leave  it  square 
and  flush  with  the  band.  In  some  cases  it  is  advisable  to  allow 


it  to  extend  slightly  beyond  the  outer  surface  of  the  band, 
particularly  on  the  labial  surface,  when  proper  alignment  of 
the  facing  requires  that  it  be  set  to  the  labial  of  the  band 
surface. 

CONSTRUCTING   CAP  BY   THE   INDIRECT   METHOD 

In  making  a  cap  by  the  indirect  method,  the  excising  of 
the  crown,  removal  of  the  enamel  and  smoothing  up  of  the 
root  cone  is  the  same  as  by  the  direct  method,  in  which  the  cap 


CROWN    WORK  663 

is  constructed  of  two  pieces,  as  described.     The  steps  vary, 
however,  from  this  point  on. 

In  the  indirect  method,  tlie  root  must  be  faced  to  tlie  final 
form  desired,  the  labial  portion  being  reduced  beneath  the 
free  margin  of  tlie  gnms  the  full  extent  before  the  impression 
is  secured.  Counter-sinking  the  canal  orifice  should  also  be 
done  so  that  this  depression  may  be  reproduced  on  the  die. 

TAKING   IMPRESSION   OF    ROOT 

A  seamless  copper  band,  slightly  larger  than  the  root,  is 
contoured  to  its  general  peripheral  outline,  and  the  con- 
toured end  trimmed  to  ai^proximate  the  curve  of  the  gingiva. 
The  band  should  be  slightly  longer  than  the  proximating  teeth 
for  convenience  in  handling. 

The  band  is  filled  slightly  in  excess  with  softened  model- 
ing compound,  then  introduced  between  the  proximating  teeth. 


BAND   FlI.Lrn    WITH    MODELlNf; 

COMPOl  M)       I'KI  l'\RlTOEY       TO 

TAKINf!     IMPBESSION     OF     ROOT 

FAfE   AND    PEBiniERY 


and  evenly  centered  over  the  root.  Pressure  is  now  applied 
to  force  the  compound  against  the  root  face  and  at  the  same 
time  telescope  the  band  over  the  root  periphery  so  as  to  con- 
fine the  compound  and  press  it  closely  against  the  sides  of 
the  root.  The  thumb  or  finger  should  be  placed  over  the 
outer  or  open  end  of  the  band  to  prevent  the  compound  escap- 
ing in  this  direction.  The  Ivory  impression  cups,  a  number  of 
varying  sizes  of  which  are  suyiplied,  which  fit  into  a  universal 
handle,  are  well  adapted  to  this  work. 

When  properly  carried  out,  the  gum  margin  is  pressed 
apically  and  aft  imjiression  of  the  face  end  of  the  root  and  of 
the  sides  as  well  can  bo  secured.  Because  of  the  limited  com- 
pressibility of  the  gum  tissues,  an  impression  of  the  root 
sides,  as  far  apically  as  the  band  will  eventually  extend,  can 


664  CROWN    WORK 

seldom  be  securcil,  but  sufficient  of  the  root  surfaces  can  be 
embraced  so  that  the  die  when  developed  can  be  filed  away 
to  represent  a  longer  root.  Wlien  tliis  plan  is  followed  care 
sliould  be  taken  to  jireserve  llic  original  flare  of  tlie  root  cone. 

CONSTRUCTING  THE  ROOT  DIE 

Any  excess  impression  material  tiiat  may  have  been 
forced  out  beyond  the  periphery  of  the  impression  band  is 
removed.  A  section  of  rubber  tubing  which  neatly  fits  the 
outside  of  the  band  is  slipped  over  it  and  allowed  to  project 
aliout  oue-eighili  iudi  beyond  flic  im])i-ession,  to  confine  the 


nUBBER    BIM>     VIl'IIFD    TO    IM 

I'RESSION     I  I  Rll>lil  HI     lit    COX 

UNF     THI       VMiU.VM 


amalgam  or  cement  and  thus  increase  the  depth  of  the  die. 
A  mix  of  amalgam,  such  as  is  used  for  die  pui'poses,  is 
made  and  carefully  worked  into  all  inequalities  of  the  im- 
pression, being  careful  while  doing  so  not  to  mar  any  of  the 
surfaces.  Not  only  the  impression,  biit  the  rubber  ring  is 
filled  to  give  sufficient  base  to  the  die  to  resist  the  stress  of 
.swaging  and  that  it  may  be  well  anchored  in  the  swaging  ring. 

IMBEDDING  THE  DIE   IN  THE   SWAGING  RING 

The  die,  when  hardened,  is  removed  from  the  impression 
by  warming  the  latter,  and  set  in  a  base  of  modeling  com- 
pound in  the  swaging  ring,  placing  it  well  al»ove  the  margin 


of  the  ring,  so  that  the  counterdie  material  may  press  the 
gold  against  the  sides  of  the  root. 

Should  any  change  of  form  of  the  die  lie  indicated,  as  in- 
creasing" the  length  of  the  root  apically,  it  can  be  made  at  this 
time.     In  practically  all  cases  such  change  should  be  made, 


CROWN    WORK 


even  to  the  extent  of  iuereasiun'  the  length  of  the  root  hci/oiid 
what  is  required.  The  band  of  the  cap  when  swaged  will 
naturally  be  wider  than  necessary,  but  in  fitting  to  the  root  it 


DIE     IMBEDDED      IN     KING     WITHIN      SWACiEI! 


can  readily  be  reduced  to  correct  width,  while  if  too  narrow 
the  form  of  the  die  must  be  changed  as  outlined  and  the  cap 
reconstructed. 

SWAGING  THE  ROOT  CAP 

The  swaging  I'ing  is  now  placed  in  the  base  of  the  swager, 
a  disc  of  pure  gold,  of  34  or  36  gauge,  slightly  larger  than 
will  be  required  to  form  the  face  and  sides  of  the  cap,  is  oiled 
on  both  sides  and  adapted  by  finger  pressure  and  burnishing, 
to  the  die.  The  general  outline  of  the  cap  can  thus  be  defi- 
nitely determined  and  the  surplus  gold  removed  practically 
to  the  band  margins. 

The  swager  is  set  in  position,  niivulcaiiiz(Ml  rubl)er  or 
moldiue  being  interposed  between  the  iilunger  and  the  root 


666  CROWN    WORK 

cap,  and  with  two  or  three  heavy  Mows  of  tlie  swaging  ham- 
mer the  cap  is  swaged. 

The  band  margins  are  now  trimmed  to  as  near  the  correct 
width  as  possible  before  trial  in  the  mouth,  and  the  cap  re- 
swaged  to  correct  the  distortion  from  trimming.  Since  a  die 
formed  in  the  manner  described  shows  distinetlv   the  entrance 


SWAGED    CAP.     IN    POSITION    ON 

DIE.     SURPLUS    NOT    TET 

HEMOVED 

to  the  root  canal,  and  this  is  indicated  by  a  depression  in  the 
cap,  the  hole  for  the  dowel  may  be  punched  before  the  last 
reswaging. 

The  cap  is  boiled  in  acid  to  remove  any  adlierent  amalgam 
and  cleanse  the  surfaces,  then  washed  to  remove  the  acid, 
when  it  is  ready  for  fitting  to  the  root. 

FITTING  THE  CAP  TO  THE  ROOT 

The  principle  fitting  to  the  root  consists  in  trimming  the 
band  to  proper  width.  The  cap  is  placed  on  the  root  and 
light  pressure  applied.  If  any  obstruction  is  met  the  loca- 
tion and  cause  are  ascertained  and  correction  made.  The  usual 
change  necessary  is  to  shorten  the  cervical  end  of  the  band 
so  that  it  will  not  encroach  on  the  tissues  around  the  root 
cervix.  When  the  cap  can  be  firmly  seated  without  impinge- 
ment on  the  tissues,  a  thin,  flat  burnislier  is  applied  under 
the  gum  margin  and  the  band  burnished  into  close  contact 
with  the  root  periphery.  While  doing  so  the  cap  must  be  held 
in  close  contact  with  the  root  face. 

From  now  on,  the  steps  are  similar  to  those  described 
for  the  two-piece  crown,  the  next  step  being  securing  the  rela- 
tion between  cap  and  dowel  and  attaching  them  as  previously 
described.  In  flowing  the  solder  which  unites  cap  and  dowel, 
the  entire  cap  should  be  covered  at  the  same  time  with  a 
thin  layer  of  solder  to  give  it  rigidity. 


CROWN    WORK  667 

ENLARGING  ROOT   CANAL  FOR   RECEPTION   OF   THE   DOWEL 

If  the  root  canal  liys  not  already  been  prepared  to  receive 
the  dowel,  it  must  be  at  this  time,  since  the  following  steps 
relate  to  the  fitting  and  adjustment  of  the  dowel  to  the  root 
and  cap. 

The  reaming  out  of  a  root  canal  is  a  comparatively  simple 
step  when  the  prosthetist  himself  has  treated  the  root  and 
lilled  the  apex.  When,  however,  the  case  presents,  the  root 
having  previously  been  filled  by  another  operator,  an  eit'ort 
should  be  made  to  determine  the  probable  length  of  the  root 
and  its  position  in  the  border.  If  any  doubt  exists  as  to  its 
anatomic  form,  its  position,  or  the  thoroughness  of  the  root 
filling,  a  skiagraph  should  be  secured  to  determine  as  accu- 
rately as  possible  the  existing  conditions. 

Examination  of  the  labial  tissues  overlying  the  root  will 
frequently  disclose  a  slight  elevation  of  the  mucous  membrane 
and  underlying  alveolar  plate,  which  will  indicate  the  position 
of  the  root  in  the  process.  If  no  visible  evidence  is  present, 
pressure  with  the  ball  of  the  linger,  particularly  in  the  apical 
region,  will  frequently  locate  the  direction  of  the  root.  It  is 
of  the  utmost  importance  that  the  general  trend  of  the  root  be 
known  before  attempting  to  ream  out  and  enlarge  the  canal. 
When  for  any  reason  it  is  impossible  to  determine  it,  the  great- 
est care  should  be  observed  in  keeping  the  cutting  instrument 
within  the  canal  and  pointed  in  the  right  direction  or  serious 
injury  is  liable  to  occur. 

A  rigid,  inflexible  drill,  bur  or  root  reamer,  having  a 
cutting  point,  is  a  dangerous  instrument  in  the  hands  of  an 
unskilled  or  careless  operator.  Perforation  of  the  side  of  the 
root  is  very  liable  to  occur  as  a  result  of  the  instrument  point 
leaving  the  canal  and  boring  its  way  through  the  dentin  and 
into  the  alveolus.  The  tissues  injured  as  a  result  of  such  acci- 
dent seldom  ever  recover  their  normal  tone,  the  root  having  a 
feeling  of  chronic  soreness,  while  frequently  its  extraction  in 
a  short  time  becomes  necessary. 

The  safest  method  of  removing  a  root  filling  and  enlarg- 
ing the  canal  to  the  required  diameter,  or  to  such  size  that  a 
reamer  may  with  safety  be  used,  is  by  means  of  various  sizes 
of  round  engine  burs.    The  technic  is  as  follows : 

Determine,  if  possible,  the  general  direction  of  the  root, 
and  keep  this  constantly  in  mind  at  all  times  until  the  initial 
reaming  of  the  canal  to  proper  depth  has  been  accomplished. 


668  CROWN    WORK 

Place  a  No.  V2  round  l)ur  in  the  liandiiiccc  and  iatroduee 
the  point  in  tlie  extrauoe  to  the  eanal. 

Line  the  handpiece  up  to  conform  to  the  general  direction 
of  the  root,  hokling  it  loosely  with  tlie  pen  grasp. 

Start  the  engine  and  apply  light  pressure  with  tiie  point  of 
the  bur,  removing  it  frequently  to  l)ring  out  tlie  guttapercha 
cuttings  and  keep  the  canal  clear. 

Do  not  attempt  to  guide  the  point ;  it  will  follow  the  canal 
if  the  handpiece  is  held  loosely  and  in  proper  alignment,  and 
the  cuttings  are  removed  frequently. 

Since  a  dowel  should  extend  as  far  apically  as  the  crown 
extends  incisally,  it  will  be  necessary  to  ream  out  the  canal 
to  this  dei3th  when  the  length  of  root  will  permit. 

As  soon  as  the  bur  begins  to  bind,  and  the  feel  or  vibra- 
tion of  the  handpiece  indicates  that  the  bur  is  cutting  dentin 
instead  of  root  filling,  an  examination  should  be  made  with  a 
straight  explorer  to  determine  whether  the  bur  is  leaving  the 
canal  and  if  so,  the  cause. 

Should  the  tapering  shank  of  the  small  bur  jam  against 
the  sides  of  the  canal  before  the  latter  has  been  opened  to  re 
quired  depth,  a  No.  3  round  bur  can  be  substituted  and  the 
canal  slightly  enlarged  from  without  inward  for  a  short  dis- 
tance, thus  making  room  for  the  smaller  bur  with  which  the 
opening  of  the  canal  can  be  completed  to  the  required  depth. 

The  No.  3  bur  is  now  used  in  the  manner  as  described  for 
No.  %  bur,  holding  the  handpiece  loosely  and  allowing  the  bur 
to  make  its  own  way  in  the  now  open  canal  as  far  as  the  lat- 
ter has  been  opened  by  No.  \'2. 

The  canal  can  now  safely  be  enlarged  to  the  required  size 
for  the  reception  of  the  dowel  with  either  Nos.  4  or  5  round 
burs,  depending  on  the  diameter  of  the  dowel  to  be  used.  Any 
of  the  ordinary  forms  of  reamers  can  also  with  safety  be  used, 
since  there  is  little  danger,  except  when  grossest  carelessness 
is  displayed,  of  perforating  the  side  of  the  root. 

Great  care  should  be  taken  to  avoid  passing  the  small 
round  bur  through  the  apical  end  of  the  root,  or  of  disturlnng 
that  portion  of  the  filling  which  closes  the  terminal  of  the 
canal.  Pressure  on  the  Inir  nuist  be  extremely  light  at  all 
times,  but  particularly  so  in  the  final  steps  of  removing  the 
root  filling. 

COUNTERSINKING  THE  CANAL   OPENING 

To  give  rigidity  to  the  cap  and  a  firmer  attachment  to  it 
of  the  dowel  when  soldered,  the  entrance  to  the  root  canal 


CROWN    WORK 


slionld  be  slightly  countersunk  with  a  No.  10  round  bur,  and 
into  this  depression  the  cap  disc  is  depressed. 


LABIAL  VIEW  OF  KOOT  SHOW- 
ING CANAL  ENTRANCE  SLIGHT- 
LY ENLARGED 


PROXIMATE   VIEW   OP   ROOT 

SHOWING  ENL,\KGED  CANAL 

ENTRANCE 


INDENTING  THE   CAP   IN   COUNTERSUNK  AREA 

The  cap  is  now  returned  to  position  on  the  root  and  the 
small  end  of  the  large  egg  Ijuruisher  is  applied  to  its  central 
area  with  sufficient  force  to  press  it  into  the  depressed  area. 


BOOT  CAP  IN  POSITION.  NOTICE 
THAT  LABIALLT  THE  BAND  IS 
BENEATH  GDM  MARGIN.  WHILE 
L  I  N  G  U  A  L  L  Y  IT  PROJECTS 
SLIGHTLY-    BEYOND 


Usually,  when  the  burnisher  is  somewhat  pointed,  the  gold 
will  be  forced  slightly  beyond  the  countersunk  area  and  into 
the  entrance  of  the  root  canal  itself,  thus  giving  the  exact 
location  of  the  hole  in  the  cap  for  the  dowel. 


PERFORATING  THE  ROOT  CAP  FOR  THE  DOWEL 

A  heavy  instrument,  witli  a  sharj)  ))oint,  the  diameter  of 
which  is  slightly  less  than  the  dowel,  is  now  forced  against 
the  cap  directly  over  the  opening  in  the  root,  and  the  gold 
punctured.  A  small  engine  drill  may  be  used  for  the  same 
purpose,  or  the  ca'p  can  be  removed  and  the  hole  punched 
with  the  plate  punch.  The  opening,  as  before  stated,  should 
be  smaller  than  the  dowel,  so  that  when  the  latter  is  forced 
through  it  the  margins  of  the  disc  may  ht  tiglitly  against  and 
hold  the  dowel  firmly  in  position. 


t;70  CROWN     WORK 

FORCING  THE  DOWEL  THROUGH   THE   CAP  INTO  THE  ROOT 

The  dowi'l,  usually  of  16  or  15  g.  iridio-platinum,  or  clasp 
metal  wire,  is  cut  slightly  longer  than  the  actual  depth  of 
the  reamed  canal  so  that  it  may  project  beyond  the  root  cap 
and  be  surrounded  by  the  solder  which  forms  the  lingual  con- 
tour of  the  crown.  Its  apical  end  should  be  slightly  reduced 
so  as  to  readily  enter  the  hole  iu  the  root  ca]i.     Better  reten- 


FOKCING    THE    DOWEI 


\l,    THROUGH    ROOT    CAP 


tion,  however,  will  be  afforded  the  crown  if  the  sides  of  the 
dowel  are  not  tapered  as  is  the  common  practice. 

With  a  pair  of  parallel  jaw  pliers,  the  dowel  is  grasped 
firmly,  the  reduced  apical  end  outward.  This  end  is  entered 
in  the  opening  in  the  root  cap,  the  dowel  brought  in  alignment 
with  the  root  canal,  and  forced  through  the  cap  and  into  the 
root,  the  full  depth  of  the  reamed  out  portion. 

As  the  dowel  is  forced  into  the  root  through  the  con- 
stricted opening  in  the  cap,  the  margins  of  the  latter  will  be 


CROWN    WORK 


enlarged  and  carried  into  the  entrance  of  the  canal,  and  tlie 
bearing  of  the  gold  against  the  dowel  be  much  increased. 


DIAGRAM    OF    INTRODUCTION  OF 

DOW-EL      THROUGH      CAP.      WITH 

PARALLEL    JAW    PLIERS 


ROOT      CAP      WITH       ATTACHED 
DOWEL   IN  POSITION  ON  BOOT 


MAINTAINING   CORRECT    RELATION    BETWEEN   DOWEL    AND 
CAP  WHILE   REMOVING   FROM   ROOT 

The  cap  and  dowel  are  now  ready  for  attaching  together 
with  solder.  To  preserve  the  exact  relationship  which  they 
now  sustain  to  each  other,  on  the  root,  during  the  soldering 
process,  a  piece  of  wax  or  modelling  compound  which  will 
enter  the  space  of  the  missing  crown,  is  softened,  pressed 
against  the  projecting  dowel  and  root  cap  and  chilled.  A 
small  G-2-23  hoe,  or  iuotrument  of  similar  shape,  is  carefully 
passed  under  the  free  margin  of  the  gum,  labially  or  lingually, 
hooked  over  the  cervical  margin  of  the  band  and  the  cap 
loosened. 

Should  the  cap  and  dowel  cling  to  the  root  and  fail  to 
come  away  witli  the  impression  as  it  is  removed,  they  can  be 
released  and  set  in  position  without  difficulty. 

Frequently,  wli.en  the  dowel  fits  tightly  in  the  cap  open- 
ing, and  the  ca|>  and  dowel  release  easily  from  the  root,  they 
can  be  removed  from  position,  a  little  sticky  wax  applied  to 
and  melted  on  the  cap  and  against  the  dowel,  after  which  they 
are  returned  to  the  root  to  correct  any  disturbance  of  align- 
ment of  the  dowel  that  mav  have  occurred  in  removal.     The 


672  CROWN    WORK 

wax  is  now  (^liilk'd  and  the  two,  now  tiruily  held  together  in 
correct  relation,  are  removed  and  invested  for  soldering. 

At  times  the  dowel  may  be  held  so  tirmly  by  the  cap  that 
(he  two  mav  be  removed  and   sol(hT('(l   without  investment. 


SOLDERING     CAP     AND     DOWEL  SOLDEMNG     CAP     AND     DOWEL 

WITHOUT      INVESTMENT,      PER-  WITHOUT    INVESTMENT.      HORI- 

PBNDICULAR  POSITION         OF  ZONTAI,      POSITION      OF      DOWEL 

DOWEL.         NOTICE      REFLECTED 
MARGIN        OF        DISC        AROUND 
DOWEL 

Althoiis'li  r<'(iuirin,i>'  a  little  longer  time  than  by  the  method 
just  mentioned,  it  is  much  the  safest  plan  to  take  the  small 
impression  and  invest  the  two  for  soldering. 

INVESTING  THE   CAP  AND   DOWEL   FOR   SOLDERING 

A  small  mix  of  investment  material  or  plaster  alone,  be- 
cause of  its  greater  rapidity  in  setting,  is  prepared  and  ap- 
plied to  the  root  side  of  the  ca])  and  around  the  dowel,  build- 
ing it  up  the  full  length  of  the  latter  and  squaring  it  off  to 
form  a  base  on  which  to  rest  while  soldering. 


CAP  ANT)  DOWEL  INVESTED  FOB 
SOLDERING.         THIS      PLAN      IS 
PREFERABLE  TO  THE  T«'0   PRE- 
CEDING    METHODS 


When  set,  the  investment  is  reduced  to  small  size  to  facil- 
itate soldering,  the  wax  and  moisture  removed,  a  little  flux 
applied  over  the  surface  of  the  cap  and  around  the  dowel 
where  it  is  desired  the  solder  should  flow,  a  piece  of  solder  is 


CROWN    WORK  673 

ap]ilied,  one  eud  rt'stiiig  on  the  cap,  the  otlier  against  the 
dowel,  and  with  the  blowpipe  flame  is  fused. 

The  investment  is  now  removed,  the  cap  pickled  in  acid 
to  cleanse,  and  thoroughly  washed  in  water  to  remove  the  acid, 
when  it  is  ready  to  return  to  the  mouth  for  final  impression. 

TAKING  THE  BITE  AND  IMPRESSION 

Although  there  are  many  ways  by  which  an  acciirate 
relation  may  be  secured  between  the  backed  facing  and  cap 
in  assembling  the  crown  for  final  soldering,  without  taking 
an  impression  and  bite  and  constructing  casts,  the  safest  plan 
for  the  beginner  at  least  is  to  carry  out  the  steps  as  now 
outlined. 

USE  OF  THE  FACE  BOW   IN  CROWN  WORK 

To  secure  esthetic  results,  it  is  essential  that  at  least  two 
teeth  on  either  side  of  the  s^iace  in  which  the  crown  is  to  be 


ADJUST.ME^'T    OF     WAX 


THE     UlTE 


placed  should  be  reproduced  on  the  cast,  in  order  that  correct 
alignment  and  length  of  crown  may  be  determined  acciirately, 
therefore  the  bite  should  include  from  five  to  six  teeth.     It 


B74  CROWN    WORK 

is  also  essential  that  llie  crown  be  so  constructed  as  not  to 
interfere  with  the  teeth  in  the  opposite  arcli  in  lateral  as 
well  as  incisive  movements.  The  use  of  the  face  bow  will 
enable  the  prosthetist  to  so  construct  the  crown  that  sul)se- 
cjuent  changes  by  grinding  will  not  be  required. 

In  crown  work  the  bite  should  be  secured  before  the  im- 
pression is  taken,  for  the  reason  that  when  the  impression 
is  taken  in  plaster,  as  in  most  cases  it  should  be,  the  project- 
ing end  of  the  dowel,  being  imbedded  in  the  plaster,  will  bring 
the  cap  away  from  the  root  with  the  impression.  In  case  the 
impression  is  taken  first  and  the  cap  comes  away  with  it,  the 
cap  must  be  removed  and  replaced  on  the  root  before  taking 
the  bite  or  the  latter  will  be  useless  or  at  least  unreliable. 

Some  prosthetists  take  a  combined  bite  and  impression  in 
modeling  compound,  which  in  simple  cases,  where  there  are  no 


SECTIONAL      ^■IE\V      OF      COMBINED 

IMPRESSION  AND   BITE.     BOOT   CAP 

AND    DOWEL    IN    POSITION 


undercuts  present,  will  answer  for  the  separate  bite  in  wax, 
and  impression  in  plaster. 

DETAILS   OF  TAKING  THE   BITE 

The  cap  is  set  in  position  on  the  root,  care  lieing  taken 
to  see  that  it  is  firmly  seated. 

A  piece  of  wax  is  formed  into  a  compact  mass,  about 
1/2x1x2  inches,  introduced  between  the  teeth  and  the  patient 
instructed  to  close.  The  wax  should  extend  sutKiciently  far 
labially  of  the  teeth  to  receive  and  firmly  hold  the  bite  fork 
of  the  face  bow,  which  is  now  applied  and  the  face  bow  ad- 
justed in  the  usual  manner. 

While  the  wax  is  still  soft  the  patient  is  instructed  to 
press  it  against  both  upper  and  lower  teeth  with  the  tongue 


CROWN    WORK 


SO  as  to  secure  as  accurate  an  iiupressiou  of  them  as  possible. 
Stress  should  be  laid  on  forcing  the  wax  against  the  loiver 
as  well  as  the  tipper  teeth,  otherwise  the  tongue  will  raise  it 
against  the  upper  teeth  only. 


APPEAKANCE     IN     MOUTH     01''     ROOT     CAP     WITH     PROJECTING 

DOWEL.      EXTREME    LABIAL    MARGIN    OF    BAND    IS 

OBSCURED  UY  GUM  MARGIN 

The  wax  is  now  chilled,  the  condyle  rods  of  the  face  bow 
released,  the  patient  instructed  to  open  the  mouth,  and  the 
bite  attached  to  the  face  bow  is  removed  and  laid  aside  until 
the  cast  is  secured. 


A  bite  fork,  modified  by  having  the  inner  edge  of  each  end 
reduced  by  grinding  to  increase  its  inner  arc,  will  serve  the 
purpose  better  than  one  of  regular  form. 


Cuo  runwN  work 

Still  anotlior  modiiicutiun  which  will  be  found  very  use- 
ful for  taking  side  bites,  as  for  cuspids,  bicuspids  and  the 
first  molar,  can  be  made  as  follows :  Saw  off  one  of  the  fork 
prongs  next  the  stem,  to  the  other,  lit  a  sleeve  wliich  will  slide 
freely  along  the  fork,  but  which  can  be  firmly  fixed  with  a 
set  screw  at  any  point  desired.  The  inner  margin  of  the 
sleeve  is  supplied  with  a  projection  for  extending  into  the 
space  of  a  missing  tooth.  A  firm  hold  is  secured  in  the  bite 
by  having  sufficient  bulk  of  wax  outside  the  arch  to  enclose 
the  inner  margin  of  the  fork.  The  projection  of  the  sleeve 
should  be  set  so  as  to  enter  the  space  of  the  missing  crown. 

When  the  root  cap  comes  away  with  the  bite,  as  is  fre- 
quently the  case,  it  must  be  removed  and  returned  to  the  root 
before  taking  the  impression. 

DETAILS  OF  SECURING  AN  IMPRESSION  WITH   PLASTER 

In  crown  work  it  is  just  as  imi)ortant  to  secure  an  accu- 
rate impression  of  that  part  of  the  mouth  involved  as  in  full 
denture  construction.  When  much  irregularity  of  surfaces 
exists,  as  in  teeth  witli  constricted  cervices,  or  when  the  em- 
brasure spaces  are  open  as  a  result  of  tissue  absorption,  the 
impression  should  always  be  in  plaster. 

In  order  to  preserve  the  essential  parts  of  such  an  im- 
pression, so  that  the  teeth  involved  may  be  reproduced  as 
perfectly  as  possible,  it  will  be  necessary  to  fracture  it,  care- 
fully remove  the  pieces,  and  re]ilace  them  in  proper  order  for 
the  production  of  the  cast. 

Any  one  of  three  methods  may  be  adopted,  as  follows : 

First,  a  tray  of  suitable  size  is  selected  and  oiled  to  pre- 
vent the  plaster  from  adhering  to  it.  Plaster  sufficient  to 
secure  an  impression  of  the  teeth  involved  is  placed  in  the 
tray,  introduced  in  the  mouth  and  given  sufficient  time  to  thor- 
oughly harden.  The  tray  is  then  carefully  removed  so  as  not 
to  disturl)  the  impression.  With  the  point  of  a  knife  an  incisal 
groove  is  cut  in  the  plaster  to  weaken  it.  The  groove  should 
extend  well  into  the  space  of  the  missing  crown.  Pressure  on 
the  ends  or  the  extreme  border  surface  outward  will  fracture 
the  labial  portion,  which  will  usually  come  away  intact.  With 
careful  manipulation  the  lingual  portion  may  be  released 
and  removed  without  further  fracture.  The  tray  and  frac- 
tured surfaces  of  the  impression  are  now  cleared  of  all  par- 
ticles of  debris,  the  pieces  replaced  in  the  tray,  luted  firmly 
with  wax  and  the  cast  secured  in  the  usual  way. 

Second  method :    A  piece  of  cardboard  is  cut  in  the  form 


CROWN    WORK  677 

of   a   square    about   IVoxlVo    inches,    and   the   four   corners 
rounded  slightlj'. 

Two  opposite  sides,  each  a  littk'  less  than  one-half  inch 
wide,  are  turned  up  at  right  angles  to  form  an  improvised 
impression  tray,  the  bottom  of  wliicli  is  a  little  more  than  one- 


half  inch  wide.  The  sides  and  floor  of  -the  tray  may  be  varied 
in  width  to  confoi*m  to  any  special  requirements,  as  a  greater 
or  less  curvature  of  the  arch  or  a  deep  or  shallow  alveolar 
border. 

The  plaster  is  mixed  to  medium  thick  consistency,  placed 
in  the  tray  carried  against  the  teeth  so  as  to  divide  it  about 
equally  labially  and  lingually,  and  pressed  borderward  until 
the  iueisal  edges  of  the  teeth  touch  the  tray  floor. 

Since  the  sides  of  the  tray  are  not  rigid,  they  should  be 
supported  with  the  thumb  and  fingers  while  introducing  the 
plaster  and  until  it  has  begun  to  set. 

When  the  plaster  has  set,  it  is  unnecessary  to  remove  the 
tra>'  from  the  impression,  since  the  cardboard  will  be  easily 
Ijent  along  the  line  where  fracture  will  occur.  Neither  is  it 
necessary  to  groove  the  impression,  for  when  the  tray  is  car- 


mXGE    TRAY    OI-EN 


ried  borderward  until  its  floor  comes  in  contact  with  the  teeth, 
the  plaster  is  already  practically  divided  into  two  sections  and 
will  readily  break  along  the  incisal  line  with  the  application 
of  slight  force.  Furthermore,  the  cardboard  serves  the  same 
purpose  as  a  hinged  tray,  for  by  removing  the  particles  of 


1)78  CROWN    WORK 

debris  from  the  fi-acturcd  surfaces,  the  two  luilves  of  the  im- 
pression can  be  brought  together  in  exactly  tlie  right  relation 
to  each  other,  and  on  hitiiig  with  wax  or  wrapping  a  strand  of 
tine  binding  wire  around  the  outside,  is  ready  for  the  produc- 
tion of  the  cast. 

Third  method:  A  very  serviceable  and  permanent  tray 
may  be  constructed  of  an  ordinary  brass  hinge,  so  bent  as  to 
present  a  floor  and  sides  of  about  the  same  dimensions  as 
those  of  the  cardboard  tray.  The  joint  of  the  tray  is  in  the 
center  of  the  floor,  while  the  hinge  projects  a  little  below  and 
serves  as  a  handle,  or  fiiiyer  hold  in  introducing  the  tray. 

PRODUCTION    OF   CAST    FROM    THE    IMPRESSION 

The  impression  having  been  secured,  and  the  fractured 
pieces  correctly  adjusted,  it  is  coated  with  separating  medium 
and  allowed  to  dry. 

Usually  when  an  impression  is  fractured  in  removal,  the 
cap  will  remain  in  position  on  the  root.  It  may,  however, 
come  away,  but  its  position  in  the  impression  will  usually  be 
disturbed. 

Before  replacing  it,  the  several  parts  of  the  impression 
are  first  placed  together  and  firmly  attached  with  sticky  wax. 
The  cap  is  then  cleaned  and  a  thin  film  of  wax  flowed  over 
the  dowel  and  inside  the  cap  to  obliterate  any  undercuts  that 
may  be  present.  The  object  of  this  is  to  permit  the  ready 
removal  subsequently  of  the  cap  from  the  cast,  without  break- 
ing the  latter.  Before  the  backed  facing  is  finall)'  attached 
to  the  cap,  the  latter  is  heated  slightly  to  soften  the  wax,  after 
which  it  is  carefully  removed  from  the  cast,  the  wax  cleared 
away  and  the  cap  returned  to  position,  the  outer  periphery 
and  dowel  opening  guiding  it  accurately  to  place  on  the  cast. 
Then  when  the  facing  is  attached  with  sticky  wax,  in  the  exact 
and  final  relation  it  should  sustain  to  the  cap,  the  assembled 
crown  can  be  removed  for  investment  without  danger  of  dis- 
turbing the  relation  so  estalilished. 

The  cap  is  now  returned  to  its  exact  position  in  the  im- 
pression where  it  is  luted  firmly  with  a  little  wax  applied  to 
the  outside  of  the  lingual  band  surface. 

Plaster  is  then  mixed  and  the  impression  filled  as  for  any 
partial  case,  special  care  being  taken  that  no  air  is  confined 
in  the  deeper  parts  of  the  impression. 


CROWN    WORK  t>79 

ATTACHING  THE  CASTS  TO  THE  OCCLUDING  FRAME 

When  the  face  bow  has  been  applied  in  taking  the  bite  as 
described,  the  most  convenient  as  well  as  accnrate  method 
of  monntiug  the  casts  ou  the  occluding  frame  is  to  mount  the 
bite  and  produce  the  occlusion  cast  first. 

The  face  bow  with  bite  fixed  to  the  fork  is  attached  to  the 
frame  and  the  latter  inverted.  The  lower  bow  is  thrown  back- 
ward out  of  the  way,  the  interior  of  the  bite  coated  with  a 
thin  film  of  oil  and  filled  with  plaster,  building  it  well  above 
the  bite  margins.  The  bow  of  the  frame  is  brought  down  in 
position  and  plaster  applied  around  it  to  unite  it  with  that  in 
the  bite. 

When  the  plaster  has  hardened,  the  face  bow  and  bite 
fork  are  removed,  and  both  labial  and  lingual  portions  of  the 
bite  in  which  the  upper  cast  is  to  be  fitted  are  pared  down 
so  as  to  permit  the  teeth  to  enter  freely.  The  labial  side  of 
the  bite  should  be  cut  away  so  as  to  expose  the  imprint  made 
l)y  the  incisal  edges  of  the  natural  teeth  in  the  wax,  so  that 
in  placing  the  cast  in  position  it  can  readily  be  seen  when 
the  plaster  teeth  are  in  contact  with  the  deepest  portion  of 
the  bite.  Sufficient  wax,  however,  should  be  left  to  guide  the 
cast  into  correct  vertical  ])osition. 


FUU.    I'ASTS    MOrXTED     ON     OCCLUDING     FRAME.       CAI"     IN    POSITION. 
DSCALLY    ONLY    P.iRTIAL    CASTS    ABE    DEVELOPED 

The  upper  cast  is  now  set  in  the  bite,  the  upper  bow  of 
the  frame  dropped  down  upon  its  base,  and  plaster  applied 
to  attach  the  two  firmly.  When  the  plaster  has  set  the  wax 
is  thoroughly  warmed  to  prevent  breaking  the  teeth  and  is 


680  CROWN    WORK 

then  removed.     The  case  is  now  ready  for  the  scsh'ction  and 
grinding  of  tlie  facing. 

SELECTION   OF  THE   FACING 

By  means  of  the  shade  guide,  the  tints  displayed  in  the 
natural  teeth  of  the  patient  can  he  determined,  the  number  of 
the  shade  required  noted,  and  a  facing  of  corresponding  color 
and  of  suitable  form  selected. 

The  form  of  the  facing  selected  should  correspond  to  the 
type  of  proximating  natural  teeth.  In  case  such  a  tooth  is  not 
procurable,  one  of  the  correct  shade  but  sliglitly  larger  than 
required  can  be  selected  and  by  grinding  be  modified  to  meet 
the  requirements.  The  ground  surfaces,  when  the  proper  con- 
tour is  developed,  can  be  finished  with  fine  discs,  and  after- 
ward given  a  fine  glaze  with  putty  powder  on  a  hard  felt  lathe 
wheel. 

The  facing  should  be  wide  enough  to  fill  the  space  and 
restore  strong  proximate  contact  with  the  adjoining  teeth, 
unless  for  some  special  reason  this  is  not  advisable. 

Usually  the  facing  selected  should  be  slightly  longer  than 
required,  since  both  incisal  edge  and  ridge  lap  must  be  re- 
duced to  required  form  by  grinding. 

Since  the  pins  afford  tlie  only  anchorage  of  the  porce- 
lain to  the  metal  structure  of  the  crown,  a  facing  should  be 
selected  having  the  pin«  located  as  close  to  the  incisal  edge  as 
possible,  so  as  to  bring  the  anchorage  near  the  point  of  stress. 

GRINDING   THE   FACING   TO   THE    ROOT   CAP 

To  facilitate  the  soldering  of  the  backed  facing  to  the  root 
cap,  the  ridge  lap  of  the  facing  is  beveled  from  its  cervico- 


RIDGE  LAP  AND  INCISAL  EDGE 
OF  PORCELAIN  PACING  GROUND 
AND    ADJUSTED    TO    ROOT    CAP 


labial  margin  to  the  lingual  surface.  This  leaves  a  V-shaped 
space  of  greater  or  less  width  between  the  base  of  porcelain 
and  the  root  cap. 


CROWN    WORK 


In  grinding  the  cervical  end  of  a  facing  to  the  required 
form,  care  should  be  taken  to  develop  a  distinct  line  angle  be- 


CUT  SHOWING  DIREPTION  STONE 

SHOULD     ROTATE    IN     GRINDING 

TO      OBVIATE      CHIPPING      MAB- 

GINS   OF    PORCELAIN 


tween  the  ridge  lap  surface  and  the  laliial  surface  to  avoid  a 
defective  joint  between  the  porcelain  and  backing. 

The  stone  should  revolve  from  the  labial  surface  lingually 
to  prevent  fracture  of  the  margins. 

BEVELING  THE  INCISAL  EDGE  OF  THE  FACING 

The  incisal  edge  of  the  facing  should  be  ground  to  har- 
monious alignment  with  the  proximating  teeth,  the  facing, 
however,  being  shortened  slightly  to  allow  for  the  thickness 
of  the  gold  tip  to  be  added,  and  also  for  the  backing,  which 
must  cover  the  ridge  lap. 

The  inciso-lingual  line  angle  should  be  reduced  to  about 
30  degrees  with  the  lingual  surface  taken  as  a  base.  This  is 
somewhat  less  than  is  usually  recommended,  but  when  so 
formed  will  result  in  a  metal  tip  of  equal  or  greater  strength 
with  less  labial  exposure  of  gold  than  where  the  porcelain  is 
beveled  at  an  angle  of  45  degrees.  Special  care  should  also 
be  observed  in  developing  the  bevel  to  avoid  fracturing  the 
labial  margins  of  porcelain  with  the  stone. 

CHANGE  OF  COLOR  IN  PORCELAIN  DUE  TO  METAL  BACKING 

Different  metals  are  used  and  various  methods  are  in 
vogue  in  backing  facings  in  crown  and  bridge  work.  The 
technic  of  applying  the  various  metals  is  similar,  but  the  color 
elTect  on  the  porcelain  of  the  metal  employed  as  a  backing 
should  be  known  in  order  to  avoid  luidesirable  change  of  tint 
in  the  facing  of  a  finished  crown. 

Pure  gold  imparts  a  slightly  yellowish  tint  to  very  light 
porcelain,  and  increases  or  darkens  the  tint  of  yellow  porce- 
lain, particularly  when  the  facing  is  thin. 


(;82  CROWN    WORK 

AlloWHiiee,  therefore,  should  be  made  in  the  selection  of  a 
facing  when  pure  gold  is  to  be  used  as  a  backing  by  choosing 
one  having  the  correct  basic  color,  but  slightly  lighter  than 
the  shade  desired,  the  variation  depending  on  the  thickness 
of  the  facing  selected. 

When  22  k.  gold  is  used,  a  similar  effect  is  produced,  but 
to  a  lesser  degree,  because  of  its  less  pronounced  yellow  color. 

Coin  gold  perceptibly  darkens  thin,  translucent  facings  of 
any  shade. 

Platimun  imjiarts  a  bluish  tint  to  light  porcelain,  in  some 
cases  darkening  it  perceptiltly. 

A  greenish  yellow  tint  can  be  imparted  to  light  yellow 
Ijorcelain  by  using  an  18  k.  alloy  known  as  "green  gold,"  com- 
posed of  18  parts  of  pure  gold  and  6  parts  of  pure  silver. 
This  gold  is  almost  as  soft  and  easily  worked  as  pure  gold. 

BACKING  THE  FACING  WITH   GOLD 

Pure  gold  is  most  generally  used  as  a  backing  because  of 
the  ease  with  which  it  can  be  adapted  to  irregular  surfaces. 
When  conformed  to  a  surface  it  shows  but  little  tendency  to 
warp  or  spring  away  as  does  gold  of  the  lower  carats. 

Two  general  methods  are  in  vogue  for  applying  the  back- 
ings to  teeth,  first,  by  burnishing,  and,  second,  by  swaging,  both 
of  which  will  be  outlined. 

PERFORATING  THE  BACKING  FOR  THE  PINS 

Spread  a  thin  film  of  wax  over  the  surface  and  near  the 
corner  of  the  piece  of  plate.  Place  the  facing,  pins  resting 
on  the  wax,  so  that  a  slight  margin  of  gold  shows  at  the  end 


METHOD   OF   MABKING   CORRECT   POSITION 

OF    HOLES,    ON    BACKING,    FOR    TOOTH 

PINS 


and  along  the  side.  Press  the  pins  into  the  wax  to  indicate  the 
location  of  the  holes  for  the  pins.  Punch  the  holes  as  marked 
in  the  wax.  Apply  the  facing  and  with  a  sharp  instrument 
mark  the  outline  of  the  tooth  on  the  backing,  allowing  a  little 
surplus  all  around,  particularly  at  the  cervical  and  incisal 
ends.    The  gold  is  then  cut  to  the  outline  marked. 


CROWN    WORK  683 

Another  method  is  to  puiieh  one  hole  near  the  edge  of  the 
plate  for  the  outer  pin.  Apply  the  facing,  entering  the  pin  in 
the  hole  already  punched,  and  rotate  the  tooth.  Remove  the 
facing  and  punch  the  other  hole,  its  inner  margin  or  tliat  next 
the  first  hole  heing  on  the  rotation  line. 

Whatever  method  is  employed,  care  should  be  taken  to 
punch  the  holes  the  proper  distance  apart  to  avoid  straining 
the  porcelain  as  the  gold  is  forced  over  the  pins  and  against 
the  facing.  When  the  space  between  the  pin  holes  is  either  too 
wide  or  narrow,  such  an  accident  is  liable  to  occur. 

The  holes  should  be  of  the  exact  diameter  of  the  pins  or 
slightly  smaller,  but  never  larger,  to  obviate  the  danger  of 
fracture  in  final  soldering,  from  the  flux  and  solder  being 
drawn  into  and  through  the  holes  next  the  pins,  thereby  com- 
ing directly  in  contact  with  the  porcelain. 

THE   MASON   SPACING   CALIPER 

The  Mason  spacing  calipers  and  auxiliaries,  consisting  of 
a  pointed  puncli  and  an  engine  burnishing  tool,  was  designed 
to  and  does  effectually  obviate  the  liability  of  both  too  large 


APPLICATION  OF  .MASON  SPACING  CAI/Il'ER  IN  PEIIFORATING  THE  BACKING 


(i84  CROWN    WORK 

or  iucorrectly  located  holes.     The  directions   for  using  the 
appliances  are  as  follows: 

"The  pins  of  the  facing  are  placed  in  tiie  holes  on  the 
side  of  the  caliper  which  have  guide  slots  to  guide  the  pins  into 
the  holes ;  this  accurately  spaces  the  holes,  which  register  with 
pins  of  the  tooth,  held  in  that  position  by  the  thumb  nut;  the 
backing  is  then  marked  or  pierced  by  the  hardened  points, 
which  gives  the  exact  spacing  for  the  pins;  now  place  the 
backing  thus  marked  on  a  piece  of  lead;  then  with  the  pointed 
punch  the  metal  or  gold  is  pierced,  throwing  u])  a  lip,  giving 
an  a]3erture  the  same  size  as  the  pins;  the  backing  thus 
pierced  is  placed  on  the  tooth,  the  lips  extending  on  the  pins; 
finally,  to  burnish  this  lip  of  gold  to  the  pin,  the  lathe  tool  is 
used ;  this  has  an  aperture  in   the  end  which  fits  over  the 


THE    MASON    SPACING    CALIPER    AND    ACCESSOKIES 

pin;  with  a  high  speed  engine  or  lathe  the  gold  is  tightly 
burnished  around  and  slightly  raised  against  the  sides  of  the 
pins     .     .     .     ." 

The  writer's  experience  with  this  appliance  has  proven 
it  to  be  a  most  valuable  addition  to  the  laboratory  equipment. 


THE  YOUNG  PLATE  PERFORATOR 

This  is  another  convenient  appliance  by  means  of  which 
the  tooth  serves  as  a  gauge  for  setting  the  double  end  punch 


TTTE  YOUNG  PLATE  PERFOHATOR 


so  that  both  holes  are  punched  at  the  same  time  and  at  exact- 
ly the  proper  distance  apart. 


CROWN    WORK  685 

ADAPTING   THE    BACKING   TO    THE   FACING    BY    BURNISHING 

The  backing,  cut  slightly  larger  than  the  surfaces  it  is 
to  cover,  and  with  holes  punched,  is  applied  to  the  facing  and 
adapted  as  closely  as  possible  to  the  porcelain  with  finger 
pressure.  By  means  of  the  contra-angle  burnisher  or  one  of 
the  Wilson  type,  general  surface  adaptation  is  secured,  after 
which  the  borders  are  gradually  worked  into  close  contact 
with  the  margins  of  the  facing.  The  gold  should  be  removed 
and  annealed  occasionally  to  reduce  the  hardness  developed 
by  burnishing.  Finally,  when  as  close  adaptation  as  possible 
has  been  secured  by  burnishing,  the  backing  is  removed,  an- 
nealed, returned  to  place  and  the  facing  pressed,  pins  down, 
with  backing  interposed,  into  a  broad  cork  that  has  previously 
been  grooved  to  the  general  lingual  contour  of  the  facing.  A 
piece  of  wood  about  the  size  of  a  lead  iieneil,  concaved  on  the 


ADAPTING     THE     BACKING      TO 

FACING     AGAINST     COKK     WITH 

I.K;UT    IIAMIIEB   BLOWS 


end.  is  set  on  the  facing  and  with  both  jn-essure  and  light  ham- 
mer blows  final  and  close  adaptation  of  the  gold  to  the  porce- 
lain is  secured. 

Previous  to  this  final  adaptation,  the  surplus  gold  extend- 
ing over  the  margins  of  i^orcelain  should  be  reduced  with  a 
file,  applied  so  as  to  force  the  backing  toward  rather  tlian 
away  from  the  facing  As  before  mentioned,  a  slight  surplus 
of  the  backing  should  be  allowed  to  remain  on  both  incisal 
and  gingival  margins,  until  the  final  finishing  of  the  crown,  so 
that  the  solder  may  be  drawn  outward  to  the  full  extent  de- 
sired. Under  no  circumstances  should  the  backing  on  these 
two  ends  be  reflected  over  and  onto  the  labial  surface,  as  frac- 
ture of  the  porcelain  will  occur,  due  to  contraction  of  the 
applied  lingual  solder. 

It  is  absolutely  essential  that  the  backing  be  brought  into 
close  and  positive  contact  with  the  porcelain,  not  only  at  the 
margins,  but  on  the  lingual  surfaces  as  well,  to  avoid  the 
formation  of  a  space  between  the  two,  into  which  organic  mat- 
ter will  gradually  find  its  way.     When  food  accumulates  in 


686 


CROWN    WORK 


such  spaces  it  gives  rise  to  disagreeable  odors,  and  as  it  de- 
composes and  darkens  will  inddil'y  the  shade  of  the  ])orcelain. 


SWAGING  THE    BACKING 


When  the  backing  lias  been  cut  to  proper  size,  the  holes 
inmehed  for  the  pins,  and  general  adaptation  secured  with  a 
burnisher,  the  facing  is  invested,  labial  face  down,  in  modeling 
compound,  in  the  swaging  ring. 


UNVULCANIZED 
RUBBER.-- 


MODELING 
COMPOUND^ 


ADAPTING    THE    BACKING    TO    FACINC    IN    S.    S.    W     SWAOER 


SIMILAR  METHOD  OF 
ADAPTING  FACING  TO 
BACKING  IN  AJAX  SWAGER 


It  should  set  well  above  the  ring  margins  so  as  to  freely 
expose  the  beveled  incisal  tip  on  one  end  and  the  ridge  lap  on 
the  other.  The  com])ound  should  be  trimmed  so  that  the  mar- 
gins of  the  facing  are  freely  exposed  to  permit  the  gold  being- 
forced  in  close  contact  by  the  unvulcanized  rubber. 

When  the  thinner  gauges  of  gold  or  platinum  are  used,  as 
34  or  36  g.,  two  or  three  light  blows  on  the  plunger  will  set 


CROWN    WORK  687 

the  backing  in  close  contact  witli  tlie  facing.  Heaviei'  gauges 
of  metal  will  require  more  force.  When  swaged,  the  backing 
is  removed  and  trimmed  to  desired  correct  outline,  and  the 
backing  returned  to  the  facing  and  reswaged  to  correct  any 
distortion  that  may  have  occurred. 

FIXING   THE   BACKING   TO   THE   FACING 

When  final  adaptation  has  been  developed  between  facing 
and  backing,  the  latter  should  be  firmly  fixed  to  the  porcelain 
so  that  the  close  and  essential  relation  between  the  two  may 
not  be  disturbed  while  assembling  and  soldering  the  crown. 

A  common  practice  is  to  bend  the  pins  over  in  contact 
with  the  backing.  As  a  result,  however,  the  porcelain  is  sub- 
jected to  undue  strain,  and  if  not  fractured  immediately,  as  is 
frequently  the  case,  is  very  liable  to  be  in  the  subsequent  sol- 
dering process. 

A  much  safer  and  quite  as  effectual  method  is  to  apply 
a  sharp  blade  or  chisel  to  the  side  of  pin  and  turn  a  light 
shaving  of  the  platinimi  down  upon  the  backing.  Tliis  puts  no 
strain  upon  the  porcelain  and  holds  the  gold  firmly  in  place. 
The  Eeese  Pin  Shaver,  a  small,  cylindrical,  hollow  mandrel, 
the  Oldening  in  which  is  slightly  larger  than  the  diameter  of  a 
tooth  pin,  can  also  be  used  for  shaving  the  pin  and  burnishing 
the  shaving  down  in  close  contact  with  the  backing.  The  in- 
strument is  passed  over  the  pin  in  a  slightly  diagonal  direc- 
tion, and  as  it  is  forced  along  the  pin  toward  the  backing,  the 
sharp  inner  margin  of  the  tool  cuts  and  carries  a  shaving  of 
platinum  down  in  contact  with  the  gold. 

FITTING  THE  BACKED   FACING  TO  THE  ROOT  CAP 

The  facing  now  having  its  backing  conformed  and  at- 
tached as  described  is  ready  for  adjustment  to  the  root  cap, 
A  small  piece  of  soft  wax  is  placed  over  the  projecting  dowel 
and  on  the  lingual  half  of  the  cap,  and  the  facing  pressed 
against  it  so  as  to  secure  proper  aligiiment  with  the  prox- 
imating  teeth. 

If  in  adjusting  the  facing  the  labial  surface  of  the  dowel 
interferes  with  its  labial  alignment,  the  dowel  may  be  partially 
ground  away.  Sometimes  it  is  necessary,  when  the  facing  is 
thick  or  the  •labio-lingual  diameter  of  the  root  is  short,  to 
remove  the  greater  portion  of  the  i^rojecting  dowel.  When 
the  root  is  countersunk  and  the  cap  has  been  burnished  into 
it  as  previously  described,  the  removal  of  the  dowel  projection 


688  CROWN    WORK 

will  not  ap!>rfci;ihl>-  wciikcii  I  lie  attachiiiciil  ol'  llic  ddwd  to 
tlie  finished  crown. 

It  is  sometimes  iulxisaldc  to  ream  out  tlic  liiii;ual  side  of 
tlie  root  canal,  so  that  in  adjusting  the  dowel  it  may  be  bent 
slightly  to  the  lingual,  and  thus  give  more  space  for  the  facing. 

Special  care  should  be  observed  to  set  the  cervical  mar- 
gin of  the  facing  in  line  with  the  labial  surface  of  the  band. 
It  may  even  project  slightly  if  tlie  alignment  of  the  facing 
recjuires,  but  should  never  be  set  to  the  lingual  or  the  labial 
band  surface,  or  a  jn-ojecting  shoulder  of  gold,  wliicli  cannot 
be  obliterated,  will  result. 

The  long  axis  of  the  facing  must  be  set  at  a  similar  angle 
of  divergence  from  the  perpendicular  line  of  the  face  or,  in- 
ciso-apically,  as  the  corresponding  tooth  on  the  opposite  side 
of  the  arch,  the  line  of  direction,  however,  being  reversed. 

In  most  cases  the  backing  which  covers  the  ridge  lap  of 
the  facing  can  be  slightly  reduced  in  thickness  by  filing,  and 
that  portion  of  gold  on  the  root  cap  against  which  the  facing 
rests  may  also  be  thinned  by  grinding.  The  object  of  this 
is  to  bring  the  porcelain  in  as  close  contact  as  possible  with 


LINGUAL   SIDE  OP   BOOT   CANAL 

REAMED      TO      RECEIVE 

BENT    DOWEL 


the  root  face,  and  thereby  reduce  the  width  of  the  labio-gin- 
gival  margin  of  gold  in  the  finished  crown.  By  this  step,  in- 
stead of  two  thicknesses  of  gold  being  interposed  between  the 
face  end  of  the  root  and  facing  there  is  the  equivalent  of  only 
one.  When  the  facing  is  adjusted  in  the  exact  desired  relation 
to  the  cap,  the  point  of  a  heated  instrument  is  passed  into  the 
wax  supporting  it  and  the  two  are  firmly  united. 

INVESTMENT  OF  THE   ASSEMBLED   CROWN   FOR   SOLDERING 

The  crown  is  now  carefully  removed  and  its  full  lingual 
contour  developed  in  wax.  Special  care  should  be  taken  to 
flow  wax  into  the  space  between  the  backing  and  root  cap 
around  the  labial  surface  to  exclude  the  investment  in  which 
crown  is  later  on  inclosed  for  soldering. 


CROWN    WORK  689 

The  crown  is  now  assembled,  but  all  of  the  several  parts 
are  not  yet  permanently  united.  It  must  therefore  be  enclosed 
in  some  material  capable  of  resisting  heat  without  perceptible 
change,  that  will  hold  the  cap  and  facing  in  correct  relation 
to  each  other  after  renio\  al  of  the  wax  and  during  the  solder- 
ing i^rocess. 

Anj'  of  the  standard  investment  materials  prepared  and 
sold  for  this  ynirpose  may  be  employed,  or  one  can  be  com- 
pounded in  the  laboratory.  One  of  the  best  "home  made" 
investments  for  soldering  purposes  consists  of  a  mixture  of 
two-third  coarse  ground  asbestos  (short  cut  fibre),  and  one- 
third  plaster. 

The  two  ingredients  sliould  be  measured  out  in  proper 
proportions  and  "dry  mixed,"  thfen  placed  in  the  bowl,  a  suf- 


BACKED  FACING  AND  CAP  AS- 
SEMBLED AND  HELD  WITH 
WAX,    BEADY    FOR    INVESTMENT 


ficient  quantity  of  water  added  to  make  a  rather  stiff  mass, 
and  spatulated  thoroughly. 

An  oiled  slab  should  be  prepared  or  a  piece  of  paper 
placed  on  the  bench.  On  this  the  investment  is  placed,  build- 
ing it  up  to  an  inch  or  more  in  thickness.  The  crown  cap  is 
completely  filled  with  investment  before  enclosing  in  the  mass 
to  subsequently  exclude  the  solder. 

The  crown  is  now  pressed  into  the  plastic  mass,  being 
careful  to  keep  its  labial  face  at  least  one-half  inch  above  the 
base  of  the  investment,  so  that  the  latter  may  not  be  fractured 
when  subjected  to  heat,  as  is  frequently  the  case  when  the  bulk 
of  investments  is  too  limited.  The  investment  is  now  built 
around  the  sides  of  the  facing  and  even  with,  but  not  above, 
the  incisal  end. 

The  crown  should  be  settled  into  the  plastic  mass  in  a 
diagonal  position  rather  than  horizontally.  This  is  to  bring 
the  linguo-gingival  edge  of  the  root  cap  and  the  incisal  end  of 


690  c:ro\vn  work 

the  facing  on  a  level,  so  that  in  flowing  the  solder  gravity  will 
assist  in  gi\ing  the  lingnal  snrface  its  proper  contour. 

TRIMMING  THE  INVESTMENT  PREPARATORY  TO  SOLDERING 

It  is  necessar}',  in  order  that  the  flame  may  be  readily  ap- 
plied to  all  essential  parts  of  the  crown  and  the  solder  read- 
ily fused  where  needed,  that  the  surplus  investment  be  re- 
moved and  the  investment  reduced  to  the  smallest  possible 
dimensions  consistent  with  strength  and  the  protection  of  the 
porcelain. 

First,  the  sides  of  the  investment  are  trimmed  close  to 
the  mesial  and  distal  surfaces  of  the  facing,  leaving  a  suffi- 
cient thickness,  however,  to  protect  the  porcelain. 

Second,  the  ends  are  reduced  close  to  but  not  so  as  to  ex- 
pose the  incisal  edge  of  porcelain  or  the  dowel  at  the  oppo- 
site end. 

Third,  an  opening  should  be  carefully  made  from  one 
side  to  the  other  so  as  to  expose  the  labial  surface  of  band 


fROWN    INVESTED    FOR    SOLDERING. 

NOTIC^    THE     JOINT     IS    ENTIBELY 

EXPOSED.      WHILE     PORCELAIN     IS 

PROTECTED 

and  margin  of  backing  which  projects  beyond  the  ridge  lap 
of  the  porcelain,  but  not  the  facing. 

The  investment  along  the  sides  of  the  facing  and  extend- 
ing down  to  the  labio-cervical  opening  is  now  beveled  so  as 
to  freely  expose  the  entire  backing  and  joint  area.  The  in- 
vestment next  the  incisal  tip  should  be  removed  so  that  the 
solder  may  be  freely  drawn  to  the  outermost  limits  of  the 
backing  and  thus  stiffen  the  gold  which  forms  the  incisal  tip 
of  the  crown. 

By  so  forming  the  investment  the  entire  joint  between 
the  backing  and  root  cap  is  exposed  to  view,  so  that  in  flow- 
ing the  solder  it  can  readily  be  seen  when  i^erfect  union  and 
required  contour  has  been  effected. 

REMOVAL  OF  THE  WAX 

The  investment,  trimmed  as  described,  is  cleared  of  de- 
bris, the  wax  warmed  and  removed  with  a  small  instrument. 


CROWN    WORK  691 

That  in  the  more  coustrieted  space  can  be  entirely  cleared 
away  witli  a  fine  streani  of  hoijins'  water. 

APPLYING   THE    FLUX 

A  thin  film  of  thick  borax  paste,  made  by  grinding  crystal 
borax  with  water  on  a  ground  glass  slab,  is  now  applied  to 
the  backing  and  root  cap  on  those  surfaces  to  be  covered  by 
the  solder.  With  a  thin  wooden  spatula  or  toothpick  it  should 
be  carried  into  the  constricted  V-shaped  opening  between  the 
ridgelap  and  the  root  cap,  and  along  the  cervical  joint. 

The  flux  should  not  be  spread  on  the  investment  along 
the  margins  of  the  backing,  where  it  can  come  in  contact  with 
the  porcelain  during  the  soldering,  nor  be  applied  so  plenti- 
fully that  it  will  overflow  on  these  margins  when  heated. 

Should  this  occur,  fracture  of  the  porcelain  is  liable  to 
result,  due  to  difference  in  contractility  of  porcelain  and  borax, 
which,  under  heat,  unite.  When  an  oily  soldering  paste  is 
used  instead  of  one  composed  of  borax  and  water,  the  same 
care  should  be  observed  in  keeping  it  away  f  i-om  the  porcelain. 

DRYING   OUT   AND   HEATING   THE    CASE    FOR   SOLDERING 

The  investment  is  now  set  on  a  sheet  of  gauze,  near  the 
edge  or  slightly  above  the  Bunsen  flame,  to  gradually  drive 
off  the  moisture  and  thoroughly  heat  it  preparatory  to  sol- 
dering. 

When  dry  and  thoroughly  hot  it  is  transferred  to  the 
soldering  block,  where  the  blowpipe  flame  is  applied  around 
the  base  and  sides  until  the  investment  is  red  hot,  when  the 
solder  can  be  applied  and  fused. 

DEVELOPING  THE  LINGUAL  CONTOUR  OF  THE  CROWN  WITH 
SOLDER 

It  is  common  practice  to  cut  the  solder  into  small  pieces, 
apply  a  number  of  them  at  a  time  to  the  backing,  and  when 
fused  to  discontinue  the  flame  until  more  is  added,  then  re- 
apply the  flame,  continuing  this  process  until  the  desired  lin- 
gual contour  is  developed. 

Wliile  this  method  is  effective  so  far  as  developing  the 
required  contour  of  the  crown  is  concerned,  it  frequently  re- 
sults in  fracture  of  the  facing,  due  to  repeated  change  of  tem- 
perature and  consequent  repeated  expansion  and  contraction 
of  the  porcelain. 

By  far  the  quickest,  most  convenient  and  safest  method 
of  applying  the  solder  is  to  cut  it  in  thin  strips  about  one- 
eighth  inch  wide  and  from  three  to  six  inches  in  length.      All 


(!!I2  CROWN    WORK 

surfaces  should  bo  covered  with  a  tliiu  iiliii  of  ilux  before 
use.  One  of  these  sti'ips  is  clamped  in  the  beaks  of  the  sol- 
dering pliers,  and  when  the  investment  is  thorona,hly  heated 
and  red,  the  point  of  the  strip  is  directe(l  intn  llic  deepest 
part  of  the  V-shaped  opening. 

The  flame  of  the  blowpipe  is  now  applied  to  that  area, 
when  the  solder  will  be  instantly  fused.    As  it  settles  into  the 


joint  more  of  the  strip  is  fed  into  the  molten  mass,  until  the 
proper  contour  is  developed. 

Special  care  should  be  observed  in  lliickening  the  back- 
ing over  the  incisal  tip  and  also  allowing  the  solder  to  over- 


THE    STIVER   BLOWPrPE 


flow  the  lingual  surface  of  the  root  cap.  When  the  lingual  sur- 
face of  the  crown  is  developed  to  resemble  the  natural  cingu- 
lum  of  the  tooth,  much  better  protection  will  be  afforded  the 


CROWN    WORK  693 

gum  margin  than  where  this  surface  presents  an  inclined 
plane. 

The  blowpipe  flame  should  never  be  directed  against  the 
platinum  pins  of  a  facing  until  the  porcelain  itself  is  thor- 
oughly heated  and  well  expanded.  The  reason  for  this  is 
obvious:  porcelain  is  f liable  and  easily  broken;  the  platinum 
pins  expand  quickly  when  heated,  and  when  highly  heated 
exert  great  force,  within  certain  limits ;  this  limit  of  expansive 
force  is  greater  than  the  porcelain  can  stand  without  fractur- 
ing unless  itself  first  expanded. 

The  three  principal  causes  of  fracture  of  porcelain  facings 
have  now  been  mentioned,  viz.,  contact  with  and  fusing  of 
borax  to  the  porcelain,  expansion  of  the  platinum  pins,  sud- 
den changes  of  temperature  or  the  intermittent  application 
of  the  flame. 

FINISHING  THE   CROWN 

After  the  soldering  has  lieen  completed,  the  investment 
should  be  allowed  to  cool  down  gradually,  or  again  fracture 
of  the  facing  is  liable  to  occur.  The  investment  should  be  pro- 
tected against  strong,  cold  drafts  of  air  by  placing  over  it 
an  inverted  cup  or  plaster  bowl  until  the  temperature  is  re- 
duced to  such  point  that  it  may  be  comfortably  handled  with 
the  fingers. 

The  investment  is  then  broken  away,  the  crown  examined 
to  see  that  no  accident  has  happened,  and  that  the  desired 
contour  has  been  developed.  Should  contour  be  deficient  at 
any  point  the  crown  must  be  reinvested  and  corrections  made 
as  needed. 

The  crown  is  now  pickled  in  acid  to  loosen  any  adherent 
investment  and  flux.  A  convenient  method  is  to  boil  it  in  acid 
in  a  test  tube,  after  which  it  should  be  thoroughly  washed 
to  remove  the  acid. 


The  sur])li]s  gold  can  lie  economically  removed  with  a 
file,  the  filings  being  caught  in  the  gold  drawer  or  on  a  sheet 
of  paper.  The  finer  finish  is  accomplished  with  engine  stones 
and  discs,  followed  by  the  use  of  fine  pumice  stone  first  and 
afterward  rouge,  applied  with  felt  wheels  on  the  lathe.    Every 


694  CROWN    WORK 

file  mark  and  all  scratclios  iirodiiccd  by  the  coarser  polishing 
powders  must  be  removed  and  the  metal  parts  polished  as 
well  as  the  finest  piece  of  jewelry.  The  cervical  margin  of 
the  band  must  be  beveled  and  slightly  roimded  so  that  it  may 
not  prove  an  irritant  to  the  gingival  tissues  or  for'm  a  shoulder 
for  the  lodgment  of  food. 

Too  much  care  cannot  be  bestowed  on  the  finish  of  the 
cervical  band  margin,  for  on  this,  together  with  restoring  close 
])roximate  contact  with  tlie  adjoining  teeth,  will  depend  the 
future  service  and  comfort  of  the  substitute. 

SETTING  THE  CROWN 

One  of  the  most  essential  requirements  in  the  setting  of  a 
crown  is  to  thoroughly  dry  the  root  and  adjacent  parts  and 
keep  them  so  until  the  operation  is  completed  and  the  cement 
well  set. 

Since  the  rubber  dam  cannot  be  applied,  the  lip  should 
be  raised  with  a  cotton  roll  to  prevent  the  oral  fluids  from  in- 
terfering with  the  immediate  and  subsequent  steps. 

The  general  moisture  is  removed  from  the  mucous  tissues 
and  root  face  with  pellets  of  cotton,  from  the  canal  with  cot- 
ton on  a  brooch  and  small  cotton  or  bibulous  paper  points. 


Finally,  with  blasts  of  air  from  the  chip  blower  or  the  com- 
pressed air  point,  the  parts  are  thoroughly  dried  and  made 
ready  for  the  reception  of  the  crown.  The  crown  itself  should 
be  dry,  clean  and  free  from  polishing  ]iowder,  grease  or  wax. 

A  previously  tested  crown  cement  should  be  mixed  to 
thin-medium  consistency  and  thoroughly  spatulated. 

With  a  root  canal  plugger,  a  small  portion  of  the  cement 
is  carried  into  the  canal  and  worked  against  the  sides  and  to 
the  apex,  continuing  this  until  the  entire  opening  is  filled.    A 


CROWN    WORK  695 

thin  layer  should  be  worked  over  the  face  end  of  the  root. 
The  crown  cap  is  now  partially  tilled  with  the  cement,  a  little 
smeared  on  the  dowel  and  the  crown  is  qnickly  pressed  into 
position  on  the  root. 

Heavy  but  intermittent  pressure  should  be  exerted  at  hrst 
and  afterward  steady  pressure  to  force  out  the  excess  cement 
contined  within  the  cap  and  root  canal,  and  which,  if  not  ex- 
pelled, would  elongate  the  crown  to  a  greater  or  less  extent. 
Mallet  blows  are  much  less  effective  in  seating  a  crown  than 
heavy  maintained  pressure,  because  the  cement  being  more 
or  less  plastic  and  sluggish  and  closely  confined  within  the 
cap,  is  scarcely  affected  by  heavy,  sudden  blows,  while  main- 
tained pressure  causes  it  to  flow  as  long  as  there  is  any  open- 
ing through  which  it  can  escape. 

REMOVAL  OF  THE  EXCESS  CEMENT 

When  the  cement  has  set  reasonably  hard,  which  usually 
requires  from  fifteen  to  twenty-five  minutes,  the  excess  ce- 
ment wluch  can  be  removed  without  danger  of  disturbing  the 
crown  should  be  cleared  away,  first  with  pellets  of  cotton,  fol- 
lowed by  the  use  of  the  blunt  explorer.  When  time  is  limited 
it  is  advisable,  as  soon  as  the  excessive  surplus  is  removed, 
to  dismiss  the  patient  until  the  cement  is  thoroughly  hardened, 
or  after  the  lapse  of  two  or  three  hours,  when  the  removal  of 
the  remainder  can  be  effected  without  danger  of  loosening  the 
crown. 

When  satisfied  that  every  trace  of  the  cement  has  been 
removed  from  beneath  the  gingival  tissues,  the  jsarts  should 
be  syringed  with  warm  normal  salt  solution,  and  the  gums 
massaged  to  restore  normal  circulation  and  tone. 

Finally  before  dismissing  the  patient  a  close  examination 
should  be  made  to  see  that  the  opposite  teeth  do  not  strike  the 
crown  in  either  occlusion  or  lateral  movements.  Should  such 
be  the  case,  correction  must  be  made  b}^  grinding  away  the 
points  of  contact  on  either  the  crown  or  natural  teeth  or  both, 
as  good  judgment  dictates. 

SETTING  A  CROWN  TEMPORARILY 

Sometimes  it  may  be  deemed  advisable  to  set  a  crown  tem- 
porarily in  order  to  test  its  efficiency  or  for  other  reasons. 
This  may  be  done  as  follows: 

A  piece  of  gutta  percha  bas(^plate  matei'ial  is  cut  and 
formed  into  a  roll  or  cylinder  which  will  approximately  fill  the 


l)9G  CROWN    WORK 

root  camil.  The  riuial,  root,  and  adjoiniug  tissues  are  tlior- 
oughly  dried,  the  canal  moisteend  with  oil  of  cajaput,  or 
eucalyptus,  the  cylinder  of  gutta-percha  is  warmed  and  in- 
serted in  the  canal.  The  crown  itself  is  gradually  heated, 
particularly  the  dowel,  and  a  blast  of  hot  air  from  the  syringe 
directed  against  the  gutta-percha.  The  crown  is  then  forced 
to  place  on  the  root,  or  when  it  cannot  be  perfectly  seated  is 
quickly  removed  and  the  cause  determined. 

The  cause  may  be  due  to  too  much  material  or  to  the  gutta- 
percha not  being  sufficiently  plastic.  Removal  of  some  of  the 
material  and  the  application  of  more  heat,  with  quick  action 
and  heavy  pressure,  will  usually  result  in  success  on  second 
trial. 

REMOVAL  OF  A  TEMPORARY  CROWN  OR  A  BRIDGE  SET  WITH 
GUTTA-PERCHA 

Since  the  easiest  way  of  removing  a  crown  set  with  gutta- 
percha is  by  the  application  of  heat,  and  since  the  heat  must  be 
sufficient  to  soften  the  gutta-percha,  the  appliance  now  to  be 
described  will  be  found  most  efficient. 

Remove  the  bulb  from  a  chip-blower.  Pass  a  common 
twine  string,  large  enough  to  fit  closely,  through  the  nozzle  of 
the  pipe,  to  form  a  wick.  Pour  a  few  drops  of  alcohol  into  the 
pipe  and  cork  the  large  end.  This  forms  an  alcohol  lamp,  the 
wick  projecting  from  the  small  end.  Trim  the  wick  short  so 
that  it  projects  but  slightly  from  the  nozzle.  A  flame  varying 
from  one-half  inch  in  length  to  one  no  larger  than  a  pin-head 
may  be  produced,  depending  on  the  projection  of  the  wick. 

With  this  lamp  a  small  flame  is  applied  to  the  crown.  The 
heat  thus  applied  is  transmitted  through  the  dowel  to  the 
gutta-percha  in  the  canal,  which,  when  sufficiently  softened, 
will  release  the  crown. 

DIFFERENT  METHODS  OF  APPLYING  PORCELAIN  FAC- 
INGS  AND   REPLACEABLE  TEETH   IN   SINGLE 
CROWNS,  AND  DUMMIES  FOR  BRIDGES 

Porcelain  is  utilized  in  various  ways,  other  than  that  de- 
scribed, as  a  veneer  or  partial  crown  in  single  crown  work, 
and  bridge  construction  as  well. 

Since  a  bridge  is  nothing  more  or  less  thau  an  assemblage 
of  full  crowns,  combined  with  partial  crowns  called  dummies, 
some  of  the  various  methods  of  construction  of  the  different 
factors  of  bridges  will  now  be  considered. 


CROWN    WORK  S9T 

INTERCHANGEABLE    TOOTH    FACINGS 

To  obviate  fracture  in  soldering  and  facilitate  repairs  of 
facings  in  crowns  or  bridges,  various  forms  of  interchangeable 
or  replaceable  porcelain  facings  are  used  instead  of  regular 
long  pin  plate  teeth. 

Replaceable  teeth  and  facings  of  different  forms  are  now 
procurable  and  in  many  cases  are  useful,  not  only  in  repair 
cases,  but  are  coming  into  general  use  in  crown  and  bridge 
construction. 

The  three  most  common  forms  of  flat  back  teeth,  or  fac- 
ings of  this  type,  are  the  Steele,  the  Evslin  and  the  Dimelow. 
In  addition  to  these,  a  number  of  types  of  partial  crowns  of 
the  replaceable  class,  for  both  anterior  and  posterior  teeth  as 
well,  are  now  available. 

Among  these  partial  crowns  may  be  mentioned  the  Gos- 
lee,  Gardiner,  Merker  and  posteriors  of  Steele  and  Evslin 

STEELE'S  INTERCHANGEABLE  TOOTH 

This  consists  of  a  facing  of  porcelain  and  a  backing  of 
metal.  In  the  back  of  the  facing,  beginning  at  the  ridge  lap, 
a  hole  extends  into  the  porcelain,  toward  hut  not  to,  the  incisal 


edge.  This  hole  is  slotted  lingually  to  receive  a  projection 
from  the  backing.  The  backing  consists  of  a  piece  of  flat 
metal  plate,  to  which  is  affixed  a  tubular  post  which  enters  the 
hole  in  the  facing,  and  forms  the  attachment  between  facing 
and  crown  or  bridge. 

APPLICATION    OF   THE    STEELE   FACING 

The  application  of  a  Steele  facing  to  a  central  incisor 
crown,  as  just  described,  is  as  follows : 

The  cap  havi-ng  been  constrvicted  and  in  position  on  the 
cast,  a  facing  is  selected  and  ground  to  fit  the  root  cap.  The 
backing  is  then  adjusted  and  the  surplus  trimmed  to  the  mar- 
gins of  porcelain,  leaving  the  incisal  edge  longer  than  the 
porcelain. 


698  CROWN    WORK 

Sliould  tlu'  (uliular  ])(ist  ol'  tlic  hacking-  extend  beyond  tlie 
porcelain  at  the  ridge  laj),  it  is  ground  flush  witli  the  latter. 

The  facing  and  backing  are  now  ad,iust(>d  to  the  cap. 
Sticky  wax  is  applied  to  the  backing  and  melted  against  the 
root  cap,  being  careful  to  keep  it  from  flowing  on  the  porcelain. 


STEELE   FACING   WITH   BACKING 

TBUUrED      AND      IN      POSITION 

ADJUSTED   TO   ROOT   CAP 

The  assembled  crown  is  now  renioviMl  from  the  cast  and  the 
facing  slipped  from  the  backing. 

A  thin  film  of  Anti-Flux  is  applied  to  backing  on  that 
surface  against  which  the  porcelain  rests.  This  is  necessary 
to  prevent  the  solder  or  borax  flowing  over  the  backing,  as  the 
slightest  amount  of  either,  if  adherent  to  this  surface,  will 
prevent  the  facing  i^assing  to  place. 

The  metal  parts  of  the  crown  are  now  invested  and  sol- 
dered as  usual. 

To  clean  the  metal  structure  and  remove  the  borax  after 
soldering,  the  crown  should  be  heated  and  dropped  in  a  pickle 
of  30  per  cent  H.  CI.  If  boiled,  as  is  usually  the  case,  the  metal 
of  which  the  tube  is  composed  will  be  corroded  or  honey- 
combed. 

The  facing  is  slipped  in  position  on  the  backing,  and  the 
surplus  gold  reduced  with  stones  and  discs.  The  incisal  edge 
of  gold  should  be  continuous  with  the  labial  contour  of  porce- 
lain for  a  short  distance  to  afford  protection  to  the  latter 
against  incisal  stress.  When  the  metal  parts  are  polished,  the 
facing  is  set  in  position  with  cement  and  the  crown  is  ready 
for  setting  on  the  root. 

STEELE'S  INTERCHANGEABLE  TOOTH— TECHNIC  FOR 
POSTERIOR  CROWNS 

Bicuspid  and  molar  teeth  of  the  Steele  type  can  be  em- 
ployed in  crown  construction,  although  they  are  more  often 


CROWN     WORK  699 

used  as  dummies  in  bi'id.ne  work.  The  method  of  procedure 
is  as  follows : 

The  root  is  prepared,  a  root  cap  constructed  and  dowels 
extendiug  into  the  root  canals  are  fitted  and  attached  to  the 
cap  by  soldering.  At  the  same  time  the  cap  should  be  stiff- 
ened by  flowing  solder  over  it.  Casts  should  be  constructed 
and  mounted  on  the  occluding  frame. 

A  porcelain  tooth  of  suitable  size  is  selected  and  ground 
to  proper  length,  allowing  for  the  interposed  backing  of  gold 
over  the  ridge  lap. 

The  backing  is  then  fitted  to  the  porcelain  in  the  usual 
manner.  To  its  cervical  end  is  attached  an  extension  of  22  or 
24k.  gold  13'ate,  to  cover  the  ridge  laj)  and  extend  slightly 
beyond  the  buccal  margin  of  the  tooth. 

The  backed  tooth  is  now  set  in  position  on  the  root  cap 
and  waxed  in  proper  relation  to  the  latter,  after  which  the 
assembled  crown  is  removed  from  the  cast,  the  porcelain  re- 
moved from  position,  Anti-Flux  applied  to  the  buccal  surface 
of  the  backing,  the  metal  structure  invested  and  developed  to 
proper  contour  with  solder.  By  using  inlay  wax  in  assembling 
the  crown,  the  cap  and  backing  may  be  united  and  the  lingual 
contour  develo]3ed  liy  the  casting  method. 


STEELE     INTERCHANGEABLE     TOOTH,     TECHNIC     FOR     CAST 
DUMMIES 

A  facing  is  selected  and  ground  to  the  cast.  The  backing 
is  then  applied  and  trimmed  to  correct  peripheral  outline. 

Inlay  wax  is  now  applied  to  the  lingual  surface  of  the 
backing  and  the  desired  contour  of  the  tooth  is  developed  by 
carving. 


BICUSPID  DUMMY  CONSIST- 
ING OP  STEELE  PACING. 
BACKING.  OCCLUSAL  SUR 
FACE.  PARTIAL  LINOITAI. 
CONTOUR  DEVELOPED  .  IN 
IKL.\T    WAX 


RACKING  AND  WAX  WITH 
STEELE    PACING     RE- 
MOVED 


THE  DUMMY.   MINUS  PORCE- 
LAIN.   INVESTED   FOR    CAST- 
ING 


The  facing  is  now  removed,  a  sprue  former  attached  to 
the  wax  in  such  manner  that  when  invested  the  gold  will  enter 
the  matrix  at  the  highest  point. 


700  CROWN    WORK 

The  case  is  invested  and  cast  t)y  usual  methods  of  ijro- 
cedure. 

CONSTRUCTION    OF    DUMMIES    WITH    SWAGED    CUSPS 

When  it  is  deemed  advisabk>  to  construct  the  dummy  with 
swaged  occlusal  surface  the  larocedure  is  as  follows : 

A  tooth  of  suitable  size  is  selected,  ground  and  backed 
as  previously  described.  A  cusp  is  carved  in  plaster  or  some 
medium  by  means  of  wliich  a  counterdie  may  be  secured  and 
a  cusp  swaged. 

This  is  trimmed  and  fitted  to  the  backing,  the  facing  is 
adjusted  and  the  assembled  dummy  tested  as  to  its  occlusal 
relations  witli  the  opposite  teeth.  When  satisfactory,  the  fac- 
ing is  removed,  and  the  metal  structure  is  invested  and  sol- 
dered. 

REFLECTING    THE    BACKING    OVER    THE    CERVICAL    MARGIN 
OF  PORCELAIN 

In  some  cases  it  may  be  considered  advisable  to  reflect 
the  extension  which  is  added  to  the  principal  backing  of  a 
Steele  tooth  or  facing  over  the  gingival  margin  of  porcelain. 
The  object  in  doing  this  is  to  form  a  socked  or  gingival  cup 


WlLltum      lUtlLHjE      I  U.Ml'USED 
OF    STEELE    FACINGS.     CEN- 
TRAL INCISOK  KEMOVED 


for  the  better  protection  of  the  porcelain  against  stress.  When 
this  plan  is  followed  the  cervical  margin  of  the  porcelain 
should  be  beveled  slightly  at  the  expense  of  the  labial  or  buc- 
cal surface.  This  permits  the  reflected  gold  being  finished 
flush  with  the  porcelain  without  eliminating  the  shoulder. 

UTILIZING  LONG  PIN  PLATE  TEETH  FOR  REMOVABLE 
FACINGS 

One  of  the  main  considerations  in  the  use  of  replaceable 
facings  of  any  type,  in  addition  to  ease  of  repair  when  frac- 
tured with  use,  is  to  avoid  danger  of  fracture  of  porcelain  dur- 
ing soldering  operations. 

A  long  pin  facing,  or  ordinary  plate  tooth,  is  often  util- 


CROWN    WORK  701 

ized  as  a  removable  facing  for  the  same  reason  that  special- 
ized forms  of  interchangeable  teeth  are  employed. 

One  of  the  common  methods  of  procedure  is  as  follows: 

The  facing  is  ground  to  correct  form  and  Ijacked  witli  gold 

in  the  usual  manner.     The  pins  must  be  parallel  with  each 


LONG    PIN    TOOTH    GROtTND. 

BACIUNO        ADAPTED        ANB 

WAXED  IN  POSITION  ON  ROOT 

CAP.     FACING   11EM0\"ED 


PROXIMAL      VIEW      OF      RE 

MOVED      FACING.      SHOWING 

I'INS     BENT     GIXGIVALLY 


ASSEMBLED    BICUSPID    DUM- 
MY.   FACING   REMOVED.  CAR- 
BON   POINTS    INSERTED 


other,  but  not  necessarily  at  right  angles  to  the  inciso-gingival 
plane  of  the  lingual  surface  of  the  facing.  Usually  the  pins 
are  bent  slightly  toward  the  ridge  lap  to  give  them  a  hook- 
like contact  with  the  backing. 


LONG    PIN    FACING    GROUND 

AND  BACKED   FOB  BICUSPID 

DUMMT 


FACING     BACKED.     LINGUAL 

CONTOUR    DEVELOPED    IN 

WAX 


FACING        REMOVED        FROM 
DUMjn'.       CARBON       POINTS 
INSERTED     THROUGH     BACK- 
ING   IN  WAX 


The  backed  facing  is  waxed  in  correct  relation  to  its  root 
cap,  or  if  for  a  dummy  its  lingiuil  contour  is  developed  in 
wax  to  the  desired  form. 


The  facing  is  carefully  removed  and  in  the  openings  in 
the  wax  formed  by  withdrawal  of  the  pins,  small  pieces  of 
carbon  are  inserted,  the  ends  of  which  should  project  from  tlie 


702  CROWN    WORK 

backing.  This  is  necessary  in  order  that  they  may  be  caught 
in  and  held  by  the  investment. 

The  assembled  metal  parts  are  now  united  by  casting 
or  soldering.  The  carbon  points  are  broken  off  and  that 
enclosed  within  the  gold  is  drilled  out  to  receive  the  pins. 

The  facing  is  then  fitted  to  the  metal  and  when  correctly 
adjusted  the  pins  are  slightly  roughened  and  the  facing  set 
with  cement. 

THE  EVSLIN  INTERCHANGEABLE  TOOTH 

This  tooth  is  made  of  porcelain  in  the  form  of  facings  for 
anterior  replacements  and  with  fully  contoured  bucco-occlusal 
surfaces  for  posterior  replacemeiits. 

A  posterior  tooth  of  this  type,  in  its  general  contour,  is 
deficient  on  the  lingual  surface.  In  this  surface  a  dovetailed 
sjjace  exists  for  receiving  a  lug  of  clasp  metal  of  correspond- 
ing shape,  which  forms  a  part  of  the  metal  structure  of  the 
crown  or  dummy,  box  or  socket. 

In  this,  as  in  practically  all  other  types  of  replaceable  fac- 
ings, the  porcelain  serves  as  a  veneer  for  obscuring  the  essen- 
tial metallic  structural  parts  of  a  crown  or  bridge. 

The  dovetailed  lug  which  is  attached  to  the  socket,  and  the 
opening  in  the  porcelain  are  so  related  that,  in  adjusting  the 
two  parts  together,  the  facing  is  not  brought  into  close  con- 
tact with  the  backing  until  the  two  are  in  nearlv  correct  rela- 


tion to  each  other.  Stated  differently,  the  facing  approaches 
its  normal  position  or  seat  against  the  backing  and  base  of 
the  crown  in  an  inclined  direction  and  does  not  jam  or  become 
tightly  wedged  until  practically  seated.  For  this  reason  the 
incisal  edge  of  an  anterior  facing  may  be  beveled  at  an  angle 
and  the  backing  adapted  accordingly,  which,  when  reinforced 
with  solder,  forms  a  tip  or  metal  protection  for  the  porcelain 
against  stress. 

Backings  of  24  k.  34-gauge  gold  with  lugs  attached  may 
be  procured  or  tlie  prosthetist  may  attach  the  individual  lug 
to  any  gauge  and  carat  of  gold  he  desires  to  use  for  the 
backing. 


CROWN    WORK  703 

EVSLIN    FACINGS— TECHNIC    FOR    ANTERIOR    CROWNS 

Construct  the  root  cap  by  either  direct  or  indirect  method, 
adapt  and  solder  dowel.  Place  on  natural  root,  take  bite  and 
impression  and  mount  easts  on  occluding  frame.  Select  fac- 
ing of  suitable  form  and  color  and  grind  to  position.  Bevel 
incisal  edge  of  porcelain  at  an  angle  of  about  .35  degs.  to  lin- 
gual siirface.  The  facing  should  be  slightly  shorter  than  the 
required  length  of  crown  to  allow  for  extension  of  backing 
over  ridge  lap  and  for  the  thickness  of  the  metallic  incisal  tip. 

Anneal  backing  with  lug  attached  and  adjust  to  facing, 
passing  the  square  end  of  the  lug  into  the  slot  incisally.  Bur- 
nish and  swage  backing  directly  against  the  tooth,  annealing 


and  reswaging  until  i)erfect  adaptation  is  secured.  Trim 
backing  flush  with  mesial  and  distal  surfaces  of  facing,  but 
allow  it  to  project  slightly  beyond  both  cervical  margin  and  in- 
cisal edge. 

Apply  film  of  sticky  wax  over  lingual  surface  of  backing 
while  the  latter  is  still  on  the  facing  and  chill  it.  This  is  to 
prevent  distortion  of  the  backing  while  removing  the  facing. 
Heat  a  piece  of  stickj^  wax  and  apply  to  the  labial  surface  of 
the  facing.  This  serves  as  a  handle  in  separating  it  from  the 
backing.  The  separation  of  the  facing  and  backing  at  this 
time  is  necessary  to  see  that  the  two  have  not  become  wedged 
or  jammed  by  tlie  rough  edges  of  the  backing  left  by  the  file. 

When  this  test  has  been  carried  out  the  sticky  wax  is 
removed  from  the  facing,  the  latter  is  returned  to  the  back- 
ing, the  two  are  set  in  correct  relation  to  the  proximating 
teeth  on  the  root  cap  and  the  backing  firmly  luted  in  position 
with  sticky  wax." 

The  assembled  crown  is  now  removed  from  the  model, 
the  facing  again  removed  from  its  position,  and  tlie  liacking 
and  lug  coated  with  Anti-Flux  to  prevent  the  solder  from  flow- 


CROWN     WORK 


iiig  Oil  those  surraccs  against  whicli   tlic   iiorcclahi  comes  in 
contact. 

When  the  dniiiiny  is  constructed  witli  an  individnal  sad- 
dle, tile  backing  should  extend  over  the  ridge  lap  of  the  facing 


SEGTIONAI,     ^•IE^V     OF     FAf- 
ING.   LUG,  AND   BACKING 


Arl'EARANCE     OF     FINISHED 
CROWN 


to  the  labial  or  buccal  surface.  The  disc  of  gold  which  forms 
the  saddle  is  adapted  to  the  alveolar  border  and  extended 
labially  or  bucally  to  meet  the  backing  on  these  surfaces. 
When  assembled,  tlie  lingual  contour  of  the  dummy  is  com- 
pleted with  wax.  Usually  the  surface  of  the  plaster  cast  cov- 
ered by  the  saddle  is  scraped  slightly  before  assembling  and 
waxing  the  two  parts  together,  to  insure  firm  bearing  of  the 
completed  dummy  upon  the  ridge  when  the  bridge  is  perma- 
nently set. 

EVSLIN  TEETH— TECHNIC  FOR   POSTERIOR  CROWNS 

The  root  cap  having  been  constructed,  impression 
and  bite  taken,  casts  secured  and  mounted  on  the  occluding 
frame,  the  construction  steps  are  as  follows : 

A  posterior  tooth  of  suitable  form  and  color  is  selected 
and  ground  to  suitable  length.    The  mesial  and  distal  surfaces 


EVSLIN    MOLAR 


should  be  beveled  by  grinding  from  the  ridge  lap  occlusally. 
This  is  essential  so  that  the  sides  of  the  gold  socket  may  pass 
along  these  surfaces  without  ]:)rodncing  unnecessary  bulk  in 


CROWN    WORK  705 

the  iuterproximate  space.  Furthermore,  the  socket  iu  wliich 
the  porcelain  rests  can  thus  be  made  in  boxlike  form  and  will 
atford  better  retention  for  the  tooth. 

A  backing  with  lug  attached  is  adjusted  and  burnished  to 
the  porcelain.  The  surplus  is  then  cut  away,  the  tooth  im- 
bedded, occlusal  and  buccal  surfaces  down  in  moldine  in  the 
swaging  ring  and  the  backing  swaged  into  close  contact  with 
the  porcelain. 

Remove  the  tooth  and  backing  from  the  swager,  flow 
sticky  wax  over  the  backing  and  separate.  Correct  any  over- 
hang of  the  gold  margins,  return  tooth  to  ])lace  and  wax  back- 
ing to  root  cap,  building  the  lingual  contour  out  as  desired. 

The  assembled  crown  is  now  removed  from  the  model, 
the  porcelain  removed,  Anti-Flux  applied  to  the  buccal  sur- 
face of  the  backing,  the  case  invested,  as  usual,  for  soldering. 

The  wax  is  now  removed  from  between  the  root  cap  and 
the  socket  which  receives  the  liase  of  the  tooth,  the  case  heated 


and  solder  flowed  in  to  complete  the  lingual  contour  of  the 
crown. 

Pickle  in  acid  wash  and  return  the  facing  to  position, 
being  careful  not  to  use  much  force.  If  obstructions,  as 
nodules  or  excess  solder,  are  present,  remove  them  with  a  file 
or  engine  burs. 

The  surplus  gold  at  the  margins  is  removed  with  files,  en- 
gine stones  and  discs. 

The  direction  of  movement  in  filing,  grinding  and  polish- 
ing should  always  be  from  the  gold  toward  the  porcelain. 

When  the  metal  part  of  the  crown  is  roughh^  contoured 
and  moderately  well  smoothed  u]),  the  facing  is  cemented  in 
place. 

The  final  polishing  on  the  lathe  should  be  deferred  until 
the  facing  is  cemented  in  position,  or  the  square  margins  of 
the  metal  next  the  porcelain  will  l)e  lounded  and  thus  leave  a 
visil^le  groove  between  the  two. 


TUG  CROWN     WORK 

EVSLIN    TEETH— TECHNIC    FOR   ANTERIOR    DUMMIES    IN 
BRIDGE   WORK 

The  abutment  crowns  of  the  bridge  having  been  con- 
structed, they  are  set  in  position  on  the  roots  in  the  mouth 
and  a  bite  and  an  impression  secured.  The  casts  are  then 
formed  and  mounted  on  the  occluding  frame. 

Evslin  facings  of  suitable  color  and  form  to  meet  the  re- 
quirements of  the  case  are  selected  and  ground,  as  when  long 


THESE    fUTS    SHOW    PROTECTION    AFFORDED    INCISAI, 

EDGE  OF  PORCELAIN.  ALSO  FORM  OF  BACKING  SOME- 

TIMES  EMPLOYED  FOR  ANTERIOR  FACINGS 

pin,  flat  back  facings  are  used,  tlie  ridge  lap  of  the  facing 
being  ground  to  fit  the  irregularities  of  the  border. 

The  facing  is  then  backed  as  for  a  crown  except  that 
usually  the  backing  does  not  extend  onto  the  ridge  lap. 

The  extent  to  which  the  backing  covers  the  porcelain, 
however,  depends  upon  the  type  of  dummy  bein.g  constructed, 
as  it  is  sometimes  extended  over  the  ridge  la])  to  form  a  socket. 

INTERCHANGEABLE  TEETH 

Removable,  replaceahle  and  hiterchaugeahle  teeth  of  vari- 
ous forms  have  been  designed  for  use  in  crown  and  bridge 
work,  the  object  of  which  is  to  obviate  subjecting  the  porce- 
lain to  soldering  operations  and  thereby  avoid  danger  of  frac- 
ture from  this  cause. 

In  the  use  of  teeth  of  this  type,  the  metal  structure  is 
built  around  and  adapted  to  the  porcelain,  and  after  comple- 
tion the  teeth  are  cemented  in  position. 

A  distinction  should  be  made  between  removable  flat  bach 
facings  and  certain  types  of  removable  or  replaceahle  teeth. 
A  replaceable  facing  usually  has  within  the  body  of  porce- 
lain a  slotted  opening  which  receives  a  correspondingly  shaped 
lug  of  metal  projecting  from  the  crown  or  bridge  structure. 
A  replaceahle  tooth  usually  has,  in  addition  to  this  or  some 
similar  means  of  anchorage,  a  standardized  base  composed  of 
planes,  so  disposed  as  to  aid  in  resisting  displacement  under 
masticatorv  stress. 


CROWN    WORK  707 

A  tooth  formed  with  a  standardized  base  of  the  character 
described  can  thus  be  readily  replaced  in  case  of  fracture. 

Replaceable  teeth  represent  more  nearly  the  anatomic 
types  of  natural  teeth  than  do  facings  of  any  class.  Not  only 
are  the  labial  surfaces  of  the  anterior  teeth  represented,  but 
a  portion  of  the  lingual  surfaces  are  reproduced,  while  in  the 
posterior  teeth,  the  buccal,  occlusal  and  a  portion  of  the  lin- 
gual surfaces  are  developed  in  porcelain. 

Among  the  well-known  teeth  of  this  type,  as  well  as  new 
forms  which  have  recently  appeared,  are  the  Goslee,  the 
Steele  and  Evslin  posteriors,  the  Gardener  and  the  Merker. 
A  brief  description  of  the  Steele  and  the  Evslin  teeth  has 
already  been  outlined. 

THE  GOSLEE  TOOTH 

This  consists  of  a  partially  contoured  porcelain  crown, 
deiicient  in  its  lingual  areas.    Within  the  lingual  side,  and  at 


right  angle  to  the  long  axis  of  the  tooth,  is  developed  a  flat 
seat.    In  this  seat  is  a  cylindrical  opening,  extending  incisally 


□ 


A       GOSLEE       INCISOR       FACING 
SHOWING     BASAL.     SEAT     OPEN- 
ING   FOR    DOWEL    AND    FLAKING 
LINGUAL    SURFACES 


or  occlusally  into  the  body  of  the  tooth,  for  the  reception  of 
a  dowel  which  forms  a  part  of  the  metal  structure.    The  sides 


708  CliOWN    WOriK 


Hare   (Uilwai'dly,   and   (iccliisally   or   iiii-isall.\ ,    I'l-oiii   tlu*   seat. 
Tji  the  hic'usiiids  and  iiidlars,  the  Hai'iiii;-  sides  tcniiiiiatc  within 


and  form  a  depressed  shoulder  just  beneath  the  mesial,  distal 
and  lingual  surfaces  of  the  crown. 

TECHNIC    OF    APPLICATION    OF   THE    GOSLEE    TOOTH    IN 
CROWN  WORK 

Prepare  a  root  cap,  preferably  by  the  indirect  metho<l, 
using  36  gauge  platinum  or  pure  gold  i)late.  By  forming  a 
depressed  area  in  the  central  portion  of  the  root,  the  walls  of 
which  are  but  slightly  divergent,  the  root  periphery  may  be 
decidedly  beveled  so  that  in  the  completed  crown  no  peri- 
pheral shoulder  will  be  present.  In  forming  the  cap,  it  is 
swaged  into  the  depressed  area  and  thus  forms  a  shoulder 
for  guiding  the  cap  to  and  holding  it  in  correct  position  on  the 
root. 

Through  openings  in  the  cap,  dowels  are  introduced  into 
the  root  canals.  The  relation  between  the  dowels  and  cap  is 
secured  and  their  subsequent  attachment  b>"  soldering  is  ac- 
complished by  methods  previously  described.  At  the  time  of 
attaching  the  dowels,  high  grade  solder  or  22k.  plate  should 
be  flowed  over  the  root  cap  to  stiffen  it  and  till  the  depressed 
central  area. 

The  cap,  with  dowels  soldered  in  place,  is  now  returned  to 
the  root  and  the  perijiheral  margin  of  the  band  corrected  by 
burnishing. 

An  impression  and  bite  or  a  bite-impression  is  secured, 
removing  it  from  the  mouth  with  the  face  bow. 

A  film  of  wax  is  flowed  over  the  dowels  and  inside  the 
root  cap  to  facilitate  removal  of  the  cap  from  the  cast  later  on. 

The  cap  is  placed  in  position  in  the  imjiression  and  casts 
developed  and  attached  to  the  occluding  frame. 

A  Goslee  tooth  of  suitable  size  is  selected  and  ground,  if 
necessary,  to  meet  requirements. 


CROWN    WOJtK 


It  is  then  imbedded,  occlusal  end  down,  in  modeling  com- 
pound, in  the  swaging  ring.  The  surfaces  to  which  the  gold  is 
to  be  applied  should  be  above  the  ring  margins,  so  that  the 
rubber  in  the  swager  mav  force  the  gold  against  all  areas. 


GOSLEE    TOOTH    INVESTED    IX    SWAGING    RING.    I'REPARA 

TORY  TO  ADAPTING  SOCKET.     TOOTH  SET   IN   A   DIA(!ONAI. 

POSITION   FOR   SWAGING 

A  disc  of  36  g.  pure  gold,  or  platinum,  somewhat  larger 
than  the  areas  to  be  covered,  is  applied  to  the  crown  base,  and 
with  finger  pressure  and  burnisher  adapted  to  the  porcelain. 

When  reasonably  close  adaptation  has  thus  been  secured 
and  the  excessive  surplus  removed,  final  adaptation  is  de- 
veloped by  swaging. 


GOSLEE  TOOTH  SET  IN  UPRIGHT 
POSITION  FOR  SWAGING  SOCKflT 


BACKING    OR    SOCKET    ADjiPTED 

TO    GOSI.EE    TOOTH.      DOWEL    IN 

POSITION 


An  opening  in  the  gold  socket  is  now  made  for  the  re- 
ception of  the  short  dowel,  which  may  be  of  regular  form 
and  headed  on  one  end,  or  a  piece  of  14  g.  clasp  metal  wire, 
sufficiently  long  to  project  slightly  beyond  the  socket,  may 
be  used.    With  dowel  in  position,  the  cap  is  reswaged. 


CKOWN     WORK 


Wax  is  applied  in  the  ddwcl  and  ai;aiiist  tlic  gold,  the  two 
removed  and  nuited  witli  liish  gvade  solder.  The  gold  should 
also  be  stiffened  l)y  flowing  a  film  of  solder  over  its  general 
surfaces,  hut  not   nloiig  the  margins. 


^M 


METAL    SOt'KET.     SWACKIi,     Willi     liOWEL    ATTAIIIEI). 

GOSLEK    TOOTH.       FORM     (IK     HOOT    CAP     ISIAl.NV     KM- 

I'l.OYED    KOIl    MllLAR    TEETH 

The  socket  is  now  returned  to  the  porcelain  for  final 
swaging,  after  which  the  tooth  is  removed  from  the  moldine. 

The  tooth  in  its  socket  is  now  adjusted  to  the  root  ca]i  and 
waxed  in  position. 

Previously,  however,  the  root  cap  is  heated  slightly  to 
soften  tlie  wax  around  the  dowel,  removed,  freed  from  wax, 
and  returned  to  position  on  the  cast. 


TROWN        WITH         SOIKET,         All 

.USTED    TO     miOT     CAP.     RE.II)\ 

FOR     WAXIXr,     TOfiETIiER 


The  assembled  crown  is  waxed  to  the  desired  contour, 
removed  from  the  cast,  tlie  porcelain  removed  from  its  socket 
and  the  metal  structure  invested  for  completing  the  required 
contour,  either  by  soldering  or  casting. 

The  Goslee  tootli  is  capable  of  a  wide  range  of  applica- 
tion in  bridge  work,  when  sufficient  space  is  present  in  which. 


CROWN    WORK 


r.osi.EE  nRinnic  ix  position-  on  cast 


712  CROWN    WORK 

in  addition  to  the  porcelain  icplaccint'iits,  a  ri^id  iiii'tal  stnie- 
ture  may  be  introduced. 

The  individual  saddle  is  ol'tcn  a]i|ilicil  in  connection  with 
teeth  of  this  type  to  very  n'reat  hygienic  advantanc 

THE  GARDINER  REPLACEABLE  TOOTH 

This  tooth  is  supplied  for  both  anterior  and  posterior 
replacements.  In  form,  it  is  somewhat  novel,  having  a 
broader  base  than  occlusal  area. 

Instead  of  liaving  an  opening  within  tlie  body  of  the 
crown  for  the  reception  of  a  lug,  the  l)ase  of  porcelain  pre- 
sents a  square  or  rectangular  projection,  which  is  received 
by  and  enclosed  within  a  corresjiondingly  shaped  depression 
in  the  socket. 

To  give  the  crown  additional  stability  and  resistance  to 
stress,  the  base  is  composed  of  flat  planes,  placed  at  varying 


CERVICAI.    \IEW.    SHOWING    DIS-  PROXIMO-CERVICAL       \1EW       OF 

POSITIONS      OP      THE      VARIOUS  OAKDINER        TOOTH.       SHOWING 

BASAL,  PLANES  ANCHORAGE   LUG  OF  PORCELAIN 

angles.  These  planes  are  so  disposed  as  to  tend  to  seat  the 
crown  firmly  in  its  socket  under  masticatory  stress. 

Because  of  the  extremely  constricted  bulk  of  porcelain 
entering  into  the  construction  of  the  tooth,  it  can  be  applied 
in  many  eases  in  limited  spaces  without  requiring  appreciable 
modification  of  form. 

The  planes  are  so  disposed  as  to  give  uniformity  of  thick- 
ness to  the  occlusal  body  of  porcelain.  The  projecting  lug  is 
placed  directly  under  the  lingual  cusps,  thus  giving  support 
to  an  otherwise  weak  area  of  porcelain. 

TECHNIC    OF    APPLICATION    OF    THE    GARDINER    TOOTH 

The  root  cap  is  formed  by  any  of  the  previously  described 
methods,  an  impression  secured,  casts  developed,  and  mounted 
on  the  occluding  frame. 


CROWN    WORK  Ti:; 

A  tooth  of  8uital)l('  form  and  color  is  selected  and  titted 
to  the  root  cap,  due  allowance  beiiij;-  made  in  its  lengtli  for 
the  interposition  of  the  socket. 

The  tooth  is  then  imbedded,  occlusal  end  down,  in  mold- 
ine,  in  the  swaging  ring,  and  a  36  gauge  i)ure  gold  or  platinum 
socket  developed  by  burnishing  and  swaging. 

When  adapted,  the  margins  of  the  socket  are  trimmed  so 
as  to  form  a  collar  around  the  entii'e  peripheral  margins  of 


the  tooth,  as  should  be  the  case  in  practically  all  types  of 
replaceable  teeth. 

To  prevent  distortion  in  handling  and  soldering,  a  film 
of  high  grade  solder  should  be  flowed  on  the  under,  or  cervical, 
areas  of  the  socket,  but  not  over  tlie  peripheral  margins. 

When  this  plan  is  adopted,  the  margins  should  be  rebur- 
nished  to  the  porcelain  before  investment. 

The  socket,  with  crown  in  position,  is  now  adjusted  to  the 
root  cap,  the  two  united  with  wax,  the  assembled  crown  re- 
moved from  cast,  the  porcelain  removed  from  socket  and  the 
metal  parts  invested  for  soldering  or  casting. 

APPLICATION   OF  THE  GARDINER   TOOTH   IN   BRIDGE  WORK 

Teeth  of  suitable  form  and  width  are  selected  to  fill  the 
space  between  tlie  abutment   supixirts.     Sockets  are  formed 


LABIAL       VIEW      O^F       IIETAL 
STRITTIRK  OF  BRIDGE 


in  the  manner  described.  These  should  be  stitTened 
with  a  solder  or  plate  that  will  not  fuse  in  the  final  assembling 
and  soldering  of  the  bridge. 


CROWN    WOUK 


Before   pennaiieiilly    altacliini;'    ]i()rcelaiii    teeth   to    their 
sockets  with  eenieiit.  the  surfaces  to  he  covered  hv  the  hitter 


OUT        SHOWING        MANXEB       OF 
PLANOINi;   THE   METAI,   SOCKETS 
TO     INCREASE     PORCELAIN     AN- 
CHORAGE 


should  be  etched  with  iiydro-tiuoric  acid,  or  tlie  glaze  removed 
with  discs. 

THE  MERKER  REPLACEABLE  TOOTH 

This  tooth,  comparatively  new,  possesses  two  points  of 
interest.    The  base  is  com]iosed  of  two  flat  planes  disposed  at 

PBOXIMAL    VIEWS    OF    MERKER    ANTERIOR 

AND    POSTERIOR    TEETH.    SEATED    ON 

METAL  BASES 

right  angles  to  the  long  axis  of  the  tooth.     A  small,  rather 
deep  opening  in  each  plane  extends  occlusally  for  the  recep- 


CROWN    WORK 


715 


tiou  of  two  iridio-phitiiiiiin  anchor  dowels,  whicli,  during  con- 
stnictive  stages,  are  adjusted  to  llie  metal  socket. 


^^^l 


ANTERIOH    BRinnii    COML'OSEl)    l)F    MKRKElt 
REPI.ACEARLE    TEETH.     TWO    CENTRAL    IN- 
CISORS    OF     WHICH     ARE     REMOVED     FROM 
POSITION 


The  application  of  tliis  e 
is  practically  identical  to  tin 
crown. 


iwn  in  crown  and  bridge  work 
steps  outlined  for  the  Goslee 


THE  DIATORIC  USED  AS  A  REPLACEABLE  TOOTH 

Diatoric  ])osterior  teeth  are  often  nsed  as  replaceable 
teeth  in  bridge  structures.  When  utilized  for  such  purpose 
the  basal  periphery  is  usually  reduced  so  as  to  permit  the 


POSTERIOR    IMlllMlE    FETTED    WITH    DIA- 
TORICS     AS     REPLAC'EAm.E     TEETH.       A 
I.1)N(i    PIN.     CUSPID    PLATE    TOOTH    AP- 
PLIED   AS   A   REPLACEABLE    PACINC, 


formation  of  a  collar  around  the  socket.  In  addition  to  the 
anchorage  afforded  by  the  ]ieripheral  collar,  during  the  swag- 
ing of  the  socket,  the  gold  is  carried  into  the  central  opening 
of  the  crown  base.     This  forms  a   projection   on   the  metal 


71U  CROWN    WOKK 

structure  and  fulfills  the  jjurpusc  of  a  dowel.  In  some  cases 
.short,  grooved  dowels  are  adapted  to  the  socket,  as  in  the 
Goslee  crown. 

FULL  CONTOURED   PORCELAIN   CROWNS 

Crowns  composed  of  porcelain  and  metal,  although  ad- 
mirably adapted  to  and  indispensable  in  some  cases,  are  fre- 
quently deficient  in  esthetic  effects,  the  tinge  of  porcelain  being 
adversely  affected  by  the  presence  of  the  metal. 

To  overcome  this  very  decided  objection,  full  contoured 
porcelain  crowns  are  very  often  used  when  conditions  as  to 
mesio-distal  and  occluso-gingival  space  will  jjermit. 

Crowns  of  this  type  are  supplied  by  the  manufacturers,  in 
great  variety  of  forms  and  shades,  and  when  well  selected  and 
skillfully  applied  to  natural  roots,  are  not  distinguishable 
from  natural  teeth. 

Full  contoured  porcelain  crowns  may  be  divided 
into  two  general  classes,  viz.,  fixed  doivel  crowns  and  detached 
dowel  crowns.  The  principal  advantage  of  a  detached  dowel 
crown  over  one  having  a  fixed  dowel  is  that  the  porcelain  base 
of  the  former  can  be  readily  adapted  to  the  root  face,  the 
absence  of  the  dowel  permitting  unrestricted  grinding  on 
areas  that  interfere  with  close  peri])heral  adaptation. 

FIXED    DOWEL    CROWNS 

The  Logan,  Twentieth  Century  and  Johnson  tJc  Lund  are 
types  of  the  attached  dowel  crown,  the  dowel  l)eing  enclosed 


vAKioi  s  \ir:«.s  OF  tiii:  r.iicAN 


within  the  body  of  porcelain,  and  the  latter  fused  around  it. 
Since  the  technic  of  application  of  crowns  of  this  type  is  sim- 
ilar, a  description  of  one  will  answer  for  all,  whether  plain 
or  combined  with  a  root  cap  or  cast  base. 


CROWN    WORK  71? 

TECHNIC    OF    ADAPTING    A    PLAIN    LOGAN    CROWN    TO    A 
NATURAL  ROOT 

It  will  be  assumed  that  the  apex  of  the  root  to  be  crowned 
has  been  sealed  with  a  permanent  tilling". 

The  remaining  portion  of  the  natural  crown  is  reduced  by 
means  of  stones  and  Ottolengni  root  facers,  slightly  beneath 
the  gum  margin,  being  careful  while  doing  so  to  avoid  un- 
necessary injury  of  the  soft  tissues. 

The  root  canal  is  iirst  enlarged  with  graded  sizes  of 
round  burs  as  previously  described,  omitting  the  use  of  No. 


10  and  substituting  therefor  a  tissure  bur,  the  diameter  of 
which  is  slightly  larger  than  the  mesio-distal  thickness  of  the 
dowel,  next  the  crown  base. 

By  means  of  the  fissure  bur  the  canal  is  enlarged  labially 
and  lingually  sufficiently  to  receive  tbe  dowel  at  its  greatest 
diameter,  while  the  mesial  and  distal  dentin  walls  of  the  root 
are  not  materially  reduced  and  consequently  weakened  as  is 
the  case  when  a  taper  reamer  is  emplo^^ed. 

From  a  stock  of  crowns  one  of  suitable  form  and  color  is 
selected.  In  size  it  should  be  slightly  longer  than  required, 
since  both  base  and  incisal  edge  must  be  modiiied  by  grinding, 
the  first  to  secure  necessary  adaptation,  the  second  for  esthe- 
tic reasons.  The  width  of  the  crown  should  be  sufficient  to 
afford  strong  knuckling  contact  with  proximating  teeth.  The 
periphery  of  the  crown  base  should  slightly  exceed  that  of  the 
root  face,  since  a  subsequent  step  reduces  the  excess  of  porce- 
lain until  it  coincides  with  the  root  periphery.  If  too  small,  a 
shoulder  is  formed  which  cannot  be  obliterated,  the  root  pro- 
jecting beyond  the  crown  base. 

ADAPTING  THE  CROWN  TO  THE  ROOT 

The  crown  is  now  applied  to  the  root  and  the  points  re- 
quiring gross  reduction  are  removed  with  suitable  stones. 
Close  adaptation  is  developed  by  interposing  a  disc  of  carbon 


718  CRCnVN     WCJKK 

paper  between  the  crown  l)asc  and  root  face  to  mark  the  high 
points.  These  are  groiiml  away  and  the  steps  repeated  until 
close  23eripheral  adajitalion  between  crown  and  root  is  secured. 

Care  should  be  observed  while  making  these  tests  to  see 
that  the  crown  is  in  correct  alignment  labio-lingually,  which 
may  be  done  by  bending  the  dowel. 

When  close  adaptation  of  crown  base  to  root  face  has 
been  developed,  the  incisal  edge  or  other  areas  of  the  crown 
are  modified  with  stones  and  discs,  to  coincide  with  tlie  type 


LOGAN   CROWN   APPLIED   TO 
ROOT   BEFORE   ADAPTING   TO 
ROOT  PACE  HAS  BEEN  ACCOM- 
PLISHED 


CARBON   PAPER   INTERPOSED 

BETWEEN   CROWN   BASE  AND 

ROOT    FACE.    TO    DISCLOSE 

POINTS  OF  INTERFERENCE 


of  proximating  teeth.  When  these  show  wear  or  ridged  sur- 
face markings,  similar  surfaces  and  markings  should  be  de- 
veloped on  the  crown. 

Sometimes  the  jiroximating  natural  teeth  show  unusual 
colors  in  or  beneath  the  enamel,  and  which  cannot  be  removed 
by  any  means  employed.  The  setting  of  a  porcelain  crown 
or  replacement  of  any  type  between  teeth  so  marked,  unless  it 
is  of  closely  corresponding  color,  is  unsightly.  Porcelain 
stains,  both  oil  and  water  colors,  are  procurable,  by  means  of 
which  a  tooth  or  crown  can  be  made  to  match  the  most  unusual 
shades  found  in  natural  teeth.  The  technic  of  application  of 
such  colors  is  simple.  The  tooth  to  be  stained  is  thoroughly 
cleansed  and  washed  in  alcohol,  a  pigment  of  the  desired 
shade  is  mixed  with  water  or  one  of  the  essential  oils  as  cloves 
or  glycerin,  and  applied  with  a  small  brush  by  painting  it 
over  the  surfaces  or  stippling,  the  degree  of  color  being  de- 
pendent upon  the  layer  of  pigment  applied. 

When  applied,  the  colors  should  be  slowly  dried,  moderate 
heat  accellerating  the  evaporation  of  the  liquid.  It  is  then  in- 
troduced in  the  furnace  and  vitrified,  the  tooth  resting  on  a 
bed  of  pulverized  silex,  on  the  slab,  and  face  upward.  The 
colors  glaze  at  a  temperature  varying  from  1100  degs.  F.  to 


CROWN    WORK  719 

1500  degs.  F.  A  little  experience  with  these  stains  will  en- 
able the  prosthetist  to  produce  most  beautiful  esthetic  results. 
In  case  a  suitable  shade  of  Logan  or  any  of  the  types  of 
crowns  mentioned  cannot  be  procured,  the.y  should  be  stained 
to  coincide  with  the  colors  observed  in  the  natural  teeth. 

SECURING    PERIPHERAL    ADAPTATION    OF    CROWN    BASE 
TO  ROOT 

The  final  step  in  adaptation  consists  in  removing  the  ex- 
cess or  overhang  of  porcelain  over  the  root,  and  line  the  two 
peripheries  up  until  they  form  continuous  surfaces.  The  steps 
are  as  follows: 

A  disc  of  white  baseplate  gutta  percha,  slightly  larger 
than  the  crown  base,  is  punctured  in  its  center  and  passed 
over  the  dowel  and  against  the  porcelain.    Moistening  the  sur- 


GlITTA  PERCHA  INTERPOSED 
BETWEEN  CROWN  BASE  AND 
ROOT  FACE  TO  DISCLOSE  EX- 
TENT OP  PROJECTING  PORCE- 
LAIN   OVER    ROOT    MARGINS 


face  of  the  disc  next  the  crown  base  with  oil  of  cajaput  will 
cause  the  gutta  percha  to  adhere  flrmlv  to  the  porcelain. 

The  crown  and  disc  are  warmed  and  the  crown  forced  to 
place  on  its  root.  Under  pressure,  the  gutta  percha  being 
forced  against  the  root,  an  impression  of  not  only  the  face  but 
of  the  periphery  as  well  is  secured.  A  blast  of  cold  air 
directed  on  the  disc  will  chill  it  so  that  removal  can  be  ef- 
fected without  distortion.  If  the  steps  have  been  properly 
carried  out  a  distinct  impression  of  the  root  periphery  will 
be  seen  in  the  gutta  percha. 

A  coarse,  large  size  engine  stone,  running  at  a  high 
speed,  is  lightly  applied  to  the  surplus  gutta  percha,  and  the 
latter  removed  until  the  stone  comes  in  contact  with  the  pro- 
jecting shoulder  of  porcelain.  The  grinding  is  continued  until 
the  porcelain  is  reduced  to  the  peripheral  margin  of  the  root 


720  CIJOWN     WORK 

as  indicated  in  the  gutta  perciia  impression.  During  the  grind 
iiig  [)roeess  tlie  crown  and  disc  slionld  he  inunorscd  in  cold 
water  from  time  to  time  to  ol)viat(>  distortion  of  the  gntta 
perclia  from  frictional  heat  of  the  stone. 

During  lirst  grinding  tlie  prosthetist  shouhl  not  attempt 
to  develop  correct  axial  contour  to  the  crown,  but  merely  to 


ATPLICATION       OK       STONE       TO 

RKMOVE      EXCESS      PERITHERAI. 

PORCELAIN 


remove  tlie  projecting  shoulder,  after  which  the  gutta  perclui 
may  be  removed  and  axial  contour  developed  with  suitable 
stones.  The  tinal  polish  on  surfaces  which  have  been  ground 
and  disced,  is  accomplished  with  putty  powder,  applied  with 
a  soft  wood  or  hard  felt  wheel,  running  at  high  speed. 

The  crown,  having  been  ground  to  correct  outline  form, 
its  base  shaped  to  coincide  with  the  root  periphery,  its  sur- 


faces polished,  and,   if  necessary,   stained,   it   is   ready  for 
mounting  on  the  root. 

SETTING  THE  CROWN 

Cotton  rolls  should  be  jjlaced  under  the  lip  or  in  such 
location  as  to  guard  against  moisture  during  the  setting  of 
the  crown.  The  root  canal  and  root  face  should  be  thoroughly 
dried  with  cotton  points  and  warm  air.  Cement  of  medium 
consistencv  is  thoroughlv  mixed  and  worked  into  the  root 


CROWN     WORK  721 

canal  and  applied  oxer  the  root  face.  The  dowel  and  crown 
base  is  also  covered  with  a  thin  tihn,  and  if  a  depression  is 
present  in  the  base  of  the  crown  it  shonld  also  he  filled.  The 
crown  is  now  set  in  position,  considerable  force  l)eini;-  recpiired 
to  seat  it  and  expel  the  excess  cement. 

Pressiire  should  lie  maintained  upon  the  crown  until  the 
cement  has  set,  which  usually  requires  from  eight  to  ten  min- 
utes. Further  time  should  he  given  the  cement  to  thoroughly 
harden  before  removing  the  peripheral  surplus.  A  small, 
angular  blade  instrument  like  a  gold  knife,  used  in  finishing 
the  margins  of  gold  fillings,  can  be  used  in  removing  the  sur- 
plus cement  which  should  be  cut  or  shaved  rather  than  broken 
from  along  the  joint. 

When  loosened  and  the  particles  ai'e  removed  as  well  as 
can  be  witli  cotton  and  pliers,  the  gum  tissues  should  be 
syringed  with  warm  water  and  the  crown  tested  as  to  its  in- 
cisal  or  occlusal  relation  with  opposite  teeth.  If  satisfactory 
the  patient  is  dismissed  with  instructions  to  avoid  subjecting 
the  crown  to  any  stress  for  several  hours,  in  order  that  the 
cement  may  not  be  disturbed  until  thoroughly  crystallized. 

THE  BANDED  LOGAN  CROWN 

The  technic  of  construction  of  a  l)anded  Logan  crown  is 
as  follows:  A  root  cap  is  constructed  by  methods  previously 
outlined  under  the  heading,  "Construction  of  a  Porcelain 
Faced  Crown"  (page  641).  The  enlargement  of  the  root  canal 
for  the  reception  of  the  rectangular  dowel  of  the  Logan  crown 
is  essentially  the  same  as  detailed  for  a  plain  Tjogau  crown. 

ADAPTING  THE  LOGAN  CROWN  TO  THE  ROOT  CAP 

Before  jierforating  the  root  cap  for  the  reception  of  the 
dowel  the  root  canal  should  be  enlarged  and  the  crown  adapted 
to  the  root  face  by  grinding.  The  lingual  side  of  the  crown 
base  sliould  he  reduced  to  form  a  V-sbaped  space,  which  later 
on  is  filled  with  solder. 

The  general  ada]itation  of  the  crown  to  root  face  having 
been  developed,  the  root  caj)  is  set  in  position  on  the  root 
and  with  a  burnisher  indented  to  indicate  the  location  and  ex- 
tent of  the  opening  for  dowel.  A  series  of  small  holes  can 
be  drilled  through  the  cap  while  in  position  on  the  root,  or  it 
can  be  removed  and  the  holes  punched  with  plate  punch.  In 
either  case  the  several  holes  are  connected  by  passing  a  fine 
fissure  bur  through  the  intervening  divisions. 


722 


CROWN    WORK 


The  dowt'l  is  now  forced  through  the  more  or  less  irregu- 
hir  slot,  the  excess  gold  being  forced  into  the  entrance  of  the 
root  canal,  the  margins  of  gold  thus  fitting  tightly  against  the 
dowel. 


PREPARED       ROOT      WITH      CAP. 

NOTICE    FORM    OF    OPENING    IN 

CAP    REQUIRED    FOR    DOWEL 


CROWN    liESTINO    (IX    ROOT    CAP. 
DOTTED    LINE    SHOWS    LINGUAL 
REDUCTION    OF    PORCELAIN    RE- 
QUIRED 


A  disc  of  gold,  slightly  larger  than  the  crown  base,  is 
perforated  with  a  corresponding  rectangular  slot,  placed  on 
a  large  corjv  and  the  dowel  forced  through  it  until  the  crown 
base  rests  upon  the  disc.  By  repeated  burnishing  and  an- 
nealing the  disc  is  closely  adapted  to  the  porcelain. 

The  i^eripheral  excess  of  the  disc  is  removed,  close  to, 
but  not  exactly  even  with  the  crown  periphery,  a  slight  sur- 


plus being  necessary  to  insure  the  solder  being  drawn  out  to 
full  contour. 

The  cap,  disc  and  crown  are  now  assembled  on  the  root 
and  their  relation  noted.  Particular  attention  should  be  given 
the  labial  alignment  of  the  crown  and  band.  Wlien  the  crown 
sets  to  the  lingual  of  the  labial  band  surface,  it  may  be  brought 
forward  by  bending  the  dowel  to  the  lingual  and  extending 
the  slot  in  the  cap  to  the  labial,  it  being  necessary  in  some 
cases  to  ream  the  root  canal  also  for  the  accommodation  of 
the  dowel.    When  the  crown  extends  to  the  labial  of  the  band 


CROWN    WORK 


surface  and  its  labial  aligiinient  is  approximately  correct,  the 
solder  ma.y  be  drawn  through  so  as  to  till  the  space  between 
the  disc  and  labial  band  surface,  and  the  gold  and  porcelain 


SECCRING    RELATION    BETWEEN 

CBO\VN.    DISC.    AND    ROOT    CAP. 

\VITH    WAX 


dressed  smoothly  to  form  a  continuous  surface  in  the  final 
finishing  of  the  crown. 

Two  thicknesses  of  gold  plate,  the  disc  and  cap  top,  are 
interposed  between  the  root  face  and  crown  base.  Both  of 
these  may  be  reduced  somewhat  to  bring  the  crown  closer  to 
the  root,  and  lessen  the  display  of  gold  on  the  labial  surface  of 
the  finislied  crown. 

ASSEMBLING    THE    SEVERAL    PARTS    OF    THE    CROWN 

The  cap,  disc  and  crown  having  been  fitted  in  correct  rela- 
tion to  each  other  on  the  natural  root,  they  are  assembled  as 
follows : 

The  crown  and  disc  are  removed,  all  of  the  parts  dried, 
sticky  wax  is  a])plied  around  the  dowel  and  a,gainst  the  disc 
and  softened  with  a  hot  spatula.     The  crown  is  then  forced 


THE       ASSEMIil.ED     PARTS     RE- 
MOVED,     READY      FOR      INVEST- 
MENT 


against  the  cap,  the  inter]iosed  wax  pressing  the  cap  against 
the  root,  and  the  disc  against  the  crown  base.  AVlien  the  wax 
is  chilled,  the  three  parts,  now  firmly  united,  are  removed  from 


724  CKOVVN    WORK 

the  root,  tlie  surplus  wax  trimmed  away  and  auy  openings 
between  cap  and  disc  tilled  in  with  wax,  when  tlie  crown  is 
ready  for  investment. 

INVESTING  THE   BANDED  LOGAN    FOR   SOLDERING 

The  investment  of  a  banded  Logan  crown  for  soldering 
is  essentially  the  same  as  the  investment  of  a  porcelain-faced 
crown.  The  joint  surfaces  between  disc  and  root  cap  must 
be  entirely  exposed  to  prevent  the  confinement  of  air  in  con- 


L-RO\VN  INVESTED  FOR  SOLDER- 
ING. NOTICE  SMALL  WEDGE  OF 
METAL  TO  BE  INSERTED  BE- 
TWEEN ROOT  CAP  AND  DISC 
TO  PREVENT  DISPLACEMENT  OF 
THE    LATTER    IN    SOLDERING 


stricted  spaces,  and  further,  so  that  in  soldering  it  may  read- 
ily be  seen  when  the  joint  is  filled. 

When  the  investment  has  hardened,  the  surplus  trimmed 
away,  and  the  joint  surfaces  freely  exposed,  the  wax  is  re- 
moved by  pouring  a  fine  stream  of  boiling  water  into  the  space. 
Care  should  be  taken  to  remove  every  particle  of  wax,  for  if 
any  is  left  and  flux  is  ajjplied,  it  will  act  as  a  carrier  for  the 
latter,  for  when  heat  is  applied  the  wax  will  melt  and  pass 
beyond  the  gold  surfaces  and  onto  the  porcelain,  thus  invit- 
ing fracture  of  the  crown. 

SOLDERING  THE  CROWN 

The  joint  areas  to  be  soldered  are  covered  with  a  thin  film 
of  thick  borax  paste,  a  thin  piece  of  wood,  as  a  delicate,  wedge- 
shaped  toothpick,  being  most  useful  in  introducing  it  in  con- 
stricted spaces. 

When  fluxed,  the  invested  case  is  set  on  a  gauge,  over  a 
Bunsen  burner,  and  thoroughh^  heated,  until  the  base  of  the 
investment  is  red,  when  it  may  be  removed  to  the  soldering 
block  and  the  blow-pijie  flame  aj^plied  to  bring  it  to  suitable 
temperature  for  soldering. 

The  solder,  in  the  form  of  a  long  strip,  is  applied  in  the 


CROWN     WORK  725 

deepest  part  of  the  joint  area,  and  as  it  melts  is  fed  into  tlie 
fused  mass  lantil  proper  contour  is  attained. 

To  obviate  the  tendenoy  of  the  disc  being  drawn  away 
from  the  crown  base  by  the  contraction  of  the  solder  in  cool- 
ing, a  wedge  of  plate  metal  should  be  inserted  between  the 
cap  and  disc,  before  placing  the  case  on  the  Bunsen  burner. 

FINISHING  THE  CROWN 

When  cooled,  tlie  investment  is  broken  away,  the  crown 
placed  in  a  test  tube  and  boiled  in  a  jjickle  of  25  per  cent  H  CI, 


after  which  it  is  finished  in  the  usual  manner  with  stones  and 
discs,  the  final  polishing  being  accomplished  with  fine  pow- 
ders on  the  lathe  wheel. 

THE  DAVIS  CROWN 

The  Davis  is  a  fully-contoured  porcelain  crown,  having  a 
central  cavity  within  its  base  for  the  reception  of  an  anchor- 
age dowel. 

The  dowel,  which  accompanies  the  crown,  and  of  which 
there  are  varying  sizes,  consists  of  a  pin  having  a  shoulder 


SECTIONAL  VIEW  OK  DAVIS  CROWN  BEFORE  AND 
AFTER  THE  BASE  HAS  BEEN  MODIFIED.  SPECIAL 
CARE  MUST  BE  OBSERVED  TO  PRESERVE  THE  SHOUL- 
DEIJ  DEPRESSION  IN  CROWN  BASE  FOR  RECEPTION 
OF    DOWEL    COLLAR 

near  the  crown  end.  From  the  shoulder,  one  portion  tapers 
apically  for  insertion  in  the  root,  while  the  other  is  parallel 
sided  for  insertion  in  the  crown  base.    The  dowel  is  grooved 


726  ("ROWN    WORK 

in  several  places  tlirouniiout  its  Iciintli  t(»  at'i'ord  better  anchor- 
age within  the  cement.  From  13  to  ](j  gauge  iridio-platimun 
or  clasp  metal  wire  may  be  used  as  dowels  if  desired. 

There  are  three  general  methods  of  applying  crowns  of 
this  type  to  the  roots  of  natural  teeth,  the  crowns  so  applied 
being  designated  as  plain,  cast  base,  and  ha-mled. 

APPLICATION   OF   THE    PLAIN   DAVIS    CROWN 

A  Davis  crown  without  cap  or  metal  base  may  l)e  applied 
to  the  I'oot  of  a  tooth  in  several  ways,  the  following  of  which, 
if  carefully  carried  out,  will  yield  good  results.  After  the 
root  has  been  properly  treated  and  filled,  the  remaining  por- 
tion of  natural  crown  is  reduced  slightly  beneath  the  gum 
margin. 

The  root  face  should  usually  be  given  a  distinct  labio- 
lingual  convexity  sufficiently  marked  to  guide  the  crown  base 
to  position  without  any  tendency  to  rotate. 


ROOT     REAMKIi 


DOWEL    IN    LANAL 


The  root  canal  is  opened  up  first  with  small  burs  and 
afterward  enlarged  with  a  reamer  corresponding  in  taper  with 


the  dowel.  To  avoid  excessive  enlargement  of  the  root  canal, 
the  dowel  should  lie  inserted  from  time  to  time  and  tested  as 
to  closeness  of  adaptation  to  the  canal  walls.     The  shoulder 


CROWN    WORK  727 

should  rest  s(iiiart'ly  upon  the  root  face,  while  the  sides  of  the 
dowel  lit  closel}'  within  the  canal.  This  latter  requirement, 
however  desirable,  cannot  always  be  realized,  it  being  neces- 
sar.y  at  times  to  incline  the  dowel  in  some  direction  to  bring 
the  crown  in  alignment  with  proximating  teeth. 

A  crown  should  be  selected  slightly  longer  than  required 
and  with  base  a  little  larger  than  the  root  face. 

The  dowel  is  now  remo\-ed  from  the  canal  and  the  crown 
base  adapted  to  the  root,  first  removing  the  grosser  points  of 
contact  with  moderately  coarse  stones. 

Close  adaptation  is  developed  by  returning  the  dowel 
to  the  root  canal,  placing  a  disc  of  carbon  paper  over  it  and 
applj-ing  the  crown  to  the  root  face,  the  interposed  carbon 
indicating  the  points  of  interference. 

In  all  of  these  tests,  care  should  be  taken  to  hold  the 
crown  in  correct  alignment  with  the  proximating  teeth  be- 
fore applying  pressure  against  the  carbon  ]3a])er. 

The  points  indicated  on  the  base  of  the  crown  by  the  car- 
bon are  ground  away  and  the  tests  repeated  until  close  adap- 
tation, particularly  peripherally,  is  obtained. 

In  some  cases  it  may  lie  found  necessary  to  hem\  the 
dowel  slightly  to  bring  the  crown  into  correct  alignment  with 
the  proximating  teeth.    In  other  cases  an  offset  dowel  may  be 


THREE    SIZES    OF    OFFSET    DOWELS 


required,  and  again  it  may  be  necessary  to  ream  the  canal 
wall  away,  thus  permitting  the  dowel  to  move  liodily,  in  the 
direction  indicated. 


728  CHOVVN    WORK 

Special  care  sliould  lie  cihscrvcd  to  sec  that  tlic  slidulder 
of  the  dowel  rests  in  tlic  depression  in  tlie  crown  liase.  When 
it  fails  to  rest  within  the  dejjression  in  the  i)orcelain  designed 
for  it,  the  attachment  of  crown  to  dowel  will  be  weakened 
because  of  the  shorteninn-  of  the  latter. 

REDUCING   THE    PERIPHERAL    SHOULDER 

Apply  a  disc  of  white  baseplate  gutta  percha  to  the  crown 
base,  having  first  moistened  the  disc  with  oil  of  cajaput  and 
warmed  the  porcelain  slightly  to  develop  adhesion.  Perforate 
the  disc  in  its  central  area  to  allow  the  dowel  to  pass  through. 


PLAIN       DAVIS.      AD.iTTED      TO 
ROOT      PAl'E,      EXCESS      PERIPH- 
ERAL   SHOULDER    NOT    YET    RE- 
MOVED 


Moisten  the  face  end  of  root  with  water.  Direct  a  blast  of 
hot  air  on  the  gutta  percha  and  force  the  crown  to  place.  A 
few  drojis  of  cold  water  will  chill  the  gutta  percha,  and  on 
removal  of  the  crown  it  will  adhere  to  and  come  away  with 
the  latter. 

The  excess  porcelain  is  now  ground  away  to  the  line  of 
root  periphery  as  indicated  in  the  gutta  percha  impression. 
The  steps  are  similar  to  those  of  correcting  the  base  of  a 
plain  Logan  crown.     (See  page  719.) 

GENERAL   MODIFICATION   OF  THE   CROWN   BY   GRINDING 

The  incisal  or  occlusal  relation  of  the  crown  is  tested  and 
any  modification  as  to  length  or  general  contour  corrected. 
All  surfaces  so  modified  should  be  polished  with  tine  discs, 
followed  with  putty  powder  on  the  lathe  wheel. 

SETTING  THE  CROWN 

The  crown,  dowel,  root  face  and  canal  are  thoroughly 
dried.    A  mix  of  cement  of  medium  consistencv  is  made  and 


CROWN    WORK 


introduced  in  the  canal  and  in  tiie  opening  in  crown,  after 
wliicli  more  is  added  to  the  crown  base.     The  crown  is  now 


forced  to  place  and  held  iirnily  until  the  cement  has  liardened, 
when  the  surplus  is  carefully  removed. 

THE   DAVIS   CROWN    IN    BRIDGE   WORK 

The  Davis  crown  can  often  he  aiiplied  to  advantage  in 
bridge  work.  When  so  utilized,  the  base  of  the  crown  selected 
for  the  dunnny  must  be  reduced  sufficiently  to  give  space  for 


S\\Ai;lXt:     DISl'     AGAINST     CROWX     BASK     AND     IIOXVKL     COLLAR 


730 


CROWN    WORK 


ROOT  CAPS   WITH  PERrENDICULAR  RIBS,   DESIGNED  TO  UNITE  WITH  CORRESPONDING  RIBS 
OF   DUMMY  SOCKET.     FIRST  VIEW  REMOVED.   SECOND   VIEW  IN   POSITION 

the  metal  structure.  It  is  also  advisable  to  groove  the  prox- 
imating  surfaces  of  crowns  and  swage  base  caps  or  sockets, 
the  sides  of  which  are  conformed  to  and  tit  within  the  prox- 
imal grooves.    These  perpendicular  ribs  add  greatly  to  the  sta- 


IXTERPROXIMAL  EXTENSIONS. 
INOISAIJA'.  OF  GOLD  IN  SMALL 
URIDGE  STRUCTURE  FORMED  BY 
GROOVING  DAVIS  CROWNS  ON 
THEIR  MESIAL  AND  DISTAL 
SURFACES.  OB.IECT,  TO  RESIST 
TENDENCY  OF  CROWNS  TO  TIP 
BUCALLY  OR  LINGITALLY  UNTJER 
STRESS 


THE   CO»n"LETED  IiniDGE 

READY    FOR    PERMANENT 

SETTING 


bility  of  the  i^orcelain,  tending,  as  they  do,  to  resist  torsional 
strain.  The  principal  anchorage  is  secured  by  means  of  short 
dowels  set  within  the  sockets,  to  whicli  they  are  attached  dur- 
ing the  consti'uctive  stages  of  the  individual  dummies. 


3USTI    CROWN    SHOWING    CRESCENT    OPEN- 
ING    FOR     DOWEL.       ALSO     CROWN     WITH 
DOWEL   IN  POSITION 


CROWN     WORK  731 

THE  CAST  BASE  DAVIS  CROWN 

The  prostlietist  who  cau  grind  a  perfect  joint  between 
crown  base  and  root  face  will  find  only  occasional  need  for 
interposing  a  cast  base  between  crown  and  root. 

A  cast  base  as  ordinarily  constructed  neither  obviates 
splitting  of  the  root  nor  displacement  of  the  crown  under 
stress. 

The  insertion  of  short  dowels,  of  iridio-iilatinum,  in  lin- 
gual areas  of  the  root  face,  to  the  mesial  or  distal  of  the  root 
canal,  or  beveling  the  lingual  peri))hery  of  the  root  so  that  the 
projecting  lip  of  the  cast  base  may  engage  with  it,  will  largely 
reduce  the  tendency  of  a  root  to  split  under  stress. 

These  and  other  similar  means  of  obviating  root  splitting, 
although  simple  and  efficient,  are  often  ignored  in  the  class  of 
work  under  consideration. 

Cast  bases  are  most  strongly  indicated  in  those  cases 
where  consid(>ral)le  loss  of  root  structure  has  occurred,  and 
when  the  fitting  of  a  peripheral  band  would  be  difficult,  if  not 
impossible. 

CONSTRUCTION   OF  A   CAST  BASE  DAVIS   CROWN 

After  tlie  apex  of  th<'  root  is  filled  the  remaining  portion 
of  the  natural  crown  is  remo\-ed.    In  case  the  crown  has  been 


ROOT     I'REl'ARED     WITH     IN- 
SIDE     SHOULDER      DEPRES- 
SIOX.     SHOWING     LABIAL     V- 
SHAI'ED    NOTCH 


lost  through  extensive  caries,  all  leathery  decay  should  lie  re- 
moved and  the  root  margins  rendered  smooth  and  firm. 

A  crown  is  now  selected  and  ground  to  meet  requirements. 

When  the  root  has  not  suffered  loss  of  structure  from 
caries,  space  for  the  cast  base  is  gained  at  the  expense  of 
grinding  both  root  and  lingual  areas  of  the  crown  base. 


732 


CROWN    WORK 


When  space  Id  he  occupied  l)y  the  cast  l)ase  is  limited  it 
is  advisable,  in  order  to  impart  rigidity  to  tlie  wax  pattern, 
to  extend  a  V-sliapod  groove  I'loiii  the  canal  to  the  labial  sur- 
face of  the  root.  NotcJiin.n'  of  the  crown  base  will  also  prove 
beneficial,  but  the  notcli  should  terminate  within  the  labial 
periphery. 

Such  notches  t'()r)n  streii,i;theiiiii_i>-  I'ilis  in  the  wax  pattern 
and  prevent  distortion  while  handling  and  investing. 

The  crown  having  been  ground  to  requirements,  the  root 
face  prepared,  the  canal  reanu'd  and  dowel  fitted,  the  next 
step  is  to  form  the  wax  pattern. 

The  crown  base  is  coated  with  a  thin  film  of  oil,  the  dowel 
inserted  in  the  crown,  a  piiece  of  softened  inlay  wax  passed 
over  the  dowel  and  against  the  crown  base.     The  crown  is 


DAVIS    CROWN    IN    POSITION 

ON    BOOT    WAX    MODET,    FOR 

CAST    BASE    INTERPOSEn 


CROWN     AND     UNITED     WAX 

BASE  AND  D0m5L  REMOVED 

FROM    ROOT 


now  forced  firmly  against  the  root  face,  being  careful  to  keep 
it  in  proper  alignment  with  the  proximating  teeth. 

When  chilled,  the  surplus  wax  is  trimmed  away,  even  with 
root  and  crown  peripheries.  This  step  must  be  carefully 
carried  out  or  the  peripheral  nuirgins  of  the  iiattern  will  be 
disturbed. 

The  crown  is  now  removed,  which  usually  is  easily  accom- 
plished if  the  base  was  previously  oiled. 

The  wax  pattern  is  removed  by  grasping  the  projecting 
end  of  the  dowel  lightly  with  the  pliers,  being  careful  not  to 
rotate  or  oscillate  it. 

If  satisfactory,  the  oil  is  removed  with  a  camel 's-hair 
brush  and  soapy  water,  or  its  surfaces  can  be  cleansed  with 
a  spray  of  acetone,  which  will  dissolve  the  oil  without  aflfect- 
ing  the  wax. 


CROWN    WORK 


A  sprue  foniicr  is  now  iittai-lii'd  in  the  thickest  poiiitm 
of  the  lingual  area,  usually  at  right  angles  to  the  dowel,  and 
it  is  ready  for  investment  in  tiie  easting  ring 


THE  BANDED  DAVIS  CROWN 

The  following  method  of  applying  a  Davis  crown  to  a 
banded  or  ca]iped  root  is  comparatively  simple  and  satis- 
factory : 

After  treatment  and  filling  of  the  canal,  the  remaining 
portion  of  natural  crown  is  removed,  the  peripheral  ring  of 
enamel  cleaved  away,  and  the  root  faced,  practically  at  right 
angles  to  its  long  axis.  To  this  the  cap  is  fitted  in  the  usual 
manner  and  perforated  in  line  with  the  root  canal,  previously 
reamed,  for  the  reception  of  the  dowel. 

The  crown  is  now  selected  and  ground  away  on  its  lin- 
gual side  to  form  a  V-shaped  opening  with  the  cap. 

In  the  base  of  the  crown  a  shallow,  yet  distinct,  V -groove 
should  be  cut,  extending  from  the  lingual  surface  to  the  cen- 
tral area.  The  gold,  when  forced  into  this  groove,  forms  a 
ril)  which  guides  the  crown  into  proper  position  on  the  base. 

The  crown,  base  upward,  is  now  imbedded  in  moldine,  in 
the  swaging  ring.  A  short  dowel  is  inserted  in  the  crown  and 
a  disc  of  36  gauge  pure  gold,  perforated  in  the  center,  is 
passed  over  the  dowel  and  against  the  base  of  the  crown. 

The  disc  is  now  adapted  to  the  crown  base  with  burnish- 
ers and  the  adaptation  comiileted  by  swaging  Care  should 
be  taken  to  force  the  gold  into  the  V-shaped  groove  in  the 
crown  base. 

The  peripheral  surplus  is  now  removed  and  the  disc,  if 
distorted,  is  reswSged. 

The  short  dowel  is  formed  by  excising  the  apical  four- 
fifths  of  a  dowel  of  regular  size.  It  is  used  so  that  a  place 
may  be  made  in  the  disc  for  the  regnlai"  dowel,  which  is  now 
substituted. 


CROWN    WORK 


The  several  parts  are  asseinblod  in  the  following  order: 
The  cap  is  set  in  position  on  the  root,  the  dowel  inserted  in 
crown  base,  and  the  disc  passed  over  the  dowel  until  it  rests 
against  the  porcelain.    A  pellet  of  softened  wax  is  placed  on 


DAVIS      CROWN.      MODIFIED. 

I.V  POSITION  ON  BOOT.    DISC 

AND    CAP    INTERPOSED 


CROWN,  DISC.  INTERPOSED 
WAX.  DOWEL  AND  ROOT 
CAP.    REMOVED    PBOM    ROOT 


FINISHED      BANDED      DAVIS 
AS   IT   iVPPEARS  ON  ROOT 


the  root  cap,  the  dowel  inserted  in  the  wax  and  the  crown 
and  disc  forced  to  position  on  the  root. 

If  the  parts  are  free  from  moisture  and  the  wax  suffi- 
ciently plastic  and  adhesive,  the  assembled  crown  can  be  re- 
moved without  difficulty. 

To  obviate  disturbance  of  relation,  a  hot  spatula  should 
be  applied  to  the  wax  at  several  points  between  disc  and 
cap. 

All  spaces  should  be  filled  in  with  additional  wax  where 
needed,  and  the  structure  contoured  to  desired  form. 

The  crown  is  now  removed  and  the  assembled  metal  parts 
united  either  by  casting  or  soldering. 


CHAPTER     X  X  A"  1 1 1 
THE  GOLD  SHELL  CROWN 

(MORRISON    CROWN) 

The  two-piece,  gold  shell  crown,  as  ordiuaiily  constructed, 
consists  of  an  axial  band  and  a  swaged  occlusal  surface,  both 
developed  from  plate  gold,  so  contoured  and  united  as  to 
represent  the  anatomic  form  of  the  lost  natural  crown  it  is 
designed  to  replace. 

ADVANTAGES 

A  crown  of  this  type  is  strong,  economical  and  efficient. 
The  constructive  details,  although  requiring  care  in  their 
execution,  are  comparatively  simple.  Because  of  the  ease 
with  which  sheet  gold  can  be  wrought  in  this  method  of  crown 
construction,  most  beautiful  esthetic  forms  can  be  produced 
by  "the  man  who  knows"  anatomic  tooth  forms,  and  technic 
as  well. 

DISADVANTAGES 

The  color  of  .gold  as  compared  with  porcelain  for  tooth 
replacement,  is  objectionable,  therefore  gold  crowns  should 
not  be  placed  in  conspicuous  locations. 

WHERE  INDICATED 

Gold  shell  crowns  are  most  commonly  indicated  in  the 
restoration  of  badly  decayed  molars  in  either  arch,  occasion- 
ally in  second  bicuspids,  and  sometimes  but  rarely  in  first 
bicuspids,  when  filling  operations  are  likely  to  prove  unsatis- 
factory. In  bridge  work,  when  oecluso-gingival  space  is  too 
limited  for  the  combined  use  of  metal  and  porcelain,  a  shell 
crown  of  the  type  under  consideration,  or  some  modification 
of  it  for  an  abutment  is  practically  indispensable. 

MODIFICATIONS   OF  THE   METAL   SHELL   CROWN 

There  are  many  modifications  in  constructive  details  of 
the  metallic  shell  crown,  consisting  principally  of  the  manner 
of  obtaining  axial  contour  of  the  band  and  of  forming  and 
attaching  the  cusp  surfaces  to  the  axial  section. 

A  sufficient  knowledge  for  practical  purposes  of  these 
various  types  of  crowns,  can  be  gained  from  a  full  description 

73.5 


736  THE  GOLD  SHELL  CROWN 

of   llic   two-])i('('(>   Morrison   crown,   as   now   constructed,   to- 
gether with  a  hrief  description  of  the  cast  crown. 

TECHNICAL  DETAILS  OF  GOLD  SHELL  CROWN 
CONSTRUCTION 
PRELIMINARY    PREPARATION    OF   THE    TOOTH    OR    ROOT 
The  preliminary  work  of  most  ini])ortance  in  tliis  as  in 
all  classes  of  crown  constnietion  is  the  proper  treatment  and 
successful  tilling  of  the  root  canals.     This  shcmld,  in  prac- 
tically all  cases,  be  completed  before  attempting  the  peripheral 
reduction  of  the  tooth  oi'  root. 

RESTORING  A  BADLY  DECAYED  NATURAL  TOOTH  FOR 
ANCHORAGE  PURPOSES 

When  most  of  the  natural  crown  has  been  lost  from  any 
cause,  it  is  imperative  that  a  considerable  portion  of  it  be 
restored  by  operative  procedures,  to  afford  firm  anchorage  for 
the  substitute  crown.  This  may  be  accomplislied  in  two  ways: 
first,  with  amalgam,  and  second,  by  means  of  a  suitaVily  shaped 
casting,  usually  of  Weston's  metal  or  silver. 

THE   AMALGAM   METHOD  OF   RESTORATION 

When  the  roots  have  been  properly  filled,  the  canals  are 
reamed  out  to  receive  one  or  more  anchorage  posts,  deiiending 
on  the  requirements  for  snch  means  of  anchorage.  The  wire 
posts  should  extend  deeply  in  the  canals  to  avoid  danger  of 
loosening  when  the  crown  is  set  and  later  subjected  to  stress. 
The  How  anchor  screw  post  is  most  useful  for  such  purpose. 
Also  a  special  form  of  screw  made  by  the  Blue  Island  Spe- 
cialty Co.  By  this  method  both  root  canal  and  post  are  thread- 
ed, and  when,  in  setting  the  post,  a  little  cement  is  applied 
around  it,  firm  anchorage  of  the  post  within  the  canal  of  the 
root  is  insured. 

After  posts  are  set,  a  soldered  copper  band  constructed 
to  fit  the  root  is  adapted  to  its  periphery  and  trimmed  suffi- 
ciently short  to  clear  the  occlusal  surfaces  of  the  opposite 
teeth.  Into  this  matrix  amalgam  is  packed  and  the  patient 
dismissed  for  twenty-four  hours  or  longer,  so  that  the  amal- 
gam may  harden,  and  will  not  be  disturbed  in  removal  of  the 
matrix  or  in  subsequent  root  preparation. 

On  removal  of  the  matrix,  iisually  acconqilished  by  cut- 
ting with  a  shar]>  chisel,  the  amalgam  stunqi  is  treated  as  if  it 


THE    GOLD    SHELL    L'KOWN  737 

wert'  tooth  stiuctuii',  and  rediu-ed  with  stones,  discs  and  files 
in  conjunction  witli  the  iieriiilieral  ring  of  enamel. 

RESTORATION    BY    MEANS    OF    A    CASTING 

To  restore  a  delcftive  cniwn  with  a  casting,  the  root 
canals  should  be  enlarged  as  prcx  'musly  mentioned.  When 
two  posts  are  to  supply  the  anchorage,  the  canals  which  re- 
ceive them  should  be  reamed  i>arallel  with  each  other,  so  that 
the  posts  may  come  away  with  tiie  wax  model  without  dis- 
torting their  relatioiu     If  this  is  not  possible,  one  good-sized 


g  g  Q  g  g  g 


s     .     i    I 
?     f     f    f 


g  g  gi 


IIULAR    ROOT     BANDEll,     AN- 

CllOll    SIREWS    SKT    IN    ROOT 

CAN'AI.S.      MATRIX      IN     I'OSI- 

TION 


MOLAR  RESTORED  WITH 
AMALGAM.  BAND  STILL  IN 
POSITION.  FOR  CROWN  RE- 
STORATION THE  BAND 
SHOULD  NOT  BE  CONTOURED 
NOR  TIIE  OCCLUSAL  SUR- 
I'WCES  DEVELOPED 


post,  deei)ly  seated,  in  conjunction  with  such  additional 
anchorage  as  may  be  developed  l)y  s(|uaring  out  the  pulp 
chamber  will  usually  fullill  re(purements. 

The  posts  are  set  in  jjosition  in  the  canals,  after  wliicli 
inlay  wax  is  applied  and  built  to  re(pured  form.  The  wax 
model  is  then  removed — the  post,  or  posts,  coming  away  with 
it — invested,  cast,  and  set  in  position  with  cement. 

The  object  in  making  such  restoration  is  to  increase  the 
hold  of  the  crown  to  the  uatural  root,  as  well  as  afford  a 
solid  foTindation  for  the  crown  when  subjected  to  masticatory 
stress.  Without  such  means  the  attachment  of  the  srrbstitute 
to  the  natural  crown,  when  the  latter  is  badly  decayed,  is 
liable  to  pi-ove  unstable. 


738  THE    GOLD    SHELL    CROWN 

CASES   IN   WHICH   EXCESSIVE   ROOT    RESTORATION   IS 
REQUIRED 

Cases  frequently  ])i'cseiit  in  wliidi  the  axial  walls  of  a 
tooth  may  be  partially  or  wholly  decayed  oi-  broken  away  be- 
neath the  gum  margin.  In  sndi  ease  peripheral  root  prepara- 
tion cannot  be  undertaken  williout  forcing  back  the  soft  tis- 
sues and  freely  exposing  the  loot  face  and  margins. 

When  the  pulp  chamber  is  open  and  of  such  form  as  to 
afford  anchorage,  baseplate  gutta  percha  can  be  packed  into 
it  and  over  the  face  end  of  the  root,  of  sufficient  thickness 
wlien  compressed,  to  "overflow"  and  force  the  soft  tissues 
beyond  the  root  perii^hery.  The  packing  should  be  left  in 
position  for  twenty-four  or  forty-eight  Inmrs.  If,  on  re- 
moval, the  root  face  is  not  sufficiently  exposed,  the  packing 
should  be  renewed  so  as  to  still  further  force  the  tissues  out- 
ward beyond  the  root  periphery. 

Should  the  ])ul}">  chamber  anchorage  provt^  insufficient  to 
hold  the  gutta  percha  in  position,  a  small,  flat-head  screw, 
about  one-fourth  to  three-eighths  of  an  inch  long,  or  longer  if 
necessary,  may  be  screwed  into  the  root  canal,  and  the  pack- 
ing material  built  around  the  projecting  head.  In  case  the 
root  canals  have  not  yet  been  treated  and  filled,  extreme  care 
should  be  exercised  not  to  force  any  putrescent  matter 
through  the  a]iex.  It  is  also  usually  best  to  puncture  the  gutta 
percha  with  a  small  instrument  to  permit  any  gas  that  might 
accumulate  in  the  pulp  chamber  to  escape  during  the  com- 
pression process. 

When  sufficient  clearance  sjiace  has  been  gained  in  the 
manner  described  a  matrix  should  be  applied  and  adapted 
to  the  root  periphery.  The  entire  band  is  then  filled  with 
cement,  which  is  allowed  to  set,  when  an  opening  may  be 
drilled  through  the  center,  into  the  pulp  chamlier,  through 
which  the  canals  may  be  treated  and  filled. 

The  matrix  must  remain  in  position  during  the  entire 
treatment  of  the  root  to  prevent  return  of  soft  tissues.  After 
treatment  is  completed  the  cement  is  removed  from  the  matrix 
and  amalgam  substituted,  as  previously  outlined. 

WEDGING 

When  the  teeth  adjoining  the  space  the  crown  is  to  occupy 
have  moved  toward  each  other,  thus  reducing  it,  they  should 
be  forced  a]iart  by  wedging,  so  that  interproximal  space  next 
the  crown,  both  mesially  and  distally,  may  be  restored. 


THE    GOLD    SHELL    L'ROWN  739 

A  wedge,  shaped  from  palm  wood  (the  handle  of  a  palm 
leaf  fan)  should  be  inserted  tightly  between  the  inclined  teeth, 
its  base  resting  on  the  stump  of  root  to  be  crowned.  The 
fibers  of  wood  should  run  bucco-lingually.  When  inserted 
dry  the  wood  tibers  will  swell  and  gradually  force  the  teeth 
apart,  usuallj'  without  much  inconvenience.  While  the  process 
is  slow,  requiring  a  week  or  more  of  time  and  insertion  of 
progressively  larger  wedges  as  space  is  gained,  it  is  an  essen- 
tial step  and  should  in  all  cases,  when  possible,  be  accom- 
plished by  this  or  other  effective  means. 

PREPARATION  OF  THE  TOOTH  OR  ROOT  FOR  THE  BAND 

The  same  general  principles  of  root  preparation  previ- 
ously outlined  in  the  porcelain-faced  anterior  crown,  of  con- 
verting the  remaining  portion  of  natural  tooth  into  a  slightly 
tapering  cone,  the  base  beneath  free  margin  of  gum  at  point 
of  termination  of  crown  band,  apex  pointing  occlusally  or  in- 
cisallv,  apply  with  equal  force  in  preparing  posterior  teeth 
for  the  reception  of  shell  crowns. 

REDUCTION    OF    OCCLUSAL    SURFACE    OF    THE   CROWN 

The  preparation  of  a  root  or  tooth  for  the  reception  of 
a  shell  crown  does  not  involve  the  shortening  of  the  natural 
crown  when  present  to  the  same  extent  as  is  required  for 
anterior  porcelain-faced  restorations.  In  fact,  the  natural 
crown  is  left  as  long  as  possible  to  furnish  anchorage  and 
obviate  displacement  of  the  substitute  crown  under  lateral 
stress.  Sufficient  reduction,  however,  must  be  made  to  afford 
space  for  a  thick,  well-reinforced  occlusal  cap  to  the  shell. 
About  one-sixteenth  of  an  inch  space,  seen  from  the  buccal, 
when  the  teeth  are  in  occlusion  will  usually  be  ample.  Should 
this  not  prove  sufficient,  the  face  of  the  root  may  be  readily 
reduced  later  on  when  fitting  the  band.  The  occlusal  surface 
is  cut  away  to  the  required  extent  with  a  five-eighths  to  three- 
fourths  inch,  coarse  carborundum  stone.  Care  should  be  taken 
not  to  mar  the  proximating  teeth. 

REDUCTION  OF.  THE  AXIAL  WALLS   OF  THE  TOOTH 

A  thin  edge  carborundum  stone  is  used  to  reduce  the 
mesial  and  distal  surfaces.  The  wheel  is  allowed  to  touch  the 
tooth  lightly,  yet  must  be  held  firmly  and  under  perfect  con- 
trol of  the  operator  to  avoid  injury  to  the  lips,  cheeks,  tongue 


TIIK     COM)     SUKIJ,     CltOWN 


iiiMl  .ituiiis.  'I'hc  lirst  cut  is  liciiuii  sli;;litl\  inside  (if  (ir  at  the 
(-U'litd-ciiaiiicl  ,iuiictii)ii,  and  liic  stone  so  held  (lial  ils  cdnc  will 
come  llii-oui;li  to  tlic  p|-ipxiniatc  surface  of  cnanii'l  at  the  ixlu- 
gival  line.     A  second  cut  is  usually   re(|uii-ed  on   liotli  mesial 


and  distal    surfaces,   to   complete   the    rou,i;ii    hlockiii.ii,'   off  of 
these  surfaces. 

The  buccal  and  lin,i;ual  surfaces  are  reduced  with  rather 
small  square-faced  stones  so  a|i])lied  as  to  a\oid  injury  to  the 


^ 


iW] 


DIAGRAMMATIC    WF.W    OF    rOSI- 

TION     OF     STONE.      CtlTTINT!     AT 

EXPENSE    OF    MOLAR    TOOTH 


cheeks  and  tongue.    The  removal  of  enamel  with  these  stones 
cannot  usually  be  carried  below  the  gingival  line. 

With  small  knife-edge  stones  and  discs  the  peripheral 
ring  of  enamel  just  under  the  gum  margin  can  be  partially, 
and  in  some  areas  entirely,  removed.  It  is  frequently  a  diffi- 
cult task  to  rejuove  the  enamel  from  those  locations  where  the 


■PHE    GOLD    SHIiLL    t'ROWN  741 

surfaces  turn  t'l-oin  Imccal  and  lingual  into  tlir  mesial  and 
distal  embrasures.  Small  rubber  and  earbonuidum  wIuh'Is 
carried  in  the  port  polisher,  ai)plied  so  that  tlieir  outer  sur- 
faces or  euds  can  reaeli  the  constricted  areas  will  be  found 
very  useful  in  reducing  the  root  to  symmetrical  form. 

The  enaiTiel  cleavers  of  ordinary  form  are  of  but  little 
service  in  removing  enamel  from  molar  teeth,  since  it  is  not 


.VPPtlCATION  OF  SMALL  STONE  IN 
RIGHT  ANGLE  HAND  PIECE  TO 
DISTOLINGUAL    ANGLE    OF    CROWN 


possilile  to  ai)ply  the  necessary  force  effectively  back  of  the 
bicuspids. 

Dr.  W.  K.  Harper  has  (h'signed  a  contra-augle  handle 
which  holds  a  variety  of  short  shank,  regular  and  other  forms 
of  cleavers  and  tiles.    These  can  be  used  to  advantage  in  the 


LEFT  CUT  SHOWS  API'I.ICATION  OF  STONE 
INBEMOVAL  OF  BUCCAL  ENAMEL.  DOTTED 
LINE,  THE  USUAL  AMOUNT  OP  TOOTH 
STP.UCTURE  REMOVED.  RIGHT  CUT.  OUT- 
LINE   OF    PREPARED    TOOTH 


removal  of  enamel  in  difticult  locations,  where  the  ordinary 
forms  of  cleavers  are  ina])plicable. 

By  carefully  introducing  carborundum  ])aper  discs  and 
warping  them  around  the  angles,  much  of  the  final  prepara- 
tion can  be  accomplished  without  serious  injury  to  the  soft 
parts. 

The  root  iiles  can  be  used  to  advantage,  ])articularly  in 
the  emlirasures.  When  the  instrument  is  held  in  the  right 
hand,  the  thumb  of  the  left  is  placed  against  the  buccal  border 


742  THK    CUM)    SllKLL    CKOVVN 

surface,  the  iudex  finger  to  the  liug'uaJ.  The  thumb  is  used 
as  a  fulerum  with  the  result  tliat  greater  and  mure  direct  force 
can  be  applied  against  the  enamel  in  the  interproximate  spaces 
than  is  ]i()ssih]e  with  any  othei'  position. 

GENERAL  FORM  OF  THE  PREPARED  ROOT  OR  TOOTH 

The  flare  of  axial  sui'faees  should  be  plainly  noticeable, 
bnl   not  too  marked;  that  is,  the  convergence  of  peripheral 


GENEHAL  FOHM  OF  REVEKSEIl  (DM:  AKTKI!  r,KM(l\AI.  (II'  EXAMEI, 

surfaces  from  the  base  of  the  cone  under  free  margin  of  the 
gum  outward  or  occlusally  siiould  range  from  two  to  five 
degrees. 

Certain  facts  must  be  kept  continually  in  mind  during 
root  preparation,  viz.,  the  gingival  cone  of  the  natural  tooth 


CDT   SHOWING   RELATION   OF 
PREPARED  TOOTH  TO  OCCLUD- 
ING TEETH 


must  in  all  cases  be  reversed;  the  base  of  the  new  cone  must 
be  extended  apically  as  far  or  even  slightly  beyond  the  point 
where  the  cervical  end  of  the  band,  when  permanently  set, 
will  rest;  the  formation  of  shoulders    or    grooves,    or    any 


THE    GOLD    SHELL    CROWN  743 

irregular  surfaces  that  will  interfere  with  the  correct  fitting 
of  the  band,  must  be  avoided. 

TESTING   THE    CORRECTNESS    OF    ROOT    PREPARATION 

The  two  tests  previously  mentioned  under  root  prepara- 
tion for  a  porcelain-faced  crown  are  applicable  for  proving 
the  correctness  of  root  preparation  for  shell,  as  well  as  other 
classes  of  crowns.  The  first  of  these — passing  a  delicate  in- 
strument apically — is  dependent  quite  as  much  on  tactile  sense 
as  on  the  eye,  for  revealing  irregular  surfaces,  grooves,  shoul- 
ders or  any  remaining  portions  of  enamel,  and  for  determin- 
ing whether  the  sides  have  the  proper  flare. 

The  final  test  is  in  the  root  measurement  itself,  which, 
if  easily  removed,  indicates  that  the  remaining  portion  of 
the  tooth  between  the  position  of  measurement  and  its  occlu- 
sal end  converges  or  becomes  smaller. 

TAKING    THE    PERIPHERAL    MEASUREMENT     OF     ROOT     FOR 
BAND 

The  wire  loop  is  formed,  placed  in  a  holder,  applied  to 
the  root  and  tightened.  The  loo]i  shonkl  seldom  ever  be 
pressed  under  the  free  margin  of  the  gum,  unless  the  root  is 


excessively  cone-shaped,  the  idea  being  to  form  the  band 
slightly  smaller  than  actually  required  and  drive  it  to  place 
in  fitting,  thus  insuring  a  close  and  accurate  adaptation  to 
the  root  periphery.    On  removal  of  the  measurement,  the  loop 


744  THE    GOLD    SHELL    CROWN 

is  ciil  (i)i]>()si1('  the  twist,  in II I  laid  aside  until  t  lie  ini'asurcinciil 
I'di-  the  liaiid  width  is  dhtaiiu'd. 

DETERMINING   WIDTH    OF    BAND 

As  a  uuittt'i-  of  ('coiKiiuy,  the  hand  should  he  cut  of  ap- 
proximately correct  width.  The  width  may  be  determined  by 
measuring'  the  distance  lietween  the  deepest  curve  of  the  gin- 
giva of  the  root  to  be  crowned  to  the  tips  of  the  cusps  of  the 
opposing  teeth.  Should  the  dip  of  the  gingival  gum  curva- 
ture approach  the  root  apex  more  closely  on  one  side  than 
the  other,  the  greater  width  must  be  used  for  the  band  meas- 
urement. For  example,  when  marked  tissue  absorption  ex- 
tends apioally,  exposing  more  or  less  of  the  surface  of  the 


lingual  root  of  an  upper  first  molar,  the  band  should  be  wide 
enough  to  cover  the  entire  exposed  area.  There  are  better 
methods,  however,  of  adapting  crowns  to  teeth  around  which 
gingival  absorption  has  occurred  to  a  considerable  extent 
than  by  the  application  of  a  band.  In  such  cases  the  shoulder 
crown  in  which  no  overlapping  of  gold  on  the  root  occurs,  is 
far  more  hygienic  and  serviceable  than  any-  type  of  banded 
crown. 

A  piece  of  ordinary  cardboard,  cut  on  a  taper  with  the 
narrow  end  squared,  serves  as  a  convenient  gauge.  If  too 
wide,  the  sides  of  the  card  are  reduced,  wliile  if  too  narrow 
the  end  is  cut  away  until  tlie  width  coincides  with  the  distance 
designated.  A  pair  of  dividers  may  also  be  used  for  securing 
the  measurement.    The  length  and  width  of  band  havino-  been 


THE    GOLD    SHKLL    CROWN  745 

dctcriiiiiicd.  the  next  step  is  to  lay  it  out,  and  cut  it  t'ruui  the 
piece  of  gold  plate. 

CUTTING  THE  BAND  ACCORDING  TO  MEASUREMENT 

As  has  been  previously  pointed  out,  the  outer  envelop  of 
the  average  posterior  natural  tooth  represents  two  cones,  an 
occlusal  and  a  gingivah  revei-sed,  and  with  their  bases  meet- 
ing in  a  coinnion  plane  in  the  mid-crown  region. 


SCIlIlilXG  THE  CERXICAL  END  OP   AXIAl,   CONE   HAND.      THE  OUTEll  ARC  REPRESENTS 

THE    OCCIA'SAI,    END    OF    THE    BAND.      THE    DlSTAXl'E    BETWEEN    THE    TWO    ARCS    IS 

DETERMINED    liV    THE    CARDHOARD    iMEASl'REMENT 

'I'o  reproduce  sucli  an  enxclop  in  gold,  one  of  two  plans  is 
followed:  first,  form  the  band  as  a  cylinder  and  by  swelling 
and  stretching,  gain  contact  with  proximating  teeth,  in- 
crease the  mesio-distal  diameter  of  the  band  at  the  occlusal 
surface,  and  the  bucco-lingual  diameter  in  its  mid-crown  area 
to  represent  the  axial  contour  of  the  natural  tooth.  Second, 
form  the  band  as  a  section  of  a  cone,  representing  the  flare 


746  Tllh;    (;()I,I)    SIIKLL    CKOVVN 

ol'  the  iivcrnnc,  naluial  gingival  cone,  and  reduce  tlie  occlusal 
end  by  compression  contouring  to  the  required  dimensions. 
Of  the  two  methods,  the  latter  is  much  the  simpler  and  better 
in  every  way. 

By  referring  to  anatomic  forms  of  teeth  on  page  G34  it 
will  be  seen  that  the  average  flare  of  the  gingival  cone  of 
molars  is  25  degrees.  Unless  the  space  which  the  crown  will 
occupy  is  constricted,  a  cone  having  this  flare  sliould  l)e  used. 

CUTTING  A  CONE  BAND 
To  cut  a  liand  liy  this  method,  the  dividers  are  placed  at 
the  edge  of  the  card  oi-  piece  of  gold  jdatc,  the  iioints  set  at 


314  inches  apart  and  an  arc  is  struck,  somewhat  longer  than 
the  root  measurement.  The  radius  is  then  increased  the 
width  of  the  band,  as  determined  by  the  cardboard  measure- 
ment, and  from  the  same  center  a  second  arc  is  struck,  rep- 
resenting the  occlusal  end  of  the  band. 

When  curvature  of  the  gingival  gum  margin,  around  the 


THE    GOLD    SHELL    L'ROWN 


root  being  crowned,  is  very  marked,  as  is  frequently  the  ease, 
the  cervical  end  of  the  cone  band  must  be  reduced  by  scribing 
and  trimming,  to  conform  to  such  curvature  This  naturally 
reduces  the  lieiglit  of  the  cone,  entirely  at  the  expense  of  its 


smaller  end,  and  enlarges  its  cervical  diameter  or  peripheral 
length  proportionately. 

On  returning  the  band  to  the  root  it  will  usually  be  fonnd 
entirely  too  large.  And  while  reduction  of  its  cervical  diame- 
ter may  be  effected  with  contouring  pliers,  anatomic  outlines 
of  the  axial  surfaces  will  be  disturbed. 

When  it  is  evident  that  much  reduction  of  the  cervical 
end  of  the  cone  must  be  made,  the  band  should  be  marked 


748  THIO    COLD    SHKLI.    CROWN 

and  ciil  Irciiii  one  to  tlncc  thirty-sccoiitls  of  ;m  inch  shortci' 
than  tlic  root  measurciiiciit. 

The  measurement  is  h-iiil  olT  on  tiir  L^ohl  phitc  ami  tiie 
hand  cut  as  follows  : 

Tlie  wire  measnrcnicnl  is  mrxcd  In  r(iiTcs|i(ind  with 
the  gingival  arc  on  which  i1  is  now  laid,  one  end  of  the  wire 
l.ieing  bronghl  e\'en  with  the  ontcr  margin  of  the  gohl  ])late. 
The  other  end  of  the  hand  is  iMark<'d  cxcn  witli  the  wire  meas- 


LIXK  URAWX   WITH  nul.E  TO  INUICATK  l)lVEI!<;ENrE  111'-   IX.NEll    KNh 

OF   BAND.      THE  OUTER  END  OF  THE  BAND   AT  THE  EDGE  OF  PLATE 

IS   CORRECT.      UPPER   LEFT  CORNER   SHOWS   FORM  OP    BAND 

urement,  or  in  case  of  decided  gingival  enrvature,  ])roi)or- 
tionately  shorter,  in  accordance  with  the  slight  or  pronounced 
curvature  of  the  gingival   tissues. 

Liay  a  rule  against  this  point  and  the  center  from  which 
the  arc  was  develojied  and  mark  the  end  of  the  band.  When  the 
gold  plate  is  placed  parallel  with  the  outer  edge  of  the  card  the 
opposite  or  outer  end  of  the  band  will  have  the  proper  flare. 
The  gold  is  cut  and  bent  in  the  form  of  a  cone,  the  two  ends 
abutting  squarely  against  each  other. 


THE    tJOLD    SHELL    CROWN 
WIRING  THE  BAND 


'I'he  hand  ends  should  be  held  in  contact  with  binding  wire, 
for.  although  they  may  be  soldered  without  the  use  of  the 
binder,  they  will  usually  spring  apart,  at  one  or  the  other  edge 
of  the  band,  and  the  union  l)e  imperfect. 


IIAXI)     ENDS     ABUTTED     AND 

HEM)    WITH    CROSSED    BIND- 

IN'Ci    WIRE 


Since  the  wire  will  not  keep  its  position  on  the  cone  as 
ordinarily  applied  it  should  be  crossed  and  carried  around  the 
band  occluso-gingivally  and  t^nsted  tightly,  the  surplus  being- 
placed  on  the  0])posite  side  of  the  cone,  from  the  joint. 

SOLDERING   THE   BAND 

Borax  is  applied  to  the  joint,  a  small  piece  of  solder  laid 
across,  and  the  band  ends  united  in  the  usual  manner. 

FITTING  THE  BAND  TO  THE  ROOT 

The  band  is  conformed  to  the  general  outline  of  the  root 
and  pressed  down  until  in  contact  with  the  gingiva.  The 
scribing  tool  is  a]iplied  and  the  gingival  line  marked  on  the 
Imccal  surface.  Usually,  because  of  difficulty  in  applying  the 
scriliing  instrument  to  the  lingual  surface  an  explorer  can  be 
substituted  and  the  lingual  curvature  approximately  marked  in 
this  manner.  It  is  advisable  to  mark  too  close  rather  than  too 
far  from  the  gingiva  and  cut  accordingly  to  avoid  shortening 
of  the  band  width.  After  trimming  off  the  gross  surplus  a 
second  application  of  band  to  root  will  disclose  the  points 
needing  further  reduction. 

Naturally,  when  much  curvature  is  pi'esent  the  band, 
when  trimmed,  will  become  enlarged.  This  may  be  compen- 
sated for  in  two  ways:  first,  by  cutting  the  band  slightly 
shorter  than  the  measurement  at  the  start,  and  second,  by 
reducing  the  gingival  ]ieri])hery  with  suitable  contouring 
pliers  of  the  Peso  or  I'cuson  txpc 

CONTOURING    THE    BAND 

In  forcing  the  liaiid  to  place  its  bncco-lingual  diameter 
will  be  somewhat  increased  bevond  true  anatomic  dimension. 


THE    (iOI.L)    SHKLL    I'ROWN 


This  distortion,  however,  can  be  readily  corrected  by  apply- 
ing the  round  beak  of  the  Benson  plier  inside  the  band  about 
the  middle,  occluso-gingivally,  and  with  careful  pressure  on 
the  outer  side  with  the  flat  beak  the  occlusal  cone  can  be  re- 
duced to  proper  form.     No  appreciable  pressure  should  be 


REDUCING    THE    OCCLUSAL    END    l)K    BAND    WITH    BENSON    PLIERS 

exerted  on  the  handles  to  force  the  beaks  together,  as  this, 
by  thinning  the  gold,  would  increase  the  diameter  and  contour 
of  the  band  in  the  mid-crown  area. 

The  Benson  pliers  are  designed  primarily  for  effective 
contouring  of  bands  in  any  location  where  convex  surfaces 
are  required,  the  heavy  handles  and  short  beaks  being  spe- 
cially adapted  for  developing  great  force.  One  beak  is  flat, 
the  other  round,  the  latter  acting  on  gold  plate  as  a  ball  pene 
hammer  does  against  metal  on  an  anvil. 

The  accompanying  cut  shows  an  extensively  contoured 
crown,  formed  with  these  pliers  by  Dr.  Benson,  the  axial  band 


SKCOND  MOLAR  INCLINED  FORWARD 
FROM  LOSS  OF  FIRST  JIOLAB  I'BOWN 
CONTOURED  TO  FORM  PROXIMAL 
CONTACT  WITH  SECOND  BICUSPID 
(BENSON) 


lilCrSI'ID  BANDS  CONTOURF.D. 
STRIP  AT  BOTTOM  SHOWS  DOTT- 
BLEB  ATTACHED  TO  MAIN 
BAND.  NOTICE  FLAKING  ENDS 
OF    LATTER    (BENSON) 


THE    GOLD    SHELL    CROWN  751 

being  expanded  in  order  to  develop  contact  with  a  tootli  some 
distance  removed.  lu  this  case,  a  piece  of  gold  was  sweated 
against  tlie  sti'aight  baud  to  give  additional  material  for  ex- 
l)anding  and  tlms  obviate  weakening  of  the  crown  walls. 

The  thickening  of  the  band  walls  is  essential  where  ex- 
tensive contouring  is  carried  out.  It  is  not  essential  when  the 
band  is  developed  to  represent  the  section  of  a  cone  except  in 
unusual  cases. 

FORCING  THE  BAND  TO  PLACE  ON  ROOT 

When  properly  contoured,  it  should  be  forced  to  position 
under  the  free  margin  of  the  gum,  usually  about  one-twentieth 
of  an  inch,  in  some  cases  a  little  more,  when  the  peridental 
attachment  will  permit. 

By  placing  a  flattened  piece  of  wood  on  the  occlusal  sur- 
face of  the  liaud,  the  ])atient  can  assist  in  setting  it  liy  biting 


CONTOURING   AND  BAND-EXrANDING    PLIERS   DESIGNED    BY    WRITER 

on  the  wood.  Test  of  the  length  of  band  is  made  by  closure  of 
the  teeth,  and  any  points  of  interference  are  reduced  bj^  trim- 
ming. The  occlusal  end  of  the  band  should  be  squared  with 
the  flat  side  of  a  file  so  that  the  cusp  when  developed  and 
similarly  treated  will  form  a  close  joint  with  the  band. 


TESTING   THE   BITE 

The  band,  having  been  fitted  to  the  root,  a  wax  bite  should 
be  taken  with  the  band  on  its  root,  together  with  the  proximat- 
ing  teeth.  The  mass  of  wax  should  be  large  enough  to  re- 
ceive and  firmly  hold  the  bite  fork  of  the  face  bow.  It  should 
also  be  of  the  hard  variety,  so  that  when  chilled  it  will  re- 
tain its  shape,  and  not  become  distorted  in  subsequent  han- 
dling. 


752  THIC    (!()l,l)    SIIKI.L    CltOW.X 

Tlie  l)ito  fork  is  insci'lcd  in  llic  \\;i\.  (d  1hc  outside,  in 
such  nianiicr  as  nol  Id  intrrrci-c  with  (iccliisidii.  the  wax  iii- 
ti-(>ilnri'(l    ill    ilic    iiioiitli    anil    the    haticnt    iiist  nii-t('(|    td   ddsc. 


OCCLCSAL    VIEW    OF    Till!    rdXTOl'HEn    BAMI    IN    POSITION 

The  face  bow  is  adjusted  to  tlie  bite  fork,  and  over  the  con- 
dyles, the  several  clamps  tig'htened,  and  the  bite,  attached  to 
the  bow.  removed  from  the  mouth. 


THE    COLD    SHKLL    CROWN 


All  iiiipn'ssioii  of  tlu'  liaiid  mi  its  root  is  olitaiucil,  tonctlicr 
witli  two  or  three  of  the  .-Kljoininn'  tcelli  on  citlicr  side.  Kroiu 
tliis  n  east  is  developeil,  whidi,  wlicii  iciiiox-ed  and  tiinnned. 


BITE    MOl'NTEI)    OX    OCl'l.l  l)IX<i    KllAMK.    I.dWEK    CAST    DEVlOr.orEI) 

is  fitted  to  tlie  wax  bite  and  attaelied  to  the  upper  bow  of  the 
frame.  The  sides  of  the  wax  bite  should  be  trimmed  as  previ- 
ously deseribed  to  permit  tlie  oechisal  siirfaees  of  the  teeth  to 
become  seated  against  the  wax. 


754  THE    (;OI>I)    SlIKM.    CliOVVN 

MOUNTING  THE  BITE  ON  THE   OCCLUDING  FRAME 

The  face  bow  is  ad.juKted  to  the  occluding  frame,  the  wax 
bite  oiled,  and  that  side  which  is  to  form  the  occlusion  cast 
is  tilled  with  plaster,  and  at  the  same  time  attached  to  the  bow 
of  the  frame.    When  hardened,  the  cast  carrying  the  band  is 


fitted  in  its  bite  and  attached  to  the  opposite  bow.  After 
removal  of  the  bite,  the  occlusal  surfaces  of  the  occluding 
teeth  opposite  the  band  are  coated  with  separating  medium. 

"developing   the   cusps   OF  THE   CROWN   IN   PLASTER 

When  the  occlusal  surface  of  a  crown  is  to  be  swaged,  it 
is  necessary  to  develop  a  pattern  of  the  form  desired,  in  plas- 
ter or  some  medium,  by  means  of  which  a  suitable  counterdie 
can  be  constructed.  One  of  the  most  common  methods  of 
carrying  out  this  step  is  as  follows : 

A  mix  of  plaster  is  made  and  applied  in  the  occlusal  end 
of  the  band,  slightly  in  excess  of  the  amount  required  for  the 
cusps.  While  soft,  the  two  casts  are  occluded,  the  surplus 
plaster  being  forced  buccally  and  lingiaally.  On  separating 
the  casts  it  will  be  seen  that  the  central  groove  of  the  occlusal 
surface  to  be  carved  has  been  fairly  well  developed  by  the 
buccal  marginal  ridges  of  the  lower  occluding  teeth.  The 
groove,  however,  should  be  deepened  slightly,  and  some  small, 
unnecessary  ridges  on  the  occlusal  surface  reduced,  to  bring 


THE    GOLD    SHELL    CROWN  755 

out  the  general  anatomic  form  of  the  tooth.  The  peripheral 
surplus  is  trimmed  even,  and  continuous  witli  the  axial  walls 
of  the  band  at  this  time,  but  later  on  nmst  be  rounded  in  to 
form  the  marginal  ridges. 

The  frame  should  be  subjected  to  lateral  movements  and 
the  iJoints  of  interference  noted  and  trimmed  accordingl.y.  This 
step  might  be  termed  development  of  clearance  paths.  The 
trimming  of  tlie  peripheral  margins  of  the  plaster  to  represent 
the  marginal  ridges  of  the  crown  should  be  carefully  carried 
out,  since  these  boundaries  of  the  occlusal  surface  give  char- 
acter and  individuality  to  the  substitute. 

Finall}',  the  developmental  lines  and  finer  surface  mark- 
ings are  carved  in  tlie  occlusal  surface.  To  do  this  well,  the 
prosthetist  should  have  a  knowledge  of  typical  forms  of  the 
teeth. 

TYPICAL   FORMS    OF  NATURAL  TEETH 

A  number  of  sketches  of  natural  teeth  have  been  care- 
fully drawn,  showing  various  surfaces,  among  them  the  occlu- 
sal surfaces  of  seven  types  of  teeth  that  the  crown  and  bridge 
worker  should  be  thoroughly  familiar  with,  able  to  draw  in 


DIAGRAMMATIC 


pencil,  carve  in  wax  or  plaster,  or  model  in  clay.  These  are 
not  presented  in  reverse,  it  being  taken  for  granted  that  famil- 
iarity with  one  type  of  tooth  will  enable  the  prosthetist  to 
carve  it  for  either  right  or  left  side. 


'I'Hli;    COI.l)    SHKLl,    CKUWN 
UPPER   RIGHT   FIRST   MOLAR 


oci'i.rsAT- 


LOWER  RIGHT  FIRST  MOLAR 


THE    GOLD    SHELL    CROWN 


LOWER   RIGHT   SECOND   MOLAR 


LINGUAL  MESIAL 


UPPER    LEFT    FIRST    BICUSPID 


IircCAL  LIXULAL 


<i> 


occi.rsAL 


THE    GOl^U    SHELL    CROWN 


UPPER  RIGHT  SECOND  BICUSPID 


LOWER  LEFT  FIRST  BICUSPID 


THE    GOI>D    SHELL    OROWN 


LOWER  LEFT  SECOND   BICUSPID 


OCCLUSAL 

REPRODUCING  THE  CUSP  SURFACES  IN  GOLD 

Two  general  methods  are  in  vogue  for  forming  the  oeclu- 
sal  surfaces  of  a  crown.  First,  by  swaging  the  cusps,  and  sec- 
ond, by  casting  them.  When  swaged,  a  counterdie  is  con- 
structed and  in  this  the  cusps  are  formed.  When  east,  the 
cusps  are  carved  in  wax,  in  tlie  gold  band,  the  two  invested, 
and  the  cusps  cast  directly  to  the  axial  band. 

CONSTRUCTING  THE  COUNTERDIE— DIRECT  METHOD 

A  common  procedure  in  forming  the  counterdie  is  as  fol- 
lows :    The  cusps  having  been  developed  in  plaster,  the  crown 


CROWN     IJANJi      l.MIU;l')iEl>     IN     MOLDINB. 
CABVBD       I'USrS      HXPOSKD      READY      FOR 
PLACING   THE    SWAGING    BING    AND    CAST- 
ING   THE    COUNTERDIE 


band  with  cusps  attached  is  removed  from  the  cast  and  im- 
bedded, cervical  end  down,  in  moldine  to  the  line  of  junction 


TBO  'llll':    liOl.li    SHKIJ.    CltOWN 

<tl'  llic  ,i;()l(l  willi  llic  piaslrr,  tlnis  Icaxiii.i;  <>i\\y  llic  cusps  ex- 
IHiscd.     A  small   rulihcr  liii.n'.  or  llic  iiidal  i-iu!;  of  a  swaging 

(lc\icc,  is  (•entered  oxer  tl nsjis,  on  llie  iiioldiiie,  and  fusible 

metal  iioiireil  in  Hie  ring  and  o\-er  the  cusp  surfaces  in  suffi- 
cient quantity  to  form  a  resistant  counlerdie.  Wlien  chilled, 
tlie  moldiiie  and  crown  are  removed  and  the  matrix,  it'  satis- 
factory, is  oiled,  tile  gold  annealed,  and  swaged  into  the  cus]i 
depressions. 

V^ery  often  thi'  cusp  sui-faces  of  the  connterdie  m.itrix  will 
he  defective,  as  a  lesult  of  iiouring  the  heated  metal  over  tJie 
imperfectly  dried  i)]aster  carving.  Tliis  may  lie  largely  over- 
come hy  eliminating  all  moisture  from  the  plaster  before  im- 
bedding the  crown  in  moldine.  Two  or  three  very  small  holes 
may  be  drilled  througii  the  plaster  cusps  and  after  the  crown 
is  imbedded  in  the  I'ing  a  small  wire  is  introduced  through  the 
holes  and  passed  entirely  through  tlie  moldine  base,  to  form 
free  vents  for  the  downward  escape  of  steam  The  disturb- 
ance of  (he  molten  metal  wliile  hardening  is  tluis,  in  most 
cases,  averted. 

CONSTRUCTING  THE   COUNTERDIE— INDIRECT   METHOD 

A  very  excellent  method  of  constructing  a  connterdie 
without  casting  directly  to  the  carved  surfaces,  and  which  will 
yield  a  dense  casting,  is  as  follows: 

It  is  well  known  that  dense  castings  of  fusible  metal,  free 
from  porosity  or  surface  imperfections,  can  lie  successfully 
cast  against  moldine,  liecause  the  latter  contains  no  moisture. 
Neither  does  the  glycerine,  with  which  moldine  is  mixed,  to 
render  it  plastic,  volatilize  under  the  fused  metal.  Therefore, 
by  reproducing  the  reverse  of  the  desired  connterdie  surfaces 
in  moldine  a  dense  connterdie  will  result  from  casting  fusible 
metal  against  such  surfaces. 

The  cusjis  art'  carx'ed  in  the  same  maimer  as  i)reviously 
described.  By  this  method  hard  wax  or  modeling  com])onnd 
will  serve  quite  as  well  as  plaster  as  a  medium  in  which  to 
carve  the  cusps. 

When  carved,  remove  the  crown  from  cast,  make  a  mix 
of  plaster  and  spread  on  a  piece  of  paper,  forming  a  flat  mass 
about  three-eighths  inch  thick  and  one  and  one-half  inches  in 
diameter.  With  the  point  of  a  knife  or  a  brush  fill  in  the  in- 
equalities of  the  carved  surfaces  and  quickly  press  the  crown, 
occlusal  end  down,  in  the  soft  plaster.  The  cusps  should  be 
fully  imbedded  to  the  band  margin.  Remove  the  surplus  plas- 
ter from  around  the  crown.     When  plaster  has  set,  remove 


THE    GOLD    SHELL    CROWN  7G1 

erowii  and  carving.  Trim  the  margins  ol'  tlic  matrix  to  elim- 
inate nndercnts.  The  plaster  with  oiisp  depression  now  repre- 
sents the  essential  surfaces  of  a  eounterdie.  This  must  be  re- 
produced in  metal  whicli  can  be  accomplished  as  follows : 
Dust  the  cus])  surfaces  and  plaster  slab  with  talcum  powder 
and  brush  oft'  the  surplus.  Press  a  small  mass  of  moldine  in 
the  cusp  depressions  and  a  larger  mass  over  the  upper  surface 
of  the  plaster  slab.  The  two  masses  of  moldine  should  tirmly 
unite,  which  will  occur  if  surfaces  are  fresh  and  sufficient  pres- 
sure is  applied.  The  upper  surface  of  the  moldine  should  be 
flat,  to  afford  a  firm  ])ase  on  which  to  rest  when,  later  on, 
it  is  inverted. 

The  plaster  and  moldine  are  carefully  sei)arated  to  avoid 
distorting  the  latter.  On  the  surface  of  moldine.  which  was 
pressed  against  the  plaster,  will  be  seen  a  raised  occlusal  sur- 
face of  exactly  the  same  size  and  form  as  the  plaster  pattern. 
The  moldine  is  set  on  the  bench,  a  casting  ring  centered  over 
the  cusps  and  tilled  with  fusible  metal. 

When  the  metal  has  hardened  and  the  ring  and  moldine 
are  separated,  the  eounterdie  surfaces  will  he  found  dense,  and 
with  finest  details  reproduced.  Since  the  steps  are  carried  out 
quickly  while  the  plaster  is  damp,  the  surface  of  the  moldine 
may  absorb  a  little  moisture  from  the  latter.  This  can  be  re- 
moved before  casting,  by  dusting  freely  with  talcum  iiowder 
and  removing  the  suriilns  with  n  soft  brnsli. 

DEVELOPING  A  COUNTERDIE  WITH  METALLINE  COMPOUND 

Mcfdiliiii'  ( 'iiiHjioifiiil  is  a  moderately  hard  substance,  hea\'- 
ily  loaded  with  graiihite,  somewhat  resembling  modeling  com- 
pound in  that  it  becomes  plastic  with  heat  and  hardens  (piickly. 
Fusible  metal  can  be  cast  direi'tly  against  it  without  distorting 
its  surfaces,  since  a  higher  temperature  is  re(|uired  to  soften 
it  than  modeling  compound. 

It  can  be  carved  readily,  and  if,  in  carving,  too  much  is 
removed,  more  can  be  added  with  a  hot  spatula  and  the  sur- 
faced corrected.  By  its  use  a  most  excellent  eounterdie  can 
be  quickly  formed  as  follows:  With  the  casts  mounted  on  the 
occluding  frame  and  the  band  in  position  on  its  cast,  a  jtellet 
of  Metalline  C'omjiound,  slightly  larger  than  that  required  for 
the  cusps,  is  ijoftened,  placed  in  the  occlusal  end  of  the  band 
and  Ihe  casts  occluded.  When  hard,  the  cusps  are  carved  as 
usual.  With  a  small  bui'uisher  the  cusp  surfaces  are  rendered 
perfectly  smooth. 

The  Metalline  car\iiig  is  carefully  lifted  ont  of  the  band, 
to   prevent    distoi'tion,    and    thai    ]iorti(in    wliicli    cntei'ed    H\o 


762  THE    GOI.D    SHELL    CROWN 

l»;ui(l  is  pared  away  with  a  sliarp  kiiifp,  even  with  the  impres- 
siou  of  its  occlusal  end.  This  converts  the  Metalline  carving 
into  an  occlusal  form  of  exactly  the  right  depth  for  the  cusps. 
It  now  resembles  in  form  one  of  the  Ilollingsworth  metal  cusp 
l)atterns. 

The  upper  or  occlusal  surfaces  are  now  coated  with  a 
thin  film  of  glycerin,  and  all  surplus  removed  with  absorbent 
cotton. 

A  small  iK'lict  of  soft  moldine  no  larger  than  a  pin-head 
is  thinly  sjiread  on  a  flat  surface  of  polished  steel.  On 
this  the  metalline  carving  is  set  and  pressed  lightly  against 
the  moldine,  to  cause  the  cnsj^s  to  adhere  to  the  steel.  The 
object  in  cementing  the  cusp  to  the  steel  is  to  prevent  its  dis- 
placement by  the  metal  in  casting.  If  the  cusp  carving  is  not 
adherent  to  the  steel,  the  fusible  metal,  because  of  its  greater 
specific  gravity,  will  settle  under  and  cause  it  to  rise  to  the 
surface.  Another  method  of  obviating  displacement  of  the 
carving  is  to  press  it  against  the  steel  with  a  small  wire  while 
pouring  the  metal.  The  steel  should  be  moderately  cool,  so 
as  to  chill  the  fusible  metal  quickly  before  the  cusp  forms 
are  softened. 

A  ring  is  centered  over  the  cusp  and  the  fusible  metal 
cast  into  it.  When  the  steps  are  properly  carried  out,  a  sharp, 
well  defined  counterdie  is  obtained. 

SWAGING  THE  CUSPS  IN  AN  OPEN  COUNTERDIE 

A  piece  of  soft  wood  about  four  inches  long  and  one-half 
inch  square  is  shaped,  on  one  end,  to  the  general  outline  of  the 
cusp  depression  and  driven  into  it  and  the  counterdie  is  oiled. 


DISC  OP  GOLD   WITH   SOFTWOOD 
IN  POSITION  READY  FOR  SWAG- 
ING   IN  COUNTERDIE 


A  disc  of  31  or  32  gauge,  22  carat  gold  plate  is  annealed, 
evenly  centered  over  the  cusp  depression,  the  conformed  end 
of  the  stick  set  squarely  on  it  and  given  a  sharp  blow  with 
the  hammer. 


THE    GOLD    SHELL    CROWN 


Any  folds  that  have  hegiui  to  t'onii  around  the  margins 
are  corrected  with  pliers,  and  the  swaging  process  continued 
until  general  adaptation  is  secured.  The  finer  lines  and  sharp 
ridges  of  the  cusps  are  developed  witli  a  blunt-pointed  hick- 


DEVI  I  <I1MN(.    I  III     I  l\l  It  (M'C'Lr- 

SAL    SURFACE    MVItKIVCS    WITH 

HARDWOOD   POINT 


cry  stick,  or  a  rather  small  but  round  edge  chaser,  using  light, 
rapid  hammer  blows.  Finally,  liy  applying  the  piece  of  soft 
wood  with  heavy  hammer,  the  gold  is  driven  against  all  sur- 
faces of  the  matrix.  The  gold  is  pickled  in  acid,  polished  with 
pumice  to  remove  all  traces  of  base  metal,  when  it  is  ready 
for  the  final  step  of  fitting. 

REMOVING   PERIPHERAL   SURPLUS   OF   GOLD 

With  a  pair  of  shears  the  marginal  surplus  of  gold  is 
removed,  and  the  surfaces  of  the  cusp  to  l)e  united  with  the 
band  are  flattened  with  a  file. 

ADAPTING  THE  OCCLUSAL  CAP  TO  THE  BAND 

By  placing  a  pellet  of  soft  wax  in  the  band  to  steady 
the  cusps  and  returning  the  latter  to  position,  from  time  to 
time,  on  the  band,  both  length  and  occlusal  relations  may  be 
determined  and  corrected  as  required. 

The  cusp  margins  should  rest  flat  upon  the  occlusal  end 
of  the  axial  band,  while  the  peripheries  ot  both  should  coin- 
cide. 

When  trimmed  to  correct  length,  so  that  in  lateral  move- 
ments the  cusp  planes  do  not  interfere  with  the  opposite 
occluding  teeth,  the  crown  can  be  removed  from  its  cast  and 
the  two  permanently  united  by  soldering. 

DEVELOPING    THE.  MARGINAL    RIDGES    OF   THE    CROWN    ON 
THE   AXIAL  BAND 

A  most  excellent  method  of  developing  the  cusp  eleva- 
tions on  a  ei'own,  and  which  largely  reduces  the  difficulties 
of  carving  the  occlusal  surface,  is  as  follows: 


764  TIIK    liOl.l)    Slll':i,l,    CliOWN 

'I'lic  axial  band  is  roriiictl  as  wide  or  cncii  sliiililly  wider 
than  I  he  oeclusu-ccrvical  height  of  the  liiiished  crdwii. 

The  steps  of  fitting  oi"  liaiid  lo  rcmt  and  contdniiiig  of 
axial  surfaces  are  carried  out  as  prcN  ioiisly  desciilied.  Since 
the  length  of  hand  will  not  permit  the  teeth  to  occlude,  a  bite 
cainiot  l)e  taken  until  the  occlusal  band  margins  are  corrected. 

instead  of  Irinnning  this  end  of  the  band  to  re])resent  a 
lioi'izonlal    jilane,   as   is  usually  done  and   as   luis   been  pre- 


TIIE    AXlAr.    I'lillWN     I'.ANII    NdTI'lIKII    T( 


■l.rllK     WITH 


■-111     II  hTH 


viously  described,  it  is  utitched  to  represent  tlie  xarious  cusp 
elevations  and  sloping  planes  of  the  marginal  ridges. 

The  mesial  and  distal  occlusal  margins  must  also  be 
notched  to  receive  the  opi)osite  occluding  cusps  which  rest 
in  the  central  groove. 

This  can  easily  and  quickly  lie  carried  out  in  the  mouth, 
the  general  alignment  of  the  cusps  of  proximating'  teeth  and 
the  cusps  of  the  occluding  teeth  serving  as  guides  while  trim- 
ming the  band  margin. 

The  patient  should  subject  the  mandible  to  lateral  move- 
ments to  test  the  correctness  of  clearance  jmths. 

When  trimmed  so  that  the  occlusal  band  margins  inter- 
cuspate  properly,  not  only  in  occlusion,  but  in  lateral  mandib- 
ular movements  as  well,  the  bite  may  be  taken  as  usual,  casts 
developed  and  the  crown  finished  by  any  of  the  ordinary  meth- 
ods desired. 

If  the  cusps  are  to  be  cast,  inlay  wax  may  l)e  a])])lied  and 
carved  in  the  mouth,  the  ci'own  and  carving  removed  and  in- 


THE    GOLD    SHKLL    t'ROWN  765 

Vfi^tt^'d  (lirt'ctly,  witlunit  tnkiiii;-  an  iiiii)rcssi()ii  or  bite  or  de- 
veloping easts. 

Carving  tlic  cusps  is  a  \cry  simple  operation,  since  the 
cusp  elevations  and  depth  of  grooves  are  already  established 
and  the  central  groove  is  clearly  indicated  by  the  cusps  of  the 
occluding  teeth  in  the  l)ite. 

DEVELOPING   THE   CUSP   SURFACES   IN   A   SWAGER 

("I'own  swagers  are  \cry  coinnionly  used  in  dental  labora- 
tory jirocednres,  and  for  many  jiurposes  are  most  useful  and 
convenient.  A  swager,  however,  is  not  as  etTeetive  in  the 
development  of  cusp  surfaces  from  thick  gold  plate  as  the 
method  previously  outlined,  'riierefore,  when  the  swager 
alone  is  employed,  the  cusps  must  be  developed  from  light 
gauges  of  gold  i)late,  or  when  a  heavy  gauge  is  used,  which 
in  all  cases  is  more  desirable,  the  two  methods  may  be  com- 
bined.   The  following  plan  is  ]iroductive  of  good  results: 

Before  placing  the  counterdie  in  the  swager  its  surfaces 
are  oiled.  A  disc  of  HO  or  ."il  gauge  22  carat  gold  plate  is 
annealed  and  c<'ntered  oNcr  Ihe  depression,  into  which  it  is 


I'OrNTEBDIE    IN    I'dSlTKIN    IN    SW.' 


swaged  by  means  of  the  soft  and  hard  wood  i)unches,  as  pre- 
viously described. 

Remove  the  excessive  ]ieri])heral  surplus,  pickle  and  an- 
neal the  partially  developed  caj),  return  it  to  the  counterdie, 
place  the  latter' in  the  swager,  and  with  a  heavy  rawhide  mal- 
let drive  the  gold  into  the  matrix.  ITsually  it  will  be  neces- 
sary to  develop  the  finer  surface  markings  of  the  cusps  with 
the  lilunt  hardwood  point,  or  fine-pointed  steel  chaser.    Final 


7(JG  THE    (iOI.I)    SHKLI.    CROWN 

adaplatidii  ami  i-ciii(i\al  of  wariianc  ai-<'  ai'r(iiii])lisli('(l  in  tlu; 
swagcr. 

Fitting  the  occlusal  cap  to  llic  axial  hand  is  accomplished 
as  previously  outlined.  11  should  he  pickled  in  acid,  cleansed 
and  ])olished  to  remove  all  traces  of  base  metal. 

ASSEMBLING     AND     SOLDERING     THE     BAND     AND 
OCCLUSAL   CAP 

Remove  the  band  from  tlie  cast,  jiickle  in  acid  and  cleanse 
in  water.  Apply  boi-ax  to  the  inner  cusp  surfaces  and  the 
occlusal  end  of  the  band. 

Adjust  the  occlusal  cap  and  band  in  proper  relation  to 
eacli  other  as  indicated  by  the  coincidence  of  their  peripheries, 
and  bind  together  with  untinned  binding  wire,  bringing  the 
ends  over  the  cervical  end  of  tlie  crown,  to  form  a  loop  for 


holding  while  soldering.  The  wires  may  be  crossed,  if  neces- 
sary, to  hold  the  occlusal  cap  in  proper  relation. 

The  occlusal  cap  and  band  may  be  held  in  proper  relation 
to  each  other  without  wiring  by  means  of  the  Kerr  soldering 
tweezers.  One  beak  of  this  appliance  is  bent  at  right  angles 
to  the  handle.  Opposite  this  point  and  attached  to  the  other 
beak  is  a  loose,  three-prong  table.  The  crown  is  held  by  set- 
ting the  cervical  end  of  the  band  on  the  adjustable  table,  while 
the  right  angle  point  rests  in  the  central  area  of  the  occlusal 
cap. 

Small  pieces  of  fluxed  solder  are  placed  within  the  crown, 
the  latter  carried  to  and  held  within  the  Bunseu  flame,  occlu- 
sal end  down,  where  it  is  carefully  and  uniformly  heated  until 
the  solder  fuses.  Sufficient  solder  should  be  applied  to  form 
a  thick,  rigid,  occlusal  cap,  three  or  four  times  thicker  than 
the  swaged  cusps.  Care  should  be  taken  to  see  that  not  only 
the  joint  areas  are  perfectly  united,  but  that  the  solder  has 
been  drawn  up  slightly  along  the  inner  margins  of  the  liand 


THE    GOLD    SHELL    CROWN 


767 


as  well.  The  solder,  when  so  disposed,  strengthens  the  oceln- 
sal  surface  and  obviates  the  danger  of  it  wearing  tlnoiigh 
under  masticatory  stress. 

FINISHING  THE   CROWN 

The  finishing  of  the  crown  is  accomplished  with  engine 
stones  and  discs,  and  the  final  |)olish  developed  with  felt 
and  brush  wlieels  on  the  lathe. 

A  piece  of  wood  about  four  inches  long  and  three-eighths 
inch  in  diameter,  reduced  at  one  end  so  as  to  fit  loosely  within 
the  crown,  will  serve  as  a  handle  for  holding  it  while  polish- 
ing. The  handle  is  applied  by  ]ilacing  a  pellet  of  heated  model- 
ing comi)ound  on  the  reduced  end,  iiressing  it  into  the  crown 


CROW^    HOLDER 


CUOWX    IIOI.nEK    APPLIED 


and  chilling.  When  the  crown  is  ])()lished,  by  warming  it 
slightly  to  soften  the  comi^ound,  the  handle  may  be  removed. 
A  convenient  appliance  designed  for  holding  crowns  con- 
sists of  a  group  of  divergent  steel  springs,  set  in  a  handle. 
When  compressed  inwardly,  and  introduced  in  the  crown,  the 
springs  press  outward  and  Iiold  it  firmly  wliile  polisliing. 

SETTING   THE    CROWN 

Wiien  finislied  and  the  ])(ilishing  powder  is  removed,  the 
crown  is  washed  in  alcohol  and  laid  aside  while  the  tooth  is 
cleansed  and  dried  and  the  cement  mixed. 

Cotton  rolls  may  be  used  to  guard  against  the  encroach- 
ment of  saliva, during  the  earlier  stages  of  setting  the  crown 
and  imtil  the  cement  begins  to  set. 

The  cotton  may  be  held  in  various  ways,  one  of  the  most 
convenient  being  to  apply  a  clamp  to  a  proximating  tooth, 
and  place  cotton  rolls  under  its  lingual  and  buccal  bows. 


THK    (iOLU    SHKLL    CROWN 


A  eonvenioiit  type  o['  cottnii  roll  holder,  s|irciiilly  dcsiiiiicd 
for  such  purpose,  tlu'  Ivory,  is  here  illustrated. 

Oue  objection  to  tiie  use  of  any  clamp  in  this  o|icriitioii 
is  that  when  ap])lie(l  before  the  setting  of  the  crown.  I  he  occhi- 


^V 


THE    IVClltl     ('(ITTCJN    11(11. 1.    HOLDER 


sion  cannot  be  tested,  the  clanip  bows  interfering;'  with  closure 
of  the  opposing  teeth. 

After  forcing  the  crown  to  place,  a  clani|)  may  be  a])piii'<l 
to  advantage. 

The  usual  order  of  ])i()ce(lure  is  to  ajiply  cement  within 
the  crown  somewhat  in  excess  of  the  amount  required,  and 
quickly  carry  it  to  place. 

It  should  lie  forced  in  position  with  tinger  pressure,  after 
which  the  ])atient  is  instructed  to  bite  the  crown  to  place. 
Usually  a  piece  of  soft  wood  is  inserted  lietween  the  occlusal 


THE  COTTON   UOEI,    HOI.IJEK    Al'I'MED  TO  TEETH 

surface   of   the   crown   and   the   opposing  teeth   to   act   as   a 
cushion  on  which  to  bite. 

This  procedure  will  force  out  the  excess  cement  if  the 
latter  is  of  suitable  consistency  to  tlow.  If  too  stitT  to  flow 
under  steady  pressure,  mallet  blow^s  will  be  even  less  effective, 
although  the  latter  method  is  frequently  adopted,  usually  to 
the  injury  of  the  peridental  membrane. 


THE    GOLD    SHKLL    CROWN  769 

When  seated  and  tlie  eenient  has  set,  tlie  sni-jilns  sliouhl 
he  removed,  the  gums  syringed  with  warm,  normal  salt  solu- 
tion, and  massaged  to  relieve  the  general  discomfort  resulting 
from  the  operation. 

CASTING  THE  CUSPS 

The  occlusal  surface  of  a  crown  may  1k>  cast  directly  to 
the  axial  band.  This  method,  in  some  cases,  obviates  the  con- 
struction of  a  counterdie,  as  well  as  the  necessity  for  form 
ing  casts  of  the  mouth.  Technical  procedures  of  this  method 
of  develojiing  a  crown  vary  considerably,  but  the  general  lu'in- 
ciples  are  similar.  TIic  following  is  a  sinijile  and  conunon 
method  of  procedure: 

Form,  fit  and  contour  the  axial  liaiid  to  the  tooth  as  de- 
scribed. Apply  a  block  of  softened  inlay  wax  to  the  occlusal 
end  of  the  tooth,  within  the  band.  Instruct  the  patient  to  close 
in  simple  occlusion.  Trim  oft"  peripheral  surplus  of  wax 
and  instruct  the  patient  to  bite  sideways  and  in  various  direc- 
tions. This  step  develops  clearance  ]iaths  for  the  cusps  of 
opposite  teeth.  With  small  carving  instruments,  the  fine 
lines  and  sui-face  markings  are  developed  in  the  wax,  and  the 
occlusal  surface  given  its  desired  form  and  contour. 

Eemove  the  band  and  carxing  fi-oni  the  tooth.  Usually 
the  bulk  of  wax  within  the  band  is  greater  than  necessary  to 
reproduce  in  gold.  It  may  lie  removed  by  chilling  the  wax 
and  scraping  from  the  interior  of  the  crown  with  a  discoid 
instrument.  The  wax  may  be  reduced  to  a  layer  of  uniform 
thickness,  over  the  entire  occlusal  area,  by  holding  the  crown 
against  a  strong  light  while  scraping  away  the  excess.  The 
transmission  of  light  through  the  wax  clearly  indicates  the 
thick  and  thin  areas.  This  method  was  suggested  by  Dr.  J. 
W.  Birkland  a  number  of  years  ago.  Another  method  of  re- 
moving the  wax  is  as  follows : 

A  small  metal  tube  with  a  receptacle  for  holding  the 
melted  wax  is  heated  and  passed  against  the  interior  of  the 
crown.  As  the  wax  melts  it  is  withdrawn  by  suction,  a  small 
rubber  hose,  attached  to  the  metal  tube,  being  held  in  the 
mouth.  This  is  a  design  of  Dr.  F.  E.  Eoach  and  is  called  a 
wax  suclier. 

A  sprue  foi'mer  is  attached  to  the  cusp  surfaces  at  some 
convenient  point,  the  crown  invested  in  a  casting  ring,  so  that 
the  wax  occupies  as  nearly  a  central  position  as  possible  in 
the  ring.     Casting  is  accomplished  in  the  usual  manner. 


770  'I'HE    GOLD    SilKLL    CHOWN 

Sometimes  the  cast  ciisiis  I'liil  lo  unite  perfectly  with  the 
axial  band  at  all  points,  and  in  some  instances  not  at  all. 
When  this  occurs,  the  casting  may  be  soldered  to  the  band. 

To  obviate  the  failure  of  union  mentioned,  the  occlusal 
end  of  the  band  may  be  notched  with  the  shears,  and  the  den- 
tated  edges  bent  slightly  before  ajiplying  the  wax  and  carving 
the  cusps.  This  method  develo])s  positive  mechanical  anchor- 
age between  the  band  and  casting. 


CAST  CROWNS 

Various  other  methods  are  in  vogue  for  casting  crowns, 
either  whole  or  in  part,  which  have  proved  more  or  less  sat- 
isfactory. 

One  of  these  methods  consists  in  prejiaring  the  root  de- 
cidedly cone  shaped  or  so  that  tlie  band,  wiien  adajtted  closely 
to  it,  will  withdraw. 

The  band  is  now  formed  to  fit  the  root  closely,  so  that 
when  driven  on  it  will  cling  to  the  axial  walls  firmly.  It  may 
have  a  disc  soldered  to  the  occlusal  end,  thus  converting  it 
into  a  deep  cap,  or  the  occlusal  end  may  l)e  left  open. 

Inlay  wax  is  applied  to  the  axial  walls  and  occlusal  sur- 
face of  the  cap  and  the  crown  developed  to  the  desired  con- 
tour by  carving. 

Since  it  is  difficult  to  adapt  the  wax  to  tlie  cap  in  the 
mouth,  an  imjiression-bite  should  be  taken  with  the  band  or 
root  cap  in  position.  From  this  casts  are  developed  and 
mounted  on  the  occluding  frame.  The  f)and  is  then  carefially 
removed  from  its  cast,  being  careful  not  to  disturb  its  cervical 
matrix.  Inlay  wax  is  now  applied  to  and  melted  against  its 
outer  surface  and  over  its  occlusal  end.  It  is  uow  returned  to 
position  on  the  cast,  the  occlusal  area  softened  and  the 
occluding  teeth  pressed  into  it,  after  which  the  cusps  are 
carved  to  desired  form.  The  axial  outlines  of  the  crown  are 
developed  by  removing  surplus  or  making  additions  of  wax 
as   required. 

The  waxed  crown  can  be  returned  to  the  mouth  if  neces- 
sary for  testing  its  occlusal  adaptation,  length,  general  con- 
tour, etc. 

When  satisfactory,  it  is  invested  and  cast  in  tlio  usual 
manner. 

Oftentimes  in  casting  a  crown  of  this  ty])e,  the  contrac- 
tion of  investment  within  the  liand  walls  is  sufficient  to  per- 


THE    CJOI.D    SHKLL    CKOWN  771 

mit  the  gold  to  cuter,  thus  intei-t'eriiig  with  tlie  fit  of  closely 
adapted  bands. 

Dr.  Weinsteiu  suggests  the  insertion  of  a  closed  end  cop- 
per thimble,  slightly  smaller  than  the  interior  of  the  crown. 
The  crown  is  first  tilled  with  investment,  and  the  thimble  in- 
serted, closed  end  first,  so  as  not  to  tonch  the  crown  walls. 


THIMBLE  INSERTED  IN  CKOWN 
TO  PREVENT  EXCESSIVE  CON- 
TRACTION     OF      INCLOSED      IN- 

\E.STMENT 

The  interior  of  the  thimble  is  also  filled  with  investment,  after 
which  the  crown  may  be  invested  in  the  nsnal  manner. 

The  contraction  of  investment  between  interior  crown 
walls  and  thimble  is  so  slight  that  no  gold  will  enter  in  casting. 

THE  SHOULDER  CROWN 

The  SltDiildt'r  Cnniii  is  designed  to  oliviate  the  overlay- 
ing" of  a  band  against  the  peripheral  surfaces  of  a  tooth.  The 
joint  junction  between  tooth  and  a  crown  of  this  type  being 
continuous,  is  similar  to  that  of  an  inlay  w'ith  adjacent  tooth 
surfaces.  The  advantages  of  such  a  crown,  therefore,  when 
well  adapted,  are  obvious. 

PREPARATION  OF  THE  NATURAL  TOOTH 
The  axial  surfaces  of  the  tooth  are  prepared  so  as  to 
converge  more  or  less  uniforml.v  cervico-occlusally.  Instead 
of  terminating  cervically,  in  a  cone,  the  base  of  which  is  more 
or  less  indefinite,  the  axial  surfaces  should  terminate  in  a  dis- 
tinct cervical  shoulder.  This  shoulder  should  be  formed  at 
right  angles  to  the  long  axis  of  the  tooth.  Should  be  about 
one  thirty-second  of  an  inch  wide,  more  or  less,  and  should 
follow  the  curve  of  the  gingival  gum  tissues. 

When  possible  it  should  be  located  under  the  free  gum 
margin,  but  if  inconvenient  to  so  locate  it,  the  hygienic  value 
of  the  crown  will  not  be  impaired,  since,  as  before  stated,  the 
surface  of  the  crown  with  that  of  the  tooth  is  continuous. 


772  THE    (iOI.I)    SHKLL    CROWN 

CONSTRUCTION   OF  THE  CROWN 

'I'ln'  usn.-il  iiictluxl  dl'  ciinsl  nictinii  foiisisis  in  tiiking  an 
impression  (<\'  tlic  |iic|i;iic(l  Idnlli  in  an  open  end  l)and,  fillwl 
with  softcncil  inodcliii.ti'  conipdniiil.  This  is  lilicd  with  aiiial- 
.ii'iitn.  roi'iiiini;-  (he  liasc  sullicicnt  l\'  wi<h'  and  deep  to  I'csist 
st  fcss  of  swaying. 

Wlicii  separateil  from  the  impi-cssion  the  die  is  imhcddcd 
in  moldine,  in  tlie  swaging  ring,  and  a  cap  fitted  to  it.  A  ligiit 
gauge,  '22  carat  gold,  seandess  thimble,  slightly  longer  than 
the  eervico-oceliisal  length  of  the  prepared  tooth,  is  adapted 
to  the  metal  die,  first  with  tlic  iiorn  pene  mallet  and  afterward 
))y  swaging.  The  cervical  end  of  the  cap  should  he  reflected 
against  the  shoulder  and  its  outer  margin  trimmed  to  coincide 
with  the  root  periphery.  The  cap  may  lie  formed  of  a  band, 
and  its  occlusal  end  closed  with  a  disc 

Heavy  platinum  or  gold  foil  is  sometimes  used,  being 
conformed  to  the  die,  first  by  burnishing  and  afterward  by 
swaging.  The  folds  or  wrinkles,  which  naturally  result  from 
this  method  of  adapting  the  foil,  in  no  way  seriously  interferes 
with  the  adaptation  of  the  crown. 

When  the  cap  is  developed  it  is  returned  to  the  root  for 
an  impression-bite,  from  which  casts  are  developed. 

Inlay  wax  is  now  applied  to  the  outer  surfaces  of  the 
cap  and  the  crown  carved  to  meet  occlusal  and  esthetic  re- 
quirements, after  which  it  is  cast  in  the  usual  manner. 

SEAMLESS  GOLD  CROWNS 

A  seandess  crown  is  formed  from  a  single  disc  of  gold 
plate,  and  is  therefore  devoid  of  soldered  joints. 

With  mandrels  of  gradually  decreasing  size,  the  disc  is 
forced  through  a  series  of  holes  in  a  device  much  like  a  draw 
plate,  and  is  thus  converted  into  a  thimlile.  From  this  thimble 
the  crown  is  developed  by  swaging. 

Thimbles  are  comparatively  simjile  to  construct,  but  most 
prosthetists  use  the  maimfactured  thimbles  which  the  su|)ply 
houses  carry  in  stock  in  various  sizes  and  gauges  of  gold. 

Although  there  are  many  variations  in  detail,  there  are 
only  two  general  methods  of  constructing  seamless  gold 
crowns. 

First,  by  swaging  the  thimlile  within  a  matrix,  and  sec- 
ond, by  swaging  it  over  a  die.  By'  either  method  a  model  or 
pattern  of  the  desired  form  of  crown  must  first  be  foi'uied, 
in  order  to  construct  the  matrix  or  die.     The  construction  of 


THE    GOLD    SHKLL    CROWN  773 

the  iiattcni  is  practically  the  same  in  citlu'r  case  except  that 
ill  the  die  method  the  pattern  iiiiisl  he  sligh.tly  smaller  than 
the  proposed  crown  is  to  be,  since  the  gold  is  adapted  over  or 
outside  of  the  die.  and  is  tlieret'ore  larger  than  the  latter,  or 
the  pattern  from  which  the  die  is  (h'Vel()[ied. 

THE  MATRIX  METHOD 

First,  the  tooth  is  prepared  as  for  an  ordinary  shell 
crown.  To  this  is  fitted  a  seamless  or  soldered  copper  band 
of  the  same  gauge  as  the  gold  thimble  to  be  used.  The  band 
should  be  scribed  and  fitted  niuler  the  gingival  margin  of  the 
gums  exactly  the  same  as  a  gold  band  is  fitted. 

Its  axial  walls  should  be  contoured  to  the  desired  form, 
its  occlusal  end  notched  to  represent  the  cusp  elevations. 

The  occlusal  surface  is  filled  in  with  softened  metalline 
compound  and  when  caixcd  to  correct  form,  the  band  and 
carving  are  removed  from  tiie  tooth. 

Fill  the  inside  of  the  band  with  moldine,  flush  with  its 
gingival  margin,  and  within  this  insert  a  small  wood  or  metal 
peg,  allowing  it  to  project  about  one-fourth  inch,  to  serve  as 
an  anchorage  for  the  pattern  in  casting  the  counterdie. 

Form  some  moldine  into  a  cake  about  two  inches  in  diam- 
eter and  one-half  inch  thick,  giving  its  upper  central  surface 
a   slightly   convex  form. 

Set  the  crown  on  this  convex  surface,  cervical  end  down, 
the  projecting  ]>eg  entering  the  moldine  base.    AVith  the  point 


LEKT     CIT      SHOWS    PATTERN     CROWN     SET    ON    MOLDINE    SL.\B     WITH 

CAROHOARU  SET  IN  POSITION  TO  DIVIDE  THE  SIETAI.  AS  IT   IS  POURED. 

IIIOHT    CIT    snows    SWAGING    RING    READY    TO    APPLY    OVER    CROWN, 

ON  MOLDINE  BASE 


of  a  knife  adai)t  the  moldine  neatly  to  the  cervical  margin  of 
the  band,  being  careful  not  to  imbed  the  latter  in  the  clay. 
The  ui)]ier  surface  of  moldine  on  Avhich  the  cervical  end  of 
the  crown  rests  gives  form  to  the  cer\  ical  margin  of  the  coun- 


774  THK    liOLI)    SHELL    CROWN 

Ici'die,  and  siiic<'  tlic  ,i;iii;;i\al  ciirNatiirc  as  well  us  length  of 
crown  (lc|icii(ls  u[iiin  lliis  margin  of  the  conntcrtlie,  care 
should  !)('  taken  Id  carry  (Hit  this  step  accurately 

A  siieciul  riii.i;-,  (it  which  there  are  two  genei'al  tornis,  is 
used  in  wliicli  to  cast  the  counterdie  matrix.  Both  forms  of 
rings  liave  tapered  openings  extending  through  them  so  that 
counterdies,  wlien  cast,  will  part  readily  from  them.  In  one 
ring  there  are  two  slots  formed  in  the  inner  wall  and  opposite 
each  other  for  holding  a  U-shaped  piece  of  cardboard,  for  par- 
tially dividing  the  metal  in  casting.  In  the  other,  there  are 
two  metal  ribs  extending  centrally  toward  the  ])attern,  which 
fulfill  the  same  purpose  as  the  cardboard.  A  plain,  heavy- 
walled  ring  with  a  taper  opening  will,  however,  answer  the 
jmrpose  equally  as  well. 

The  U  shaped  cardboard  is  now  cut  and  fitted  in  the  ring 
slots,  the  central  portion  of  the  card  being  removed,  and  the 
opening  made  sufficiently  large  to  avoid  eucroachuient  of  the 
card  margins  on  the  pattern  crown. 

The  ring  should  be  so  centered  over  the  i^attern  that  tlu- 
card  edges  are  opposite  its  greatest  diameter,  so  that  when 


\(,    TUNC,    KRSTING    ON    MOLDING 
HI    M)\      rOB     TTin     (  OI  NTEItnlE 


east  and  the  counterdie  is  split,  both  halves  wil'  be  readily  re- 
leased from  the  ^lattern. 

Fusible  metal  is  now  cast  into  the  ring,  around  and  over 
the  model  crown.  When  hardened,  the  casting  is  removed, 
the  lilade  of  a  knife  is  inserted  in  the  slot  made  by  the  card- 
board, and  with  a  sharp  hammer  blow  the  die  is  split  in  two 
pieces. 

The  ])attern  is  now  removed  and  the  counterdie,  if  sat- 
isfactory, is  trimmed,  oiled,  and  returned  to  the  casting  ring. 


THK    COM)    SHKLL    CROWN 


775 


SWAGING  THE  CROWN 

A  gold  tliiiuhlc  is  selc'ctcd,  slightly  loiigiT  than  the  dciitli 
of  matrix  and  which  tits  closely  into  it.  The  interior  of  the 
thimble  is  filled  with  baseplate  gutta  ])ercha,  a  square  end. 
steel  mandrel,  which  will  i)ass  into  the  thimble  and  lit  it  closely, 
is  pressed  against  the  gutta  percha  and  given  two  or  three 
blows  with  the  hammer. 

The  thimble  is  now  remoxcd  and  examined,  to  note  the 
result  of  the  tirst  swaging.     The  ]irincii)al  accident  liable  to 


occur  during  swaging  is  tearing  of  the  gold.  By  thoroughly 
cleaning  the  crown,  ])olishing,  annealing  and  continuing  the 
swaging  process  slowly,  the  gold  can  be  forced  out  against  the 
matrix  walls  and  partially  into  correct  occlusal  form. 

Development  of  the  fine  occlusal  lines  u-<nally  reciuires 
the  a]i])lication  of  a  hardwood  ])oint  or  a  small,  somewhat 
round-i)ointed  steef  mandrel.  At  no  time  during  the  swag- 
ing process  can  the  gold  be  forced  too  rapidly,  or  splitting  of 
the  walls  will  most  likely  result.  When  developed  to  correct 
form,  tlie  cervical  surplus  of  the  crown  is  removed  even  with 
the  cervical  margin  of  the  matrix. 


776  THK    (JOLU    SHIOLL    CKOVVN 

Usuallx'  ;i  little  (•(in-cctioii  i)\'  tlii>  end  ol'  liic  ci-dwii  with 
the  eontoiiriiii;-  jilicrs  is  rciiuii'cd. 

Tlie  inner  ciis])  snrl'ai'es  sliduld  he  tliickeiicd  hy  lIowiuK 
solder  inside  the  crown. 

Sometimes,  to  avoid  daiiger  of  the  nin^ival  end  of  a 
seamless  erowii  stretching,  when  set  and  sul)jected  to  stress, 
a  tihn  of  high  grade  solder  is  flowed  around  its  entire  oTiter 
periphery'.  AVhen  ^lolished,  snch  addition  will  not  \n' 
noticeable. 

The  steps  of  linishing  and  setting  the  einwii  ai'e  similar 
to  those  of  any  gold  shell  crown. 

SWAGING  A  SEAMLESS  CROWN  BY  THE  DIE  METHOD 

When  the  crown  is  to  he  swaged  o\-er  a  die,  the  ])attern 
must,  as  before  stated,  be  smaller  timn  the  required  crowu  by 
an  amount  equal  to  the  thickness  of  the  walls  of  the  gold  thim- 
ble, otherwise  when  completed  the  finished  crown  will  be  cor- 
respondingly larger  than  the  pattern. 

A  convenient  and  accurate  method  of  forming  the  ]iattern 
is  as  follows: 

A  copper  band  of  the  same  gauge  as  the  gold  to  be  used 
is  fitted  to  the  root,  as  previously  described.  The  a.xial  walls 
should  be  contoured  and  the  occlusal  end  notched  or  occluded 
with  the  opjiosite  teeth.  The  cusps  are  carved  in  plaster  and 
when  the  crown  is  removed  the  inner  walls  of  the  band  are 
coated  with  a  thin  film  of  oil.  'I'lie  remaining  interior  space 
is  filled  with  plaster,  wdiich  should  unite  with  the  cusp  carv- 
ing. The  plaster  last  added  should  also  extend  about  one- 
eighth  inch  beyond  the  cervical  end  of  tlie  crown  to  form  a 
pedestal  for  the  pattern. 

The  band  is  now  carefully  divided  with  a  tine  fissure  bur 
usually  applied  on  the  lingual  side,  being  careful  not  to  mar 
the  jilaster  while  doing  so.  The  ends  are  then  bent  outward 
and  the  band  carefully  removed,  leaving  a  pattern  of  the  tooth 
in  i^laster. 

The  plaster  cusps  overhang  the  axial  surfaces  an  amount 
equal  to  the  thickness  of  the  band  walls. 

This  overhang  should  be  carved  away  so  that  the  sur- 
faces are  continuous.  No  reduction  of  the  occlusal  surfaces 
is  necessary,  as  the  slight  amount  in  extra  length  of  the  crown 
(about  1-100  of  an  inch)  can  be  removed  from  the  cervical 
end  in  final  fitting.  The  pedestal  or  cervical  extension  should 
be  trimmed  so  as  to  show  a  slight  shoulder,  to  outline  the 
termination  of  the  cervical  end  of  the  crown. 


THE    (iOI.D    SHELL    t'KOWN  777 

'I'lic  [»;itl('rii,  now  \vlioll>'  (•(iinpost'd  of  jilastcr,  is  coated 
with  separating  medium. 

A  small  mix  of  plaster  is  made  and  spread  on  a  siieet  of 
palmer.  It  should  be  about  three-eighths  inch  thicli  and  one 
and  one-fourth  inches  square,  flattened  on  its  upper  surface. 


Into  tliis  the  varnished  pattern  is  jjressed,  so  as  to  imbed  the 
occlusal  area  and  some  of  the  axio-occlusal  jteriphery,  usually 
about  one-eighth  inch  of  the  occlusal  end  of  the  pattern.  When 
hardened,  the  ))laster  is  trimmed  smoothly,  small  depressions 
made  in  the  four  angles  to  serve  as  guides  for  the  subsequent 
pieces  to  be  constructed,  and  its  surface  varnished. 

Another  mix  of  ])laster  is  now  made  and  applied  to  one- 
half  the  crown  and  pedestal.     This  should  embrace  approx- 


imately one-half  the  pattern,  the  line  of  greatest  diameter 
indicating  the  amount  of  surface  to  cover.  Its  ends  and 
sides  should  be  squared  up,  and  the  surfaces  extending  from 
the  pattern  outward,  trimmed  perpendicularly.  Guide  depres- 
sions sliould  also  be  made  in  these  surfaces. 


77S  -PUK    liOl.l)    SIIKIJ,    CUOWN 

W'licii  liiinlciicil,  llic  fi-csli  areas  of  |iiaslcr  ai'c  \'ariiislu'd 
and  auotlicf  mix  inailc  and  applied  a.i^aiiisl  the  opjto.site  side 
of  the  pattern,  Iniihlinn  il  np  in  conjunctioii  witli  tlie  other 
two  ]iiocos  to  I'diin  a  reelani;ulai-  lihick,  in  the  top  of  which 
I  he    liase   ol'  1  he   lieileshd    is   seen. 


PI.ASTEU   MATRIX    rdMIT-ETE,    liUT   NOT 
SEI'AltATKll 


MATJtlX     Si;i'AIlATi:il 


I'ATTKHX    I'KCIVVX     KHMIIVEH 


When  hardened  and  squared  up,  a  few  light  hammer 
lilows  will  loosen  the  several  pieces  and  the  pattern  is  removed. 

On  placing  the  three  pieces  together,  a  matrix  will  lie 
formed,  representing  in  reverse  the  form  of  the  pattern. 

The  external  ojiening  is  now  beveled  slightly,  the  block 
bound  together  witli  rubber  bands  or  binding  wire,  tlie  ring 


THE    GOI.U    SHELL    CKOVVN 


779 


of  a  swaging  de\ioe  is  set  on  top  of  the   block  and  e\('nly 
centered  over  the  opening. 

Fusible  alloy  is  now  melted  and  cast  into  the  matrix  and 
ring. 


When  cold,  and  the  jilastei-  is  remoxcd,  a  die  of  the  tooth 
witli  a  cervical  extension  will  he  seen,  attached  to  and  stand- 


The  rongh  margins  of  the  die  are  smoothed  up,  the  latter 


780  'nil':    (!()l,l)    SHIOLI.    CliOWN 

oiled,  and  a  lliinihlc  scliM-tcil  that  will  tclcscdiic  o\ci-  the  die 
loolli  and  cxlciid  1(1  its  cervical  line  or  slii;lilly  lielow. 

SWAGING  THE  CROWN 

The  thinilile  and  nppei-  surface  ol'  the  die  are  now  co\'- 
ercd  witli  tissue  i)a])('r,  to  i)re\-ent  the  swag'ing  material  of 
wliatever  kind  from  iinding  its  way  between  gold  and  die. 

The  ring  is  placed  in  the  swager,  the  outer  ban-el  set 
over  it  and  with  one  heavy  hanunei-  blow  tlie  ada])tation  of 
gold  to  die  is  beiiun.     An  examination  of  llie  thimble  is  now 


■rniMHT.E  ix  t'osition  on  dm; 


made.  Invariably,  after  the  first  swaging,  one  or  more  folds 
of  gold  have  begun  to  form  around  the  cervical  constriction. 
These  can  be  obliterated  without  removing  the  thimble  from 
the  die  by  means  of  light  blows  with  the  horn  pene  mallet  or 
the  small  riveting  hannner. 

When  corrected,  the  gold  is  again  subjected  to  another 
single,  heavy  hammer  blow  in  the  swager,  and  wrinkles  or 
folds  removed  as  l)efore. 

This  process  is  repeated  until  the  gold  is  constricted  gin- 
givally  so  that  folds  cannot  develop. 

The  occlusal  surface,  in  the  meantime,  has  become  only 
partially  conformed.    With  the  riveting  hammer  and  a  small 


THE    GOI.U    SHKLI>    ([{OWN 


steel  luaiiilrcl.  the  orclusiil  surracc  lines  arc  developed,  after 
which  the  erowii  is  om-e  more  i-etiini(Ml  Id  the  swager  for  final 
adaptation. 

Since  in  practically  every  case  the  crown  pattern,  and 
consequently  the  die,  are  bell-shaped,  the  gold  cannot  be 
removed  from  the  die  during  the  swaging  process. 

It  is  finally  removed  l)y  placing  the  die  with  crown  at- 
tached, in  water  and  bringing  it  to  l)oiling  point,  at  which 
temperature  the  fusible  metal  melts.     This  method  prevents 


contamination  of  the  gold  by  the  base  metal,  which  usually 
occurs  when  the  die  metal  is  melted  in  the  open  flame. 

By  this  method  of  construction  the  crown  walls  are  thick- 
ened, while  in  the  matrix  method  the  walls  are  to  a  greater 
or  less  extent  reduced  in  thickness. 

FINISHING  THE  CROWN 

The  gingival  surplus  is  trinnned  to  the  line  of  .iunction 
of  crown  with  pedestal,  the  crown  boiled  in  acid  and  polished. 
The  occlusal  or  incisal  ends  should  be  stiffened  interiorly,  and 
the  cervical  end  covered  exteriorly  with  a  thin  film  of  high- 
grade  solder. 

GENERAL  REMARKS 

In  all  cases  of  pattern  construction,  a  copper  band  should 
l)e  carefully  scribed  and  fitted  to  the  natural  tooth.  This  may 
be  wide  or  narrow,  deiiending  on  how  the  pattern  is  to  be 
formed.  On  or  within  this  band,  the  wax,  plaster  or  other 
material  is  built  and  carved  as  required. 

It  will  be  seen'  that  since  the  pattern  is  at  no  time  sub- 
jected to  heat,  it  may  be  formed  of  wax  or  any  material  suffi- 
ciently resistant  to  carve  well  and  retain  its  form  in  handling. 

One  who  can  carve  well  can  produce  very  satisfactory 
forms  of  crowns  by  this  method.     One  who  cannot  carve 


782  THK    LiOLD    SHELL    CROWN 

slioiikl  not  attempt  this  niothod  of  construction,  for  he  will 
most  cortainly  be  disappointed  with  esthetic  results. 

Certain  mechanical  aids,  however,  can  be  resorted  to, 
which  will  relieve  one  of  most  of  the  carvinsj-,  but  not  of  nice 
adjustment  of  the  several  ]iarts  of  the  wlioh'. 

REPRODUCING  NATURAL  TOOTH  FORMS  IN  INLAY  WAX 

One  of  these  mechanical  aids  that  may  be  applied  in  vari- 
ous ways  consists  in  pressing  the  crown  of  a  natural  tooth,  or 
a  typically  formed  artificial  tooth,  into  moldine,  the  surface 
of  which  should  be  dusted  with  talcum  i)owder.  On  removal, 
a  distinct  matrix  is  seen,  into  which  melted  inlay  wax  is 
poured.  Since  this  wax  cools  quickly,  and  when  cool  is  quite 
hard,  the  reproduction  may  he  carved  to  any  desired  form.  At 
any  rate,  it  furnishes  a  very  good  basis  on  which  to  Ijuild  the 
form  desired. 

This  method  is  often  adopted  in  forming  dummies  in  wax 
that  are  to  be  reproduced  by  casting. 

In  the  hands  of  the  writer  the  swaging  of  crowns  over  a 
die  has  proven  very  satisfactory. 


CHAP  ^1^  K  R     XXIX 

BRIDGEWORK 

ENGINEERING  PRINCIPLES 

In  scientific  fields  it  is  a  recognized  fact  tliat  the  use  of 
exact  terms  encourages  tlie  development  of  exact  methods.  It 
is  therefore  of  advantage  to  the  student  to  become  familiar 
with  the  terms  connuonly  used  in  dental  hridgeworl^,  and  their 
concise  meaning  as  understood  and  applied  in  engineering, 
from  which  field  these  terms  have  been  selected  and  adapted 
to  dental  purposes. 

A  bridge  is  a  structure  which  spans  a  space,  and  which 
is  designed  for  sustaining  or  supporting  not  only  its  own 
weight,  but  additional  loads  or  stresses  that  may  be  brought 
upon  it. 

A  bridge  consists  of  a  substructure  and  a  superstructure. 
The  substructure  of  a  bridge  is  the  supporting  foundations, 
while  tlie  superstructure  is  that  part  which  rests  upon  the 
foundation  supports,  spans  the  space  and  carries  the  load. 

The  term  abutment  is  defined  as  "the  terminal  mass  of  a 
bridge,  usually  of  masonry,  which  receives  the  thrust  of  an 
arch  or  the  end  weight  of  a  truss;  in  distinction  from  a  pier 
which  carries  intermediate  points.  .  .  ."  (Century  Dic- 
tionarj'.) 

APPLICATION  OF  STRESS  TO  THE  SUBSTRUCTURE  OF  A 
BRIDGE 

There  are  five  principal  types  of  bridges  recognized  in 
engineering,  differentiated  l)y  the  manner  in  which  the  weight 
of  the  superstructure  and  load  is  sustained  by  the  foundation 
supports. 

First,  the  arch  bridge  of  masonry,  in  which  the  abutments 
must  not  only  support  vertical  stress,  but  end  thrust  as  well. 
In  a  bridge  of  this  type  the  arch  is  not  a  complete  factor  in 
itself,  but  is  dependent  upon  constant  end  compression  be- 
tween opposing  abutments  for  maintainance  of  form  and 
capacity  for  sustaining  load.  This  end  compression,  which 
tends  to  force  the  abutments  apart,  is  usually  provided  for  by 
broadening  the  end  terminals  of  the  abutments  with  flaring 
walls,  and  filling  the  inclosed  space  between  these  abutting 

783 


I!i;iih;k\v()i;k 


walls  and  the  iiriiiripal  foinMlat inii  with  I'artli  or  lork.  Tb(^ 
L'lid  abiitiiR'iit  lliercrdrc  dciiv-'s  its  iiaiiu;  t'ruiii  thu  fad  tliat  it 
(ibuts  the  bank. 


A   STONE  ABCH  BBIDGE 


The  weight  of  the  structure  and  applied  load  exerts  down- 
ward vertical  stress  and  an  outward  ])ush  against  the  abut- 
ments. 

GIRDER  OF  TRUSS  BRIDGES 

Second.  The  finder,  or  tniss  bridge,  is  one  in  which  the 
structure  which  bridges  the  space  between  the  two  abutments, 
or  wlien  consisting  of  more  than  one  span,  between  an  abut- 
ment and  a  pier,  is  a  complete  factor  in  itself,  rigid,  and 
capable  of  sustaining  its  own  weight  and  of  the  applied  load 
as  well.  The  span  may  be  solid,  consisting  of  simple,  solid 
girders  of  wood  or  iron,  or  it  may  consist  of  several  members 
so  united  as  to  act  as  a  solid  beam.  As  an  example,  the  Howe 
Truss  is  composed  of  an  up]ier  and  a  lower  chord  united  by 


A  HOWE  TRUSS  BRIDGE 


vertical  and  diagonal  web  members.  This  truss  is  so  framed 
that  the  upper  chord  is  always  in  compression,  the  lower  al- 
ways in  tension,  the  vertical  members  under  tensile  strain, 
and  the  diagonal  under  compressive  stress.  The  weight  of  the 
truss  an^  load  exert  a  downward  vertical  stress  upon  the  abut- 
ments and  piers. 


BRIDGE  WORK 


SUSPENSION  BRIDGES 


Third.     A  SKspcnsion  bridge  consists  of  a  ])latform,  liuiig 
on  cables   which  span  the  space  and  ai-e  snpi)orted  by  abut- 


A   SUSPENSION  BRIDGE 


ment  towers.  The  weiglit  of  the  structure  and  the  load  it 
carries  exert  a  vertical  stress  and  an  inward  pull  upon  the 
abutments. 

PONTON   BRIDGES 

Fourth.  A  ponton  bridge  consists  of  a  platform  super- 
structure, supported  by  shallow  vessels,  or  boats  which  float 
upon,  and  are  anchored  in  a  stream  of  water.  Bridges  of  this 
type  have  no  solid  or  tixed  abutments  or  piers,  except  the  ter- 
minal banks,  each  boat  carrying  its  proportion  of  weight  of 
the  immediate  superstructure,  and  yielding  under  the  immedi- 
ate load  imposed,  according  to  its  capacity  for  displacement  of 
water. 

The  term  "pontic"  has  been  suggested  as  a  substitute  for 
"dummy"  in  describing  a  bridge  tooth  replacement.  The  term 
seems  scarcel}'  appropriate,  since  practically  all  fixed  bridges 
are  of  the  rigid  truss  type.   • 

THE  CANTILEVER  BRIDGE 

Fifth.  A  cantilever  bridge  is  a  structure  consisting  of 
two  or  more  rigid  trusses  which  span  a  space,  each  of  which  is 
sui)i)orted  in  or  near  its  center  by  a  foundation  pier.  That 
portion  of  the  truss  extending  from  the  foundation  pier  to  the 
abutment  bank  is  called  the  shore  arm,  wliile  its  opposite  end 
is  called  the  river  arm. 

In  a  structure  of  this  type,  consisting  of  two  trusses  which 
bridge  a  river,  the  length  or  weight  of  the  shore  arm  is  in- 
creased over  that  of  the  river  arm.  To  counteract  the  eti'ect 
of  load  applied  at  the  terminal  end  of  the  river  arm,  the 
shore  arm  is  tied  down  to  the  bank  al)utment.  This  is  neces- 
sary, since  the  terminal  end  of  the  river  arm  is  unsupported 
and  its  stability  under  load  depends  upon  the  rigid 'ty  of  the 
entire  truss  structure. 


BRIIKJKVVOKK 


l''()i-  tlic  |iiii|i(is('  (iT  (Miiializiiii;'  stress  iis  well  as  for  coii- 
vciiiciicc  in  consl  ruction,  particiilai'ly  wiicii  the  space  to  lie 
bridged  is  wide,  an  independent  truss  is  interjiosed  hetween 
and  supported  liy  the  tei'niinal  ri\'ei'  anus. 


A   CANTILEVER   BRIDGE 


Tlie  stress  upon  the  central  foundation  of  a  cantilever 
bridge  is  downward,  while  that  upon  the  bank  abutment,  when 
the  weiglit  of  the  river  arm,  together  with  its  load,  exceeds 
the  weiglit  of  the  shore  arm,  is  upward. 

DENTAL  BRIDGEWORK 

Bridgework,  in  its  dental  meaning,  refers  to  the  replace- 
ment of  some  of  the  lost  natural  teeth  by  means  of  substitutes 
or  dummies,  which  are  attached  to  and  held  in  position  by 
some  of  the  remaining  natural  teeth  or  roots.  The  teeth  or 
roots  so  utilized,  according  to  the  nomenclature  ]irevionsly 
outlined,  are  termed  ahiitmoits  and  piers. 

GENERAL  CLASSIFICATION  OF  BRIDGES 

Bridges  naturally  fall  into  two  classes,  fixed  and  reinov- 
ahle.  Both  types  mentioned  are  capable  of  division  into  sub-' 
classes,  generally  similar  in  form,  yet  varying  in  detail,  ac- 
cording to  the  means  of  retention  or  attachment  employed, 
the  forms  of  the  individual  factors  or  dummies  of  which  they 
are  composed,  and  the  class  and  arrangement  of  the  materials 
entering  into  their  construction. 


DISTINCTION   BETWEEN   FIXED  AND  REMOVABLE 
BRIDGES 
FIXED  BRIDGES 
A  fixed  bridge  is   so  designated   because,   when   perma- 
nently set,  it  cannot  be  removed  by  the  patient.    As  ordinarily 
constructed,  a  fixed  bridge  cannot  be  removed  by  the  operator 


BRIDGEWORK  787 

without  more  or  less  mutilation  of  some  of  its  parts.  Occa- 
sionally, when  a  l)ridge  has  previous!}'  been  partially  loosened 
through  disturbance  of  the  cementing  medium,  as  from  stress 
of  mastication  or  other  causes,  it  may  be  removed  without 
mutilation. 

FIXED  BRIDGES  SO  CONSTRUCTED  AS  TO  BE  REMOVABLE 

It  is  possible,  and  practicable  as  well,  to  construct  a  bridge 
of  the  fixed  or  stationary  type,  wliich  can  readily  be  removed 
and  replaced  by  the  operator,  but  not  by  the  patient.  This  is 
a  decided  convenience,  for  in  ease  of  repair,  or  if  the  roots 
forming  the  substructure  require  treatment,  removal  may  be 
made  without  mutilation  of  the  substitute,  or  injury  to  the 
supporting  roots,  and  the  bridge  later  returned  to  and  set  in 
position. 

A  bridge  in  which  the  "Corcoran"  block  and  screw  is 
applied  is  a  representative  of  this  type.  (See  page  835.)  Vari- 
ous other  attachments  have  been  suggested  and  successfully 
used.  One  of  the  most  practical  of  these  consists  of  a  projec- 
tion extending  from  a  crown  or  inlay,  wliich  is  received  in  a 
correspondingly  shaped  socket  in  the  substitute.  An  opening- 
extends  througli  both  bridge  and  projection  and  in  this  a  dowel 
or  screw  is  fitted. 

By  reference  to  "Application  of  stress  to  tlie  substructure 
of  a  bridge"  it  will  be  seen  that  fixed  bridges  come  under  the 
second  classification,  viz.,  rigid  truss,  A-ertical  stress,  no  end 
thrust  on  abutments. 

FIXED  SADDLE  BRIDGES 

Fixed  bridges  are  sometimes  constructed  with  saddles  to 
rest  upon  and  cover  the  border  to  a  greater  or  less  extent. 
By  some  it  is  thought  that  two  advantages  are  gained  by  the 
use  of  a  saddle  in  a  fixed  bridge. 

First.  It  is  claimed  that  the  saddle  affords  some  resist- 
ance to  stress,  and  thereby  relieves  the  sub-structure  or  abut- 
ments and  piers,  of  some  of  the  exti'a  load  they  must  neces- 
sarily sustain,  in  performing  their  own  work  and  that  of  the 
substitute  crowns  as  well. 

Second.  That  by  the  use  of  a  saddle,  better  gem-ral  con- 
tour can  be  given  the  individual  members  of  the  bridge,  and 
the  formation  of  constricted  spaces  between  the  structure  and 
the  border,  in  which  food  will  accumulate,  can  to  a  great  ex- 
tent be  obviated. 


788  KKIIKIEWOKK 

It  is  the  oitinioii  (it  (he  wi'itcr',  hased  on  oljsoi'vation  and 
experience,  tliat  the  iirst  of  tliese  so-called  advantages  is  ex- 
tremely doubtfnl.  A  saddle  wliicli  bears  so  firmly  upon  the 
mucous,  and  indirectly  upon  the  bony  tissues  when  in  a  state 
of  rest  as  to  yield  support  under  the  slight  movement  of  the 
abutment  roots  in  their  peridental  membranes,  will  sooner  or 
later  result  in  absorption  of  the  bony  tissues.  The  constant 
pressure  exerted  may  or  may  not  result  in  absorption  of  the 
mucous  tissues.  In  any  event,  the  slight  resistance  to  stress 
afforded  by  these  tissues,  even  though  they  may  not  be  per- 
ceptibly absorbed,  is  not  worth  considering. 

The  second  advantage,  that  of  better  contour  afforded  the 
substitute  teeth,  however,  is  unquestionable  in  those  cases 
where  a  saddle  is  applicable.  Wide  saddles  are  always  objec- 
tionable and  should  never  be  applied.  Even  with  a  narrow 
saddle,  it  is  sometimes  impossible  for  the  patient  to  maintain 
correct  hygienic  conditions  around  the  structure  because  of 
the  difficulty  in  removing  food  particles  which  find  their  way 
beneath  it.  Discrimination,  therefore,  should  be  observed 
in  the  application  of  saddles  of  any  fyjie  in  fixed  bridge  work. 

INDIVIDUAL  SADDLES 

More  than  thirty  years  ago.  Dr.  H.  H.  Keith  of  St.  Louis 
advocated  the  use  of  individual  saddles;  that  is,  an  individual 
saddle  for  each  dummy,  not  greater,  usually  less  in  area,  than 
the  normal  cross-section  at  the  border,  of  the  natural  tooth 
replaced.  Within  recent  years  this  method  has  been  revived, 
and  is  being  used  by  many  with  very  satisfactory  results. 

The  advantages  of  an  indi\idiud  saddle  are  threefold, 
viz:  first,  more  esthetic  form  may  be  given  the  dummy;  sec- 
ond, the  structure  feels  more  comfortable  to  the  tongue,  the 
dummy  being  given  the  approximate  lingual  contour  of  the 
natural  tooth,  and,  third,  there  is  less  tendency  for  food  to 
accumulate  in  bulk,  or  become  as  tightly  wedged  as  when  the 
dummies  approach  close  to  or  rest  against  the  labial  or  buccal 
border  surfaces  only. 

As  before  stated,  a  saddle,  either  continuous  or  of  the 
individual  type,  cannot  afford  any  appreciable  resistance  to 
masticatory  stress,  in  fixed  bridge  work,  and  should  not  be 
applied  in  those  eases  where  the  abutment  teeth  are  inherently 
weak  and  unable  of  themselves  to  withstand  the  stress.  In 
such  ease  a  bridge  is  contra-indicated. 


BKIDCKWORK 


SANITARY   BRIDGES 


A  type  of  iixed  Iji-idiic,  (•(HiiiiKuily  known  as  a  .s(tiiitari) 
bridge,  is  frequently  constriK'tcd.  in  lnwer  restorations  ot" 
bicuspids  and  molars  partieulai-I> .  wlicn  absorption  of  tbe 
ridge  lias  progressed  to  a  eonsiderahli'  extent,  and  when  tbe 
detieient  portion  of  tbe  substitute  is  not  visible  wben  tbe 
moutb  is  opened  as  in  speaking  or  laugbing. 

A  bridge  of  this  type  consists  of  an  ocdasal  platfunii, 
attacbed  to  abutment  crowns  or  inlays.  Tbe  buccal  and  lin- 
gual margins  of  tbe  dummies  are  I'ounded  in  and  terminate  in 
a  more  or  less  convex  surface  ]iresenting  toward  tbe  border. 
Not  more  than  one-tbird,  usually  less,  of  tbe  buccal  and  lin- 
gual surfaces  are  deve]o])ed  to  anatomic  form,  tbe  idea  being 
to  preserve  as  mucb  space  as  possible  between  ridge  and  dum- 
mies, so  that  food  may  be  readily  removed.  In  most  cases 
these  bridges  are  constructed  entirely  of  metal.  Certain  types 
of  replacable  porcelain  teeth  may,  however,  l)e  utilized  in  such 
structures  when  conditions  are  favorable. 

EXTENSION  BRIDGES 

An  extension  bridge  is  purely  and  simply  a  cantilever 
bridge.  The  cantilever  princi])le  is  often  misapplied  in  bridge 
work,  one  abutment  root  having  to  carry  one,  or  even  two, 
))roximating  teeth  without  any  additional  anchorage,  furtbei- 
than  that  afforded  by  contact  of  the  terminal  dummy  with  a 
proximating  tooth.  This  principle  is  wrong  under  any  circum- 
stance, even  in  the  attachment  of  a  single  dmnmy  to  a  single 
root. 

When  two  proximating  roots  are  available  as  aljutments, 
if  it  is  possible  to  so  rmite  them  that  the  structure  will  not 
impinge  upon  the  soft  tissues,  and  it  can  be  kep^t  clean,  this 
principle  may  at  times  be  emjiloyed  to  advantage. 

Again,  in  bridges  of  considerable  length,  where  teeth  or 
roots  and  spaces  alternate,  an  extension  dummy  can  be  ap- 
plied to  fill  tbe  terminal  space  at  one  or  the  other  end  of  tbe 
structure,  thus  reducing  the  nunilx'i'  of  su])]iorting  crowns 
without  curtailing  necessary  sup]U)it. 

Practically  the  only  advantag<'  of  an  extension  bridge 
under  any  conditions  is  in  obviating  the  crowning  or  inlaying 
of  a  sound  and  useful  tooth.  Tlie  problem  tbe  in'ostbetist 
must  determine  is  whether  a  rigid,  well-supported,  sanitary 
structure  can  be  introduced  without  a  terminal  sn]iport  at 
each  extremity. 


790  liUlDliKWOKK 

IMPORTANT   FACTORS  TO   BE  CONSIDERED  IN   PLANNING 
FIXED  BRIDGES 

Tlie  eiigiiiccr,  in  |ilaiinin,ii'  and  constructing  a  lii'iilgc,  can 
select  the  material  and  Imild  tlic  foundations  for  the  structure 
in  wliatever  location  is  best  calculated  for  its  support. 

The  prosthetist  cannot  Iniiltl  1  he  foundation  for  the  bridge 
he  constructs.  He  must  select  f  loni  among-  the  teeth  and  roots 
present  those  which,  in  his  judgment,  are  most  favorably 
located  and  best  calculated  to  i)erform,  not  only  their  own 
work,  but  sustain  the  extra  stress  thrown  upon  them  by  the 
added  masticatory  area  of  the  teeth  supi)lied. 

ABUTMENTS  AND   PIERS 

No  engineer  will  ])lau  or  construct  a  bridge  truss  with 
lateral  curvature.  In  case  a  curve  in  the  road  is  required 
he  will  either  construct  short,  straight  trusses  with  piers  at 


GltOUND    I'LAN  OK   A   CfBVEI)    riUSS   SI  TI'dUTED    IIY  ONl.V   TWO  Am  TMKNTS, 
CORKECT    BECAUSE   WHEN    UJAl)    IS    Al'I'MED    TO    OITKRMOST    CLRVE 
THE   TENDE.VrV    «dr[,l)    HE  TO    ROTATE 


TIIL   SAME  TRISS  SUl'I'ORTEl)   IIV 


\1UTMENT    IN   THE   CENTKl! 


each  end,  and  dispose  them  in  curved  alignment,  or  plan 
somewhat  longer  trusses  of  greater  breadth  on  which  the 
required  curve  of  roadbed  may  be  laid  out.  In  any  case, 
change  of  direction  requires  that  the  outermost  curve  shall 
have  a  firm  foundation  to  support  it  or  the  structure  will  fail. 


BRIUGEWORK  791 

Again,  ill  engiiit'i'iiiii;'  the  t'oinidations  of  a  bridge  rest  upon 
bedroclv  or  its  equivalent,  and  the  abutments  are  not  sviscepti- 
ble  to  any  marlved  lateral  stress  or  vibration.  Neither  does 
the  substructure  suffer  materially  under  direct  stress,  being 
capable  of  successfully  sustaining  not  only  the  weight  of  the 
constant  suiierimposed  structure,  but  many  hundred  times 
more  than  the  heaviest  intermittent  load  that  will  be  applied. 

.V  bridge  designed  and  built  in  a  manner,  or  of  such  ma- 
terials, that  the  dividing  line  between  safety  and  disaster  is 
indelinite,  would  subject  the  designer  to  severest  criticism,  if 
not  criminal  ijrosecution. 

In  the  construction  of  dental  bridges,  the  prosthetist  is 
confronted  with  more  serious  problems  than  arise  in  the  engi- 
neering field.  The  foundations  of  a  dental  bridge  are  not  firm 
and  unyielding.  They  are  su))ject  to  depression  under  direct 
and  a  much  greater  degree  of  movement  under  lateral  stress. 

The  power  of  resistance  to  stress,  without  injury,  of  the 
peridental  membranes  of  teeth,  varies  in  dift'erent  individuals. 
The  dividing  line  between  the  amount  of  stress  ordinarily 
delivered  upon  the  abutment  roots  under  a  bridge,  and  that 
which  will  cause  permanent  injury  to  the  peridental  mem- 
brane is  very  indefinite,  so  close,  in  fact,  that  frequently  in- 
jury beyond  repair  occurs  before  the  patient  is  aware  of  it. 

The  amount  of  stress  actually  delivered  upon  a  bridge 
to  the  supporting  roots  is  directly  dependent  upon  two  fac- 
tors; first,  the  habitual  masticatory  effort  of  the  individual, 
and  second,  the  occlusal  area  of  the  bridge  involved. 

This  stress  cannot  be  determined,  or  at  least  only  ai> 
proximatel}',  nor  can  the  power  of  resistance  of  the  peridental 
membrane  to  withstand  stress,  without  injury,  be  estimated. 
The  necessity,  therefore,  of  selecting  sound,  healthy  roots 
or  teeth,  in  sufficient  number,  and  properly  located  for  sup- 
porting a  bridge,  is  obvious. 

Since  the  vital  factors  which  determine  the  possibility 
of  placing  a  successful  bridge  depends  upon  the  position  and 
condition  of  health  of  the  abutments  and  piers,  the  utmost 
care  should  be  observed  in  their  selection. 

Long  span  bridges,  extending,  for  exami)le,  from  cuspid 
or  first  bicuspid  to  third  molar,  inclusive,  without  an  inter- 
mediate pier,  are",  as  a  rule,  unsatisfactory.  In  such  case 
the  abutment  teeth  or  roots  are  required  to  perform  not  only 
their  own  functions,  but  siistain  the  stress  delivered  ui»on  the 
intervening  teeth  as  well,  for  which,  jihysiologically,  they  are 
not  capable. 


7!»2  liKlliCKWOliK 

A  r;i\(ii';ilil('  rouiidnlidii  for  siicli  a.  span  would  !)(',  cusiiul 
and  third  molar  for  alintniciits,  and  serond  liicnspid  or  lirst 
JiK.lar  for  a  pier. 

in  case  no  ititcrxcning  pier  is  present,  tlie  prostlielist 
cannot  Iniild  oiu'  as  can  the  engineer.  A  saddle  will  not  i'ul- 
lili  the  requirement,  thcrcFoi-e  some  form  of  removable  den- 
ture of  the  saddle  iy['<'  should  be  considered,  in  which  the 
border  will  receive  the  burden  of  stress,  the  terminal  teeth 
serving  principally  to  retain  the  a])pliance  in  i)osition. 

A  simple  anterior  bridge  in  which  the  two  lateral  incisors 
are  to  be  replaced,  the  two  central  incisors  serving  as  abut- 


Sl.MI'l.E      AXTEIUOIt.      ('A:NTI- 
LEVEI!    BRIDGE 


ments,  will  frequently  i)rove  successful.     A  structure  of  this 
tyioe  is  classed  as  a  cantilever  bridge. 

A  simple  anterior  bridge,  involving  the  replacement  of 
the  four  incisors,  the  two  cuspids  serving  as  abutments,  is 
not  usually  successful,  when  the  anterior  curvature  is  con- 
siderable, even  though   the  incisive  stress  is  moderate.     In 


such  case  the  line  of  force  against  the  abutment  roots  is 
outward,  instead  of  apically  as  it  should  be. 

The  cantilever  principle,  however,  can  fre(|U('ntly  be  em- 
ployed to  advantage  by  extending  the  bridge  distally  at  each 
end.  to  include  the  first  bicuspids.  When  extended,  the  cuspid 
and  bicuspid  crowns  should  be  so  united  as  not  to  impinge 
on  the  soft  tissues.  This  may  be  done  by  joining  them  at 
their  contact  surfaces,  leaving  the  inter]n-oximal  space  free 
and  open. 

Again  a  frequent  combination  consists  of  cuspids  and 
second  bicuspids  utilized  as  supporting  roots,  the  four  an- 
terior and  the  two  first  bicuspid  teeth  being  replaced.    This 


BKIUliKWOKK 


is  a  complex  bridge  of  stahlc  t'oi'iii  liascd  on  the  cantilever 
priuciple  and  when  eoiiditioiis  aic  faxorahle  will  prove  suc- 
cessful. 


SAMr-:   imiDCK   .\s   ox  rBErEDix<; 

PACK        EXTENDKD        TO        INl'LUOE 

EiusT  urcrsriDs.  Tnrs  formixo  a 

(.'OMIM.EX      STIUCTtRE 


(_'O.Ml>I.EX  BKIDGE,   OF  THE  ('AXTILE\ER 
TYl'E,  OP  THE  CUSPID  AND  SBCOXU  BI- 
CUSPID SERIES 


A  com])lex  bridge,  extending  from  the  first  bicuspid  on 
one  side  to  the  corresponding  opposite  tooth,  with  a  sound 
and  healthy  central  incisor  present  to  serve  as  a  pier,  might 
possibl.v  prove  successful  if  the  stress  of  occlusion  is  light. 
Under  these  conditions,  however,  a  fixed  bridge  is  usually 
contraindicated. 

Frequently  the  space  resulting  from  the  loss  of  one  tooth 
or  of  two  teeth  that  proximated,  can  be  successfully  filled 
by  a  fixed  bridge  of  the  cantilever  type,  that  is,  having  only 
one  fixed  abutment.  To  suj)iiort  the  extension,  a  lug  is  at- 
tached to  and  carried  beyond  the  terminal  end  of  the  dummy, 
on  a  line  with  or  slightly  below  ils  occlusal  surface.  This 
lug  rests  in  a  depression,  in  an  inlay  carried  by  the  proxi- 
mating  tooth.  Such  an  attachment  converts  the  extension 
bridge  into  one  of  the  regular  type,  since  the  tooth  carrying 
the  inlay,  although  not  attached,  serves  as  an  abutment. 

A  very  connnou  type  of  simple  ])osterior  rejilacement  con- 
sists in  utilizing  the  cuspid  and  first  molar  as  abutments,  the 
two  bicus])ids  being  su]iiilied. 


I'.rcrAL    AMI    I.IXCIAI,    VIEW    OK   SIMri.E    rosTi: 

lilOR    IlIUlJliE.      IX    THIS    CASE    THE    S1'A<'E    OCIT- 

PIEI)    BY    THE    SECOXD    BICUSPID    HAS    WIDEXKI) 

AXD    A    MOLAR    DUMjrV    IS    SUBSTITUTED 


A  SIMIM.E.  POSTERIOR  BRIDGE. 
KIltST  UiCUSlMD  AXn  SECOND 
MOLAR  SERIES,  IX  WHICH  SADDLE 
HACK  TEETH  ARE  UTILIZED  FOR 
THE  SUBSTITUTES 


Sometimes  the  cuspiil  and  second  molar  are  used  as  alnit- 
ments,  the  two  bicuspids  and  first  molar  dunnnies  being  swung 
between.    Tn  this  case  the  cusjiid  and  second  molar  must  sus- 


liKIDCKWORK 


lain  not  only  their  own  load,  lint  (■a<'ii  |)crl'oini  the  work  of 
uiie  and  uiu'-liall'  additional  teeth.  In  many  instanees  a  liridj^e 
of  this  type  will  pi-oxc  iiiisiiceessrnl. 


.  k  .jilL^lvJPii^ 


\     SIMIM  I      I'OSILRKIR     FltllM   I      111 

IHF     IISPII)     AND     &E   <)\II     Mill   Mi 

bERILb.     IIIATORIC  TEIiTH  IU1I,1/L1I 

FOR  SUBSTITUTES 


A  type  of  stnicture  called  an  interrnpted  l)rid^e  is  some- 
times construeted  to  avoid  involving  sound  ]iroxiniatino-  teeth, 
'{'he  lividge  is  converted  into  a  rigid  structure  l»y  joiniui!,'  the 


A    COMPLEX    CANTILEVER    BRIDGE   I'OKMKH    in     IMT- 
ING  A  CENTRAL  AND  CUSPID  SERIES  WITH  A  CUSPID 
AND  SECOND  MOLAR   SERIES 

several  factors  with  lieavy  iridio-)ilatinuin  wire,  l)ent  to  lie  in 
contact  with  the  tissues,  yet  so  as  to  avoid  contact  with  the 
teeth  not  involved.    This  tyjx'  of  bridge  was  suggested  I)y  Dr. 


lililDCKWORK  795 

,1.  l.cdii  W'illiiiius  iilimit  ISSli  and  illustrated  in  the  Dental 
L'osnio8  of  that  year. 

Occasionally  a  i'nll  denture  liritlge  is  constrneted  in  which 
practically  all  of  the  miissing  teeth  and  the  natural  teeth  |»res- 
ent  are  united  to  form  a  rigid  structure. 

ITsually  bridges  of  this  type  are  unsatisfactory.  First. 
because  of  constrictive  difficulties  encountered;  second,  he- 
cause  of  danger  of  fracture  under  masticatory   sti'ess,  and. 


third,  the  lial)ility  of  the  almtment  and  pier  roots  giving  way 
under  the  excessive  strain  to  which  subjected. 

Some  form  of  removable  denture  will,  in  most  cases, 
]n'ove  very  much  more  satisfactory  than  a  structure  of  this 
type. 

PREPARATION  OF  ABUTMENT  ROOTS  AND  PIERS 

The  al)utment  and  pier  attachments  of  a  bridge  which 
rest  upon  the  supporting  roots  usually  consist  of  crowns. 
Since  these  differ  in  no  essential  detail  from  individual 
crowns,  the  preparation  of  roots  and  teeth  for  their  reception 
differs  but  little  from  the  outlines  previously  given  under 
"Crown  Construction."  There  is,  however,  one  imjiortant 
consideration  in  bridge  work  that  does  not  apply  to  individual 
crowns  which  must  be  carefully  observed. 

When  the  supporting  crowns  of  a  bridge  which  rest  upon 
the  roots  consist  of  either  shell  or  dowel  crowns,  the  axial 
surfaces  of  the  teeth  involved  must  be  parallel  as  nearly  as 
l)ossil)le.  This  is  ;iecessary  in  order  that  the  abutment  and 
pier  pieces  may  be  withdrawn  from  and  returned  to  position 
on  their  respective  roots  without  hindrance. 

Tn  some  cases  excessive  reduction  of  the  axial  surfaces 
of  divergent   or   convergent   natural   crowns   is   required   to 


Tilti  Bi;il>(iK\V()l{K 

liriii.n'  lliciii  in  |i;ir;illcl  ivljiliuii.  I''i-c(|iicn1 1>',  iilso.  the  ciuial, 
of  a  root  oiil  of  i;i'iicral  ali,i;iiiiii'Mt.  imist  he  rcaniiMl  I'l-oin  its 
race  end,  a|iically.  Id  I  he  ln(•^ial  or  ilistal,  t(i  release  and  re- 
ceive the  dowel  of  the  Miper  imposed  crown. 

When  such  ])rocednres  ai'e  necessary,  extreme  caution 
must  be  observed  1o  a\did,  Hrst,  the  i'ormatiou  of  cervical 
shoulders  on  suiiportim;-  teetii  or  projecting  margins  on  the 
substitute  crowns,  and  second,  to  avoid  weakening  a  root  to 
too  great  an  extent  by  excessive  lateral  reaming  of  its  canal. 

Various  methods  have  been  suggested  for  overcoming  the 
difficulties  of  the  class  just  mentioned,  one  of  the  simplest 
and  most  practical  of  which  can  be  illustrated  in  a  case  shown 
by  Dr.  C.  L.  Anderson  of  Tomah,  Wis.     (See  page  840.) 

This  case  consisted  of  an  upper  bridge  extending  from 
cusjiid  to  first  molar  inclusive.  The  divergence  of  the  roots  of 
the  two  abutments,  apico-incisally  and  occlusally,  was  so 
marked  that  excessive  reaming  of  the  cuspid  root  canal  and 
reduction  of  the  distal  surface  of  the  molar  would  be  required 
to  permit  the  introduction  of  the  bridge.  The  case  was  con- 
structed as  follows: 

The  molar  tooth  was  prepared  and  a  shell  crown  con- 
structed for  it  by  the  usual  method.  A  close-fitting  cap,  extra 
heavy,  was  constructed  foi-  the  cuspid  root,  in  the  center  of 
which  and  in  alignment  witii  the  root  canal  was  an  oijening. 
A  lingual  half-band  disc  was  conformed  to  the  root  cap  and 
on  this  base  a  cuspid  dowel  crown  was  constructed,  being 
adapted  to  but  independent  of  the  root  cap.  The  bicuspid 
dummies  were  luiited  to  the  molar  crown  and  root  cap. 

The  bridge  was  set  by  cementing  the  molar  crown  and 
cap  on  their  respective  roots,  and  inunediately  forcing  the  in- 
dependent cuspid  crown  in  position,  its  dowel  passing  into  the 
root  canal  through  the  central  opening  in  the  root  cap. 

Another  method  consists  in  removing  the  crown  of  the 
inclined  tooth  constructing  a  cap  for  or  adapting  an  inlay  to 
the  root.  The  appliance  in  either  case  should  be  supplied  with 
dowels  of  suitable  size  and  length  for  anchorage  purposes. 

On  the  cap  or  inlay  is  fitted  and  soldered  a  vertically  in- 
clined block,  of  the  Corcoran  or  Pleddy  type.  It  should  be 
l)laced  parallel  with  the  line  of  axial  surfaces  of  the  other 
involved  teeth  or  roots.  To  this  block  is  fitted  a  removable 
jacket,  around  and  over  which  a  crown,  of  the  anatomic  form 
required,  is  constructed.  By  means  of  an  occlusal  screw  pass- 
ing through  the  ci-own  and  into  the  block,  or  a  set-screw  pass- 


BRIDGEWORK  797 

iug  throiigli  the  axial  wall  of  tlie  erown  and  against  the  Ijlock, 
the  removable  crown  may  be  tirmly  locked  in  position. 

Various  types  of  paralleling  devices  are  procurable,  with 
which  the  aligmuents  of  the  several  canals  aud  tooth  surfaces 
involved  may  be  tested.  An  instrument  made  by  the  J.  W. 
Ivory  Company  is  very  convenient  for  general  paralleling 
purposes,  although  possibly  not  sutiSciently  exact  for  com- 
plicated eases  of  removable  bridgework  in  which  the  structure 
is  attached  to  several  widely  separated  roots  or  teeth. 

INLAY  ABUTMENTS 

Inlays  are  frequently  used  as  abutment  and  pier  sup- 
ports in  bridgework.  There  is  a  tendency  to  utilize  this  form 
of  attachment  in  extensive  cases,  oftentimes  with  disastrous 
results.  The  most  frequent  accidents  which  occur  are  dis- 
lodgement  of  the  inlay  or  splitting  of  the  tooth  under  side 
stresses. 

DISPLACEMENT  OF  INLAYS 

The  fact  should  be  kept  in  mind  that  the  stresses  and 
strains  to  which  an  inlay  l)ridge  abutment  is  subjected  vary 
radically  from  the  stress  to  which  the  same  inlay  in  tlie  same 
tooth  will  be  subjected  when  not  so  involved. 

First,  torsional  stress  is  very  marked  as  when  the  inlay 
occupies  a  comparatively  central  position  in  the  mesial  or 
distal  axial  surface  of  a  tooth  while  buccal  and  lingual  luar- 
ginal  ridges  of  the  dummies  occupy  a  position  to  the  outside 
and  inside  of  the  jjerpendicular  line  or  anchorage  of  the  inlay. 

In  masticatory  effort,  the  resulting  torsional  strain  in- 
vites not  only  dislodgment  of  the  inlay,  but  fracture  of  the 
tooth  itself,  i^articularly  in  case  of  weakening  of  the  tooth 
from  caries. 

Second,  when  two  inlays  carry  one  or  more  (.lummies,  aud 
the  roots  of  the  teeth  diverge  or  converge  relatively  to  each 
other,  the  yielding  of  either  tooth  in  its  socket  or  the  synchro- 
nous movement  of  the  two  under  direct  stress  exerts  a  lev- 
erage either  in  the  gingival  or  occlusal  areas  on  the  inlays, 
which,  unless  very  firmly  anchored,  will  result  in  their  dis- 
placement. 

These  observed  facts  have  proven  conclusively  that  the 
use  of  inlays  as  abutments  must  l)e  confined  to  favorable  cases, 
and  that  in  practically  every  instance  some  form  of  pin  an- 
chorage should  be  emjiloyed. 

Various  forms  of  modi  lied  iulavs  or  oiilaiis  are  made  use 


798  UKllHilOVVORK 

III'  for  al)u1niciil  purposes,  aiiuinii'  which  may  Ix'  mentioned 
the  ('aimiehael  Attaehment,  applieahle  more  iiaitienlarly  to 
the  euspids,  and  a  modified  form  of  altachment  for  bicuspids 
as  well  as  cuspids  suggested  by  Di-.  iv  A.  Kennedy. 

In  this  latter  attachment  the  tooth  is  pi'epared  and  the 
inlay  attached  to  its  mesial  or  distal  half  instead  of  the  lingual 
half  of  tlie  tooth  as  in  the  ( 'armicliael  Attachment. 


A   CLASSIFICATION   OF   FIXED   BRIDGEWORK 

Dr.  A.  J.  Bush,  Professor  of  C'i'own  and  Bridge  Work  in 
the  Ohio  University,  Dental  Department,  of  Columbus,  pre- 
sented a  paper  before  the  National  Dental  Association  at 
liochester,  N.  Y.,  in  1914,  on  "A  Classification  of  Fixed 
Bridgework. "  In  Jamiary,  1915,  a  similar  paper  was  also  pre- 
sented by  the  same  essayist  before  the  National  Association 
of  Dental  Teachers  at  Ann  Arbor,  Midi.  (C^opyriglited  by 
Dr.  Bush.) 

In  these  papers  Dr.  Bush  expressed  his  views  of  the 
fundamental  principles  on  which  the  present  system  of  fixed 
bridgework  is  or  should  be  leased.  That  these  principles  are 
logical  and  in  general  accordance  with  tlie  views  of  the  most 
thoughtful  men  in  the  profession  is  conceded. 

The  essayist's  idea  was  not  to  encourage  tlie  more  ex- 
tended application  of  denture  restorations  by  means  of  fixed 
bridgework,  but  to  call  attention  to  those  principles  which,  if 
properly  considered  and  applied,  will  lead  to  success  in  this 
field. 

By  means  of  a  series  of  charts  Dr.  Bush  has  shown  that 
according  to  location,  bridges  naturally  are  resolved  into  three 
well-defined  classes — simple,  compound  and  complex. 

These  are  further  subdivided  into  series  according  to  the 
teeth  which  serve  as  abutment  supports,  as  central  and  cuspid 
series,  cuspid  and  third  molar  series,  etc. 

This  does  not  constitute  a  new  system  of  bridgework,  but 
is  a  presentation  in  clear  and  concise  form  of  commonly  con- 
structed simple  bridges  and  combinations  which  have  not 
heretofore  been  classified. 

It  is  the  writer's  opinion  that  for  teaching  and  general 
descriptive  purposes,  this  classification  of  fixed  bridgework 
will  prove  of  great  value,  not  only  for  teacliing  and  general 
descrijitive  purposes,  but  will  encourage  more  careful  consid- 
eration of  the  underlying  pirinciples  which  lead  to  success  in 
the  field. 


BRIUGEWORK  799 

Pfrniissioii  for  the  following  reiirint  of  the  subject  mat- 
ter and  the  reiiroduction  of  tlic  charts  has  kindly  lieen  granted 
b}'  Dr.  Busli  to  the  writer  for  use  in  this  ))ook. 

CLASSIFICATION   OF  FIXED   BRIDGEWORK 

.  .  .  "Because  of  the  rapid  advancement  in  the  prac- 
tice of  crown  and  bridge  work  during  the  last  half  century  and 
in  ■\'iew  of  the  phenomenal  develojunent  of  bridgework  in  the 
last  decade  especially,  most  teachers  in  this  tield  no  doubt  have 
foimd  it  difficult  to  preserve  the  student's  mind  free  from  con- 
fusion in  about  the  same  ratio  as  the  various  methods  and 
numerous  modifications  of  procedures  have  been  multiplied. 

"While  much  has  been  accomplished  toward  the  formula- 
tion of  principles  and  requirements  governing  their  indica- 
tions, contra-indications,  adai»tation  and  construction  in  an 
effort  to  place  crown  and  bridge  work  on  a  more  scientitic  and 
teachable  basis,  yet  confusion  still  confronts  our  efforts  in 
this  direction  and  the  reason  becomes  very  ayiparent  when 
we  stop  to  consider  that  every  teacher  of  crown  and  Inidge- 
work  in  the  average  dental  college  essaj's  to  teach  the  average 
student  the  principle  and  requirements,  indications  and  con- 
tra-indications  and  methods  of  construction  of  any  one  of 
fifty  thousand  or  more  possible  bridge  replacements  that  may 
present  for  solution  in  any  one  oral  cavity. 

MULTIPLICITY  OF  METHODS 

"  'Multiplicity  of  Methods,'  therefore,  is  no  longer  an 
empty  phrase  and  its  significance  liecomes  more  apparent 
when  it  is  known  that,  according  to  my  unabridged  classifi- 
cation, one  method  alone  is  flexible  enough,  under  ordinary 
conditions,  to  be  applicable  to  any  one  or  more  4,410  different 
conditions  which  may  be  present  in  any  one  mouth. 

"In  view  of  these  considerations,  we  may  safely  assert 
that  the  teaching  of  crown  and  bridgework  in  the  modern  den- 
tal college  is  a  task  which  has  resolved  itself  into  a  proI)lem  of 
no  small  proportions  and  one  wliich  seems  of  enough  moment 
to  demand  that  every  teacher  of  this  subject  should  at  least 
have  given  it  enough  serious  consideration  to  justify  his 
possession  of  a  viewpoint. 

PRIME  OBJECT  OF  CROWN  AND  BRIDGE  APPLICATION 

"In  gixing  you  my  \iew,  I  assume  two  things,  both  of 
which  I  believe  may  be  accepted  as  facts  without  argument. 
First,  that  crowns  and  bridges  are  employed  in  the  effort  to 


800  HKllHiKWOKK 

iiici'cnsc  llic  iiscfuiiH'ss  of  the  (Iciitiil  ;i| i) ini'iitus  wliicli  lias 
hccii  iriiiiaiicil  l)y  l|ic  partial  iir  total  loss  of  a  few  tcotli,  and 
second,  that  the  practice  n\'  ciciwii  and  liridncwork  should  bo 
taus'ht  in  accordance  witii  tlie  coricct  ]irinciiiles  and  re(|uire- 
nieiits   \vhi<'li   iioxcrii   Ihcir  eiii|iln\  incut. 

"It  is  ()l)\i(ilis,  (liercfni-c,  that  the  teaciiiiiii'  of  the  priii- 
ci]ih's  and  rei|uireinents  l)ee(nne  of  lirst  inipoi-taiice  and  serves 
as  the  oidy  possihh^  f()nn(hiti()ii  npoii  which  methods  of 
restoration  nia_\'  he  coi-icctiv  taui^ht. 

THE  BASIS  OF  SUCCESS 

"Every  student  should  he  taui^'ht  tliat  success  can  be 
aclneved  oidy  thronnh  a  stiict  compliance  with  the  principles 
and  requirements  and  conversely  that  failures  are  invariably 
the  direct  result  of  their  non-observance;  that  crown  and 
bridgework  should  not  be  practiced  with  tlie  thought  of 
rendering  a  service  to  his  patients  by  increasing  the  functional 
efficiency  of  the  dental  apparatus  through  the  nu'chanical 
requirements  alone;  but  furthermore,  that  tlie  jihxsiological 
and  hygienic  requirements  mnst  also  be  observed,  lest  this  at- 
tempt to  increase  the  functional  efficiency  of  the  dental  ap- 
paratus be  more  than  offset  by  establishing  conditions  which 
may  prove  far  more  serious  to  the  patient  than  would  be 
caused  by  the  impairment  of  the  dental  apparatus  through 
the  physical  loss  of  the  few  teeth  he  is  striving  to  replace. 

"The  greatest  proposition  that  confronts  the  teacliers  of 
crown  and  bridgework  in  oui-  dental  colleges  today,  is  the 
problem  of  teaching  a  more  lively  respect  for  the  require- 
ments, to  instill  into  the  student's  mind  a  more  thorough  re- 
gard for  their  importance,  a  more  intelligent  conception  of 
their  true  significance  and  to  bring  the  student  into  a  fuller 
realization  tliat  the  most  valuable  lesson  that  can  be  learned 
regarding  the  five  requirements  is  the  fact  that  only  one  of 
the  five  is  mechanical. 

"My  viewpoint  relative  to  tliis  )ihase  of  the  subject  may 
be  best  stated  by  saying  that  humanity,  enlightened  by  the  oral 
hygiene  and  iirophylaxis  propaganda,  will  sooner  or  later 
demand  that  all  of  the  requirements  be  observed  in  the  ])rae- 
tice  of  crown  and  bridgework  and  that  sooner  or  later  teachers 
in  this  field  will  be  compelled  by  a  long-suffering  public  to 
place  less  emphasis  upon  the  mechanical  and  esthetic  require- 
ment, exce]it  as  a  means  to  gain  an  end,  and  devote  more  time 
to  the  teaching  of  those  requirements,  which,  from  a  humani- 
tarian standpoint  are  more  vital  and  which  in  fact  constitute 
the  essential  consideration  underlying  the  physical  diagnosis 


BKIDGEWORK  801 

of  oral  conditions  wliieii  demand  the  execution  of  these  me- 
chanical prescriptions  as  applied  to  living  tissues,  namely  the 
physiological  and  hygienic. 

"A  practical  knowledge  of  the  correlated  sciences  of 
anatomy,  physiology,  physics,  metallurgy,  orthodontia,  and 
oral  jiathology  and  ))hvsiology  as  viewed  and  comprehended 
by  the  periodontologist,  is  presupposed  as  subjects  which  are 
fundamental  to  the  study  of  the  requirements  and  through 
the  combined  consideration  of  which  we  form  our  conceptions 
regarding  indications  and  contraindications,  and,  according 
to  my  viewpoint,  these  correlated  subjects  are  so  fundamental 
to  the  scientific  teaching  of  crown  and  bridgework  that  this 
fact  alone  would  justify  our  giving  them  a  prominent  position 
in  the  dental  corriculum,  even  in  the  absence  of  any  other  con- 
sideration. 

"My  viewpoint  relative  to  tiie  teaching  of  the  princijiles 
which  govern  the  employment  of  fixed  bridgework,  and  my 
idea  regarding  the  best  plan  of  teaching  metliods,  are  incor- 
porated in  the  following  classification  of  fixed  bridgework 
based  upon  a  ]iroposed  law  or  rule  which  has  been  formulated 
in  accordance  with  accepted  principles  of  practice. 

ADVANTAGES  OF  CLASSIFYING  FIXED  BRIDGES 

"In  attempting  to  classify  fixed  bridgework  T  have  en- 
deavored, first,  to  broaden  the  foundation  upon  which  the  su- 
perstructure of  our  present  conception  thereof  rests,  an<l  to  es- 
tablish more  thoroughly  our  comprehension  of  the  principles 
and  their  a])))lication  which  constitutes  the  very  superstruc- 
ture of  the  foundation  itself;  second,  to  systematize  and  facili- 
tate the  teaching  of  fixed  bridgework  in  accordance  with  the 
accepted  principles  of  practice  which  govern  tlieir  employ- 
ment;  and  third,  to  formulate  a  law  that  embodies  the  princi- 
ples which  modern  practice  has  approved,  a  law  which  will 
assist  in  teaching  the  proper  selection  of  abutments,  accord- 
ing to  princijile,  for  the  support  and  retention  of  fixed  bridge- 
work,  and  one  which  will  likewise,  impose  restrictions  to  the 
employment  of  those  types  of  construction  which  are,  from 
the  standpoint  of  principle,  indefensible 

"The  tcniihioloffi/  used  in  the  classification  is  simply  a 
correlation  of  terms  selected  from  our  nomenclature,  that 
constant  usage  has  rendered  familiar,  and  which  have  been 
selected  because  they  seem  to  be  the  most  expressive  of  any 
terms  available. 


802  UKIDCKWOKK 

"Most  writers  of  (Iciitistry,  in  icrcriiiiii-  to  tcetli  of  certain 
position  in  tlie  ai'eli,  liiive  nsed  the  teiiiis  anterior  teetli  and 
posterior  teetli  as  best  calculatetl  to  convey  the  idea  of  the 
association  between  object  and  position,  likewise  anterioi'  and 
posterior  have  l)een  used  as  the  most  expressive  terms  in 
referring  to  bridge  replace)nents  tliat  su])ply  a  missing  tooth. 
or  group  of  teeth,  in  either  of  tiiese  locations. 

"Accordingly,  then,  tixed  Ijridgework  a))iilie(l  iiiid  conlined 
within  these  limits  may  be  divich-d  into  tnifcriin-  hridges  and 
posterior  bridges. 

"In  referring  to  Plate  1  (i)age  <S07)  illustrating  possible 
tixed  bridge  replacements,  it  will  be  observed  that  the  l)ridges 
represented  as  applicable  to  the  various  positions  arrange 
themselves  into  well-defined  groups  that  are  characterized  by 
the  teeth  chosen  for  abutments  in  connection  with  the  tooth 
or  teeth  supplied.  Accordingly,  therefore,  anterior  bridges 
may  be  subdivided  into  a  central  and  lateral  series  and  a  cen- 
tral and,  cuspid  series;  likewise,  ]iosterior  bridges  may  lie  sub- 
divided into  a  cuspid  and  third  molar  scries,  and  a  first  bi- 
cuspid and  second  molar  series. 

SIMPLE   BRIDGES 

"A  single  bridge  of  any  one  of  the  above  series  may  be 
said  to  form  a  simple  bridge. 

COMPOUND  BRIDGES 

"Any  bridge  that  can  be  effected  by  connecting  unilatcr- 
ally,  any  one  of  the  simple  bridges  forming  either  of  the  an- 
terior series,  with  any  one  of  the  simjile  bridges  formuig 
either  of  the  i)Osterior  series,  may  lie  said  to  form  a  compound 
bridge. 

COMPLEX   BRIDGES 

"Any  bridge  that  can  l)e  effected  by  connecting  bilater- 
(dly,  any  one  of  the  simple  bridges  forming  either  of  the  an- 
terior series,  with  any  one  of  the  simple  bridges  forming 
either  of  the  posterior  series,  may  be  said  to  form  a  compter 
bridge. 

"To  recapitulate,  first,  fixed  bridgework  may  be  divided 
according  to  extension,  into  simple,  compound  and  complex 
bridges ;  second,  simple  bridges  according  to  location,  may  be 
divided  into  anterior  and  posterior  bridges;  third,  according 
to  attachment  and  teeth  snp])lied,  simple  anterior  liridges 
niav  lie  sulxlivideil   into  a  central   and   lateral   series,  and   a 


BRIDGEWORK 


central  and  cuspid  scries;  and  simple  posterior  bridges  may 
be  subdi\ided  into  a  cuspid  and  third  molar  series,  and  a 
first  bicuspid  and  second  molar  series;  and  fourth,  the  simple 
bridges  of  the  anterior  series  when  joined  unilaterally  and 
bilaterally  to  the  simple  bridges  of  the  posterior  series,  form 
compound  and  complex  bridges  respectively.     The  adjectives 


Central  and  Lateral  Serie» 

Simple 

Anterior 

Central  and  Cuspid  Series 

Bridges 

Cuspid  and  3rd  Molar  Series 
Posterior 

1st  Bicuspid  and  2nd  Molar  Series 

Class,fi 

,  _               Cuspid  and  3rd  Molar  Series 
Central  and  Lateral  Series             "^ 

cation 

Compound 

joined  to  Right  or  Left         ,^j  g  ^_^j  2nd  M.  Series 

of 

FIXED 

BRIDGE- 

Bridges 

„          ,        .  „        J  c     ■           Cuspid  and  3rd  Molar  Series 
Central  and  Cuspid  Series 

joined  to  Right  or  Left         ,  ^^  g  ^^^  jnd  M.  Series 

WORK 

R.  and  L.  Cuspid  and  3rd  M.  Series 
R.  andL.  1st  B.and  2nd  M.  Series 

Central  and  Lateral  Series 

R.  Cuspid  and  3rd  M.  Series  with 

connecting 

L.  1st  B.  and  2nd  M.  Series. 
L.  Cuspid  and  3rd  M.  Series  with 

Complex 

R.  1st  B.and  2nd  M.  Series. 

Bridges 

R.  and  L.  Cuspid  and  3rd  M.  Series 
R.  and  L.  1st  B.  and  2nd  M.  Series 

Central  and  Cuspid  Series 

R.  Cuspid  and  3rd  M.  Series  with 

connecting 

L.  1st  B.  and  2nd  M.  Series 

PLATE 

n 

L.  Cuspid  and  3rd  M.  Series  with 
R.  1st  B.and  2nd  M.  Series 

Upper  and  lower,  right  and  left,  are  used  as  prefixes  and  com- 
plete the  terminology. 

"Again  referring  to  Plate  1  (page  807),  it  will  l)e  noticed 
that  all  simi)le  bridges  are  of  comi)arativcly  straight  align- 
ment and  have  at  least  one  sup])ort  or  attachment  at  each  end ; 
and  furthermore,  that  all  the  simple  bridges  of  the  various 
series,  in  heing  joined  or  connected  to  form  compound  and 
complex  bridges  form  extended  bridges  of  curved  alignment 
with  one  or  more  intervening  i)iers  or  attacliments. 

■'In  view  of  this  fact,  therefore,  it  seems  litting  and  much 
more  in  accord  with  the  scientitic  ])hase  of  this  class  of  work, 
that  a  general  law  be  ado]ited  that  will  furnish  a  safe  plan 
for  teaching  the  application  of  all  fixed  bridgework  in  general, 
and  which  will  serve  the  same  jiurpose  as  the  various  rules 
that  have  been  formulate(l  from  time  to  time  to  cover  a  com- 


S04  BRIDGEVVORK 

paratively  small  number  of  cases,  more  or  less  typical,  all  of 
which  are  fmidamentally  based  upon  the  same  principles. 

PROPOSED   LAW 

"The  hnv  propo.sed  is  as  follows:  J//  /i.trd  hri/lficiiniL  (if 
tttiaiyht  aligiunoit  should  he  attached  to,  or  supported  Ijij, 
one  or  more  abutments  at  each  end,  and  should  receive  addi- 
tional attachment  and  support  from  one  or  more  intervening 
abutments  or  piers  ivhen  of  curved  alignment. 

"In  accordance  to  the  classification  and  law  proposed, 
the  following  definitions  are  derived. 

SIMPLE   BRIDGE   DEFINED 

"A  simple  fi.xcd  bridge  may  be  defined  as  a  bridge  used  to 
replace   one   or  more  teeth  missing  from  the   anterior   or 


posterior  positions  of  the  arch,  attached  to  or  supported  by 
at  least  one  or  more  abutments  at  each  end  and  are  of  com- 
paratively straight  alignment. 


COMPOUND  BRIDGE  DEFINED 


"A   co)up(iin/(/   liridf/e   may   Ik*   defined   as   an    extended 
bridge  effected  by  a  simple  anterior  Ijridge  joined  iniilaferallii 


to  a  simple  posterior  bridge  to  suj^ply  two  or  more  missing 
teeth  from  the  anierior  and  posterior  ]iortions  of  the  arch,  at- 


BRIDGEWORK  805 

tacbed  to  or  sii^jported  by  one  or  more  abutments  at  eacb  end 
and  one  or  more  additional  attaelmients  or  supports  from  one 
or  more  intervening  abutments  or  piers,  and  are  of  carved 
alignment. 

COMPLEX  BRIDGE  DEFINED 

"A  cdiuplc.i:  jixed  bridge  may  be  depued  as  an  extended 
bridge  effected  by  connecting  a  simple  anterior  bridge  hi- 
laterally  with  a  simple  posterior  bridge  to  supply  four  or 
more  missing  teeth  in  the  arch  and  are  attached  to  or  sup- 


ported by  one  or  more  abulnicul^.  at  each  end  and  one  or  more 
additional  attachments  or  supports  from  one  or  more  inter- 
vening abutments  or  piers,  and  are  of  curved  alignment. 

ARGUMENT  IN  SUPPORT  OF  THE  CLASSIFICATION 
AND  LAW  PROPOSED 

''In  support  of  the  proposed  classitication  and  in  defense 
of  the  law  which  embodies  the  principles  upon  which  the  classi- 
fication is  largely  based  I  wish  to  quote  the  following,  taken 
from  a  former  paper : 

POSSIBLE  MASTICATORY  STRESS 

"  'If  the  muscles  of  mastication  are  capable  of  exerting  a 
stress  of  275  pounds  upon  the  first  molars  and  if  the  support- 
ing tissues  of  the  first  molars  have  lieeu  capable  of  developing 
a  structure  which  will  safely  bear  such  a  strain,  it  must  be 
concluded  that  the  development  of  the  muscles  and  the  sup- 
porting tissues  of  the  teeth  are  co-incident  and  in  accordance 
with  physiological  laws. 

"  'It  is  also"  true  that  this  muscular  power  is  normally 
intended  to  be  exerted  within  physiological  directions,  and 
that  the  supporting  tissues  of  the  teeth  are  developed  and 


sdi;  i!i{ii)(;io\V()i!K 

|ili\  siologically  (IcsigiMMl  hi  rccciNc  and  supiiorl  lliis  strain 
only  wlicii  this  niusciilar  stress  is  I  lansniitted  to  them  iu  a 
nninial   direction   and   accoidinn   to    physiological   principles. 

•'  'Tlie  woiKh'rl'nl  power  that  the  muscles  of  mastication 
are  capable  of  exerting,  and  the  wonderful  plan  upon  which 
Nature  has  constructed  the  human  teeth  iu  order  to  utilize 
this  energy  in  the  mastication  of  food,  and  the  wonderful  de- 
sign of  the  tissues  wJiich  support  the  teeth  while  performing 
these  functions,  all  seem  to  be  iu  perfect  accord  with  the 
nuu'velous  schemes  of  Nature.  Yet,  it  must  be  remembered 
that  this  muscular  energy  is  intended  to  be  exerted  only  within 
certain  limitations,  bounded  by  the  normal,  and  the  design  of 
the  teeth  render  them  etificacious  in  performing  their  functions 
only  when  nuiscular  energy  propels  them  normally,  and  that 
the  tissues  which  support  the  teeth  wiiile  performing  their 
functions  are  capable  of  yielding  normal  support  only  when 
the  nuiscular  stress  of  mastication  is  normally  directed. 

"  'Therefore,  it  would  not  be  in  accordance  with  physio- 
logical laws  to  expect  a  lirst  molar  which,  if  normally  capable 
of  withstanding  a  stress  of  1275  pounds,  and  the  suppoi'ting 
tissues  normally  capable  of  resisting  the  stress,  to  physiologic- 
ally resist  this  stress  if  the  direction  of  the  stress  be  per- 
verted, and  the  supporting  tissues  compelled  to  receive  the 
stress  contrary  to  the  direction  that  they  are  normally  de- 
signed to  receive  it. 

"  'Hence,  it  seems  oljvious  that  if  lixeil  lu'idgework  be  con- 
structed with  occlusal  and  incisal  masticating  surfaces  after 
Nature's  plan  and  iu  accordance  with  physiological  law  gov- 
erning normal  articulation  and  occlusion,  and  if  the  stress  as 
received  by  the  abutments  is  normally  directed,  that  such 
bridgework  may  be  successfully  attached  to  tiie  roots  of  teeth 
without  inviting  pathological  manifestations." 

"But,  on  the  other  hand,  //  p.rrd  hridficivoil;  be  con- 
st lucted  without  due  rrr/did  for  thesr  principles,  and  the  occlu- 
sal or  incisal  surface  be  so  niodc.  as  to  (tlninnnnltu  direct  tlie 
restdtant  force  to  the  utiutuicnl  tcrth.  nr  thr  cniitloi/nient  of 
abutments  he  such  as  to  subject  them  la  stress  perverted 
through  leverage,  then  will  the  supportiufi  tissues  surrounding 
the  root  fail  to  render  support,  just  in  })nip(irtion  as  the  stress 
is  perverted,  and  the  support iur/  tissm-s  ore  oliliged  to  offer 
resistance  in  a  direction  u'hich  tlnti  n-erc  never  intended  to 
furnish. 

"Unquestionably,  there  are  many  fixed  bridges  outside  the 
scope  of  this  proposed  law  and  classification  which  are  a]i- 
parently  giving  good  service,  and  which,  by  reason  of  this  n\^- 


BRIUGEWOKK  8« 

pareut  st'rvice,  aud  their  coiitiuued  eiuijloymeut,  have  th;is. 
seemingly,  been  sanctioned  as  good  practice  nevertheless, 
the  soundness  of  the  iirinciples  underlying  the  proposed  law 
cannot  he  questioned,  neither  can  it  be  denied  that  these  same 
bridges  in  question  might  have  rendered  a  still  greater  serv 
ice  had  they  been  elTected  more  strictly  in  accordance  with  the 
principle  involved. 


CLASSIFICATION    OF    FIXED    BRIDGES 
ACCORDING    TO    LOCATION 
ATTACHMENT    AND    TEETH    SUPPLIED 

9765432112343678 

ANTERIOR           , 
BRIDGES             \ 

1 

POSTERIOR              , 
BRIDGES                \ 

[ 

A 

•  X 

•' 

i  central  and 
/lateral  series 

>  central  and 
^ cuspi d  seri e3 

,      cuspid  and 
^  3"molar  series 

itbicuspid  and 
/   2mmolar  series 

B 

•  X 

X  •! 

c 

X  • 

•   X 

D 

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F 

A 

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s 

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r 

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z 

• 

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A 

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X 

• 

PLATE     I 

"Showing  series  classification  of  simple  bridges  according 
to  location,  attachment  and  teeth  supplied.  The  incompleted 
bridges  E  and  F  of  the  Central  and  Lateral  Series,  also  G 


808  BRIDGEWORK 

and  N  of  the  First  Bicuspid  and  Second  Molar  Series,  when 
joined,  form  simple  bridges  E(t  and  FN,  and  are  classitied  as 
anterior  I)ridges  and  enumerated  as  belonging  to  the  Central 
and  Cuspid  Series — both,  however,  retain  tlieir  identity  when 
used  to  form  other  combinations  and  are  so  enumerated  as 
illustrated  in  charts  3,  4,  7,  8,  9,  10,  12,  13  and  14. 

"The  incompleted  bridge  C  of  the  Central  and  Lateral 
Series  is  not  classilied  as  a  simple  bridge,  but  when  joined  bi- 
laterally to  the  simple  bridges  of  the  posterior  series  it  assists 
in  the  formation  of  complex  bridges  and  is  so  enumerated  as 
illustrated  in  charts  9  and  10.  Likewise,  incompleted  bridges 
I  and  V  of  the  Cuspid  and  Third  Molar  Series  and  B,  D,  F 
and  I,  K,  M  of  the  First  Bicuspid  and  the  Second  Molar  Series 
are  not  classified  as  simple  bridges,  but  when  joined  uni- 
laterally and  bilaterally  to  the  simple  Ijridges  of  the  anterior 
series  they  assist  in  the  formation  of  compound  and  complex 
bridges  and  are  so  enumerated  as  illustrated  in  charts  3,  4, 
7,  8,  9,  10,  11,  12,  13  and  14. 

"The  two  groups  of  simple  bridges  comprising  the  two 
Anterior  Series  effect  eight  different  combinations  when 
joined  unilaterally  with  the  four  groups  of  simple  bridges  com- 
prising the  two  Posterior  Series,  thus  forming  eight  groups  of 
compound  bridges.  Likewise  the  two  groups  of  sinii)le  bridges 
comprising  the  two  Anterior  Series,  effect  eight  different 
combinations  when  joined  bilaterally  with  the  various  groups 
of  simple  bridges  which  comprise  the  two  Posterior  Series, 
thus  forming  eight  groups  of  complex  bridges. 


BRIDGEWORK 


COMPOUND  BRIDGES 

FORMED  BY 

876545;!       1:345678 

B 

•  X 

X  •! 

LEFT 

CUSPID  8i  3rd  molar 

SERIES 

SERIES 

D 

• 

X  •, 

M   • 

X  • 

O    • 

X  X  • 

P    • 

X  •   X 

• 

Q  • 

X   X   X   • 

"!• 

X   •  X   X   • 

S!« 

X  X  •   X   • 

Ti» 

X  •  •   X  • 

u,« 

X    X   X   X   • 

V 

X 

• 

X 

• 

X  • 

• 

X 

E 

w 

• 

X 

• 

X 

• 

X 

• 

X 

X 

X 

• 

87654321      12345678 

A 

•  X 

• 

CENTRAL  8t  LATERAL 
SERIES 

B 

•  X 

X 

• 

•  X 

•  a' 

•   XX 

•  B 

~i«  X  •  X 

•  c 

•  X    X   X 

•  D 

RIGHT 

•  X   X  •  X 

•  E 

CUSPID  at  3rd  molar 

•   X  •  X   X 

•  F 

SERIES 

•  X  •   •  X 

•   G 

•  X   X   X   X 

•  H 

•  X 

•  X  • 

X,  1 

PLATE     m 

•" 

X 

!E 

X 

• 

• 

x» 

J 

•   X  XX* 

K 

1    1     1 

1 

"Showing  bridges  formed  by  Central  and  Lateral  Series 
joined  unilaterally  to  Left  Cuspid  and  Third  Molar  Series, 
also  Central  and  Lateral  Series  joined  unilaterally  to  Right 
Cuspid  and  Third  Molar  Series. 


niui)('.i;\\()i{i< 


COMPOUND  BRIDGES 

FORMED  BY 

8765432112345678 

CENTRAL  a  LATERAL 
SERIES 

LEFT- 
IST BICUSPID  a 
2nd  MOLAR 
SERIES 

B 

• 

X 

X 

• 

D 

• 

x|« 

• 

X 

F 

N  X 

• 

1    X 

•   X  • 

'K|X 

•  lX|X|«; 

8765432112345678 

RIGHT 

1 

CENTRAL  a  LATERAL 
SERIES 

A 

•  X 

•  ! 

B 

•   X 

X  • 

E 

X  • 

j           1ST  BICUSPID  a 

• 

X  G 

2ND  MOLAR 

•   X   • 

X  B 

SERIES 

•  XX* 

XiD 

i 

PLATE  w: 

'  *  Showing  compound  bridges  formed  liy  Central  and  Lat- 
eral Series  joined  unilaterally  with  Left  First  Bicuspid  and 
Second  Molar  Series;  also  Central  and  Lateral  Series  joined 
unilaterally  to  Right  First  Bicuspid  and  Second  Molar  Series. 


BRIDGEWOKK 


1 

COMPOUND  BRIDGES 

FORMED  BY 

87654321       12345678 

RIGHT 

CUSPID  &  3RD  MOLAR 

SERIES 

|A 

•  {x|« 

1 

CENTRAL  a  CUSPID 
SERIES 

|B 

•  XX 

• 

c 

•  X  • 

X  • 

D 

•  X  • 

X  X 

• 

|E 

•  XX 

•  X 

• 

F 

•  X  • 

•   X 

• 

iG 

•    •  X 

•  X 

• 

H 

•    X   • 

X   •  • 

1 

•    •   X 

X  X  • 

IJ 

•  X  X 

X  •  • 

IK 

•  •  X 

X  • 

• 

L 

•    X;X 

X 

X 

• 

• 

X 

• 

A 

• 

X 

X 

• 

B 

•   X   •  X 

•  c 

•   X  X  X 

•  D 

•  X  X  •  X 

•  E 

•  X  •  X  X 

•  F 

•  X  •  •  X 

•  G 

•   X   X  X  X 

•  ,H 

• 

X|«|XI« 

J 

• 

xixlx  • 

K 

PLATE    3z: 

"Showing  compound  bridges  formed  by  Central  and  Cus- 
pid Series  joined  unilaterally  to  Right  Cuspid  and  Third 
Molar  Series, 


lilUlHiEWOltK 


COMPOUND  BRIDGES 

FORMED  BY 

87654321       12345678 

CENTRAL  a  CUSPID 
SERIES 

D 

•  Xl* 

X  X  • 

LEFT 
CUSPID  &  3RD  MOLAR 
SERIES 

E 

*'X'X 

•  <xl* 

F 

•   X  • 

•  X  • 

G 

•  •  X 

•  X  • 

H 

•  X  • 

X  •  • 

1 

•  •  X 

X  X  • 

J 

•  XX 

X   •   • 

K 

•   •   X 

X   •   • 

L 

•    XX 

XX* 

M 

•  X 

•   X  • 

N 

• 

X 

X 

O 

• 

X 

N 

X 

• 

0 

X 

X 

• 

p 

X 

• 

X 

• 

0 

X 

X 

X 

• 

R 

X 

• 

X 

X 

• 

s 

X 

X 

• 

X 

• 

T 

X 

•  • 

X  • 

u 

X 

XXX 

• 

• 

w 

•  X  •,x 

X 

•  xjx  x{* 

1      PLATE    3ZE 

"Showing  compound  bridges  formed  by  Central  and  Cus- 
pid Series  joined  unilaterally  to  Left  Cuspid  and  Third  Molar 
Series. 


BRIDGEWURK 


COMPOUND  BRIDGES 

FORMED  BY 

87654321       12345678 

RIGHT 

1ST  BICUSPID  ft 

2ND  MOLAR 

SERIES 

A 

.lx|. 

CENTRAL  ft  CUSPID 
SERIES 

B 

•  XX 

• 

C 

•  X  • 

X 

• 

,D 

•  |X  • 

X  X|« 

\"  E 

•  XX 

•  X  • 

P 

•   X  • 

•  X  • 

G 

• 

• 

X 

• 

X 

• 

H 

• 

X 

• 

X 

• 

• 

1 

• 

X 

X 

X 

• 

•  XX 

Xi*^ 

K 

•  •  X 

X  •  • 

|L 

•  x,x 

x,x,» 

• 

X 

• 

A 

• 

X 

X 

• 

c 

• 

X 

• 

X 

F 

M 

• 

X 

• 

X 

• 

• 

X 

G 

• 

X 

• 

X 

B 

• 

X 

X 

• 

X 

D 

PLATE  3zn: 

"Showing  compound  bridges  formed  by  Central  and  Cus- 
pid Series  joined  unilaterally  to  Right  First  Biscupid  and 
Second  Molar  Series. 


BKIDtiEWOHK 


COMPOUND  BRIDGES 

FORMED  BY 

876?•4:^^l       12345678 

CENTRAL  a  CUSPID 
SERIES 

1       D 

•  X* 

X  X  • 

LEFT 

1ST  BICUSPID  a 

2ND  MOLAR 

SERIES 

i       F~ 

•  XX 

•  X  • 

n  iP 

•  x« 

•  X  • 

!G 

•  •   X 

•  X  • 

H 

•   X  • 

X  X  • 

1  1 

•  •  X 

X  X  • 

J 

•   XX 

X  •   • 

|K 

•   •   X 

X  •    • 

L 

•   XX 

X   X   • 

M 

•   X 

•  X  • 

N 

• 

X  X  • 

0 

• 

X 

• 

H 

• 

X 

• 

J 

• 

X 

X 

• 

M 

X 

• 

X 

• 

C 

• 

X 

• 

X 

• 

N 

X 

• 

1 

X 

• 

X 

• 

K 

X 

• 

X 

X 

• 

PLATE    Ami 

"Showing  compound  bridges  formed  by  Central  and  Cus- 
pid Series  joined  unilaterally  to  Left  First  Bicuspid  and  Sec- 
ond Molar  Series. 


BRIIIGRWORK 


COMPLEX  BRIDGES 

FORMED  BY 

CENTRAL  a  LATERAL       SERIES 

87654321       I234567B 

RIGHT 

CUSPID  a  3RD  MOLAR 

SERIES 

B 

• 

X 

X 

• 

LEFT 

CUSPID  a  3rd  MOLAR 

SERIES 

C 

X 

• 

• 

X 

• 

X 

• 

X 

• 

X 

1 

N 

• 

X 

• 

O 

• 

X 

X 

• 

P 

• 

X 

• 

X 

• 

q!» 

X 

X  X 

• 

R   • 

Xi*    XX* 

S'» 

x\x  •  X  • 

T   • 

X  •  •  X  • 

u  • 

X   X   X   X   • 

B 

• 

X 

X 

• 

1 

C 

X 

• 

• 

X 

• 

X 

A 

V 

X 

• 

X 

• 

X 

• 

• 

X 

X 

B 

• 

X 

• 

X 

C 

• 

X 

X 

X 

D 

,•  X iX  •  X 

E 

•  X  •  X  X 

F 

•  ><J»  •  X 

G 

•  X 

X  X 

X 

H 

•  X 

•  X 

# 

X 

1 

87654521       12345678 

RIGHT 

1ST  BICUSPID  a 

2ND  MOLAR 

SERIES 

Ib 

• 

X 

X  • 

LEFT- 
IST BICUSPID  a 
2ND  MOLAR 
SERIES 

c 

!x 

• 

•  X 

1 

• 

X|G 

;NiX 

• 

• 

X 

• 

XIB 

1    X 

• 

X 

• 

• 

X 

X 

• 

X  D 

K  X 

• 

X 

X 

• 

PLATE    IX 

"Showing  complex  bridges  t'ornicd  l>y  (  V'liti'al  and  Lateral 
Series  joined  bilaterally  to  Bight  and  Left  Cuspid  and  Third 
Molar  Series;  also  complex  bridges  formed  by  Central  and 
Lateral  Series  joined  bilaterally  to  Rigiit  and  Tjcft  Bicuspid 
Series. 


BRIIXJEWORK 


COMPLEX  BRIDGES 

FORMED  BY 

CENTRAL  a  LATERAL    SERIES 

87654321       12345678 

B 

• 

X 

X 

• 

LEFT 

1ST  BICUSPID  a 

2ND  MOLAR 
SERIES 

c 

X 

• 

• 

X 

" 

• 

X 

A 

N 

X 

• 

• 

X 

X 

B 

1 

X 

• 

X 

• 

RIGHT 

- 

• 
• 

X 

• 

X 

c 

K 

X 

• 

X 

X 

• 

CUSPID  a  3rd  molar 

x 

X 

X 

D 

SERIES 

X 

X 

•  X 

E 

X 

• 

X 

X 

F 

^ 

X 

xi 

• 

• 

X 

G 

X 

X 

X 

H 

• 

X 

• 

X  • 

X 

1 

87654321      12345678 

RIGHT 

1ST  BICUSPID  a 

2ND  MOLAR 

SERIES 

B 

• 

X 

X 

• 

LEFT 
CUSPID  a  3RD  MOLAR 
SERIES 

0 

X 

• 

• 

X 

• 

X 

G 

N 

X 

• 

• 

X 

• 

X 

B 

O 

X 

X 

• 

• 

X 

X 

• 

X 

D 

P 

X 

• 

X 

• 

Q 

X 

X 

X 

• 

R 

X 

• 

X 

X 

S 

X 

X 

• 

X 

T 

X 

• 

• 

X 

U 

X 

X 

X 

X 

V 

X 

• 

X 

• 

X 

PLATE   ZX: 

"Showing  complex  bridges  formed  by  Central  and  Lateral 
Series  joined  liilateralh'  to  Eight  Cuspid  and  Third  Molar 
Series  and  Left  First  Bicuspid  and  Second  Molar  Series. 
Also  complex  bridges  formed  by  Central  and  Lateral  Series 
joined  bilaterally  to  Left  Cuspid  and  Third  Molar  Series  and 
Right  First  Bicuspid  and  Second  Molar  Series. 


BRIDGE  WORK 


COMPLEX  BRIDGES 

FORMED  BY 

CENTRAL  a  CUSPID     SERIES 
87654^21      12345673 

i 

RIGHT 

D 

•  Ix]. 

x|x|« 

LEFT 

CUSPID  a  3RD  MOLAR 

SERIES 

E 

•  X  X 

•  X  • 

F 

•    X   • 

•  X  • 

G 

•   •  X 

•   X  • 

1h 

•  xj* 

x» 

• 

h 

•   MX 

XX 

• 

■J 

•  xx 

X  • 

• 

K 

•   •    X 

X  •  • 

L 

•  XX 

X  x* 

• 

X 

• 

A 

n'» 

X 

• 

• 

X 

X 

• 

B 

o  • 

X  X  • 

• 

X 

• 

X 

• 

C 

p  • 

X  •   X  • 

• 

X 

X 

X 

• 

D 

Q  • 

X   X   X   • 

CUSPID  &  3rd  molar 

•  XX   •    X 

•   E 

R  • 

X|»  X  X  • 

SERIES 

•   X  •    XiX 

•  r 

s  • 

X   X   •   X   • 

•    X   •  •  X 

•  G 

T    • 

X  •  •y  • 

•   X   X   X   X 

•   H 

u  • 

X  X  X  X  • 

•   X   •   X   • 

J 

w 

•  X  •  X  • 

X 

X 

X 

• 

K 

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1 

PLATE    31 

"Showing  complex  bridges  t'oniicd  Ijv  Central  and  Cuspid 
Series  joined  bilaterally  to  Right  and  Left  Cuspid  and  Third 
Molar  Series. 


S18 


liI!ll)f!K\VORK 


COMPLEX  BRIDGES 

FORMED  BY 

CENTRAL  a  CUSPID     SERIES 
87654321       12345678 

RIGHT 
1ST  BICUSPID  a 
2nd  molar 
SERIES 

D 

.X. 

x[xi» 

LEFT 
1ST  BICUSPID  a 

2nd  molar 

SERIES 

E 

•  fxtx 

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PLATE    3ir 

"Showing  ('om]ilex  hridgcs  forunMl  liy  (V'litial  and  (.'ns])id 
Series  joined  bilaterally  to  Rigiit  and  Left  First  Bicuspid  and 
Seeond  Molar  Series. 


BRIDGEWORK 


819 


COMPLEX  BRIDGES 

FORMED  BY 

CENTRAL  a  CUSPID     SERIES 

87654321      12^45678 

D 

•  X  • 

X  x|« 

LEFT 
1ST  BICUSPID  & 

2ND  MOLAR 
SERIES 

Ie 

•  XX 

•  x|» 

F 

•  X  • 

•  X  • 

G 

•  •  X 

•  X  • 

H 

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X  •  • 

1 

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RIGHT 

•   X  •   X    X 

• 

F 

CUSPID  a  3RD  MOLAR 

•  X  •  •  X 

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•  H 

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F 

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G 

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H 

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•ix|x|xi« 

K 

PLATE  xnr 

"Showing  complex  bridges  formed  by  Central  and  C'usiiid 
Series  joined  bilaterally  to  Right  Cuspid  and  Third  Molar 
Series  and  Left  First  Biousjiid  and  Second  Molar  Series. 


i!inii(;K\voKK 


1 

COMPLEX  BRIDGES 

FORMED  BY 
CENTRAL  a  CUSPID     SERIES 

87654321       t      .^      •<     4     5     6     7     a 

1 

RIGHT 

1ST  BICUSPID  & 

2ND  MOLAR 

SERIES 

D 

•  lx'« 

XX  • 

LEFT 

CUSPID  a  3rd  molar 

SERIES                  1 

E 

•   XX 

•  X  • 

F 

•  X  • 

•  X  • 

G 

•  •  X 

•  X  • 

H 

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J 

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PLATE      XIV 

"Showing  complex  bridges  formed  by  Central  and  Cns])id 
Series  joined  bilaterally  to  Left  Cuspid  and  Third  Molar 
Series  and  Right  First  Bicnspid  and  Second  Molar  Series. 


BRIDGE  WORK 


TOTAL  NUMBER  OF  FIXED  BRIDGES,  UPPER  &  LOWER, 

ACCORDING  TO  SERIES  CLASSIFICATION  AND 

LAW  GOVERNING  THEIR  APPLICATION. 

SIMPLE  BRIDGES 
Ccnlr^  ^d  L.lcrid  Scrlc.                                                                                6 
Central  and  Cuipid  Seriei                                                                                34 
Cutpid  and  Third   Molar  Serie.                                                                               48 
Ut  Bicutpid  and  2nd  Molar  Strict                                                               12 

COMPOUND  BRIDGES 
Central  and  Lateral  Seriei  joined  to 

Cuipid  and  3rd  Molar  Serie*                            .                                        80 
Central  and  Lateral  Scriei  joined  to 

Ut  Bicuipid  and  Second  Molar  Scriei                                                         36 
Central  and  Cu.p.d  Senei  joined  to 

Cn-pid  and  3rd  Molar  5er.e<                                                                  480 
Central  and  Ciupid  Serie*  joined  to 

lit  Bicuipid  and  2nd  Molar  Serie.                                                     _IS6 

COMPLEX  BRIDGES 
Central  and  Lateral  Serie.  ronnecLn, 

Right  and  Left  Cu.pid  and   3rd  Motar  Serie.                                           68 
Central  and  Lateral  Serie.  conneeting 

Right  and  Left  Pint  Bicuipid  and  2nd  Molar  Seriei                            36 
Central  and  Lateral  Seriei  connecting 

Right  Cuipid  and  3rd  Molar  Serici  with 

Left  lit  Bicuipid  and  2nd  Molar  Seriei                                          108 
Central  and  Lateral  Seriei  connecting 

Right  lit  Bicuipid  and  2nd  Molar  Seriei                                    108 

Right  and  Left  Cuipid  and  3rd  Molar  Sariei                                  IS40 
Central  and  Cuipid  Seriei  connecting 

Right  and  Left  lit  Bicuipid  and  2nd  Molar  Seriei                           198 
Central  and  Cuipid  Seriei  connecting 

Right  Cuipid  and  3rd  Molar  Seriei  with 

Left  1  It  Bicuipid  and  2nd  Molar  Serie*                                       600 
Centra]  and  Cuipid  Seriei  connecting 
Uft  Cuipid  and  3rd  Serici  with 

Right  lit  Bicuipid  and  2nd  Molar  Seriei                                ^00 

Total  numher  of  combination                     ^MIO 

PLATE  jca: 

"Sliuwiug  the  total  number  of  fixed  bridges  upper  and 
lower,  according  to  proposed  classification  and  law  governing 
their  application. 

"Wliilo  this  classification  will  render  no  material  assist- 
ance in  teaching  the  requirements  which  are  fundamental  to 
teaching  of  fixed  bridgework,  and  which  should  be  regarded  as 
essential  regardless  of  the  plan  pursued,  still  it  will,  no  doubt, 
prove  of  great  lielp  in  teaching  tlie  principles  of  fixed  bridge- 
work  and  prove  to  he  of  still  greater  assistance  in  the  teach- 
ing of  method,s. 

"To  illustrate:  the  classification  recognizes  tliree  divisions 
of  fixed  bridgework,  namelj',  simple,  compound  and  complex. 
Therefore,  if  tbe  student  is  tau,ght  the  construction  of  each 
according  to  any  one  method,  be  will  have  been  taught  accord- 


822  BRIDCEWOHK 

iiiii'  to   tlic   ('lassilicatioii,   tlic   const I'liction    i>\'   4.41(1   ixissililc 
bridge  replacements. 

"Ill  a  like  iiianiicr  the  coiistructiDii  and  application  of  all 
of  the  varions  metliods  may  l)e  taught,  and  liy  thus  systematiz- 
ing our  efforts  a\'oid  the  occasions  for  confusion." 

APPLICATION   OF   FIXED    BRIDGEWORK 

Success  in  tlic  liehl  of  lixcd  hi-idgework,  to  a  very  large 
extent,  is  de]>endent  npon  the  correct  application  and  con- 
strnetion  of  full  and  partial  crowns  to  the  roots,  or  remain- 
ing portions  of  crowns  of  natural  teeth  which,  by  reason  of 
their  position,  have  been  selected  to  serve  as  abutment  and 
pier  supports  for  the  completed  truss  or  superstructure. 

The  same  general  requirements  governing  the  successful 
application  of  crowns  to  individual  roots  or  teeth  apply  with 
equal  force  to  those  employed  as  supports  for  a  bridge. 

In  addition  to  this,  certain  hygienic  requirements  must  be 
observed  in  bridge  construction,  in  the  a])plication  of  dum- 
mies or  substitutes  for  the  lost  natural  teeth,  to  so  form  and 
assemble  them  that  not  only  the  tissues  upon  which  they  rest, 
or  approximate,  but  those  around  the  adjacent  crowns  may 
be  maintained  in  a  condition  of  health. 

The  union  of  a  dummy  Mith  a  crown  in  such  manner  as 
to  form  a  constricted  space  or  ]X)cket,  difficult  of  access  to 
cleansing  ai)i>liances,  is  one  of  the  common  causes  of  failure 
in  fixed  bridgework. 

Therefore,  gingival  iuterproximate  spaces,  and  particu- 
larly the  embrasures  between  crowns  and  dummies,  should 
be  left  as  free  and  o]ien  as  is  consistent  with  esthetics,  and 
the  required  strength  of  the  structure. 

A  dummy  fitted  with  an  individual  saddle  which  rests  with 
tirmness  npon  the  border  is,  in  many  cases,  preferable  to  a 
dummy  applied  to  the  labial  or  buccal  surface  of  the  border 
in  such  manner  as  to  form  a  deep,  constricted.  V-shaped  space 
between  the  two.  A  ligature  passed  under  the  saddle  will  re- 
move debris  from  both  structure  and  border,  while  neither 
ligature  nor  toothbrush  will  ]>rove  efficient  in  the  V-shaped 
space. 

Since  the  function  of  an  in<lividual  saddle  is  not  to  afford 
support  to  a  tixed  bridge,  but  to  develo))  reasonable  lingual 
contour  to  the  dummy  to  which  attached,  its  bearing  on  the 
tissues  should  be  restricted  to  the  smallest  possible  area  con- 
sistent with  desired  contour. 


HRIDGEWOUK  S23 

l)y  means  ui'  the  iirt-ccdiiiii'  •'("lassilicatiuii  of  Fixed 
Jirid.i-es"  it  can  he  shown  that  it  is  possiljh:-  to  eoustnict  more 
than  tifty-fonr  thousand  different  varieties  of  fixed  hridges. 
To  attemi)t  to  exi)lain  in  detail  tlie  technical  methods  em- 
ployed in  the  construction  of  each  would  be  a  well-nigh  im- 
l)ossil)le  task,  and  entirely  uncalled  foi-  in  a  treatise  of  this 
character.  Fundamental  })rinciples  for  all,  however,  are  es- 
sentially the  same,  therefore,  when  the  student  has  mastered 
these  principles,  which  are  comparatively  few,  he  should  be 
capable  of  undertaking  the  coiistrnction  of  ordinarv,  as  well 
as  complicated,  cases. 

TECHNIC  OF  BRIDGE  CONSTRUCTION 

By  way  of  illustrating  some  of  the  preceding  ]>rinciples 
outlined,  tlie  technical  procedures  involved  in  the  construction 
of  a  simple,  fixed  bridge,  extending  from  right  lower  cuspid 
to  second  molar,  inclusive,  the  second  bicuspid  present  to 
serve  as  a  pier,  will  now  be  described. 

In  examining  the  mouth  and  noting  the  I'elation  of  the 
teeth  to  each  other  in  this  particular  case,  it  is  deemed  advis- 
able to  iilace  on  the  abutment  and  iiier  teeth  the  following 
crowns: 

Cuspid  root,  jwrcelain  face,  banded  crown. 

Second  bicuspid  and  second  molar  roots,  shell  crowns, 
because  of  restricted  space  occluso-gingivally. 


Tt  is  further  assumed  that  the  teeth  have  lieen  devitalized 
and  their  roois  filled,  if  such  procedure  is  considered  ad- 
visable. 

The  enamel  is  removed  from  the  axiai  surfaces  of  the 
three  roots,  as  previously  described  for  crowns  of  the  type 
indicated. 


824  BRIDCRWORK 

111  addition  to  reversing  the  cone  form  of  Hie  roots,  tlicir 
mesial  and  distal,  axial  surfaces  must  not  diveri;e.  Imt 
rather  couverge,  from  gingival  to  occlusal  surfaces.  The 
necessity  for  establishing  this  relation  is  obvious,  since 
divergence  of  these  surfaces  will  |>rc\cn1  \\\f  rciiio\al  of  the 
several  crowns  with  the  impression,  ny  tin'  rdnni  of  the  fin- 
ished bridge  to  place. 

The  line  of  direction  of  the  canal  of  the  cuspid  root  must 
also  be  considered.  When  not  in  parallel  alignment  with  the 
axial  surfaces  of  the  bicuspid  and  molar,  a  like  difficulty  will 
be  encountered  as  that  mentioned.  Since,  however,  reaming 
tlie  canal  to  any  extent  will  weaken  the  root,  in  order  to  estab- 
lish parallel  relationship,  it  is  a  better  plan  to  bring  such 
axial  surfaces  of  the  bicuspid  and  molar  as  diverge  from  the 
general  direction  of  the  root  canal  into  alignment  with  it 
rather  than  ream  the  canal  to  the  extent  of  weakening  it. 

In  practically  all  other  respects,  tlie  preparation  of  tlie 
three  roots  is  essentially  the  same  as  has  been  previously  out- 
lined for  crowns  of  similar  types  as  tliose  used  in  the  present 
case. 

When  root  preparation  lias  been  completed,  the  crowns 
are  constructed  individually,  keeping  in  mind  their  correct 
alignment  buccally  and  the  reservation  of  proportionate 
spaces  for  the  first  bicuspid  and  first  molar  dummies. 

The  crowns  are  roughly  finished,  set  on  their  respective 
roots,  a  wax  bite  taken,  the  face  bow  applied,  the  bite  mounted 
on  the  occluding  frame  and.  the  occlusion  cast  developed. 

If,  in  taking  the  bite,  the  crowns  are  disturbed,  they  are 
returned  to  position  on  their  respective  roots  and  a  plaster 
impression  secured.  Usually,  in  such  case  as  is  being  de- 
scribed, the  impression  can  be  removed  without  fracture,  the 
crowns  coming  away  with  it.  When  fractured,  however,  the 
broken  j^ieces  are  assembled,  the  crowns  set  in  their  respective 
matrices,  and  all  luted  firmly  with  wax. 

The  object  in  taking  a  bite  and  an  impression  as  well,  in- 
stead of  an  impression-bite  combined,  in  modeling  coni])Ound, 
as  is  frequently  done,  is  to  secure  an  accurate  relation  of  the 
crowns  to  each  other.  While  it  is  possible,  in  some  cases,  to 
remove  the  crowns  from  their  respective  roots  without  chang- 
ing their  relation  to  each  other  witli  a  combined  bite  and  im- 
pression in  modeling  compound,  disturbance  of  relation  is 
liable  to  occur,  and  therefore  plaster  should  always  be  used 
in  preference  to  a  material  which  is  liable  to  distort  under 
stress. 


BRIDGEWORK  825 

From  the  impression,  a  east  is  formed  whieli,  when  iiard- 
ened,  is  fitted  in  the  hite  and  attached  to  the  occluding  frame. 

By  flowing  a  film  of  wax  in  the  interior  of  the  shell 
crowns  and  in  the  cap  and  around  the  dowel  of  the  cuspid 
crown,  before  filling  the  imjjression,  the  bridge,  when  assem- 
bled and  waxed  together,  can  readily  be  removed  from  its 
cast  without  mutilating  the  latter.  The  wax  within  the  crowns 
should  be  thoroughly  removed  before  investment  of  the  bridge. 

REQUIREMENTS  OF  THE  DUMMIES 

For  esthetic  reasons,  the  first  bicuspid  dummy  should  be 
of  porcelain,  or  at  least  be  porcelain-faced.  When  consider- 
able absorption  of  the  alveolar  border  has  occurred  and  the 
cervical  half  of  the  dummy  will  not  be  exposed  to  view  in 
laughing  or  speaking,  a  space  may  be  left  between  this  end  of 
the  dummy  and  the  ridge  for  hygienic  reasons. 

The  application  of  a  short  dunnny  in  such  location  leaves 
the  gingival  tissues  next  the  crowns  which  proximate  the 
space,  more  or  Jess  exposed  and  accessible  to  the  toothbrush 
and  other  cleansing  devices. 

In  case  it  is  deemed  advisable  to  extend  the  dummy  to  the 
alveolar  border,  or  saddle  the  latter,  as  is  frequently  done, 
it  should  be  uniformly  reduced  on  its  proximal  surfaces,  so 
as  to  leave  the  interproximate  spaces  in  the  gingival  half 
areas  free  and  accessible  for  cleansing  purposes. 

Too  often  the  union  between  crowns  and  dummies  extends 
from  the  occlusal  points  of  contact  to  the  gingiva?,  thus  pre- 
cluding the  possibility  of  proper  cleansing  of  the  tissues  and 
appliance. 

CONSTRUCTION  OF  THE  BICUSPID  DUMMY 

A  dummy  may  be  constructed  by  any  (if  tlie  several  meth- 
ods outlined,  using  facings  or  teeth  of  the  removable  type,  or 
a  long  pin,  plate  tooth  may  be  employed. 

By  this  latter  method  a  facing  of  suitable  form  and  color 
is  selected  to  fit  within  tlie  space  between  the  cuspid  and  sec- 
ond bicuspid  crowns. 

Reduce  tht  mesial  and  distal  surfaces  so  as  to  taper  some- 
what from  occlusal  to  gingival. 

Bevel  the  buccal  marginal  ridge,  or  that  ]3ortion  of  the 
facing  which  corresponds  to  the  incisal  edge  of  an  anterior 


826  liKIUCiEWORK 

tooth,  to  allow  for  an  ext(Misiou  of  Warkinn  lo  the  huccal  mar- 
gin for  protection  from  stress. 

The  cervical  eml  of  the  dummy  ma>'  he  liiiishcd  in  thi'cc 
ways : 

First,  it  may  simply  be  rounded  and  swing  clear  of  the 
border,  so  as  to  leave  a  self-cleansing  space  between  the  bor- 
der and  the  strncture. 


I'ORL'EI.AIX      F  A  (•  K  O      DUMMY 

FORMED    WITH    lERVlL'AL 

L'I,EARANCE    SPACE 


Second,  it  may  be  adapted  by  grinding  to  lay  in  close 
contact  with  the  border  at  its  cervico-laiccal  margin,  with 
more  or  less  of  a  V-shajied  space,  opening  lingnally. 


rORl'EI.AIX       V  A  I'  E  D       DUMMY 
WHICH    RESTS    ON    liUCCAi 
SURFACE  OF  THE  BORDER 


Third,  a  saddle  may  be  adapted  to  the  cervical  end,  which, 
when  closely  fitted  to  the  border,  ])ermits  the  lingual  contour 
of  the  dummy  to  be  developed,  and  obviates  the  formation  of 
the  objectionalile  space  referred  to. 


l'OBCEl,AlN       FACED       DUMMY 

WITH   SADDLE   WHICH    RESTS 

UPON  THE   BORDER 


The  type  of  dummy  suitable  for  each  individual  case  can 
be  determined  l)y  setting  it  in  correct  buccal  alignment  with 
the  proximating  crowns  and  noting  the  relation  of  its  cervical 
end  to  the  border. 


BRIDGKWORK  827 

Jn  this  case,  a  (huinny,  tn  wliicli  a  saiMIc  is  apiilicil.  will 
be  euusidered  the  most  appin|irialc. 

The  facing  shoulil  be  groiiiul  at  its  eervioal  eud  to  tit  the 
inequalities  of  the  border,  and  its  l)uc('al  marginal  ridge  bev- 
eled as  i3revii)usly  deNcribed. 

A  baelving  is  now  applied  to  its  lingual  surface,  extend- 
ing from  the  ridge  lap  to,  or  slightly  beyond,  the  bucco-occlu- 
sal  margin.  When  the  ridge  lap  of  the  porcelain  does  not  tit 
closely  to  the  border  except  at  its  cervico-buccal  margin,  the 
backing  should  extend  bnccall\',  so  as  to  cover  it,  usually  slight- 
ly beyond  the  cervico-bui'cal  margin. 

A  jiiecc  of  thin,  pure  gokl  or  i)latinum  is  burnished  to 
the  border,  innnediately  on  the  area  on  which  the  dummy 
will  rest,  and  is  trimmed  to  the  approximate  outline  of  the 
dummy  base. 

The  facing  to  wliicli  the  backing  is  attached  is  set  in  cor- 
rect alignment  with  the  ])roximating  teeth  on  the  saddle,  and 
the  two  are  attached  Avith  wax. 

Sufficient  bulk  of  wax  is  now  added,  in  which  the  occlu- 
sal surface  of  the  dumm.v  can  be  carved. 

When  carved  to  desir(>d  form,  a  counterdie  can  be  con- 
structed by  the  indirect  method  by  casting  over  moldine  as 
desei'ibed. 

Develop  the  cusp  l)y  swaging  in  the  usual  manner.  Trim 
peripherally,  soften  the  wax  and  adapt  to  the  dummy,  return 
the  latter  to  the  cast  and  by  trimming  and  adjustment  de- 
velop correct  occlusal  relation. 

Remove  the  dummy  from  the  cast  and  wax  to  the  desired 
axial  form. 

The  facing  is  now  removed  from  the  assembled  dummy, 
carbon  points  are  inserted  in  the  holes  left  by  the  withdrawal 
of  the  pins  and  the  dummy,  minus  the  facing,  is  invested  in  a 
casting  ring,  and  the  ojieration  completed  liy  the  casting 
process. 

By  using  a  heavier  gauge  of  metal  for  the  saddle,  to 
prevent  warpage  or  contraction  in  fusing  the  metal,  the  lin- 
gual contour  of  the  case  can  be  developed  by  soldering. 

When  this  plan  is  followed  the  mesial  and  distal  margins 
of  the  saddle  should  project  slightly  l)eyond  the  wax  so  as 
to  be  caught  iij  the  investment. 

After  the  metal  structure  is  completed,  the  carbon  points 
are  drilled  out,  the  facing  titted  ready  for  cementation  in 
position,  after  the  lu'idge  is  com]ileted.     The  i)ins  of  the  fac- 


S2S  BRIDGEWORK 

iiig  slioiild,  ill  all  cases,  he  r(mi;|iciic(l   hcl'drc  (■ciiiciitation  to 
afford  inaxiiiiiiiii   aiicli(ira,i;c   in    llic  rciiiciit. 

The  duiimiy  is  now  rough  drcsst'd  to  the  tlesired  form,  re- 
turned to  place  between  cnsind  and  second  bicuspid  crown 
and  waxed  in  ]iosition. 

VARIATIONS  IN  THE  FORMS  OF  DUMMIES 

Various  other  forms  of  dummies  can  be  applied  with 
ecjual  facility  to  the  case  under  consideration.  For  example, 
a  Steele,  or  an  Kvslin  facing,  or  a  partial  crown  of  either 
type,  may  be  used.  Again,  a  Goslee,  or  a  Gardiner  partial 
crown  are  equally  apjilieable,  either  with  or  without  a  saddle, 
providing  sufficient  .space  exists  to  ])ermit  the  introduction  of 
a  rigid  metal  structure  beneath. 

CONSTRUCTING  THE  MOLAR  DUMMY 

To  illustrate  still  another  tyjic  of  dummy  fre(|iu'utly  used, 
the  technic  of  an  all  metal  i-e)ilaccm('iit  for  tlie  first  molar  will 
be  described. 

A  mass  of  casting  wax  is  warmed  and  pressed  into  the 
space  between  second  bicuspid  and  second  molar,  and  the 
occlusion  developed  in  the  usual  manner. 

The  gingival  half  of  the  block  of  wax  is  excised,  the  occlu- 
sal portion  being  carved  to  correct  peripheral  outline. 

Since  the  object  in  applying  a  dummy  of  this  type  is  to 
gain  space  for  cleansing  purposes,  the  buccal  and  lingual  sur- 
faces of  the  dummv  should  be  rounded  inward,  so  as  to  form 


ALL  METAL  MOLAK  DUMMY.  A 
T\T>E  OF  PUMliy  FRKQUENTLY 
USED    IN    -'SANITARY    BRIDGES" 

a  convex,  or  even  V-shape,  to  the  surface  which  looks  toward 
the  border.  By  avoiding  the  formation  of  a  flat,  or  a  slightly 
convex  surface,  to  this  portion  of  the  dummy,  practically  all 
parts  are  rendered  accessible  to  the  toothbrush  and  cleansing 
appliances. 

When  carved  to  correct  outline  form,  the  wax  is  removed, 
invested  and  cast  in  the  usual  manner. 

Another  method  whereby  practically  the  same  form  of 
dummy  may  be  i^roduced  is  by  carving  the  cusp  in  some  suit- 
able medium,  developing  a  counterdie  and  swaging  the  occlu- 


BRIDGEWORK  829 

sal  surface  and  occlusal  third  i)cri]ilH'ry  from  gold  ]>latc  in 
the  couuterdie. 

This  is  trinnued  to  i)roper  depth,  the  border  inargius  con- 
toured inward  slightly  with  pliers,  the  interior  of  the  partial 
crown  tilled  in  with  plate  scrap,  huilding  it  high  in  the  form  of 
a  mesio-distal  ridge,  and  tilling  in  the  voids  with  solder  to  the 
required  contour. 

After  developing  the  dummy,  by  whatever  method  em- 
ployed, it  is  rough  finished,  and  fitted  in  position  between  the 
second  bicuspid  and  second  molar  crowns. 

ASSEMBLING   THE   BRIDGE 

Before  the  linal  waxing  of  the  several  parts  of  the  hriclge, 
the  dummies  are  laid  aside,  the  three  crowns  warmed  suffi- 
ciently to  soften  the  film  of  interior  wax,  and  removed  from 
the  cast.  By  observing  care  in  removal,  their  cervical 
matrices  on  the  cast  will  not  he  appreciably  disturbed.  The 
wax  is  cleared  from  the  interior  of  the  crowns,  after  which 
they  should  be  boiled  in  acid,  washed  thoroughly,  and  re- 
turned to  position  on  the  cast.  A  little  sticky  wax,  applied 
at  two  or  three  points  along  the  gingival  margins,  will  hold 
them  firmly  in  position  while  assembling  the  bridge. 

The  dummies  are  now  adjusted  and  luted  firmly  with  hard, 
sticky  wax,  applying  it  in  sufficient  quantity  to  firmly  unite 
them  to  the  crowns. 

Before  final  removal  from  the  cast,  the  occlusion  should  be 
tested,  the  general  aligmnent  of  the  crowns  and  dummies 
noted  and  the  assembled  bridge,  as  a  whole,  inspected,  to 
see  that  every  part  is  in  exact  relation. 

In  grinding  and  adjusting  porcelain  facings  in  a  bridge, 
special  care  should  be  taken,  that  a  very  slight  space  exists 
between  them,  or  between  the  porcelain  and  proximating 
metal  crowns.  The  metal  backings  of  the  facings,  however, 
should,  whenever  possible,  i-est  in  close  contact  with  each  other 
and  with  adjacent  metal  crowns. 

This  is  necessary,  in  order  that  shortening  of  the  bridge 
may  not  occur  as  a  result  of  contraction  of  l»oth  investment 
and  solder.,  as  the  latter  cools. 

On  removal  of  the  bridge  from  the  cast  the  joints  between 
the  several  dmnmies  should  be  flushed  with  wax  to  prevent 
the  ingress  of  the  investment  material  the  result  of  which  is 
to  exclude  the  solder,  and  thus  weaken  the  union  lietween  the 
several  ]iarts  of  the  structure. 


f>au  HRIIK'.EWOKK 

I'^iuallx'  Ihc  cnspid  I'aciiin'  is  iciiKivcd  tVoiii  the  crown  ami 
laiil  aside  until  al'tci'  llic  several  |iarls  ai'e  soldered. 

INVESTING  THE  BRIDGE 

A  mix  of  medium  consistciiey  of  some  tlioroughly  tested 
investment  material  should  he  maile.  This  is  placed  on  a 
slali  or  piece  of  paper  on  the  hench,  Iniilding  it  ujj  to  one  inch 
or  slightly  more  in  thickness,  ai)pi()xiniately  the  same  width, 
and  somewhat  longer  than  the  bridge. 

With  the  point  of  a  small  inslrument  some  of  the  invest- 
ment is  carefully  applied  to  the  interior  of  the  cap  of  the  cus- 
])id  crown,  in  the  pin  holes  left  l)y  removal  of  the  facing,  and 
in  the  two  shell  crowns  as  well. 

The  bridge  is  now  laid,  buccal  side  down,  on  the  invest- 
ment, into  which  it  is  gradually  settled,  to  within  about  one- 
half  inch  of  the  bottom  of  the  mass.  If  pressed  too  deeply,  the 
investment,  when  trimmed,  will  ))e  weak  and  is  very  liable  to 
fracture  during  soldering. 

When  hardened,  the  surplus  inxcstnient  is  trimmed  away, 
being  specially  careful  to  clear  away  all  obstructions  from 
around  the  teeth  and  dummies  which  might  interfere  with 
the  direct  api>lication  of  the  flame  to  the  solder  in  the  various 
joints. 

The  wax  is  removed,  first  by  picking  out  the  bulky  portion, 
and  afterward  applying  boiling  water  for  the  removal  of  that 
in  the  deepest  parts. 

A  thin  film  of  thick  borax  paste  is  applied  to  all  parts  on 
which  it  is  desired  that  the  solder  should  flow,  and  the  invest- 
ment jjlaced  on  a  gauze  over  the  Bunsen  flame. 

When  heated  to  a  dull  red  heat  along  the  base  of  the  in- 
vestment, the  case  is  transferred  to  the  soldering  block,  the 
blow-piiie  flame  aiii^lied  and  strip  solder  fused  and  fed  into 
the  lingual  surfaces  and  embrasures  imtil  the  required  con- 
tour is  attained. 

FINISHING 

The  finishing  of  a  bridge  of  this  tyjie  is  similar  to  that  of 
a  single  crown.  In  bridgework,  however,  particular  care 
should  lie  taken  to  finish  the  metal  smoothly  in  the  inter- 
])roximal  spaces.  Rough  surfaces  in  any  location  invite  the 
lodgement  of  food.  Therefore,  all  file  marks  should  be  re- 
moved with  fine  discs,  and  the  finer  scratches  left  by  these 
i-emoved  by  coarse,  followed  by  fine  ])olishing  powders,  with 
felt  and  lirush  wheels,  on  the  lathe. 


BRIUGEWORK 


SETTING  THE   BRIDGE 


The  bridge  when  finished  is  adjusted  in  jiosition  on  tlie 
natural  roots  to  test  its  eorreetness  of  form,  and  proliable 
fultilhneut  of  function,  after  whicli  it  is  washed,  dried,  and 
laitl  asitle  while  tlie  mouth  is  prepared  for  its  reception. 

The  mouth  should  be  syringed  with  warm  normal  salt 
solution,  cotton  rolls  applied  to  dam  against  the  encroach- 
ment of  moisture,  and  the  teeth  and  roots  tlioroughly  dried. 

From  a  thoroughly  mixed  mass  of  mediinn  thin  cement, 
the  shell  crowns  are  ])artially  tilled  and  some  applied  around 
the  dowel  and  on  the  root  ca]).  Tiie  root  canal  is  also  filled, 
using  for  this  ]iui-]iose  a  small  pinggci-  ]>()int.  or  the  regular 
root  canal  plugger. 

The  bridge  is  now  quickly  set  in  position  and  forced  to 
place  with  heavy,  steady  ])ressure,  and  the  jiatient  instructed 
to  close  the  teeth   with   foi-ce.     If   occlusion   is  correct,   the 


BRIDGE    IX   POSITION    ON"   CAST.    SHOWING  CONSIDERABLE 

INTERPROXIMAL  SPAfE  TO  THE  MESIAL  AND 

DISTAL   OF  KIRST   BKTSPID    DUMMY 

mouth  is  0])eued  and  the  parts  guarded  from  moisture  until 
the  cement  has  had  time  to  become  fairly  hard. 

Removing  the  excess  cement  requires  care  and  close  at- 
tention not  only  from  beneath  the  gingival,  but  from  the 
various  surfaces  of  the  structure  against  which  it  may  have 
become  lodged.  If  not  removed  at  this  time  it  may  remain 
adherent  for  a  long  time,  particularly  in  jirotected  locations, 
as  in  the  interproximal  spaces,  where,  although  it  may  not 
prove  a  direct  irritant,  will  invite  the  accumulation  of  food. 

Finally  tltc  bridge  is  tested  with  carlion  paper  to  dis- 
close any  points  of  interference  in  lateral  maudebular  move- 
ment. If  any  are  present  they  are  reduced  with  stones  and 
the  roughened  surfaces  again  ixilislied. 


S32  BRIDGEWORK 

THE  CARMICHAEL  ATTACHMENT 

An  attachment  often  applied  to  good  advantage  in  fixed 
hridgework  is  that  known  as  the  "Staple  Half  Crown," 
"Carmiehael  Attaclnnent, "  and  nnder  various  other  names. 

This  attachment  is  in  reality  a  shallow  inlay,  covering  a 
considerable  area  of  tooth  surface  from  wliicli  the  cniimcl  ;uid 
a  superficial  layer  of  denture  has  been  renio\ed. 

Anchorage  of  the  attachment  to  the  tooth  is  secured  by 
means  of  interior,  peripheral  ribs  in  the  metal  structure, 
formed  during  constructing,  which  fit  within  corresponding 
grooves  in  the  prepared  tooth  surface  or  shallow  cavity. 

The  particular  advantages  of  this  attachment,  when  prop- 
erly constructed  and  applied,  are  as  follows : 

First,  it  can  be  applied  to  the  lingual  surface  of  a  vital 
tooth  without  endangering  the  pulp. 

Second,  a  secure  attachment  to  the  tooth  can  be  devel- 
oped without  involving  much  of  the  labial  or  buccal  sui'face. 

Third,  the  joint  between  the  attachment  and  cavo-surface 
angles  is  the  same  as  in  ordinary  inlay  work,  or  gold  foil  fill- 
ings, thus  obviating  the  formation  of  a  shoulder,  which,  in 
many  cases,  particularly  in  constructed  locations,  invites  the 
lodgment  of  food  and,  subsecjuently,  caries. 

Attachments  of  this  type  are  most  applicable  to  cuspid 
teeth,  although  they  may  at  times  be  applied  to  central  in- 
.cisors.  When  slightly  modified  they  may  lie  ap]ilied  to  very 
great  advantage  to  the  bicuspids. 

The  name  Staple  Half  Croivn  was  given  this  attachment 
because  formerly  an  iridio-platinum  wire  staple  was  applied 
in  the  groove  in  the  tooth,  a  gold  or  ]ilatinuni  matrix  adapted 
to  the  tooth  and  staple  and  the  two  attached.  The  staple  thus 
formed  the  interior  rib  alluded  to. 

CONSTRUCTION 

To  illustrate  the  constructive  steps,  the  application  of  a 
Carmiehael  attachment  to  a  cuspid  tooth  will  be  described: 

With  suitable  stones  and  discs  the  jilate  of  enamel  is  re- 
moved from  the  entire  lingual  and  proximal  surfaces  of  the 
tooth;  except  at  the  cervical  periphery,  and  the  incisal  edge 
beveled  at  the  expense  of  the  lingual  surface. 

Usually,  for  subsequent  protection  of  the  tooth,  removal 
of  enamel  on  proximal  surfaces  is  carried  slightly  to  the 
labial  of  the  contact  points. 


BRIDGEWORK  833 

A  gingival  shoulder  is  formed  by  moans  of  square-end 
burs.  This  should  be  carried  either  under  the  free  gum 
margin,  or  terminated  a  short  distance  to  the  incisal  of  it, 
to  avoid  the  formation  of  a  joint  at  the  margin. 

With  a  fissure  bur,  grooves  are  cut  on  the  proximal  sur- 
faces, next  the  labial  plate  of  enamel,  from  gingival  seat  to 
incisal  edge,  converging  slightly,  incisally. 


PROXIMAI-  VIEW  OF  CUSPID  LINGUAL  VIEW  OF  SAME  INCISAL   VIEW   OF    SAME 

PREPARED       FOE       A       CAR- 
MICHAEL  ATTACHMENT 

These  grooves  are  iinited  Ijy  another  transverse  groove 
located  as  close  to  the  incisal  edge  as  possible  in  order  to  de- 
velop anchorage  for  the  resistance  of  labio-lingual,  torsional 
strain. 

All  surfaces,  margins  and  grooves  should  be  so  corre- 
lated that,  when  formed,  removal  of  the  wax  model  may  be 
accomplished  without  distortion. 

This  requires  that  all  overhanging  or  rough  margins  and 
sui'faces  be  smoothed  and  all  undercuts  obliterated  before 
forming  the  model. 

A  modeling  compound  impression  enclosed  within  a  band 
or  half  thimble  cup  is  secured,  of  surfaces  and  margins  of  the 
tooth  involved. 

From  this  an  amalgam,  or  a  modelite,  die  is  developed, 
which,  when  hardened,  is  smoothed,  and  on  this  the  pattern 
is  developed  in  inlay  wax. 

The  wax  should  be  forced  into  all  grooves  and  against 
all  cavit}'  surfaces,  ]5articular  care  being  taken  to  adapt  it 
closely  to  the  margins  and  against  the  beveled  incisal  edge. 
It  is  then  carved  to  restore  the  tooth  to  its  original  form. 

Usually  it  is  best  to  test  the  wax  model  on  the  natural 
tooth  to  see  that  it  fulfills  requirement,  when,  if  found  satis- 
factory, it  is  invested  and  cast,  preferably  in  a  good  grade  of 
platinized  gold. 


BRIDGEWORK 


FINISHING 


AVhen  cast,  it  is  washed,  heated  and  dropped  in  acid,  the 
nodnlar  surfaces  corrected,  after  wliicli  it  is  fitted  to  tlie  tootli 
and  tlic  iiKi ruins  disced  to  coiiicich'  with   llie  tootli  surfaces. 


CARMICHAEL  COMPLETED, 

BEADY       FOB       ATTACHMENT 

TO   imincE 


Wiien  the  other  ahutnicut  and  i>ier  structures  are  com- 
pleted, all  are  placed  in  position,  an  impression  and  bite  se- 
cured and  the  Carmichael  attachment  is  treated  in  the  same 
maimer  as  of  full  crown. 

MODIFIED  TECHNIC 

Another  method  of  construction  consists  in  applying  a 
piece  of  34  or  36  gauge  gold  or  platinum  to  the  die,  and  by 
burnishing,  form  a  matrix  which  fits  accurately  within 
grooves  and  against  the  reduced  surfaces  of  the  tooth. 

When  perfectly  ada]ited  and  trimmed  to  correct  periph- 
eral outline,  sticky  wax  is  flowed  over  the  lingual  side  of  the 
matrix  to  prevent  distortion,  after  which  the  latter  is  re 
moved,  invested,  the  wax  burned  off  and  liigh-grade  solder 
flowed  on  the  gold  to  develop  required  lingual  contour. 

Still  another  method  consists  in  applying  inlay  wax  to 
the  burnished  matrix,  developing  the  wax  to  correct  form, 
investing  and  casting  against  the  matrix.  By  this  method 
the  surfaces  which  rest  against  the  tooth  are  free  from 
nodular  imperfections,  resulting  from  casting  the  entii'e  ap- 
pliance. 


BRIDGEWORK  835 

MODIFIED   CARMICHAEL   APPLIED  TO   CUSPIDS  AND 
BICUSPIDS 

An  application  of  the  Carmicliacl  attaehnuMit  applit^d  to 
cuspids  and  bicuspids,  suggested  l)y  Dr.  E.  A.  Kennedy,  is  as 
follows : 

The  enamel  and  a  layer  of  dentin  is  removed  from  a 
portion  of  the  lingual,  i)roximal,  and  labial  or  buccal  surfaces 
of  the  tooth,  extending  from  incisal,  or  occlusal,  to  gingival 
areas.    In  bicuspids,  an  (irchisnl  step,  having  a  decided  dove- 


MODIFIED 
CARMICHAEL 
ATTACHMENT 


TOOTH  PREPARATION  FOR  MODIFIED    CAR- 
MICHAEL FOR  BICUSPID 


MODIFIED      CjUIMICHAEL     IN,      AND 
REMOVED    FROM,    POSITION 


tail  shape,  is  formed,  while  the  giiigixal  area  terminates  in  a 
right-angle  shoulder. 

The  axial  surfaces  of  the  tooth  should  present  a  slightly 
conical  form  to  permit  the  removal  of  the  wax  pattern. 

Grooves  are  now  cut  in  the  lingual  and  labial,  or  buccal, 
axial  surfaces  in  the  dentin,  for  anchorage  purposes.  The 
process  of  forming  the  wax  pattern,  casting,  fitting  and  tin- 
ishing  is  the  same  as  described  in  the  construction  of  a  Car- 
michael  attachment. 

This  attachment  can  be  applied  to  vital  teeth  and,  when 
l)roperly  constructed,  affords  an  anchorage  for  small  bridges 
equal  to  that  of  tlie  average  crown. 


THE  CORCORAN  ATTACHMENT 

The  Corcoran  attachment  is  applied  to  aliutment  crowns 
in  those  cases  where  it  is  desirable  that  a  liridge  of  the  fixed 
type  be  removed  from  time  to  time  for  cleansing,  or  for 
treatment  of  the  supporting  teeth  and  adjacent  tissues. 

This  attachment  consists  of  a  gold  block,  threaded  in- 
ternallv.  and  which  receives  a  threaded  bushing.     The  bush- 


836 


BRIDGEWORK 


ing  also  is  threaded  to  receive  a  lioadcd  screw,  by  means  of 
which  the  crown  is  anchored. 

In  case  of  wear,  both  bushing  and  screw  may  be  replaced 
with  new  ones,  the  parts  being  interchangeable. 

CONSTRUCTION 

The  root  is  jtrcpared  as  previously  descriliod,  with  dis- 
tinctly conical   peri])hery,   and   having  an  interior   shoulder. 


IMPRESSION  CUP  AS  AP- 
PLIED IN  TAKING  MODEL- 
ING COMPOUND  IMPRESSION 
OP  ROOT  FACE  AUD  PERIPI!- 
ERY  OF  MOLAR  TOOTH 


ROOT    CAP    CONSTRUCTED 


CORCORAN  ATTACHMENT 
SHOWING  COMPLETED 

CROWN.  BLOCK  AT- 
TACHED TO  ROOT  CAI'. 
WITH  BUSHING  AND 
SCREW  IN  POSITION.  BUT 
NOT  SCREWED  TO  PLACE 


BRIDGEWORK 


837 


An  open  band  impression  is  secured  in  modeling  com- 
pound, from  which  an  amalgam  die  is  formed. 

Over  this  die  a  root  cap  is  swaged,  through  which  dowels 
are  passed  and  attached  with  high-grade  solder. 

The  central  shoulder  depression  should  be  filled  at  the 
same  time,  and  the  cap  stiffened  by  flowing  solder  over  its 
entire  area. 

A  Corcoran  block  is  now  set  in  position  on  the  cap  and 
attached  to  the  latter  with  a  lower  fusing  solder  than  that 
previously  applied. 

The  sides  of  the  block  slioukl  be  parallel  with  the  long 
axis  of  the  tooth,  or  the  line  of  direction  of  introduction  and 
removal  of  the  bridge. 


A    URIDGE    ANCHORED    liV    THE   COIirORAN    ATTACHMENTS   HEIIOVED 

FROM    ITS    MULTIPLE    ANlHORAflE,     WHICH.     IN    THIS    CASE. 

CONSISTS    OF    PI\E    ROOTS.    THREE    OF    WHICH 

CARRY    BLOCKS 

A  solid  metal  crown  can  be  formed  on  the  root  cap  and 
around  the  Corcoran  block  by  applying  and  carving  inlay 
wax  to  the  desired  form  and  casting. 

A  countersunk  opening,  directly  in  line  with  that  in  the 
block,  made  through  the  occhisal  surface  of  the  crown,  re- 
ceives the  headed  screw  which  anchors  the  crown  to  the  root 
cap. 


BRIDGEWORK 


By  setting  the  block  somewhat  to  tlie  lingual,  a  porcelain- 
faced  crown  can  be  constructed  in  the  usual  maimer. 

To  obviate  the  tediousuess  of  final  fitting  of  the  crown 
to  the  block,  which  in  all  cases  must  be  done  in  cast  work,  a 


BRIDGE  SET  IX  PCSLTICIN    AMI   TIKI, I)    in    TIIKKE  SrRKWS.      THE  TWO 
DISTAL    ROOTS    I'AIUtV     KKI,1,V    ATTA<MIMENTS    AND    ONE    ON 
LEFT     A     BAH      Folt      <ilLMOItE      ATTACHMENT.      EN- 
CLOSED   WITHIN    PARTIAL    DENTURE 

boxing,  composed  of  ])latinum  or  high  fusing  gold,  is  first 
formed  and  fitted  to  the  block  on  the  root  eaj). 

Over  this  the  crown  is  built  in  any  manner  that  the  con- 
ditions of  the  case  demand,  after  which  it  is  removed  from 
the  cap,  the  box  covering  the  block  coming  away  with  the 
pattern  crown,  and  the  solder  flowed,  or  gold  cast  against  it. 

The  crowns  and  bridge  showing  application  of  the  Cor- 
coran appliances  were  kindly  loaned  for  illustrations  by  Dr. 
H.  F.  Methven. 

Still  another  modification  is  sometimes  carried  out;  a 
disc  of  gold  or  platinum,  to  serve  as  a  crown  base  is  per- 
forated, fitted  around  the  block  and  swaged  to  accurately 
conform  to  the  root  cap.  To  this  the  boxing,  which  encloses 
the  block,  is  soldered,  and  on  this  metal  base  the  crown  is 
built. 


BRIDGEWORK 


839 


SIDE    VIEW    OF    liRIPGE    ON    CAST.     WITH    rARTIAT.    DEN- 
TURE   ABOVE 


BRIDGE    AND   DENTURE    IN    POSITION    ON    CAST 


840  BRIDGEWORK 

On  page  79(5  reference  is  made  to  a  bridge  eonstructed  by 
Dr.  Anderson,  in  which  the  substitute,  altJiough  composed 
of  two  pieces,  is  of  the  fixed  type  when  set. 


BRIDGE   rONSTRIUTED   I!Y   TiR.    C.    h.    AND- 
ERSON.     FOE    DESCRIPTION,     SEE 
PAGE    796 


Mueller  of  Zuricli,  Switzerland,  suggests  a  similar  method 
of  anchoring  a  removable  bridge  in  position. 

He  constructs  a  root  cap  fitted  with  a  tube,  near  the  apical 
end  of  which  a  slight  rib  is  attached  to  one  side.  The  dowel 
of  the  crown  is  split,  and  sprung  apart  slightly  at  its  apical 
end.  A  groove  is  formed  in  the  dowel  at  a  point  which,  when 
the  latter  is  in  jjosition  in  the  tube,  will  fit  over  the  rib  in  the 
tube.  The  split  dowel  as  it  passes  the  rib  is  sprung  together, 
and  as  the  crown  is  seated  the  notch  of  the  dowel  receives 
the  rib,  and  in  this  manner  the  crown  is  latched  in  position. 

The  structure  is  composed  of  a  perforated  root  cap, 
through  which  the  independent  doweled  crown  passes. 

A  telescoping  crown  or  heavy  stop  clasp  is  fitted  to  the 
other  supporting  root  and  the  two  connected  by  a  saddle,  to 
which  the  teeth  are  attached. 

THE  HEDDY  ATTACHMENT 

The  Heddy  attacliment  consists  of  a  metallic  lilock  simi- 
lar in  form  to  tlie  Corcoran  attachment,  differing,  however, 
in  being  solid. 


BRIDGEWORK 


841 


The  general  steps  of  root  cap  constrnction,  as  well  as 
that  of  the  crown,  are  similar  to  those  just  outlined.  Anchor- 
age of  the  crown  to  the  block  attached  to  the  root  cap  is  se- 


HOOT       CAP       IN       POSITION. 

CROWN       COMPLETED.       BUT 

NOT    SEATED 


cured  by  cutting  a  V-shaped  groove  transversely  across  the 
block,  about  midway  between  cap  and  occlusal  end. 


An  opening  is  made  througli  one  of  the  axial  surfaces  of 
the  crown.  This  is  threaded  to  receive  a  set-screw  having  a 
beveled  point. 

The  crown  is  locked  in  position  by  setting  the  screw 
firmly  into  the  V-shaped  groove  of  the  central  block. 


REMOVABLE  BRIDGES 

A  removable  bridge,  in  the  ordinary  acceptation  of  the 
term,  refers  to  a  substitute  for  lost  natural  teeth,  which  is 
held  in  position  and-supported  by  some  of  the  remaining  natu- 
ral teeth  or  roots,  and  which  can  be  removed  from  position 
and  replaced  by  the  patient  at  will. 

For  hygienic  as  well  as  esthetic  reasons,  bridges  of  this 
type  are  usually  supplied  with  saddles.     These  may  or  may 


842  BRIDGEVVORK 

not  rclicvt'  llic  almtiiicnt  and  pier  roots  of  a  certain  amount 
of  masticatory  stress.  As  i)revioiisly  stated  iii  structures 
whieli  conform  to  bridge  engineering  princijiles,  whether  fixed 
or  removable,  the  abutment  aiul  pier  roots  must  resist  prac- 
tically all  masticatory  stress,  regardless  of  the  presence  of 
saddles. 

When  the  structure  is  so  jiianned  tliat  the  saddle  will  re- 
ceive the  burden  of  stress,  the  abutment  and  pier  roots  being- 
utilized  principally  for  retention  purposes,  it  should  be  classed 
as  a  ])artial  denture. 

REMOVABLE  BRIDGE  ATTACHMENTS 

The  Roach,  Gihuore,  Morgan  and  similar  ajjplianees  are 
frequently  used  in  cases  of  so-called  removable  l)ridge  work, 
when,  in  reality,  the  structures  should  be  classed  as  partial 
dentures,  since  resistance  to  masticatory  stress  devolves 
upon  saddles,  and  not  on  the  ai)i)liances  themselves. 

Various  forms  of  attachments  and  many  peculiar  and 
ingenious  devices  have  been  designed  for  the  retention  and 
support  of  removable  bridges.  Many  of  these,  because  of 
the  exacting  care  required  in  their  construction,  or  of  certain 
weaknesses  which  developed  with  use,  have  been  discontinued. 

The  forms  of  attachments  which  have  proven  most  satis- 
factory and  capable  of  resisting  masticatory  stress  consist 
of  rigid  telescoping  devices,  as  cap  crowns  and  crowns  fitted 
with  heavj'  dowels  which  are  received  within,  and  accurately 
fitted  to.  tubes  enclosed  within  the  roots  of  natural  teeth. 

Dr.  F.  A.  Peeso  of  New  York,  who  is  a  recognized  author- 
ity in  the  field  of  removable  bridge  work,  ai)plies  this  princi- 
ple, or  some  slight  modification  of  it,  in  practically  all  cases 
where  removable  work  is  indicated.  Although  most  satisfac- 
tory, these  forms  of  attachment  require  the  use  of  compara- 
tively rigid  gold,  and  very  exact  technic  in  their  production, 
otherwise  unsatisfactory  results  attend  their  application. 

When  a  removable  bridge  structure  is  supported  by  two 
or  more  roots,  or  teeth,  these  must  be  so  prepared  that  the 
attached  crowns  or  retention  devices  may  sustain  a  parallel 
relation  to  each  other. 

This  is  necessary,  as  before  stated,  iii  order  that  the 
bridge  may  be  readily  removed  and  replaced  by  the  patient 
without  special  care  or  annoyance. 

In  addition,  a  bridge  sustained  by  abutment  and  pier  sup- 


BRIDGEWORK 


843 


IDorts  not  ill  parallel  ali.£>iimeiit  must  sooner  or  later,  in  many 
cases  at  least,  cause  irritation  of  the  enveloping  structures  of 
the  supporting  roots. 


"^tilV.-MlnMl, 


PABALI^ELIXG    DEVIl'E   FOR    rSE   IX  CROWN   AND    ISltllXiE   WORK    (IVORYl 

Various  devices  have  been  suggested  for  deteriniuing 
whether,  in  root  preparation,  the  axial  surfaces  and  root 
canals  are  being  shaped  to  meet  the  requirements. 


A  simple  appliance  is  here  shown,  with  which  the  general 
alignment  or  parallelism  of  the  surfaces  and  canals  invohed 
mav  be  tested. 


''"'■l'H||rfi;j, 


WITH    DISTAL    SL'RFACK    OF 


When  two-  or  more  removable  crowns  with  dowels  are 
emijloyed — the  dowels  fitting  accurately  within  tubes  in  the 
root  canals — the  necessity  for  establishing  accurate  parallel 
alignment  of  the  removable  with  the  stationary  parts  to  which 
they  are  adapted  is  obvious. 


844  nRIDGEWORK 

THE  TELESCOPING  CROWN 

Tliis  form  of  crown  is  applicalilo  to  l)icuspid  and  molar 
teeth,  when  such  teeth  are  properly  aligned,  or  when  they  can, 
by  suitable  preparation,  be  brought  in  correct  alignment  with 
the  other  teeth  involved. 

Briefly,  the  general  steps  of  constructing  a  crown  by  this 
method  are  as  follows: 

The  tooth  is  prepared  as  for  a  shell  crown,  its  axial  sur- 
faces being  slightly  but  uniformly  tapered,  and  its  occlusal 
end  reduced  to  a  flat  plane  sufficiently  to  provide  ample  space 
between  its  face  end  and  the  occluding  teeth  for  not  only  the 
inner  cap,  but  for  a  thick,  heavy,  occlusal  end  to  the  outer  or 
telescoping  crown. 

The  root  cap,  as  before  stated,  should  be  tapered  uni- 
formly from  gingival  to  occlusal  plane,  so  as  to  present  the 
form  of  a  more  or  less  true  frustum  of  a  very  slightly  taper- 
ing cone. 

Its  cervical  end  is  accurately  scribed  to  the  gingival  mar- 
gin and  in  fitting  is  driven  beneath  the  latter  to  the  full  extent 
permissible  by  the  peridental  attachment,  terminating  it, 
however,  on  the  still  flaring,  conical,  axial  surfaces  of  the 
tooth. 

The  occlusal  margin  is  trimmed  even  with  the  flat  tooth 
plane.  To  this  a  disc  is  soldered,  and  its  margins  trimmed 
even  with  the  axial  surfaces  of  the  band,  which  step  com- 
pletes the  assembling  of  the  root  cap. 

The  cap  is  now  mounted  on  a  wooden  mandrel,  with  mod- 
eling compound,  and  its  outer  surface  wrought  into  a  perfectly 
true  cone  by  means  of  a  fine  cut,  flat  file,  after  which  it  is 
smoothly  polished. 

On  removing  the  cap  from  the  mandrel,  its  inner  surfaces 
are  covered  with  a  thin  film  of  whiting  and  water,  in  which  a 
little  gum  arable  is  dissolved,  to  cause  the  whiting  to  adhere 
closely  to  the  metal. 

The  cap  is  now  imbedded  in  moldine,  occlusal  end  down,  a 
swaging  ring  centered  over  it,  and  a  die  cast  directly  into  the 
cap  and  ring.  By  tapping  the  cap  lightly  on  its  sides  with  a 
mallet  the   die   is   released. 

Over  this  root  cap  an  outer  or  telescoping  cap  having  the 
same  taper  as  the  latter  is  closely  fitted.  It  should,  in  fact, 
be  driven  onto  the  root  cap,  thus  insuring  close  adaptation 
between  the  two. 

Its  gingival  end  is  trimmed  so  as  to  terminate  close  to, 
but  not  pass  beneath,  the  gum  margin.  Its  occlusal  end  should 


BRIDGEWORK  845 

be  covered  with  a  disc  similar  to  that  which  completed  the  root 
cap. 

When  in  position  and  its  inner  surfaces  are  in  friction- 
tight  contact  with  the  axial  surfaces  of  root  cap,  its  occlusal 
end  should  not  rest  upon  the  latter,  a  space  of  about  one- 
sixty-fourth  of  an  inch  between  the  two  being  reserved  for 
the  bridge  to  settle  as  the  contact  surfaces  become  worn.  This 
insures  close  gripping  contact  between  the  root  cone  and  the 
inner  walls  of  the  telescoping  crown  under  continued  use. 

The  root  cap  is  returned  to  position  in  the  month,  a  bite 
and  im^jression  taken  and  casts  developed  and  mounted  on 
the  occluding  frame. 

The  occlusal  end  and  axial  surfaces  of  the  outer  cap  are 
covered  with  inlay  wax,  melting  it  on  to  insure  close  union. 

The  wax  on  the  occlusal  end  is  now  softened  and  the 
occluding  teeth  pressed  into  it  and  subjected  to  lateral  move- 
ments as  well,  after  which  these  surfaces  are  carved  to  re- 
quired form. 


The  axial  surfaces  are  developed  by  addition  or  reduction 
of  wax  as  indicated  and  the  crown  given  its  anatomic  form. 

The  outer  cap,  or  crown  proper,  is  now  removed  from 
the  root  cap,  and  after  smoothing  the  wax,  is  invested  and 
cast  the  same  as  ^ny  ordinary  cast  crown. 

THE  SPLIT  DOWEL  CROWN 

The  split  dowel  crown,  combined  with  a  tubed  root  cap, 
is  frequently  employed  in  conjunction  with  the  telescoping 
crown  in  removable  bridge  work. 


S4G  I'.IJIIHilOVVCJIlK 

C-rowns  of  this  t\|ic  arc  iiioi'c  i)articiilarl\'  apiilicaliU;  to 
cuspids  and  large-si zt-d,  siiigie-i-oot  teeth.  Tiiey  may,  how- 
ever, be  applied  to  roots  of  any  class,  under  favorable  condi- 
tions.   The  general  constructive  steps  are  as  follows: 

The  root  is  prepared  as  for  an  ordinary  cap  crown,  ex- 
cept that  the  lingual  side  is  not  reduced  to  the  margin  of  the 
gum.  In  fact,  it  sliould  jiroject  one-sixteenth  of  an  inch  be- 
yond the  margin,  so  Ihaf  tlic  lialf  band  of  the  crown  base  may 
not  encroach  n])()ii   Ihc  hitlci'. 

A  band,  usually  of  coin  gold,  or  i)late  etiually  as  jiard 
and  high  fusing,  is  formed  and  fitted  beneath  the  gum  margin. 
The  incisal  end  of  the  band  is  ti-imiiicd  even  with  the  face  end 
of  the  root,  to  whicli  a  disc  of  gold  of  similar  character  is 
attached,  either  with  high  fusing  solder  or  by  sweating. 

The  cap  is  perforated  for  the  reception  of  a  tube  whidi 
serves  the  double  purpose  of  anchoring  the  cap  to  the  root, 
and  for  the  reception  of  the  crown  dowel  as  well. 

The  size  of  the  dowel  having  been  decided  upon,  a  hard- 
ened steel  mandrel  of  corresponding  diameter  is  selected,  and 
around  this  a  piece  of  coin  gold  ])late  is  formed  into  a  tube 
and  soldered  with  high  grade  solder. 

A  reamer  of  the  exact  size  as  the  dowel  is  now  passed  into 
the  tube  and  its  inner  walls  reamed  true,  and  to  exact  size. 

One  end  of  the  tube  is  closed  with  a  small  disc  of  gold 
plate,  the  peripheral  surjilus  trimmed  even  with  the  outer  sur- 
faces of  the  tube,  and  its  corners  chamfered  or  roun<le(l 
slightly. 

The  dowel  is  formed  from  half-round  clasp  metal  wire, 
as  follows : 

A  piece  of  half-round  wire,  slightly  larger  than  the  dowel 
and  about  one  and  one-half  inches  long,  is  bent  in  the  form 
of  a  loop,  the  two  ends  bent  to  lie  in  close  contact  from  their 
terminals  inward,  for  about  one-fourth  inch,  the  remainder 
of  the  loop  being  open. 


A  little  coin  gold  is  now  ai>plied  in  the  V-shaped  space, 
next  the  contact  area,  and  the  two  ends  united  by  fusion.  It  is 
necessary  to  use  coin,  or  equally  high  fusing  gold,  to  effect 
this  union,  to  avoid  the  split  portion  of  the  dowel  from  being 
united  in  subsequent  soldering  operations. 

The  loop  portion  of  the  half-round  wire  is  now  carefully 


BRIDGEWORK  847 

battered  down  with  a  small  rawhide  mallet,  in  a  half-round, 
grooved  anvil,  until  the  flattened  surfaces  of  the  wire  are  iu 
contact. 

The  dou])l(Hl  wire,  with  ends  united,  now  presents  the 
appearance  of  a  round  wire,  about  three-fourths  of  an  inch 
long.  This  is  passed  through  gradually  decreasing  holes  in 
the  draw  plate,  until  it  is  brought  to  very  nearly  the  reipiired 
diameter  to  enter  the  tube. 

The  final  reduction  to  exact  size  is  accomplished  by  plac- 
ing the  wire  in  a  pin  vice,  resting  it  in  a  grooved  block,  and 
with  a  fine  cut,  flat  file  carefully  reducing  it  under  rotary 
action. 

It  should  be  tested  from  time  to  time  in  the  tube,  and 
when  it  just  begins  to  enter  the  latter,  the  tile  marks  are  re- 
moved with  fine  flour  of  emery  cloth  or  crocus.  The  soldered 
end  of  the  dowel  may  be  placed  iu  a  true  running  lathe  chuck, 
and  the  final  finish  given  by  api:)lying  the  fine  polishing  cloth 
against  it  by  means  of  a  flat  stick,  or  by  laying  it  on  the  flat, 
fine  file  and  running  the  lathe  at  high  speed. 

The  dowel  should  fit  the  tulie  with  friction-tight  contact, 
yet  not  so  tightly  as  to  iirccludc  its  ready  introduction  and 
removal. 

ASSEMBLING  THE  PARTS 

An  opening  is  made  in  the  root  cap  for  the  reception  of 
the  tube,  as  before  stated.  This  opening,  although  in  some 
cases  it  may  be  located  directly  in  line  with  the  canal,  is  usu- 
ally made  a  little  to  the  lingual,  and  the  canal  reamed  accord- 
ingly, so  that  the  dowel  may  not  interfere  witii  proper  adjust- 
ment of  the  facing. 

In  this  case,  as  in  that  of  all  cap  and  dowel  crowns,  the 
entrance  to  the  root  canal  can  be  reamed  out  slightly  and  the 
margins  of  the  cap  around  the  tube  opening  dei)ressed  into  the 
countersunk  area.  This  adds  strength  to  the  attachment  be 
tween  cap  and  tube,  and  further  permits  tlie  tube  opening  to 
be  countersunk  for  the  more  ready  introduction  of  the  dowel. 

The  cap  is  set  in  position  on  the  root,  the  tube  passed 
through  it,  into  the  root  canal,  which  previously  has  been  en- 
larged to  receive  it,  and  an  impression  taken  to  secure  the  re- 
lation between  the  two. 

When  secured^  and  a  small  investment  model  formed,  the 
two  are  united  in  the  same  manner  as  an  ordinary  cap  and 
dowel.  The  tube  should  be  filled  with  investment  previous  to 
soldering  to  prevent  its  becoming  filled  with  solder  during  this 
operation. 


848  BRIDGEWORK 

CONSTRUCTING  THE  CROWN  BASE 

Usually  a  lingual,  lialt'-band  c-a))  is  adapted  to  the  root 
cap  to  serve  as  a  crown  base  and  to  which  the  split  dowel  is 
attached.  Such  a  caj)  affords  resistance  to  outward  displace- 
ment, and  obviates  the  presence  of  a  second  band  beneath  the 
gum  margin. 

For  convenience  in  constinu-iion  a  full  band  is  adapted  to 
the  periphery  of  the  root  cap,  to  which  a  disc,  or  floor,  is  con- 
formed and  the  two  united  with  high  grade  solder  on  the  lin- 
gual, but  not  on  the  labial  half  of  the  cap. 

After  uniting  the  band  and  floor  of  the  telescoping  cap 
and  completing  its  adaptation  to  the  root  cap,  the  floor  is  per- 
forated for  the  reception  of  split  dowel  of  the  crown.  This 
should  be  in  perfect  alignment  with  the  opening  in  the  tube 
of  the  root  cap. 

The  telescoping  cap,  or  crown  base,  is  adjusted  to  the  root 
cap,  the  dowel  having  been  cut  to  suitable  length,  its  free  or 
divided  end  is  inserted  in  the  tube  to  full  depth,  a  small  im- 
pression taken  to  secure  correct  relation  between  the  two,  and 
in  which  they  are  placed  previous  to  running  up  the  cast  in 
investment. 

Since  subsequent  soldering  operations  must  follow,  the 
union  between  cap  and  dowel  should  be  made  with  high  grade 
solder,  or  the  special  plate  recommended  for  this  purpose  in 
the  section  on  metallurgy. 

The  labial  half  of  the  band  is  removed  and  the  terminals 
of  the  lingual  half  neatly  finished  against  floor.  This  may  be 
easily  accomplished  if,  when  soldering,  care  was  observed  to 
prevent  the  labial  joint  area  from  filling  with  solder.  Wein- 
stein  suggests  notching  the  incisal  edge  of  the  band  before 
soldering,  the  break  in  the  continuity  of  surfaces  thus  pre- 
venting the  solder  being  drawn  to  the  labial. 

When  the  several  steps  have  been  carried  out  accurately, 
the  floor  of  the  crown  base  will  rest  firmly  on  the  root  cap,  its 


A  BAND,  NOTCHED  TO  PREVENT 

SOLDER  FLOWING   TO  LABIAL 

HALF  OF  BAND 

lingual  half  band  in  close  contact  with  that  of  the  cap  over 
which  it  telescopes,  while  the  dowel  fits  with  almost  friction- 
tight  contact  within  the  tube. 


BRIDGEWORK 


On  this  base  a  crown  of  any  desired  type  is  built  to  meet 
the  requirements  of  the  case,  which,  when  completed,  would 
be  called  a  half  hand,  split  dowel  crown. 


HALF  BAND,  SPLIT  DO^VEL 
CBOWN.  PARTIALLY  KEMO^TED 
PKOM    POSITION    OX    HOOT    CAP 


CONSTRUCTING  THE  SADDLE 


The  saddle  may  be  swaged  by  methods  outlined  under 
partial  denture  construction  or  a  wax  model  of  the  desired 
form  may  be  developed  and  cast.  When  the  latter  plan  is 
followed,  ample  though  not  very  large  sprues  should  be  pro- 
vided for  the  ingress  of  gold  into  the  matrix,  two  or  three 
being  sufficient  for  the  purpose. 

"When  constructed,  the  saddle  is  adjusted  to  the  border, 
the  two  complete  crowns  being  in  position  on  their  respective 
roots,  and  an  impression  taken  by  the  pressure  method  as  de- 
scribed on  page  499. 

The  crowns  should  come  away  with  the  impression,  or, 
if  not,  they  are  set  in  their  respective  matrices  and  a  cast  of 
some  reliable  investment  material  formed. 

The  saddle  and  crowns  are  now  firmly  united,  and  if  not 
previoiisly  provided  for,  attachments  should  be  made  for  vul- 
canite anchorage.  These  attachments,  however,  are  omitted 
when  the  structure  is  to  be  composed  entirely  of  metal  and 
porcelain. 

The  now  assembled  and  uiiited  metal  framework  is  re- 
turned to  the  mouth  for  final  bite  and  impression.  The  metal 
structure  is  correctly  placed  in  its  matrix  in  the  impression, 


850  BUHKnOWORK 

the  I'oot  caps  rciiuiNcd  and  set  in  llicir  n'sjx'ctivc  (Tdwiis  and 
a  cast  oi'  one  of  tlic  liai'd  materials  t'ornicd. 

ATTACHING  THE  TEETH 

Plain  or  giun  section  teeth  may  lie  ,i;i-ound  to  position  and 
attached  to  the  saddle  in  the  usual  manner,  or  some  of  the 
replaceable  type  of  teeth  are  frequently  used.  When  this  plan 
is  followed,  gold  sockets  are  adapted  to  the  bases  of  the  sev- 
eral teeth,  the  teeth  with  sockets  attached,  waxed  in  position, 
the  porcelain  removed,  the  case  invested  and  the  union  of 
sockets  to  saddle  accom|)lished  by  flowing-  plate  or  high  grade 
solder  between  and  to  complete  tlie  contoui-  of  the  case. 

FINISHING  THE  CASE 

The  steps  of  iinishing  are  similar  to  those  followed  in 
regular  bridge  or  partial  denture  work,  the  idea  being  to 
remove  all  surplus  material,  remove  sharp  margins  that  may, 
by  their  presence,  produce  irritation,  and  finish  the  case  as 
smoothly  and  perfectly  as  the  most  finished  ]iiece  of  jewelry 
ever  produced. 

SETTING  THE  ROOT  CAPS 

In  cases  of  the  tyjie  under  consideration,  setting  the  root 
caps  is  ])ractically  the  last  operation.  This  is  purposely  de- 
layed until  this  time,  so  that,  should  any  warpage  occur  in  the 


<i-       % 


BRIDGE  OOMPOSED  OF  HALF  BAND. 
SPLIT  DOWEL  BICUSPID  CBOWTJ,  A 
TELESt'OPINO  MOLAR  CROWN  AND  TWO 
Dl'MMIES  COMPLETED,  ROOT  CAPS  IN 
POSITION 


final  assembling  and  soldering  of  the  structure,  the  exact  rela- 
tion between  root  caps  and  their  telescoping  crowns  may  be 
preserved. 


BRIDGEWORK  851 

The  caps  are  set  as  follows: 

Tiie  interior  of  the  telescoping  crowns  is  coated  with 
a  thin  tilm  of  oil,  the  root  caps  cleansed  and  dried  and  set  in 
position  in  their  respective  crowns,  cement  applied  in  their 
interior  and  to  the  roots,  and  the  entire  strnctnre  carried  to 
position  and  forced  to  place,  first  with  direct  pressnre  and 
immediately  tested  with  the  occluding  teeth  to  see  that  it  is 
correctly  seated. 

GENERAL  REMARKS 

The  details  of  this  most  excellent  system  of  removable 
bridge  work  has  been  presented  in  book  form  by  Dr.  F.  A. 
Peso,  a  man  most  eminently  qualified  by  years  of  successful 
experience  to  present  it  in  a  clear,  logical  and  practical  man- 
ner. He  is,  in  fact,  responsible  for  the  development  of  the 
finer  and  more  accurate  details,  a  neglect  of  which  would  re- 
sult in  indifferent  success,  or  total  failure. 

Coin  gold,  because  of  its  hardness  and  comparatively  high 
fusibility,  is  recommended  for  root  caps,  tubes  and  telescop- 
ing caps  as  well,  and  highly  platinized  gold  for  split  dowels. 

In  initial  operations,  when  possible,  the  joints  are  siveated 
to  obviate  danger  of  fusion  in  subsequent  operations.  When 
union  cannot  lie  thus  effected  the  highest  fusing  solder  pos- 
sible to  use  on  tlic  jilale  with  safety  is  (■mi)l()yed,  for  reasons 
before  stated. 

THE  INLAY  CLASP  ATTACHMENT 

A  combined  inlay  clasp  attachment,  suggested  by  Dr.  II. 
J.  Goslee,  can  at  times  be  used  to  advantage  in  removable 
bridge  work  when  stress  of  mastication  is  not  excessively 
heavy.  This  can  best  be  illustrated  by  descriliing  the  applica- 
tion of  such  an  attachment  to  a  crown,  in  this  case  a  lower 
first  molar. 

The  tooth  is  i)rei)ared  slightly  cone  shape,  to  which  a 
deep  root  cap  or  thimble  is  fitted,  similar  to  that  used  in  the 
telescoping  crown.  Tnlay  wax  is  now  applied  to  the  occlusal 
and  axial  surfaces  and  carved  to  meet  anatomic  and  occlusal 
requirements. 

From  the  axia-occlnsal  third  of  the  ci'own,  tlie  wax  is  re- 
moved from  the  axial  surfaces  to  form  a  shoulder  depression 
for  the  reception  of  the  clasp.  A  dovetail  depression,  similar 
to  an  occlusal  step  cavity,  is  cut  in  the  occlusal  surface  of  wax. 
The  axial  walls  of  both  inlay  step  and  outer  surfaces  of  re- 


852  BRIDGEWORK 

duced  portion  of  the  crown  are  rendered  parallel  or  slightly 
convergent  to  permit  the  withdrawal  of  the  wax  pattern  for 
the  clasp  attachment  later  on. 

The  crown,  minus  the  portions  removed,  is  cast,  and  fin- 
ished. Wax  is  filled  in  the  removed  areas  and  carved  to  com- 
plete the  anatomic  form  of  the  crown,  after  which  it  is  care- 
fully separated,  invested  and  cast.  When  made  sufficiently 
rigid  and  wide,  and  the  walls  of  the  crown  which  it  embraces 
are  formed  practically  parallel,  this  attaclmient  grasps  the 
crown  very  firmly. 

An  attachment  of  this  type  may  be  combined  with  an- 
other of  similar  style,  or  combined  with  the  telescope,  or  the 
half  band  dowel  crown,  in  the  construction  of  small  bridges. 

A  tube  attached  to  the  inlay  seat  of  the  crown,  extending 
toward  or  into  the  pulp  chamber,  for  the  reception  of  a  split 
dowel  anchored  in  the  inlay,  will  add  greatly  to  the  stability 
of  the  appliance. 

THE   SPLIT    DOWEL,    LINGUAL   HALF   CROWN 

This  attachment  is  really  a  removable  Carmichael  attach- 
ment, combined  with  a  split  dowel,  applied  to  a  partial,  arti- 
ficial crown.    The  writer  is  unable  to  state  who  first  suggested 


LINGUAIi       VIEW      OF       CKOWN. 

CERVICAI,     VIEW     OF     LINGUAL 

HALF   CBOWN 


BUCCAL       VIEW       OF        CROWN. 

CERVICAL        VIEW       OF        HALT 

CROWN,  SHOWING  SPLIT  DOWEL. 

SLIGHTLY  MODIFIED 


it  as  a  removable  bridge  anchorage.  When  accurately  con- 
structed, in  well-selected  cases,  it  is  a  very  rigid  and  service- 
able attachment.  It  is  particularly  applicable  to  bicuspids 
and  molars. 


BRIDGEWORK  853 

CONSTRUCTION  OF  THE  HALF  CROWN 

The  crowu,  or  remaining  portion,  is  reduced  to  the  gin- 
gival, the  peripheral  ring  of  enamel  removed  and  the  root  end 
prepared  decidedly  cone  shape,  and  for  which  a  root  cap  is 
swaged,  by  metliods  previonsly  outlined.  By  preparing  the 
pnlp  chamber  walls  with  a  slight  flare  oiitwardly,  an  inside 
shoulder  may  be  developed  on  the  root  cap,  which  will  hold 
the  latter  in  position,  regardless  of  the  pronounced  flare  of 
the  root  periphery. 

One  or  more  dowels  are  passed  through  the  cap  and  into 
the  root  canals  and  attached  as  in  any  similar  case. 

Usually  a  porcelain  facing  is  ground,  backed  and  applied 
to  the  root  cap  in  proper  alignment  with  the  proximating 
teeth.  The  backing  should  be  extended  so  as  to  protect  the 
buccal  marginal  ridge  of  porcelain  from  stress. 

Inlay  wax  is  melted  against  the  backing  and  on  the  root 
cap  in  excess  of  what  will  be  required  to  form  the  lingual 
shoulder,  and  when  hardened  is  carved  somewhat  in  the  form 
of  a  half  cylinder,  or  very  slightly  tapering  cone,  or  rectangu- 
lar block,  the  axis  of  which  lies  parallel  with  the  long  axis  of 
the  tooth. 

The  backing  itself  would  be  thickened  with  wax,  specially 
the  beveled  portion  extending  over  the  marginal  ridge.  Usu- 
ally the  outer  half  of  the  buccal  cusps  are  developed  in  this 
wax. 

The  sides  of  the  cylinder  terminate  within  the  mesial  and 
distal  surfaces  of  the  crown,  the  angle  between  the  backing 
and  half  cylinder  being  grooved  to  form  a  sort  of  dovetail,  by 
means  of  which  the  lingual  attachment  is  locked  in  position. 

The  occlusal  end  of  the  cylinder  is  reduced  sufficiently  to 
allow  space  for  the  thick  occlusal  cap  to  the  attachment. 

The  gingival  end  of  the  cylinder  is  squared  and  a  fiat 
cervical  shoulder  is  thus  formed  on  which  the  lingual  half  of 
the  crown  may  rest. 

The  cylinder,  as  before  stated,  should  converge  some- 
what from  gingival  toward  occlusal  areas,  to  permit  the  pat- 
tern for  the  lingual  half  crown  to  be  removed. 

A  closed  end.  tube,  of  suitable  size  to  receive  the  split 
dowel,  and  somewhat  longer  than  required,  is  heated  and 
pressed  into  the  occlusal  end  of  the  wax  cylinder,  until  its 
closed  end  rests  on  the  crown  base.  Care  should  be  taken  to 
adjust  it  parallel  with  the  line  of  direction,  of  introduction 
and  removal  of  the  half  crown. 


854  BRIDGRWORK 

The  facing'  is  now  removod  and  cai'ljon  jioiiits  inserted  in 
the  pin  holes,  the  case  invested  and  cast,  after  wliich  it  is  fin- 
ished with  phig  finishing  burs,  stones,  discs,  etc. 

The  carbon  points  are  drilled  out,  the  facing  fitted  in 
position,  its  pins  roughened,  when  it  can  be  tem])orarily  set 
in  position  with  gutta  percha  while  finishing  the  crown.  This 
is  essential,  for  if  the  metal  parts  are  ])olished  without  the 
facing  being  in  position,  the  joint  area  lu'tween  porcelain 
and  backing  will  be  impaired. 

Later  on  in  soldering  the  assembled  bridge,  the  facing 
is  removed  when,  after  comi)letion  of  the  metal  structure,  it 
is  permanently  set  with  cement. 

CONSTRUCTION  OF  THE  LINGUAL  HALF  CROWN 

A  Split  dowel,  slightly  longer  than  required,  is  adjusted  to 
tlie  tube  within  the  cylinder,  the  surfaces  of  gold  against  which 
the  lingual  half  crown  rests  are  coated  with  a  thin  film  of  oil 
and  inlay  wax  applied  in  sufficient  bulk  to  complete  the  re- 
quired contour.  By  means  of  a  metal  matrix  slightly  longer 
than  th«  crown,  an  excess  of  softened  inlay  wax  can  be  ap- 
l)lied  and  forced  into  every  angle,  groove  and  irregularity. 
On  removal  of  the  matrix  the  excess  can  l)e  carved  off  and 
the   crown   developed   to   required   anatomic   form. 

The  carved  model  of  the  half  crown  is  carefully  removed, 
care  being  taken  to  bring  the  dowel  away  with  it  without  dis- 
torting the  relation  lietween  the  two.  Should  it  become  loos- 
ened, the  wax  immediately  around  it  must  be  melted  and  the 
model  returned  to  the  metal  parts  for  final  adjustment,  when 
it  may  be  removed,  invested  and  cast. 

FINISHING  THE   ATTACHMENT 

The  natural  contraction,  together  with  the  more  or  less 
nodular  surfaces  i)resent,  demands  the  exercise  of  the  greatest 
care  in  finishing,  to  avoid  cutting  away  unnecessary  gold,  be- 
fore the  actual  points  of  interference  are  discovered. 

When  an  amalgam  die  has  lieen  formed  on  which  to  con- 
struct the  root  cap,  the  crown  can  be  returned  to  it,  and  bj^ 
tapping  the  lingual  half  crown  in  the  direction  of  the  long  axis 
of  the  tooth  and  removing,  burnished  spots  will  disclose  the 
points  of  Interference. 

These  attachments  are  used  in  conjunction  with  and  with- 
out saddles,  if  conditions  demand  their  application  in  such 
manner. 


BRIDGEWORK  855 

MODIFICATION   OF   THE   TELESCOPING   MOLAR   CROWN 

A  modification  of  the  telescoping,  shell  molar  crown, 
combined  with  si)iit  dowel  crown,  is  sometimes  employed  in 
extensive  bridges  of  the  compound  or  complex  types.  It  is 
not  adaptable  to  simple  liridges  for  the  reason  that  the  abut- 
ment being  in  nearly  straight  alignment,  torsional  strain  will 
unseat  the  ap])liance. 


Instead  of  a  deep  root  cap  with  a  telescoping  cap  of  prac- 
tically the  same  de'jith  adapted  to  it,  the  molar  root  is  reduced 
to  within  a  short  distance  of  the  gingiva  and  fitted  with  a 
doweled  cap  having  practically  parallel  sides. 

On  the  top  of  the  cap  a  Gilmore  attachment  is  soldered, 
the  flanges  presenting  occlusally. 


BRIDGBWORK 


A  crown  is  constructed  the  base  of  which  rests  upon  the 
root  cap  and  telescopes  over  it  sliglitly. 

In  the  central  portion  of  the  crown  base  is  a  recess  which 
receives  the  flanges  of  the  (rihuore  attachment,  while  extend- 


'AL    VIEW    OF    CAST    AND    BRinCE 


ing  across  the  recess  and  fixed  withiu  the  body  of  the  crown 
is  a  IJr-gauge  bar. 

This  bar  is  so  adjusted  that,  when  the  crown  is  seated  on 
the  root  cap,  the  flanges  of  the  Gilmore  attachment  grasp  it 
and  thus  aid  in  retention  of  the  appliance. 

The  appliance  here  illustrated  is  the  work  of  J.  B.  Rideout 
of  Minneapolis,  who  kindly  loaned  it  to  the  writer. 

Still  other  combinations  of  the  various  attachments  men- 
tioned are  possible,  depending  upon  the  ingenuity  of  the 
prosthetist  and  his  skill  in  carrying  out  the  ideas  conceived. 

REPAIRING  CROWNS   AND  BRIDGES 

The  most  common  accidents  which  occur  to  crowns  and 
bridges,  when  permanently  set  and  subjected  to  use,  are  frac- 
ture of  the  porcelain  teeth  or  facings  and  fracture  of  some 
portion  of  the  metal  structures. 

When  a  crown  or  bridge  can  be  removed  from  the  sup- 
porting roots  or  teeth,  without  injury  to  itself  or  to  them,  re- 
pair can  be  most  easily  accomplished  out  of  the  mouth. 

Since,  as  is  most  frequently  the  case,  removal  of  a  crown 
or  bridge  is  accompanied  by  more  or  less  mutilation  of  the 
metal  parts,  or  subjecting  the  foundation  supports  to  undue 
strain,  the  general  method  of  procedure  is  to  repair  such  cases, 
if  possible,  without  removal. 


BRIDGEWORK  857 

Tlie  replacement  of  dislodged  facings  can  frequently  be 
accomplished  quite  as  well  in  the  mouth  as  by  removal  of  the 
substitute,  with  some  of  the  available  repair  outfits.  Some  of 
the  common  methods  of  repair  will  now  be  outlined. 

REPLACING   PORCELAIN   FACINGS— THE   ASH,   FLAT  BACK 
REPAIR   FACING 

One  of  the  simplest  methods  of  replacing  a  flat  back 
porcelain  facing  where  the  pins  of  the  fractured  facing  re- 
main with  and  project  from  the  old  backing  is  accomplished 
by  grinding  and  fitting  to  the  metal  parts,  an  Ash  flat  back 
repair  tooth  shown  under  "Various  Forms  of  Teeth." 

When  the  pins  are  short  and  practically  headless,  they 
may  be  threaded  and  a  small  washer  attached  to  each  to  in- 
crease their  hold  in  the  cement  which  fills  the  dovetail  space 
within  the  porcelain. 

In  case  the  tooth  pins  have  broken  or  are  weak,  with  suit- 
able drill  and  tap,  threaded  holes  may  be  made  in  the  labial 
or  buccal  face  of  the  old  backing  to  coincide  with  opening  in 
the  porcelain  and  screw  wire  of  iridio-platinum  or  platinized 
gold  inserted  for  anchorage  purposes.  The  pins  should  be  as 
long  as  the  depth  of  dovetail  space  in  the  porcelain  will  re- 
ceive, or  they  may  be  cut  somewhat  long,  and  after  being 
inserted  in  the  backing,  bent  inwardly  toward  each  other  to 
form  a  sort  of  staple  anchorage. 

When  the  pins  are  adjusted,  cement  is  applied  to  both 
backing  and  facing,  and  the  latter  forced  and  held  in  place 
until  the  cement  has  hardened,  after  which  the  surplus  is 
removed. 

THE  DIMELOW  FACING 

A  facing  of  this  type  is  applied  in  repair  work  as  fol- 
lows: 

The  porcelain,  if  any  remains  of  the  old  facing,  and  the 
pins,  are  removed  from  the  backing. 

A  facing  is  selected  and  ground  to  meet  requirements.  A 
very  small  quantity  of  wax  is  m.elted  on  the  old  backing  in  that 
area  which  corresponds  to  the  position  of  the  pinholes  in  the 
facing. 

While  the  wax  is  soft,  the  facing  is  moistened  and  pressed 
firmly  against  it.  '  On  removal,  the  position  for  the  pinholes 
will  be  indicated  by  the  raised  points  of  wax  which  entered 
the  holes.  These  points  are  carefully  marked  on  the  backing 
with  a  sharp-pointed  instrument.  A  bi-beveled  drill  is  selected, 
corresponding  in  size  with  the  openings  in  the  porcelain,  and 


858  BRIDGEWORK 

witli  this  llic  holes  aic  (li'ilhMl  in  a  liiii^uo-gingival  diroclion  to 
porrcspoud  witii  tlie  an.niilar  iiu'liiiatioii  of  tho  holes  in  th(! 
facing. 

Two  small  pins  made  of  threaded  clasp  metal  wire,  which 
will  fit  the  holes  closely,  are  cut  of  suitahle  length,  extending 
to  the  full  depth  in  the  holes  of  both  backing  and  facing. 

Cement  is  applied  in  the  holes  of  both  backing  and  facing 
and  over  the  contact  surfaces,  the  pins  set  in  ])osili((n  in  the 
backing,  the  facing  adjusted  and  forced  to  ]>la('e. 

THE  STEELE  REPAIR  OUTFIT 

This  set  of  a])pliances,  consisting  of  drills,  ta])s,  headed 
screws,  and  a  screwdri\'er,  is  intended  to  be  used  in  conjunc- 


tion with  the  Steele  facing  in  repair  work.     The  method  of 
application  is  siiuple. 


II.D    IMXS    REMOVED 


The  old  pins  and  any  of  the  old  facing  present  are  re- 
moved and  a  Steele  facing  of  suitable  form  and  color  selected 


BRIDGEWORK  859 

and  grouud  to  meet  requirements.  It  will  usually  be  found 
more  convenient,  and  a  better  rejiair  can  be  made  by  select- 
ing a  facing  slightly  wider  and  longer  than  the  space  it  is  to 
fill,  and  adapting  it  by  grinding  rather  than  to  select  one  that 
will  drop  in  position  without  titting.  A  little  wax  is  applied 
in  the  central  area  of  tlie  ))a('king  extending  from  the  crown 
I)ase  to  near  tlie  incisal  ciliic. 


Tliis  should  be  melted  against  the  l)acking,  and  while  soft 
the  selected  facing,  having  been  ground,  is  pressed  tirmly 
against  it  being  careful  to  see  that  it  is  in  correct  alignment. 


JlKI.TINt;  THE  WAX  IIX  THE  BACKINO 


IN'ST     THE 


On  remova-1  of  the  facing  a  ridge  will  be  seen  on  the  wax 
where  it  entered  the  slotted  groove  of  the  porcelain. 

With  a  sharp-pointed  instrument  two  points  are  marked 
on  the  backing,  one  near  the  ciown  l)ase,  the  other  the  incisal 


S60 


BRIDGEWORK 


termination  of  tlie  wax  ridge.  These  points  indicate  the  posi- 
tion for  the  pins.  The;  ineisal  point  should  be  marked  slightly 
witliin  the  ridge. 


FAfINd     KEIKIVKD.     SlIOUINC     TIIK     RIDGE 

OP    WAX   WHERE    IT    ENTERED    THE 

GROOVE  OP  THE  PACING 


Holes  are  now  drilled  for  tlic  rc('(']>ti(»ii  of  tlic  licaded 
screws  at  the  points  indicated. 

Since  the  holes  must  be  very  small  and  the  drills  corre- 
spondingly so,  special  care  must  be  exercised  to  avoid  break- 
ing the  drill  in  the  backing,  an  accident  which  is  very  liable 
to  occur. 


WAX     RUKiK     I'EUFUKATlvD     TO     INDICATE 
POSITION    FOR    THE     SCREWS 


DRILLING  THE    HOLES   IN  BACKING 


The  holes  are  now  threaded  with  the  tap  for  the  reception 
of  the  screws,  and  the  latter  set  in  position. 

The  facing  is  applied,  passing  it  over  the  screws  from  an 
incisal  direction.  If,  in  its  passage  to  place,  interference 
occurs,  locate  the  cause,  which  is  proliably  due  to  setting  tlie 


BRIDGEWORK 


screws  too  deeply  in  the  backing,  thus  bringing  their  heads 
too  close  to  the  interior  wall  of  the  slot  of  the  facing. 


Till,     lliil.l.: 


If  too  long,  they  may  prevent  the  facing  resting  against 
the  backing.  The  screw  heads  should  be  so  set  as  to  permit 
the  backing  sliding  readily  to  place  yet  close  enough  to  avoid 
any  labial  move  of  the  facing  from  the  backing  when  once 
seated. 


THE  FAflXl!  SET  IN  I'OSITIOX  ON  ISACKINCi 

Cement  is  now  applied  around  the  pins,  over  the  backing,  in 
the  groove  of  the  facing,  and  the  latter  is  forced  in  position. 

THE  BRYANT  REPAIR  OUTFIT 

This  set  of  appliances  consists  of  threaded  taps,  a  taper 
reamer,  a  split  end,  screw  driver,  and  taper  nuts,  which,  in  the 
replacement   of  a  flat   back,   porcelain   facing,   are  used   as 

follows: 


nRIDGIOWORK 


Tlic  old  jiins  aro  removed,  a  layer  of  wax  is  applied  to 
tlic  hacking,  into  wliich  the  i)iiis  of  tiie  selected  facing  are 
])ressed,  to  indicate  the  position  for  drilling  the  holes. 

'I'iie  holes  are  drilled  entirely  through  the  l)acking  with 
a  bi-heveled  drill  a  little  Ini-ger  than  the  diainetei-  of  the 
])latinum  pins. 

The  facing,  which  should  lie  slightly  larger  than  actually 
reijuired.  to  ]iennit  of  icduction  foi'  exact  fitting,  is  gi'ound 
to  place. 

Tile  lingual  ends  of  the  holes  in  the  l)acking  are  enlarged 
with  the  taper  reamer  by  means  of  tlie  riglit  angle  liand  piece. 
They  should  be  large  enough  to  receive  the  taper  nuts  so  that 
the  small  ends  of  the  latter  may  approach  close  to,  but  not 
project  through,  the  labial  surface  of  tlie  backing.  Should  the 
small  ends  pass  through  tlie  labial  of  tlie  backing,  tliey  must 
be  reduced  by  grinding,  or  the  facing  cannot  lie  drawn  tightly 
against  the  backing. 


THK    liK\l\l     UH    \1I{    (II    HIT.    SH(l\VIX(i    TAPS,    KKAMEIt.    SCREWDRIVEK.    XUTS.    ETC. 

Threads  are  cut  on  the  pins,  using  first  No.  1  tap,  which 
cuts  a  partial  thread,  and  followed  by  No.  2  tap,  wliicli  cuts 
the  thread  to  full  depth. 

The  pins  should  be  oiled  and  the  taps  applied  carefully 
to  prevent  the  ]iins  being  twisted  off  during  the  cutting  of  tlie 
threads. 

Cement  is  now  applied  to  the  backing,  and  the  facing 
adjusted  in  position. 

A  nut  is  dro])ped  into  the  small  sleeve  of  the  screw  driver, 
small  end  outward,  applied  to  one  of  tlie  pins  and  tightened, 
after  which  tlie  other  is  applied  in  like  manner. 

This  step  should  be  carried  out  quickly,  liefore  the  cement 
has  perceptibly  hardened,  otherwise  the  nuts  cannot  be  forced 
into  close  contact  with  the  backing  and  the  facing  will  soon 
become  loosened. 


BRIDGEWORK  863 

The  facing  should  be  held  by  positive  mechanical  anchor- 
age, developed  by  jamming  the  nut  tightly  against  the  walls 
of  the  opening  in  the  backing,  on  the  lingual  side,  while  the 
porcelain  should  rest  firmly  against  the  backing  labially. 

The  cement  is  used  only  as  a  sealing  agent,  to  close  the 
space  between  porcelain  and  metal. 

When  hardened,  the  surplus  cement  is  cleared  away,  the 
projecting  ends  of  the  nuts  on  the  lingual  surface  reduced 
with  stones,  and  tlic  rough  surfaces  polislied  with  fine  discs. 

LONG  PIN  FACINGS  USED  IN  REPAIRS 
METHOD  OF  REPLACEMENT  SUGGESTED  BY  DR.  R.  W.  STARR 

When  the  backing  of  a  crown,  or  a  bridge  dummy  is  ex- 
ceptionally thick,  so  that  the  pins  of  the  facing  will  not  readily 
engage  with  the  Bryant  nuts,  as  ordinarily  applied,  the  mode 
of  attachment  may  be  varied  as  follows : 

Place  a  piece  of  i)latinum  foil  lietween  and  around  the 
pins,  and  bend  the  latter  down  in  close  contact  with  it,  so 
that  they  lie  parallel  and  touch  each  other. 

Invest  the  porcelain  and  unite  the  pins  with  solder.  Flat- 
ten them  somewhat  by  filing,  and  square  u])  the  sides  of  the 
rectangular  pi'ojection  which  they  now  form. 

Eemove  the  old  pins  from  the  backing,  apply  wax  and 
press  the  jjartially  prepared  facing  into  it  to  secure  an  im- 
pression of  the  ridge  formed  by  the  united  pins. 

A  groove  is  cut  in  the  backing,  of  the  same  dimensions 
as  outlined  in  the  wax,  of  sufficient  depth  to  receive  the 
folded  pins  and  let  the  facing  rest  firmly  against  the  backing. 

The  facing  is  now  ground  to  correct  position,  which  previ- 
ously could  not  be  done,  because  the  facing  was  prevented 
from  coming  in  contact  with  the  l)ai'king  on  account  of  the 
pins. 

Drill  a  hole  through  the  backing,  locating  it  in  the  center 
of  the  groove  which  receives  the  pins. 

Apply  a  thin  film  of  oil  to  the  backing,  in  the  bottom  of 
the  groove,  and  to  the  sides  of  the  opening  through  the  backing. 

Melt  a  little  sticky  wax  to  the  pins,  opposite  the  opening 
in  the  backing,  and  set  the  facing  in  position. 

A  piece  of  iridio-platinum  or  clasp  metal  wire,  about  16  g., 
preA'iously  threaded,  and  slightly  longer  than  required,  to 
pass  throng]]  the  backing,  is  heated,  and  passed  through  the 
opening,  from  the  lingual,  until  it  enters  the  wax  and  rests 
against  the  pins. 


BRIDGRWORK 


The  heated  screw  wire  melts  the  wax,  which,  wlien  cold, 
unites  it  with  metal  ridge  of  the  pins,  and  the  two  may  be  re- 
moved in  a  labial  direction  in  correct  relation  to  eacli  other, 
after  which  they  may  be  invested  and  soldered 


LEFT.    PINS    BENT    AND   SCREW    ATTACHED, 
RIGHT,     ItArKING     SLATTED    AND     DRILLED 

FOR  heception  of  facing 


LEFT,  PACING  IN  POSITION.  SURPLUS 
SCREW  AND  NUT  REDUCED  AND  POLISHED. 
RIGHT.  LABIAL  APPEARANCE  OF  FACING 


The  lingual  end  of  the  hole  in  the  backing  is  enlarged  with 
a  taper  reamer,  to  receive  a  taper  nut,  formed  to  fit  the  screw. 

Attachment  of  the  facing  to  backing  and  reduction  of  sur- 
plus screw  and  nut  are  accomplished  in  a  similar  manner  as 
described  under  the  Bryant  System. 

RIVETING  THE   FACING  TO   BACKING 

When  the  pins  of  the  new  facing  are  long  enough  to  ex- 
tend through  the  old  backing  and  permit  of  spreading,  the 
facing  may  be  attached  by  riveting. 

Mark  position  on  backing,  and  drill  holes  which  corre- 
spond closely  with  the  diameter  of  the  pins,  countersinking 
their  lingual  ends  slightly. 

Grind  facing  to  meet  requirements,  and  if  the  jains  are 
excessively  long,  cut  them  so  that  they  will  extend  but  slightly 
beyond  the  lingual  surface  of  the  backing. 

The  ends  of  the  pins  should  be  squared  and  their  centers 
depressed  with  a  delicate,  bi-beveled  drill,  to  jirevent  the  point 
of  the  riveting  punch  from  slipping  when  applied.    A  sleeve 


drill,  designed  for  this  purpose,  can  be  used  to  good  advan- 
tage, and  is,  in  fact,  indispensable. 

The  Shriver  riveting  punch,  one  beak  of  which  is  sup- 
plied with  a  cup  for  holding  a  rubber  pad,  or  modeling  com- 
pound, for  producing  pressure  on   the  porcelain,  the   other 


BRIDGBWORK 


fitted  with  a  round  end  and  a  pointed  end  punch  for  com- 
pressing and  spreading  the  pins  is  used  as  follows : 

Cement  is  spread  over  the  backing  and  the  facing  pressed 
to  place.     The  padded  beak  of  the  punch  is  applied  to  the 


Tr]}~7» 


RIVETI^&  PL\(_H  SHOWING  cvr 

BEVK  A^D  TWO  RH  ETI^G 

POINTS    (SHKIVEB) 


facing,  the  round  punch  applied  to  the  pin,  being  careful  to 
center  it  so  that  the  pin  may  not  be  bent  to  one  side,  and  pres- 
sure made  to  compress  the  pin  upon  itself.  This  step  shortens 
the  pin  but  increases  its  diameter  and  causes  it  to  fill  the 


BACKINGS     OF     CUSPID     CROWN 

AND   CENTRAL  DUMMY   DRILLED 

FOR    RECEPTION    OF    LONG    PIN 

FACINGS 


hole  in  the  backing,  just  as  a  rivet  is  compressed  endwise,  to 
fill  the  hole  before  the  head  is  formed. 

The  pointed  punch  is  ajiplied  to  spread  the  end  and  form 
the  head  of  the  rivet,  after  which  the  round  end  is  again  ap- 


866  BRIDGEWORK 

plied  to  smooth  any  rouglinoss  raised  l)y  t\w  point,  while 
any  surplus  that  remains  is  removed  with  discs. 

When  modeliii!^"  compound  instead  of  rubber  is  used  as  a 
pad,  it  should  be  softened,  placed  in  the  cup,  the  punch  ad- 
justed in  ]iosition  and  slight  pressure  applied  to  secure  an 
impression  of  the  labial  surface  of  the  tooth,  when  it  is  re- 
moved and  chilled,  after  which  the  steps  are  carried  out  as 
described. 

An  ordinary  plate  punch,  modified  as  suggested  by  Dr. 
George  Evans,  may  be  used  instead  of  the  Shriver  Punch  if 
desired.    To  the  beak  in  which  the  hole  is  located,  a  lead  block 


OKDINAKY     PLATE    I'UNtH    CON\ERTED 
INTO   A  RIVETING    PUNCH  BY  APPLICA- 
TION  OF    LEAD   BLOCK    TO   BIGHT    AND 
HEAVY    PIN    TO    LEFT    BEAK 


is  applied  for  producing  pressure  against  the  facing,  while  a 
larger  pin  replaces  the  ordinary  pin  in  the  other  beak.  The 
method  of  application  is  similar  to  that  described. 

With  either  method,  in  addition  to  gripping  the  handles 
while  compressing  the  pin,  pressure  should  be  made  lingually 
to  keep  the  facing  firmly  seated  against  the  backing. 

A  slight  side  to  side  movement  of  the  handles  will  aid  in 
compressing  and  heading  the  pin  as  well. 

REMOVING  A  BANDED,  DOWEL  CROWN 

When,  for  any  reason,  it  becomes  necessary  to  remove  a 
banded,  dowel  crowm  which  is  to  be  reset,  care  should  be  taken 
to  avoid  mutilating  the  root  cap. 

The  most  convenient  method  is  to  release  the  crown  from 
the  dowel  which  constitutes  the  main  anchorage.  This  may  be 
done  by  drilling  through  the  lingual  surface  of  the  crown,  in 
an  apical  direction,  to  the  root  face,  alongside  the  dowel. 


BRIDGEWORK 


"With  a  fissure  bur,  tlie  first  opening  is  enlarged,  cutting 
around  the  dowel  in  such  manner  that  the  latter  will  project 
bevond  tlie  root  face,  thus  facilitating  its  removal  later  on. 


LINGUAL       VIEW       OF  SAME  TOOTH,    PROXI-  PROXIMAL     VIEW     OF  CERVICAL     VIEW      OF 

fENTRAL.        SHOWING  MAL    VIEW.       DOTTED  INCISOR.    RELEASE  OF  CROW  N      PROXIMAL 

OPENING         THROUGH  LINE     SHOWS     DIREC-  DOWEL  FROM  LABIAL  VIEW       OF       BOOT 

WHICH     DOWEL     H.\S  TION    OF   OPENING  SIDE  SHOWING        PROJECT- 

BEEN    RELEASED  ING    DOWJX 

When  the  facing  is  fractured,  release  of  the  crown  can  be 
most  readily  accomplished  by  entering  the  crown  base  from 
the  labial  surface  and  cutting  around  the  dowel  as  described. 

A  single  crown,  when  thus  freed  from  its  dowel,  can  be 
removed  without  difficulty,  but  when  attached  to  a  bridge  the 
other  abutment  crowns  must  also  be  released  before  removal 
can  be  effected. 


REPLACING  A   FACING  ON   A   CROWN    REMOVED   AS 
DESCRIBED 

The  best  and  quickest  methotl  of  replacing  a  facing  on  a 
crown  is  by  removal  of  the  bulk  of  old  backing,  grinding  and 
backing  a  new  facing,  adjusting  and  waxing  it  in  position, 
investing  and  soldering  in  the  usual  manner. 

Usually,  after  the  backing  is  removed,  the  root  cap  should 
be  returned  to  position,  a  new  dowel  fitted,  an  impression  to 
secure  correct  relation  of  the  two  taken,  or  the  two  waxed  to- 
gether, removed,  invested  and  soldered,  after  which  the  fac- 
ing is  adjusted. 

When  the  facing  of  tlie  removed  crown  is  present,  the  lat- 
ter having  been  removed  by  releasing  the  dowel  from  the  lin- 
gual side,  a  dowel  is  fitted,  the  incisal  end  being  allowed  to 
project  beyond  the  opening,  after  which  it  is  waxed  in  correct 
relation,  the  crown  removed,  invested,  and  the  two  united 
with  solder 

Before  investing  the  crown,  the  o]iening  around  the  dowel, 
in  the  crown  base,  should  be  covered  with  a  small  disc  of 


868  BRinOEWORK 

platiinim  foil,  to  complete  tlie  floor  of  the  root  cap,  and  form 
a  metallic  surface  a.^ainst  which  the  solder  may  flow. 

REMOVING    DOWELS    FROM    ROOT    CANALS 

Various  devices  have  been  suggested  for  removing  dowels 
from  root  canals.  When  applicable,  appliances  of  this  type 
relieve  the  tooth  from  both  excessive  cutting  and  strain. 

LITTLE  GIANT   POST  PULLER 

The  Little  Giant  Post  Puller,  designed  by  Dr.  F.  H.  Skin- 
ner, consists  of  a  clamp,  having  thin  yet  strong  beaks,  for 


SHOULDER  FIN  OF  POST  PULLER 

grasping  the  dowel,  together  with  a  shoulder  post  for  resting 
npon  tlie  root  face. 

By  turning  the  screw,  the  shoulder  post  is  brought  in 
contact  with  the  root  face,  while  the  clami^  and  dowel  are 
moved  incisallv. 


LITTLE  GIANT  POST  PULLER 


To  a]>]jly  the  device,  the  entrance  to  the  root  canal  must 
be  enlarged  sufficiently  to  permit  the  clamp  licaks  to  enter  and 
grasp  the  sides  of  the  dowel  firmly. 

THE  S.  S.  WHITE  CROWN  REPAIR  OUTFIT 

The  devices  in  this  outfit,  intended  for  removal  of  dowels 
from  root  canals,  consist  of  trephines  for  gaining  space  around 
the  dowel  within  the  root,  and  at  the  same  time  reducing  the 
dowel  to  a  definite  size  to  correspond  with  the  opening  in  a 
threading  die. 

After  space  is  gained,  threads  are  cut  on  the  projecting, 
formed  end  of  the  dowel,  to  which  the  inner  barrel  of  a  de- 
vice, much  like  a  jack  screw,  is  applied.  By  turning  the  milled 


BRIBGEWORK 


nut  of  the  outer  barrel  until  it  rests  agaiust  the  face  end  of 
the  root,  the  inner  screw,  which  is  attached  to  the  dowel,  is 
moved  incisally,  bringing  the  dowel  with  it. 


(.■RO\\'N    POST    PUIjLER.       (S.     S.     WHITE) 

REMOVAL  OF  A  DOWEL  FROM  THE  DEEPER  PORTIONS  OF 
A  CANAL 

When  a  dowel  is  fractured  within  the  canal,  some  distance 
from  the  face  of  the  root,  the  appliances  described  are  un- 
suited  for  its  removal,  and  some  other  means  must  be 
employed. 

A  method  which  will  result  in  but  little  sacrifice  of  tooth 
structure  consists  in  squaring  the  end  of  the  dowel,  applying 
a  delicate  bi-beveled  drill  to  its  center  and  drilling  inward  a 
short  distance,  removing  the  drill,  and  with  a  square  end  bur 
reducing  the  periphery  of  the  dowel  by  end  cutting. 

These  steps  are  repeated  until,  by  careful  cutting,  the 
entire  dowel  is  removed.  Careful  manipulation  is  required 
to  prevent  the  drill  cutting  from  center  to  periphery  of  the 
dowel. 

When  the  dowel  is  very  small,  a  fine  fissure  bur  can  be 
passed  around  it,  dividing  the  cutting  as  much  as  possible  be- 
tween tooth  structure  and  metal  to  avoid  weakening  the  root 
and  excessively  enlarging  the  canal,  or  in  some  cases  the  dowel 
itself  may  be  gradually  cut  away  with  small  fissure  burs. 

This  is  a  most  unsatisfactory  method  of  removing  a  dowel, 
3'et  at  times  it  is  the  only  means  of  clearing  the  canal. 


REMOVING  A   SHELL  CROWN  BY  SLITTING 

The  quicket  method  of  removing  a  shell  crown  is  by  slit- 
ting one  of  its  axial  walls,  introducing  an  instrument  in  the 


870  BRIDGEWORK 

opening  and  prying  the  crown  walls  away  from  tlie  tooth, 
thus  break  the  adhesion  of  the  cement. 

A  fine  fissure  Imr  may  be  used  for  cutting  the  slot  from 
gingival  to  occlusal  areas.  This  method  results  in  loss  of  sub- 
stance of  the  crown  wall,  and  where  the  crown  is  to  be  re- 
placed must  be  filled  in  with  a  strip  of  gold  of  corresponding 
width  of  the  slot,  or  the  crown  when  joined  will  be  too  small. 

By  means  of  a  croivn  slitter,  the  walls  may  be  divided 
without  loss  of  gold,  and  when  properly  contoured  and  sol- 
dered the  crown  will  fit  as  before. 

This  appliance  is  a  plier-like  device,  one  beak  carrying 
a  sharp,  cutting  blade,  the  other  being  somewhat  broadened 


CBOWN   SLITTER   FOR   REMOVING    SHELL   CROWNS 

and  curved,   for   resting  upon   the   occlusal   surface   of  the 
crown. 

By  introducing  the  point  of  the  blade  against  the  cervical 
margin  of  the  crown,  the  other  beak  on  the  occlusal  surface, 
and  closing  the  handles,  the  wall  is  readily  slit. 


REMOVING  A  SHELL  CROWN  BY  LEVERAGE  FORCE 

A  shell  crown  can,  in  most  cases,  be  removed  without  much 
mutilation  by  the  following  method  : 

Drill  a  hole  at  a  convenient  point,  just  beneath  the  occlu- 
sal surface  of  the  crown,  extending  it  through  to  nearly  the 
opposite  side. 


BRIDGEWORK  871 

lu  this  hole,  which  should  be  about  the  size  of  an  engine 
bur  wire,  a  long-handled  instrument  is  inserted  to  serve  as  a 
lever. 

Brace  the  tooth  with  the  linger,  on  the  opposite  side  from 
the  opening,  and  exert  pressure  on  the  handle  in  an  occlusal 
direction.  This  forces  the  inner  point  against  the  end  of  the 
tooth,  or  body  of  enclosed  cement,  breaks  adhesion  and  re- 
leases the  crown. 

REPAIRING   CROWNS   THAT    HAVE    BEEN    SLIT    IN   THE    MAN- 
NER DESCRIBED 

When,  in  removal,  a  crown  has  been  mutilated  by  slitting 
or  by  cutting  with  a  bur,  the  tirst  step  in  its  repair  is  to  remove 
all  cement  by  boiling  in  acid.  Such  portions  as  fail  to  come 
away  readily  by  this  means  should  be  removed  by  scraping  and 
the  crown  again  treated  with  acid  as  before. 

This  is  necessary,  because,  if  not  removed,  the  oxide  of 
zinc  in  the  cement  will,  under  heat  of  the  blowpipe,  be  re- 
solved into  metallic  zinc,  which  will  unite  with  the  gold, 
forming  a  low  alloy,  and  cause  the  latter  to  fuse,  or  hum,  as  it 
is  usually  expressed. 

After  cleansing  as  described,  the  band  ends,  or  axial 
walls,  are  contoured  to  correct  form,  wax  flowed  in  any  exist- 
ing space  between  the  ends,  trimming  it  to  exact  internal  con- 
tour, the  interior  of  the  crown  filled  with  investment,  the  wax 
removed,  flux  applied  and  solder  flowed  into  and  over  the  joint. 

The  same  method  may  be  employed  in  closing  the  drill 
hole  near  the  occlusal  surface,  or  when  waxed,  invested  and 
the  wax  removed,  a  piece  of  platinum  foil  may  be  pressed  in 
the  opening  in  the  crown  to  the  investment,  and  solder  applied 
to  fill  the  depression  and  restore  axial  contour. 

REPAIRING  A   FRACTURED   BRIDGE 

When  a  bridge  is  fractured  at  some  point  between  its 
abutments,  it  may  be  repaired  in  two  ways : 

First,  remove  the  parts,  saw  otif  the  intervening  dum- 
mies, replace  the  abutment  crowns  in  position,  secure  a  bite 
and  impression,  construct  and  moi;nt  casts  on  the  occlud- 
ing frame,  readjust'and  wax  the  dummies  in  position,  remove 
and  invest  the  assembled  bridge,  and  solder. 

Second,  when  fractured  in  only  one  place,  remove  the 
broken  parts,  cleanse  thoroughly,  iiress  some  softened  model- 
ing compound  on  the  border  between  the  abutment  crowns, 


BRIDGEWORK 


return  the  two  parts  to  position,  pressing  the  dummies  into 
the  modeling  com])ouud  interposed  between  their  cervical  ends 
and  the  border;  instruct  the  patient  to  close,  thus  biting  the 
bridge  into  correct  occlusal  relation. 


SANITAHT  BRIDGE.     TO   SECURE  RELATION  OP 
PABTS.    WHEN    STRnCTURE    IS    FRACTURED    AT 
A.      INTERPOSE      MODELING      COMPOUND      BE- 
TWEEN A  AND  B 

Pressure  should  be  made  on  the  buccal  surface  of  the 
bridge  to  prevent  outward  displacement  while  the  patient  is 
forcing  it  to  place. 

When  compound  is  chilled,  secure  an  impression  of  the 
bridge  in  its  reassembled  relation,  remove,  invest,  and  solder. 


CHAPTER     XXX 

PORCELAIN  CROWN  AND  BRIDGE  WORK 
PORCELAIN  CROWN  WORK 

In  addition  to  the  many  varieties  of  crowns  it  is  possible 
to  construct  by  means  of  facings,  partial  and  full  crowns  of 
porcelain  as  shown,  still  another  type  of  crown  can  be  con- 
structed and  applied  in  certain  cases  to  advantage.  This  is 
ordinarily  known  as  the  baked  porcelain  croivn,  because  it  is 
subjected  to  the  process  of  fusion  or  baking  by  the  prosthe- 
tist  in  his  laboratory. 

Crowns  of  this  type  may  be  subdivided  into  three  general 
classes,  viz. : 

First — A  crown  supported  by  and  built  upon  a  perma- 
nent substructure  of  metal,  usually  composed  of  a  cap  and 
dowel  of  platinum,  to  which  a  facing  is  attached,  the  lingual 
portion  of  porcelain  being  applied  and  fused  to  the  cap  and 
affixed  facing  by  the  prosthetist. 

Second — A  crown  supported  by,  and  built  upon,  a  per- 
manent platinum  cap  or  base,  the  entire  crown  portion  being 
built  up  and  contoured  in  porcelain  body  and  afterward 
fused. 

Third — A  crown  built  upon  and  around  a  cap  of  platinum 
foil,  which  when  the  crown  is  fused  is  removed. 

The  two  former  crowns  are  usually  designated  as  banded, 
baked  porcelain  crowns,  the  latter  as  a  porcelain  jacket 
crown. 

The  introduction  within  recent  years  of  many  new  and 
excellent  forms  of  replaceable  facings  and  partial  crowns  of 
porcelain,  together  with  improved  methods  of  technic,  has 
to  a  great  extent  rendered  unnecessary  the  baking  of  crowns 
and  bridges,  except  in  special  cases. 

As  a  preliminary  consideration  the  fact  should  be  kept 
in  mind  that  porcelain  is  strong  only  in  bulk;  therefore,  in 
constricted  spaces  it  is  liable  to  fracture  under  stress. 

Again,  the  porcelain  used  in  inlay,  crown,  bridge  and 
continuous  gum  and  denture  construction  is  less  dense  and 
more  friable  than  that  of  which  porcelain  teeth  is  composed; 
therefore  the  former  material  will  not  stand  the  stress,  bulk 

873 


S74  PORCELAIN    CROWN    AND    BRIDGE    WORK 

for    liulk,    (hat    tooth    body   will    resist,   without    danger    of 
fraeture. 

Occasionally,  however,  cases  present  wliere  a  specially 
baked  substitute  will  fnllill  esthetic  requirements  more  satis- 
factorily than  will  one  constructed  by  any  other  method. 

INDICATIONS   FOR   USE 

Baked  porcelain  crowns  can  be  successfully  applied  in 
any  location  where  sufficient  space  is  present  for  a  reasonable 
bulk  of  porcelain  and  where  the  metal  structure  can  be  well 
adapted  to  the  supporting  roots. 

Crowns  of  this  type  are,  however,  specially  indicated  when 
departure  of  the  ordinary  anatomic  form  the  tooth  is  required, 
provided  such  departure  will  not  tend  to  weaken  the  crown 
when  constructed. 

The  porcelain  jacket  crown  is  admirably  adapted  to  peg- 
shaped  lateral  incisors  and  frequently  to  other  classes  of  teeth 
as  well.  The  placing  of  a  crown  of  this  type  on  a  vital  tooth 
in  no  way  endangers  the  pulp,  providing,  of  course,  proper 
tooth  i:)reparation  can  be  successfully  accomplished  without 
serious  inconvenience  to  the  patient. 

THE  BANDED,  BAKED  PORCELAIN  CROWN 

This  crown  consists  of  a  rigid  root  cap  of  platinum  or 
iridio-platinum,  a  dowel  of  iridio-platinum,  a  tooth  facing  ap- 
plied to  the  dowel  by  soldering,  while  its  lingual  contour  is 
developed  by  application  and  fusing  of  porcelain  to  facing 
and  root  cap. 

CONSTRUCTING  THE  ROOT  CAP 

Methods  vary  as  to  root-cap  construction  for  crowns  of 
this  type.  The  following  technic  is  adopted  bj^  many  because 
the  metal  band  on  the  labial  or  buccal  surface  may  be  entirely 
obscured  by  the  facing  and  applied  porcelain. 

Prepare  the  root  as  for  an  ordinary  cap  crown  described 
on  page  600. 

Construct  a  band  of  29  or  30  gauge  iridio-platinum. 
Platinum  may  be  used,  but  it  is  liable  to  stretch  under  stress. 

Cut  the  strip  about  1-20  of  an  inch  longer  than  the  actual 
root  measurement,  to  allow  for  a  lap  joint. 

Bend  one  end  at  right  angle  to  the  band,  turning  over  the 
amount  of  surplus  allowed.  The  other  end  is  then  brought 
under  the  bent  portion  and  butted  tightly  against  both  the 


PORCELAIN    CROWN    AND    BRIDGE    WORK 


tuniod  portion  and  band  end  proper.  Solder  with  high-fus- 
ing platinum  solder. 

Place  on  a  round  mandrel  and  tap  lightly  to  tiatten  and 
form  a  continuous,  curved  inner  surface  to  band,  being  care- 
ful not  to  stretch  or  elongate  the  metal. 

Reduce  the  excessive  thickness  of  the  joint,  from  the 
outside,  by  tiling  or  with  engine  stones. 

Fit  the  band  to  root,  scribing  and  trimming  the  cervical 
end  until  perfectly  and  uniformly  adapted  to  the  gingiva, 
when  it  is  driven  to  correct  position  under  the  gum. 

Trim  the  iucisal  end  of  the  band  to  coincide  with  gingival 
curvature,  allowing  it,  however,  to  project  slightly  beyonid 
the  gum  margin,  lingually. 


DETAllS  OP  PORCELAIN  CROWN.     A  SHOWS  LABIAL  BEVEL  OP  CAP; 
BCD.    LAP  JOINT:    E,    RIDCE   LAP    OF   PACING    CON- 
CAVED:  P   O.    PARTS    ASSEMBLED 

Drive  the  band  to  position  on  the  root,  and  face  the  latter 
to  the  iucisal  end  of  the  band. 

Eemove  the  band  and  further  reduce  the  outer  or  labial 
third  of  the  root  face  to  a  point  about  where  the  cervical  mar- 
gin of  the  band  will  rest. 

Thin  the  band  by  grinding,  along  the  labial  area  corre- 
sponding to  the  reduced  root,  being  careful,  however,  to  leave 
its  exti'eme  cervical  margin  full  thickness. 

Return  it  to  the  root  and  with  a  square  end  plugger  in 
the  automatic  mallet,  reflect  the  thinned  labial  portion  over 
against  the  root  face. 

Adapt  a  disc  of  30-gauge  iridio-platinum  plate  to  the  iu- 
cisal end  of  the  band,  being  careful  to  develop  a  perfect  joint 
between  the  two. 

Perforate  the  cap  for  reception  of  the  dowel,  locating 
the  opening  far  enough  to  the  lingual  to  avoid  interference  of 
the  facing  from  the  projecting  dowel.  When  the  opening 
does  not  coincide  -with  the  root  canal,  ream  the  latter  to  cor- 
respond. 

No.  16  or  15  gauge  iridio-platinum,  round  wire,  is  usually 
employed  for  dowels  in  central  and  cuspid  teeth,  while  17- 
gauge  is  used  in  upper  laterals,  lower  incisors,  and  when  two 
dowels  are  applied,  in  bicuspid  teeth. 


876  PORCELAIN    CROWN    AND    BRIDGE    WORK 

The  opening  in  the  root  cap  should  be  slightly  smaller 
than  the  diameter  of  dowel,  the  entrance  to  canal  counter- 
sunk slightly,  the  dowel  forced  through  cap  as  previously  de- 
scribed, relation  between  the  two  secured  with  wax,  after 
which  they  are  removed  from  root,  invested  and  soldered  with 
medium  or  high-fusing  platinum  solder. 

Pickle  and  cleanse  the  cajo  and  by  grinding  reduce  the 
labial  portion  of  the  cap  along  the  angle,  between  band  and 
disc,  so  as  to  produce  a  decided  bevel  in  this  area.  This  is 
necessary  in  order  that  the  facing,  when  reduced  to  a  thin 
edge  by  grinding,  may  cover  the  labial  surface  of  the  cap. 

Eeturn  cap  to  root,  take  impression  and  bite,  remove,  de- 
velop casts  and  mount  on  occluding  frame. 

Select  a  facing  slightly  lighter  in  color  than  the  natural 
teeth,  yet  containing  the  proper  basic  colors,  because,  when 
thickened  by  the  addition  of  lingual  porcelain,  its  depth  of 
color  will  be  increased. 

Grind  the  ridge  lap  of  the  facing  somewhat  concave,  so 
that  it  may  clear  the  cap  at  all  points,  except  along  the  ex- 
treme labial  margin,  which  should  be  brought  to  a  thin,  deli- 
cate edge,  to  rest  closely  in  contact  with  the  cervical  margin 
of  the  band. 

Flatten  the  pins  so  that  the  flattened  surfaces  lie  parallel 
with  the  dowel  in  order  that  they  may  present  a  broad  sur- 
face bearing  when  adapted  to  the  latter. 


A 


Pm  BENDING   AND   CnTTINQ  PLIERS 


The  pin  bending  and  cutting  pliers  here  shown  is  a  most 
useful  instrument  for  this  and  many  other  purposes  in  crown 
work. 


PORCELAIN    CROWN    AND    BRIDGE    WORK  877 

Set  the  facing  in  correct  alignment  and  wax  in  position. 
Test  its  length  under  lateral  movements  of  the  frame  and 
if  interference  occurs  grind  away  the  points  of  obstruction. 

When  ground  to  meet  requirements,  the  facing  is  again 
returned  to  the  cap,  the  flattened  pins  adapted  closely  to  the 
dowel,  wax  applied,  the  assembled  parts  removed,  invested, 
and  soldered  with  medium  or  low-fusing  platinum  solder. 

Care  should  be  taken,  in  removing  the  assembled  cap  and 
facing,  to  avoid  marring  the  cast,  since,  during  constructive 
stages,  the  crown  must  lie  returned  to  it,  from  time  to  time, 
for   testing  contour   development. 


CAP.     DOWEL     AND     PACING 
ASSEMBLED.  KEADY  FOR  AP- 
PLICATION   OF    THE    PORCE- 
LAIN 


Since  the  ]5oreelain  cannot  be  perfectly  protected  from  the 
blow-pipe  flame,  the  investment  should  be  raised  to  a  full  red 
heat  before  soldering  the  pins  to  dowel,  otherwise  fracture  of 
the  porcelain  is  very  liable  to  occur. 

When  soldered,  the  crown  should  be  boiled  in  acid  and 
thoroughly  washed,  after  which  the  dowel  is  grasped  in  a  pin 
vice  to  serve  as  a  handle  when  it  is  ready  for  the  application 
of  the  body. 

APPLICATION  OF  THE   PORCELAIN  BODY 

A  small  quantity  of  well  mixed  croivn  and  bridge  porce- 
lain body,  of  medium  thick  consistency,  is  taken  up  on  the 
point  of  the  spatula  and  placed  on  the  end  of  cap  close  to  the 
ridge  lap  of  facing. 

Draw  a  serrated  instrument  across  the  pin  vice,  when  the 
vibration  thus  produced  will  cause  the  granules  to  settle 
closely  together,  and  as  the  water  is  expelled  from  the  mass 
it  is  absorbed  by  a  clean  linen  napkin  or  with  bibulous  paper. 

Special  care  should  be  taken  to  fill  the  space  between 


878  PORCELAIN    CROWN    AND    BRIDGE    WORK 

ridge  lap  of  facing  and  cap  (lniiii<;-  the  first  apijlioation  of  body, 
for  if  not  packed  densely  at  this  time  it  may  be  im])ossible  to 
introduce  it  after  the  first  baking. 

The  crown  may  be  develojied  to  practically  the  required 
contour  during  the  first  application  of  the  body.  When  fused, 
additions  ai^e  made  where  needed  to  correct  loss  of  contour 
occasioned  Ijy  shrinkage  of  the  mass  in  first  baking. 

An  effort  should  l)e  made  to  complete  the  crown  in  two 
fusings.  When  a  third  or  fourth  baking  is  required  the  quality 
of  the  porcelain  rapidly  deteriorates. 

Dr.  F.  T.  Van  Woert  has  found  that  by  compressing 
plastic,  comparatively  dry  porcelain  to  a  certain  degree  by 
means  of  a  screw  press,  shrinkage  of  the  mass  during  the  first 
bake  is  reduced  to  one-tenth  instead  of  one-fifth,  as  usually 
occurs. 

By  means  of  a  metal  matrix  slightly  larger  than  the  crown 
is  to  be,  in  which  the  root  cap  is  placed,  the  porcelain  is  ap- 
plied to  it,  nnder  pressure,  and  condensed. 

The  actual  dimensions  of  the  crown  having  l)een  previ- 
ously determined,  a  doiible  end  caliper,  the  beaks  on  one  end 
of  which  register  one-tenth  more  than  the  others,  is  applied 
to  the  crown  from  time  to  time,  while  carving  the  compact 
mass  to  form. 

The  crown,  when  carved,  ready  for  the  first  bake,  is  one- 
tenth  larger  than  actually  requii-ed,  but  in  the  first  fusing  is 
reduced  to  actual  dimensions. 

It  is  possible  by  means  of  these  ingenious  devices  to  com- 
plete a  crown  in  one  baking,  while  another  advantage  of  great 
importance  is  that  there  is  less  distortion  and  greater  den- 
sity of  the  mass  when  fused. 

The  details  of  fusing  porcelain  will  be  given  under  Porce- 
lain Bridgework. 

Finishing  the  crown  consists  in  polishing  such  portions  of 
the  cervical  margins  of  the  platinum  cap  as  may  be  exposed 
after  fusion  of  the  porcelain  is  completed. 

In  setting  crowns  of  this  type,  special  care  should  be 
taken  to  avoid  the  use  of  the  mallet,  as  a  sudden  blow  is  liable 
to  fracture  the  porcelain. 

MODIFIED  FORMS  OF  PORCELAIN  CROWNS 

Various  modifications  of  the  baked  porcelain  crown  are 
constructed,  some  of  which  are  as  follows: 

A  lingual  half  band  crown,  the  dowel  and  facing  being 
attached  to  a  half  band  diaphragm,  instead  of  the  regular  form 
of  root  cap. 


PORCELAIN    CROWN    AND    BRIDGE    WORK  879 

A  bandlcss  crown  built  upon  a  disc  of  platinum;  usually 
the  root  is  faced  so  as  to  jiresent  a  decided  labial  and  a  lin- 
gual plane.  The  dowel  and  disc  are  united,  while  the  facing- 
is  ground  to  rest  upon  the  cervical  margin  of  the  disc  and  is 
soldered  to  the  dowel. 

Bicuspid  and  molar  crowns  are  frequently  constructed 
bj'  capping  the  roots  as  described  and  fitting  dowels  in  the 


ESSEN'TIAI.  TARTS  OF  AN 
UPPER  FIRST  BKUSriD 
CROWN  ASS1':J1I!I,ED.  READY 
FOR    AI'PLUATION    OF    BODY 


root  canals;  to  the  outer  or  projecting  ends  of  which  the  fac- 
ings are  attached.  In  such  cases  it  is  advisable  to  solder  some 
auxiliary  projections  on  the  root  caps  in  the  form  of  loops  or 
pins  to  afford  additional  anchorage  for  the  porcelain. 

Frequently  entire  crowns,  without  facings,  are  thus  built 
up  on  root  caps  so  constructed. 


PREPARATION  OF  A  MOLAR 
TOOTH  FOR  A  FULL  BAKED 
PORCELAIN'  CROWN  THE  FOIL 
CAP  IS  CONSTUITTKO  AND  THE 
PORCELAIN       A  1'  1'  1.  I  E  D 


AND 

SIMILAR    MANNER 

TO  THE   STEPS  JUST   DESCRIBED 


BAKED    IN 


PROXIMAL  FLANGES  OF 
IRIDIO  PLATINUM  ADDED 
FOR  STREN(!THENINC,  CROWN 
AND  AIDING  IN  HOLDING 
CONTOUR  OF  PORCELAIN 
DURING  BAKING.  SUG- 
GESTED BY  DR.  C.   A.   WHITE 


880  PORCELAIN    CROWN    AND    BRIDGE    WORK 

J^^laiiges  of  iridio-platinum  are  applied  to  the  root  cap, 
extending-  incisally  or  occlnsally,  to  give  additional  strength 
to  the  porcelain  and  assist  in  developing  contour. 

THE  PORCELAIN  JACKET  CROWN 

The  porcelain  jacket  crown,  as  before  stated,  is  specially 
indicated  in  the  restoration  of  peg-shaped  lateral  incisors. 

The  reason  for  this  lies  in  the  fact  that  an  anomaly  of 
this  type  usually  has  a  small,  sometimes  distorted,  root,  in 
which  the  placing  of  a  suitable  dowel  is  questionable.  Often- 
times it  is  impossible  to  successfully  remove  the  pulp  and  fill 
the  root  canal  in  a  satisfactory  manner.  The  crown,  also 
being  undersized,  requires  but  little  preparation  for  the  re- 
ception of  a  shell  crown  of  porcelain. 


CASE       SHOWING        PEG-SHAPE 
LATEBAI,   INCISOR  BEFORE 
PKBPABATION 


This  form  of  crown  can  be  successfully  applied  to  various 
other  classes  of  teeth,  both  vital  and  non-vital,  and  when  prop- 
erly constructed  and  permanently  set,  fulfils  esthetic  require- 
ments in  the  highest  degree. 


LABIAI,   VIEW   OF   PREPAKED 

TOOTH.    SHOWING    GINGIVAL 

SHOULDER 

TECHNIC  OF  CONSTRUCTION 


Prepare  the  tooth  so  that  it  presents  a  perceptible  cone 
form,  thinning  it  on  labial  and  lingiial  surfaces  so  as  to  give 
space  for  a  uniform  layer  of  porcelain. 


PORCELAIN    CROWN    AND    BRIDGE    WORK  881 

The  mesial  and  distal  surfaces  need  not  be  reduced  to 
the  same  extent  as  the  labial  and  lingual  surfaces,  yet  they 
must  also  converge  slightly  from  gingival  to  incisal  areas. 

The  sides  of  the  cone  should  terminate  in  a  distinct  cer- 
vical shoulder,  located  just  beneath  the  free  gum  margin. 

TAKING  IMPRESSION  OF  TOOTH 

Construct  a  reasonably  close  litting  copper  band  suffi- 
ciently long  to  handle  easily,  and  adapt  to  the  periphery  of 
the  tooth.  It  sliould  not  encroach  on  the  peripheral  shoulder 
at  any  point  nor  upon  the  gum  margin,  but  should  pass  be- 
tween the  two. 


PROXIMAL   VIEW   OF   TOOTH. 

UIPKESSION  TAIiEN   AND 

EEMOVED 


Fill  with  softened  modeling  compound  and  apply  to  the 
prepared  tootli,  at  the  same  time  closing  the  incisal  end  of  the 
band  witli  tlie  finger  to  prevent  escape  of  impression  material. 

A^jply  sufficient  force  to  secure  an  impression,  not  only 
of  the  axial  surfaces  of  the  tooth,  and  flattened  cervical  shoul- 
der, but  of  the  root  periphery  as  well. 

Chill  the  comijound,  remove  the  impression  and  trim  off 
gingival  surplus. 

CONSTRUCTING  THE   DIE 

Apply  a  section  of  rubber  tubing  to  the  band  periphery 
and  pack  the  impression  with  amalgam,  building  it  up  suffi- 


ciently to  afford  a  firm  base  for  attachment  to  the  cast, 
plaster  base. 


882  PORCELAIN    CROWN    AND    BRIDGE    WORK 

Modelite  may  be  used  to  advantage  instead  of  amalgiini ; 
in  which  case,  before  liardening,  a  small  wood  screw  should 
be  inserted  in  the  base  for  anchorage  purposes. 


OF        THE 


Secure  an  impression  in  plaster  and  a  bite  in  wax  of 
the  prei>ared  tooth  and  of  the  two  proximating  teeth  also  and 
set  aside  for  later  use. 

Iml)ed  the  die  base  in  modeling  compound  in  a  swaging 
ring  and  trim  so  as  to  freely  expose  the  gingival  shoulder. 

FORMING  THE  PLATINUM  CAP 

Cut  a  triangular  piece  of  1-1000  platinum  foil  of  sufficient 
dimensions  to  encircle  the  cervical  periphery,  and  extend 
somewhat  beyond  the  incisal  end  of  the  die  tooth. 

Anneal  the  foil  and  cut  ot¥  the  excess  points  from  the 
cervical  ends  of  the  triangle,  as  indicated  in  cut  F. 

Apply  the  foil  to  the  die  to  form  a  cone,  the  base  of  which 
should  extend  beyond  the  cervical  shoulder. 


Slit  the  foil  near  the  apex,  so  that  the  sides  of  the  triangle 
maj  be  wrapped  around  the  die. 

Before  closing  the  two  sides  together,  the  apex  of  the 
triangle  should  be  turned  over  the  incisal  edge  of  the  die  so 
as  to  lie  beneath  them  and  thus  close  the  incisal  end  of  the 
cone  cap. 

With  a  pair  of  foil  carriers  the  two  sides  are  grasped  and 
brought  together  against  the  lingual  surface  of  the  die  and 
there  folded  together  to  form  a  lap  or  stove-pipe  joint. 


PORCELAIN    CROWN    AND    BRIDGE    WORK  883 

At  the  time  of  making  the  folded  joint,  care  should  be 
taken  to  see  that  the  cone  base  is  embracing  the  root  periphery. 

Burnish  the  now  closed  cap  to  the  die,  carrying  the  bur- 
nisher along  the  axial  surfaces  and  downward  in  a  cervical 
direction. 

h. 

SECTIONS  SHOWING  PABTIAl. 
AND      COMPLETE      FORM      OF 

JOINT 

Trim  off  excessive  surplus,  both  iucisally  and  eervically, 
and  with  a  large  pellet  of  absorbent  cotton  or  punk,  enclose 
the  entire  cap  and  apply  pressure  with  the  fingers  from  all 
sides  against  the  axial  surfaces,  and  in  a  cervical  direction 
as  well. 

Care  should  be  taken  to  avoid  undue  force  at  all  times 
or  the  foil  will  be  torn. 


PLATINXIM   CAP  ADAPTKl)   TO 
DIE    AND    TRIMMED   TO    COR- 
RECT   OUTLINE    FORM 


When  the  foil  cap  is  perfectly  adapted  and  its  cervical 
margin  trimmed  close,  but  not  quite,  to  the  peripheral  cervical 
shoulder,  it  should  be  carefully  removed  and  laid  aside  until 
the  body  is  applied. 

Since  the  porcelain  must  be  applied  and  the  crown  carved 
so  that  its  incisal  edge  will  come  in  correct  alignment  with  the 
proximating  teeth,  it  should  be  formed  on  a  cast  in  whicla  these 
proximating  teeth  are  present. 

CONSTRUCTING  THE  CASTS 

The  die  is  now  removed  from  the  swaging  ring  or  base 
in  which  it  was  imbedded,  the  gingival  portion  of  the  impres- 
sion trimmed  somewhat  freely  to  admit  the  die,  the  latter 
placed  in  its  matrix  and  a  cast  developed  in  the  usual  manner. 

The  bite  is  applied  to  the  cast,  the  latter  mounted  on  the 
occluding  frame  and  the  occlusion  cast  developed. 

Trim  the  plaster  from  around  the  cervical  end  of  the  die 
tooth,  so  as  to  freely  expose  the  shoulder  and  permit  the  foil 
cap  to  be  set  in  proper  position  without  interference. 


884  PORCELAIN    CROWN    AND    BRIDGE    WORK 

Make  a  small  cylinder  of  oiled  writing  paper  and  apply 
around  the  platinum  cone,  holding  it  in  position  with  a  loosely 
tied  ligature.    This  is  to  assist  in  condensing  the  porcelain. 

APPLICATION   OF  THE   PORCELAIN 

High-fusing  tooth  body  (2560  degs.),  of  suitable  shade  to 
match  the  tooth,  is  now  mixed  ready  for  application. 

Usually  two  shades,  sometimes  three,  are  selected  and 
mixed,  the  darkest  being  applied  to  the  gingival  third,  the 
medium  to  the  middle,  and  the  lightest  to  the  incisal  third  of 
the  cylinder. 

The  body  should  be  mixed  to  medium  consistency,  and 
as  each  portion  is  applied  it  should  be  vibrated  to  place. 

When  of  medium  consistency  the  sharp  lines  of  demarka- 
tion  of  the  two  or  three  colors  will  disappear  during  vibra- 
tion and  when  fused  will  show  gradual  blending  of  the  colors. 

As  the  incisal  portion  is  added,  the  paper  cylinder  is  flat- 
tened mesio-distally  to  give  correct  alignment  to  the  incisal 
portion. 

Absorb  the  moisture  that  comes  to  the  surface  with  bibu- 
lous or  blotting  paper,  and  when  compact  and  reasonably  dry 
remove  the  ligature  and  oiled  paper. 


THE  OrTEE  DOTTED  LINE  SHOWS 
APPROXIMATELY  HOW  MUCH 
LARGER  THE  CROWN  SHOULD  BE 
FORMED  IN  THE  BODY  TO  COM- 
PLETE   IT    IN   ONE    BAKING 


The  body  is  now  carved  to  the  required  form  and  such 
additions  made  as  are  necessary. 

Particular  attention  should  be  given  the  cervical  end,  to 
see  that  the  body  comes  flush  with,  but  does  not  overlap,  the 
peripheral  root  portion  of  the  matrix. 

Smooth  up  all  surfaces  with  a  fine  sable  brush,  carefully 
remove  and  set  on  a  soapstone  base,  carved  to  the  general 
form  of  the  die,  but  slightly  smaller. 

The  interior  point  of  the  support  should  be  sufficiently 
long  to  afford  a  rest  for  the  erowii  without  its  weight  being 
thrown  on  the  cervical  end. 


PORCELAIN    CROWN    AND    BRIDGE    WORK  885 

BAKING  THE  CROWN 

Dry  out  the  moisture  in  the  body  very  carefully,  to  pre- 
vent flaking,  and  when  ready  introduce  the  crown  in  the  fur- 
nace, heat  slowly,  and  bring  to  a  semi-glazed  condition. 

Since  in  these  cases  tooth  body  is  used,  a  longer  time  will 
be  required  to  vitrify  the  material  than  is  required  for  con- 
tinuous gum  body. 


THE    FINISHED    CROWN 

When  fused,  the  crown  is  returned  to  position  on  the 
cast,  its  relations  to  the  other  teeth  noted,  correction  made 
by  addition  of  body  to  such  areas  as  need  further  contouring, 
and  the  case  is  returned  to  the  furnace,  usually  for  the  final 
baking,  this  time  bringing  the  porcelain  to  a  glaze. 

If  by  trial  on  the  cast  it  is  found  correct,  the  crown  is 
moistened,  the  matrix  carefully  peeled  out  of  the  interior, 
rough  margins  are  smoothed  and  the  crown  is  ready  for 
setting. 

THE  "LAND  JACKET  CROWN" 

Dr.  C.  H.  Land  of  Detroit  was  probably  the  first  to  in- 
troduce a  system  of  practical  technic  for  the  jacket  crown. 

The  following  outline  presents  the  essential  steps  of  the 
Land  system : 

PREPARATION  OF  THE  TOOTH 

Bemove  all  of  the  enamel  and  prepare  the  tooth  cone- 
shaped,  without  cervical  shoulder,  but  in  other  respects  much 
the  same  as  required  for  the  preceding  crown. 


CASE     SHOWING     A     PEG-SHAPE     LATERAL 
INCISOR    BEFORE   PREPARATION 


886  PORCELAIN    CROWN    AND    BRIDGE    WORK 

CONSTRUCTION  OF  THE  CAP 

Construct  and  adapt  a  wide  band  of  30-gauge  platinum 
to  the  tooth,  scribing  and  fitting  it  carefully  under  the  free 
gum  margin  as  for  any  banded  crown. 


The  band  should  extend  from  the  cervix  to  a  short  dis- 
tance beyond  the  incisal  end  of  the  prepared  tooth. 

Bevel  cuts  are  now  made  in  both  mesial  and  distal  sur- 
faces of  the  band,  in  line  with  the  labial  and  lingual  planes 
of  the  tooth,  extending  from  incisal  edge  to  near  the  cervical 
margin. 

Bend  both  labial  and  lingual  sections  outward  to  give 
space  for  adapting  and  liurnisliing  the  mesial  and  distal  sec- 
tions of  platinum  against  these  surfaces  of  the  tooth. 


PLATINUM     BAND     ADAPTED 

TO      TOOTH.        THE      DOTTED 

LINES    SHOW   WHERE    BEVEL 

CUTS    ABE    TO    BE    MADE 


LABIAL  AND  LINGUAL  SEC- 
TIONS BENT  OUTWARD. 
PROXIMAL  SECTIONS 

ADAPTED  TO  THE  TOOTH 


When  close  adaptation  of  these  sections  is  secured,  the 
edges  of  the  triangular  margins  may  be  reduced  with  discs  to 
permit  the  other  sections  of  platinum  being  brought  in  close 
contact  with  the  tooth  at  along  the  joints. 

Bend  and  adapt  the  lingual  section  of  platinum  against 
this  surface  of  the  tooth,  removing  the  excess  so  that  it  over- 


PORCELAIN    CROWN    AND    BRIDGE    WORK  887 

laps  the  mesial  and  distal  margins  of  platinum  to  a  slight 
extent  only. 

Burnish  the  joints  closely  and  solder  with  high-fusing 
platinum  solder. 

Adapt  and  trim  the  labial  section  to  the  sides,  and  solder 
in  like  manner. 


THE    CAP    COMPLETED 


After  soldering,  the  four  angles  of  the  cone  cap  may  be 
rounded  off  with  discs,  to  reduce  the  platinum  to  uniform 
thickness. 

TAKING  BITE  AND   IMPRESSION 

Take  an  impression  and  bite  of  the  proximating  teeth  with 
cap  in  position. 

Flow  a  film  of  wax  inside  the  cap,  develop  casts,  and 
mount  on  the  occluding  frame. 

Warm  the  cap,  remove,  clear  its  interior  of  wax  and  re- 
turn to  the  cast. 

SELECTION  AND  GRINDING  OF  FACING 

Select  a  facing  of  desired  shade  and  form  and  grind  to 
proper  alignment. 

This  step  usually  requires  the  concaving  of  the  facing  on 
its  lingual  side,  to  a  very  considerable  extent,  and  the  reduc- 
tion of  its  ridge  lap  to  a  thin  margin. 


METHOD    OF    GBOOVING    THE 
PORCELAIN   FACING 


Frequently,  the  porcelain  must  be  grooved  from  cervical 
near  the  incisal  areas  carrying  the  groove  between  the  pins. 
In  some  cases  the  pins  themselves  are  ground  away  in  order 


888  PORCELAIN    CROWN    AND    BRIDGE    WORK 

to  bring  the  facing  into  correct  labial  alignment.  When  this 
is  necessary,  however,  it  is  best  to  form  a  shoulder  in  the 
porcelain  to  rest  ujioii  tlie  incisal  end  of  the  cap. 


I'ROXIMAJ- 


When  ground  to  correct  labial  alignment,  the  pins,  if 
present,  are  bent  in  close  contact  with  the  cap,  the  facing  and 
cap  waxed  in  correct  relation,  when  they  are  removed  from 
the  cast,  invested,  soldered,  pickled  in  acid  and  washed. 

APPLICATION   AND   FUSING  OF   PORCELAIN 

High-fusing  porcelain  is  now  applied  around  the  mar- 
gins of  the  facing,  next  the  cap  and  with  vigorous  vibration 
worked  into  the  entire  space  between  the  two. 

Additions  are  now  made  where  needed  to  develop  required 
contour,  all  surfaces  smoothed  and  with  a  tine  sable  brush 
all  particles  are  removed  from  the  labial  surface  of  the  fac- 
ing and  exposed  root  cap. 

Frequently  during  the  application  of  the  body  some  of  it 
may  become  lodged  in  the  interior  of  the  cap,  and,  if  so,  should 
be  removed  before  fusing. 


THE  FINISHED   CROWN 


Set  the  crown  on  a  soapstone  base  having  a  projection 
for  entering  the  cap  of  suiEcient  height  to  support  the  crown 
in  an  upright  position. 


PORCELAIN    CROWN    AND    BRIDGE    WORK  889 

Eemove  the  moisture  l)y  gradually  applied  beat,  introduce 
the  crown  in  the  furnace  and  raise  the  temperature  gradually 
to  fusing  point,  stopping  the  fusion  while  the  porcelain  is  in 
a  semi-glazed  condition. 

.  Cool  slowly  and,  when  in  condition  to  handle,  additions 
of  body  are  made  to  fill  any  tissnre  that  may  be  present,  and 
develop  contour  where  required. 


THE    CROWN    IN    POSITION 


Since,  in  a  crown  of  this  type,  the  bulk  of  porcelain  is 
comparatively  slight,  and  contraction  jsroportionately  so,  two 
bakings  are  usually  sufficient  to  develop  required  contour, 
therefore  the  porcelain  should  be  fully  glazed  during  the  sec- 
ond fusing. 

PORCELAIN  BRIDGEWORK 

As  preyiously  stated,  there  is  less  necessity  at  the  pres- 
ent time  than  formerly  for  the  construction  of  porcelain 
bridges  by  the  baking  process. 

This  is  due  to  the  introduction  of  various  types  of  re- 
placeable, full  and  partial  crowns,  which,  when  properly  com- 
bined with  metal,  fulfill  esthetic  requirements,  in  many  cases, 
quite  as  well  as  do  baked  porcelain  bridges. 

Bridges  composed  of  metal,  and  to  which  replaceable  teeth 
are  adapted,  have  a  decided  advantage  over  those  of  the  for- 
mer type,  in  that  they  are  easily  repaired  in  case  of  fracture 
of  the  porcelain  parts. 

However,  cases  present  when  a  baked  porcelain  bridge 
will  fulfill  esthetic  requirements  where  one  of  another  type 
would  prove  inadequate. 

GENERAL   CONSIDERATIONS 

Most  of  the  failures  recorded  against  porcelain,  when 
used  in  bridgework,  are  due  to  its  injudicious  application. 


890  PORCELAIN    CROWN    AND    BRIDGE    WORK 

Certain  conditions  are  often  foinid  in  tlie  moiitli  wliich  pre- 
clude tlie  introduction  of  a  bridge  of  tliis  cliaracter. 

Porcelain  is  strong  only  in  bulk.  In  thin,  attenuated 
plates  it  is  friable  and  l)reaks  readily  under  stress.  The  truss 
or  platinum  framework  nmst  be  depended  upon  primarily,  to 
furnish  the  necessary  strength  to  resist  stress.  A  truss  may 
be  constructed  that  fulfills  this  requirement  and  the  case  still 
be  unsuitable  for  porcelain  if  the  remaining  spaces  not  occu- 
pied by  the  metal  structure,  is  so  limited  that  the  porcelain 
will  be  spread  over  the  framework  in  thin  layers,  especially 
on  occlusal  surfaces.  The  constantly  repeated  force  of  mas- 
tication, directed  against  the  cusps  of  porcelain,  will  fracture 
and  break  them  away  from  the  truss,  even  though  the  latter 
may  be  rigid  enough  to  retain  its  form. 

In  addition,  therefore,  to  having  sufficient  space  for  a 
rigid  truss,  there  must  be  sufficient  additional  space  remaining 
to  apply  the  porcelain  in  ample  bulk  to  resist  stress.  It  is 
impossible  to  state  just  how  wide  this  space  should  be.  A 
great  deal  depends  upon  the  hal)its  of  the  patient,  the  amount 
of  force  exerted  by  tlie  muscles  of  mastication,  the  length  of 
span  and  the  number  and  position  of  abutments  and  piers. 

It  may  be  stated  that,  as  a  general  rule,  there  nmst  be  a 
minimum  s]3ace  of  at  least  5  mm.  between  the  alveolar  border 
and  the  occlusal  surfaces  of  the  opposite  teeth  in  short  spans, 
while  longer  spans  will  naturally  require  more  space,  since 
the  truss  itself  must  be  more  bulky. 

The  length  of  span  is  a  matter  of  great  importance  and 
should  be  closely  studied.  In  long  spans,  where  much  curva- 
ture in  the  bridge  will  be  required  and  where  only  two  abut- 
ments afford  supjoort,  a  porcelain  bridge  would  most  certainly 
prove  a  failure.  If,  however,  there  is  an  intervening  pier, 
with  sufficient  space  to  insure  bulk  of  porcelain,  the  case 
would  be  suitable  for  an  appliance  of  this  character. 

The  points  to  be  carefully  observed  and  studied  are: 

First — The  number,  position  and  condition  of  the  roots 
or  teeth  that  are  to  serve  as  supports  for  the  bridge. 

Second — The  length  of  span  to  be  covered  by  the  truss. 

Third — The  amount  of  space  between  the  alveolar  border 
and  the  occlusal  surfaces  of  the  opposite  teeth. 

Fourth — The  habits  of  the  patient  as  to  the  care  of  the 
teeth. 

Fifth — The  amount  of  force  exerted  by  the  muscles  of 
mastication. 


PORCELAIN    CROWN    AND    BRIDGE    WORK  891 

Sixth — Study  carefully,  whether  a  substitute  of  any  other 
character  might  be  equally  as  serviceable  if  not  more  effi- 
cient than  porcelain. 

PORCELAIN   BRIDGE  CONSTRUCTION 

The  various  steps  involved  in  the  construction  of  a  porce 
lain  bridge  may  be  arranged  in  the  following  order: 

First — Preparation  of  the  abutment  or  pier  roots  or  teeth. 

Second — Construction  of  caps  or  shell  crowns  for  same. 

Third — Taking  bite  and  impression,  and  mounting  casts 
on  occluding  frame. 

Fourth — Locating  position  of,  and  constructing  and  sol- 
dering saddle  to  caps  and  crowns. 

Fifth — Locating  position  of,  and  fitting  truss  bars  in 
position. 

Sixth — Investing  and  soldering  same  to  caps  and  crowns. 

Seventh — Attaching  facings  to  metal  framework. 

Eighth — Application  of  body. 

Ninth — Baking. 

Tenth — Finishing. 

Eleventh — Setting  the  bridge. 

PREPARATION   OF  ROOTS   OR  TEETH 

The  preparation  of  the  roots  or  teeth  for  the  reception 
of  caps  and  crowns  which  are  to  serve  as  abutments  and  piers 
for  bridges  differs  in  no  essential  particular  from  the  instruc- 
tion previously  given  under  the  heads  of  porcelain  cro^vns  and 
shell  crouvs,  therefore  it  is  unnecessary  to  enter  into  the  de- 
tails of  this  procedure  here. 

CONSTRUCTION  OF  CAPS  AND  SHELL  CROWNS 

When  the  abutment  and  pier  crowns  are  to  be  of  porce- 
lain, the  construction  of  the  caps  is  similar  to,  or  identical 
with,  the  methods  outlined  under  the  head  of  porcelain 
crowns. 

When  platinum  shell  crowns  are  constructed  for  the  bicus- 
pids or  molars,  as  is  frequently  advisable,  the  details  differ 
in  a  few  essential  particulars,  from  the  methods  followed  in 
ordinary  shell  cr.own  construction. 

The  cusps  of  crowns,  when  platinum  is  used,  are  more 
difficult  to  swage  in  this  material  than  from  22  k.  gold  of  equal 
thickness.  Therefore,  in  order  to  have  the  needed  bulk  of 
platinum  in  the  occlusal  surface  of  a  crown,  to  withstand  attri- 


892  PORCELAIN    CROWN    AND    BRIDGE    WORK 

tioii;  two  thicknesses  of  platinum  are  swaged,  separately  at 
first,  and  then  together  and  solidly  attached  by  soldering. 

This  is  necessary  since  the  interior  of  such  crowns  can- 
not be  reinforced  with  solder,  as  is  done  in  ordinary  crown 
work,  as  the  latter  would  be  more  or  less  dissipated  by  the 
heat  necessary  to  fuse  the  porcelain. 

Special  care  should  be  taken  to  contour  the  occlusal 
margin  of  the  band  and  the  corresponding  margin  of  the  cusps 
until  they  coincide  perfectly,  then  true  both  contact  margins, 
first  with  a  flat  file,  following  this  by  dressing  on  an  oil 
stone  until  perfect  contact  is  secured,  thus  obviating  the  use 
of  much  solder  in  attaching  the  two  pieces  together. 

The  method  of  constructing  a  crown  of  this  class  in  the 
ordinary  manner,  and  afterward  swaging  a  second  piece  to  the 
interior  to  stiffen  up  the  occlusal  surface,  allowing  the  mar- 
gins of  the  second  piece  to  overlap  the  joint  between  the  band 
and  cusp,  is  frequently  resorted  to  with  satisfactory  results. 

To  give  additional  strength  to  the  crown,  at  the  point 
where  the  saddle  and  truss  bars  join  it,  a  second  piece  of 


ON    LEFT.    DRESSING    DOWN    OCCLUSAL    Cj\P    AND    AXIAL    BAND 

ON  OIL  STONE.     ON  RIGHT.  OCCLUSAL  CAP,  COMPOSED  OP 

TWO  THICKNESSES  OF  PLATINUM  PLATE 

platinum  plate  is  often  adapted  and  soldered  to  this  surface, 
on  the  outer  side  of  the  crown. 

The  caps  and  crowns  having  been  constructed  and  fitted 
in  their  respective  places,  an  accurate  bite  and  an  impression 
are  secured,  the  casts  constructed,  and  mounted  on  an  occliad- 
ing  frame. 

CONSTRUCTION   OF   SADDLE 

The  saddle,  although  not  universally,  is  frequently  used 
to  give  the  porcelain  proper  contour  on  both  labial  or  buccal 
and  lingual  surfaces. 

Formerly  broad  saddles  were  recommended  and  much 
used,  as  previously  mentioned,  but  for  reasons  already  stated 
their  use  has  been  discontinued. 

Saddles,  therefore,  when  indicated,  should  be  as  narrow 
as  possible,  yet  sufficiently  wide  to  fulfill  the  requirements  of 
proper  contouring  of  the  case. 


PORCELAIN    CROWN    AND    BRIDGE    WORK  893 

The  position  as  well  as  outline  for  the  saddle  can  be  best 
determined  by  waxing  the  facings  in  position  and  trimming 
the  wax  to  correct  form,  then  marking  on  the  line  thus 
indicated.  Another  method  frequently  followed  is  to 
make  the  saddle  broader  than  necessary,  and  after  the  first 
application  and  making  of  the  body,  cut  away  the  surplus 
margins.  This  gives  good  results,  lint  entails  considerable 
waste  of  material. 

Tlie  saddle  should  la})  well  over  caps  and  against  crowns, 
to  insure  secure  attachment  of  the  several  parts.  It  is  cut 
to  proper  length  and  width  as  indicated  by  the  outline  on  the 
cast,  and  either  burnished  and  conformed  to  it,  or  swaged  on 
Melotte's  metal  die.  Wliere  the  surfaces  on  which  the  saddle 
is  to  rest  are  very  irregular,  the  latter  method  is  an  excellent 
and  accurate  one. 

When  swaged  or  conformed  perfectly  to  the  cast  or  die, 
it  is  attached  to  the  caps  and  crowns  by  soldering  and  the 
several  connected  parts  are  fitted  in  the  mouth  for  final  ad- 
justment of  the  saddle  to  the  natural  tissues.  A  large  round 
end  burnisher,  or  one  of  the  contra-angled  form  designed 
by  the  author,  can  be  used  for  this  purpose.  The  saddle  should 
be  pressed  uniformly  against  the  soft  tissues  until  a  slight 
blanching  of  the  gum  is  noticeable.  This  should  disappear 
in  tliree  or  four  minutes  and  tlie  tissues  regain  their  normal 
appearance.  Too  great  pressure  will  produce  hypertrophy  of 
the  tissues  and  finally  atrophy  and  absorption,  while  under  a 
properly  adjusted  saddle  they  will  usually  remain  in  a  healthy 
condition  and  in  contact  with  it  for  a  varying  period. 

At  this  time  the  partially  constructed  framework  is  in 
position  in  the  mouth,  and  the  soft  tissues  in  a  more  or  less 
com])ressed  condition.  If  removed  and  placed  on  the  original 
cast,  the  saddle  would  be  distorted,  since  the  cast,  unlike  the 
gum  tissue,  is  unyielding.  Therefore  it  becomes  necessary  to 
take  a  new  bite  and  impression,  and  mount  tlie  cast  as  before. 

LOCATING  AND  FITTING  TRUSS  BARS 

In  short  spans  a  single  bar  of  16  or  15  gauge  round  iridio- 
jilatinum  wire  is  usually  sufficient  to  furnish  the  needed  rigid- 
ity and  support  to  the  bridge.  Longer  spans  frequently  re- 
quire two  bars  of  16-gauge,  or  a  single  bar  of  14-gauge. 

The  position  for  the  truss  bar  is  found  by  grinding  the 
facings  accurately  to  place  and  waxing  them  in  position.  Var- 
nish the  outer  surface  of  the  cast  with  separating  medium  and 
build  a  matrix  of  plaster  against  the  labial  or  buccal  surfaces 


894  PORCELAIN    CROWN    AND    BRIDGE    WORK 

of  tlie  teeth  and  cast.  When  set,  remove  from  t!ie  cast,  and, 
if  the  facings  have  remained  with  tlie  framework,  remove 
and  jilace  them  in  their  respective  positions  in  the  plaster 
matrix. 

The  wax  is  all  removed  and  the  plaster  matrix  carrying- 
the  teeth  returned  to  the  cast.  Tiie  truss  bar  is  then  bent  and 
conformed  to  the  lingual  surfaces  of  the  facings,  usually  occu- 
pying a  position  between  the  pins  and  the  ridge  lap.  By  plac- 
ing in  tliis  position,  more  space  is  afforded  for  the  porcelain 
and  the  liability  of  its  breaking  away  under  stress  will  be 
much  less  than  if  the  bar  was  placed  between  the  pins  and 
the  occlusal  or  incisal  margins  of  the  facings. 

Broad  surface  contact  should  be  secured  between  the  bar 
and  dowels  and  the  several  parts  held  in  absolute  contact  while 
soldering,  so  as  to  insure  the  greatest  possible  amount  of 
strength. 

The  attachment  of  the  bar  to  a  shell  crown  is  usually 
made  by  splitting  the  abutting  end  and  adapting  the  split  por- 
tions to  the  reinforced  section  of  the  crown  before  mentioned ; 
or  a  hole  may  be  drilled  through  the  axial  wall  of  the  crown 
and  the  bar  bent  so  as  to  pass  up  the  inner  side  of  the  wall  and 
across  the  occlusal  surfaces,  a  groove  being  cut  in  the  tooth, 
if  necessary,  for  the  accommodation  of  the  bar.  This  affords 
a  firm  anchorage  to  the  crown  and  one  that  will  not  pull  away, 
as  frequently  occurs  when  the  contact  of  the  bar  with  the  crown 
is  superlicial. 

Eound  or  oval  are  preferable  to  square  bars,  since  the 
sharp  angles  on  the  latter  seem  to  induce  fracture  in  the 
porcelain,  under  stress. 

If  square  wire  is  used  the  sharp  angles  should  be  rounded 
off  to  obviate  this  difficulty. 

When  the  bar  is  accurately  adapted,  the  ends  are  waxed 
to  the  dowels  and  crown  attachments. 

In  the  series  of  drawings  shown  in  Cut  I  from  a  former 
edition  of  this  text,  the  construction  of  a  two-bar  truss  of 
square  wire  is  illustrated.  In  31  d  the  bar  next  to  the  saddle 
is  first  fitted  and  attached  to  cap,  dowel  and  shell  crown. 
The  second  bar  nearest  the  occlusal  surface  is  next  fitted, 
bending  it  so  as  to  lie  in  close  contact  with  the  lingual  sur- 
faces of  the  facings  as  shown  in  .32  e.  It  can  be  bent  to 
pass  over  the  pins  if  necessary,  but  when  jjossible  should 
pass  under  them,  for  reasons  before  stated.  It  can  be  bent 
irregularly  to  follow  the  line  of  the  pins,  should  they  be  \va- 
even.    The  ends  of  the  bars  connected  with  the  dowel  can  be 


PORCELAIN    CROWN    AND    BRIDGE    WORK  895 

notched   as   indicated   in  3-1  and  the   reduced  portion   bent 
around  it,  as  shown  in  35. 

Thirty-three  shows  imperfect  contact  of  post  and  bar ;  37, 
a  condition  in  which  there  is  not  space  enough  between  the 
labial  side  of  the  dowel  and  the  lingual  surface  of  the  facing 
to  receive  the  truss  bar,  and,  to  overcome  the  difficulty,  both 
dowel  and  bar  are  notched.  In  some  cases  both  bars  lie  on  the 
same  side  of  the  dowel,  one  upon  the  other,  as  indicated  in 
31  c,  and  again  there  are  cases  whei'e,  if  arranged  in  this 
manner,  the  outer  one  would  l)e  thrown  too  far  occlusally. 


JA^ 


CDTS   SHOWING    VARIOUS    STEPS    IN   THE   FITTING    OK    SADDLES,    TRUSS   BARS.    AND    TEETH 

OP  A   PORl'ELAIX  BRIDGE.      IN  THIS  CASE  THE  MOLAR  IS  A  SHELL 

PLATINUM  CROWN 

One  is  then  placed  on  the  lingual  side  of  the  dowel  and  the 
other  one  on  the  opposite  side,  as  in  38. 

In  36  the  method  of  splitting  the  bar  and  bending  the 
split  ends  so  as  to  partly  encircle  the  shell  crown  is  illustrated. 
When  bicuspid  and  molar  roots  carry  full  porcelain  crowns 
the  bars  are  attaclied  to  their  caps  and  posts  in  the  manner 
described. 

The  bars,  when  fitted,  are  connected  by  braces,  which  are 
cut  and  accurately  fitted  in  position.  Both  ends  can  be  notched 
as  shown  in  31  /. 


896 


PORCELAIN    CROWN    AND    BRIDGE    WORK 


CDT    II  CUT    111 

URIDGE    ItEFOKB   AND    AFTER    DUPLICATION  AND    FUSING 

OF  THE  PORCELAIN  BODY 

Cut  II  shows  a  single  bar  truss,  with  short  posts  soldered 
on  the  molar  cap  and  at  intervals  along  the  truss  bar,  to  afford 
firmer  attachment  to  the  lingual  body  of  porcelain. 


FRAMEWORK  OF  AN  UPPER.  FOUR-TOOTH 
BRIDGE,  SHOWING  HEAVY  TRUSS  BAR  AT- 
TACHED TO  DOWELS  OF  CUSPID  AND 
FIRST  MOLAR  CROWN.  FITTED  WITH 
NARROW    SADDLE 


Cut  III  shows  the  \neee  after  the  porcelain  has  been  ap- 
plied and  baked. 

SOLDERING 

The  several  parts  having  been  accurately  fitted  they  are 
waxed  together,  the  facings  removed,  the  cap,  crown,  saddle 
and  truss  removed  from  the  cast  and  invested  so  that  the  in- 
vesting material  extends  over  the  bars  and  holds  them  firmly 
in  position  after  the  wax  is  removed.  When  soldered,  the 
frame  is  returned  to  the  model  and  the  facings  returned  to 
place,  waxed  in  position,  the  piece  removed,  again  invested, 
the  pins,  after  having  been  flattened,  bent  in  actual  and  close 
contact  with  the  bar  and  soldered. 

The  essential  points  to  he  observed  in  constructing  the 
framework  for  a  porcelain  bridge  are: 

First,  be  accurate  in  every  detail.  Second,  develop  close 
joints  Third,  flow  solder  into  and  between  all  junctions  so  as 
to  perfectly  unite  the  several  parts  together. 


APPLICATION  OF  THE   BODY 


Before  applying  the  porcelain  body,  the  framework  should 
be  pickled,  cleansed  and  roughened  on  those  surfaces  against 


PORCELAIN    CROWN    AND    BRIDGE    WORK  897 

which  the  porcelain  is  to  be  fused  to  afford  some  additional 
attachment  of  the  porcelain  to  the  metal  framework. 

As  mentioned  in  connection  with  crown  work,  a  pin  vice 
can  be  used  to  good  advantage  in  handling  the  piece  while 
applying  the  body. 

The  body  is  built  on  the  lingual  surfaces  of  the  facings 
and  against  the  saddle  a  little  at  a  time,  the  piece  vibrated 
to  settle  the  granules  of  powder  close  together,  the  moisture 
is  taken  up  as  it  appears  on  the  surface,  and  a  rough  contour 
given  the  piece  for  the  first  baking. 

All  particles  of  body  should  be  removed  from  the  labial 
or  buccal  surfaces  of  the  facings,  for  if  carried  through  the 
furnace  they  become  attached  and  can  only  be  removed  by 
discing  or  grinding,  which  destroys  the  fine  glaze  on  the 
porcelain. 

FUSING  THE  PORCELAIN 

The  directions,  beginning  on  page  615,  with  reference  to 
the  fusing  of  continuous  gum  body  apply  with  equal  force  in 
the  fusing  of  porcelain  in  bridgework.  Uusually,  the  piece, 
being  smaller,  can  be  fused  in  somewhat  shorter  time  than  a 


SMALL     ELECTRIC     KCRNACE     SCITARLE    FOIt     PORCELAIN 

CROWX,    HRIDOE.    AND   INLAY  WORK 

(HAMMOND) 

full  denture,  and  since  less  time  is  required,  greater  care  must 
be  observed  in  the  latter  stages  of  baking,  to  prevent  over 
fusion. 

When  possible  to  do  so,  the  bridge  should  l)e  completed  in 
two  bakings  to  avoid  friability  of  the  material,  which  char- 
acteristic, as  well  as  a  tendency  to  liecome  porous,  develops 
rapidly  after  the  second  fusion. 


S9S  PORCELAIN    CROWN    AND    BRIDGK    WORK 

FINISHING   AND    SETTING    THE    BRIDGE 

Pinisliing  and  setting  a  porcelain  bridge  differ  in  no 
essential  particulars  from  the  steps  involved  in  the  finishing 
and  setting  of  porcelain  crowns,  the  details  of  which  have  been 
given.     As  previously  mentioned,  however,  the  use  of  the 


SMALL,    GASOLLNE     FURNACE     SUITABLE     FOB     PORCELAIN     CBOWN. 
BRIDGE.  AND  INLAY  WORK   (TURNER) 

mallet,  either  hand  or  automatic,  should  be  avoided  in  the  set- 
ting of  baked  crowns  of  porcelain,  combined  with  metal,  be- 
cause of  the  very  great  danger  of  fracture. 


VARIOUS  TYPES   OF   METAL   STRUCTURES 

The  principal  thought  to  keep  in  mind  in  planning  a 
porcelain  bridge  is  to  form  a  rigid  metal  structure,  capable  of 
sustaining  all  stress  to  which  the  bridge  may  be  subjected, 
without  depending  upon  the  applied  porcelain. 

Therefore,  the  forms  of  trusses  may  be  varied  according 
to  conditions,  as  space  occluso-gingivally,  length  of  span,  posi- 
tion of  abutments,  width  of  alveolar  border,  etc. 

Frequently,  in  the  replacement  of  a  single  tooth,  a  truss 
of  the  cantilever  type  may  be  united  with  a  single  crown,  the 
opposite  end  terminating  in  a  projection  for  resting  in  a 
grooved  inlay  in  the  proximating  tooth. 

In  other  cases,  instead  of  a  saddle  being  adapted  to  the 
bordei',  a  half-round  wire  is  fitted  close  to,  or  in  contact  with, 


PORCELAIN    CROWN    AND    BRIDGE    WORK  899 

tlie  border  crest,  against  which  tlie  Iniccal  and  lingnal  surfaces 
of  ai»plicd  porcelain  may  terminate. 


FRAMEWORK  OF  AN  EXTEN- 
SION BRIDGE,  WITH  SUP- 
PORTING LDO  TO  REST  IN 
GROOVED  INTiAY  IN  CUSPID 
TOOTH 


FRAMEWORK  OP  A  LOWER  FOUR-TOOTH 
BRIDGE.  HEAVY  TRUSS  BAR  FOR  SUPPORT- 
ING TEETH.  HALF-ROUND  WERE  TO  REST  ON 
BORDER  CREST,  AND  AGAINST  WHICH  BOTH 
BUCCAL  AND  LINGUAL  SURFACES  OP  PORCE- 
LAIN WILL  TERMINATE 


FR.AME\VORK      OF      AN      UPPER.       FOUR-TOOTH 

BRIDGE    FITTED    WITH    SADDLE,    TO    WHICH    A 

LINGUAL    FLiVNGE    IS    APPLIED    FOR    SUPPORT 

OF    PORCELjUN 

Again  a  flange  of  platinum  is  adapted  and  attached  to 
the  lingual  border  of  the  saddle  or  wire  to  add  strength  to  the 
framework  and  afford  a  matrix  for  supporting  tlie  porcelain 
under  stress. 


900  PORCELAIN    CROWN    AND    BRIDGE    WORK 

The  Peeso  and  Bensou  pliers,  because  of  their  short  beaks 
and  heavy  handles,  are  partifiilarly  nsofnl  for  coiitonrins'  of 


THE  TEESO    CONTOUBINO    PLIERS 


THE   liEN'SOX    CONTOllRIXd    PI.IERS 


plate  and  bending  of  wires  in  this,  as  in  many  other  classes  of 
crown  and  bridge  work. 


CHAPTEE    XXXI 

INLAYS 

PORCELAIN   AND   METALLIC 
PORCELAIN 

Porcelain,  or  "cliiiunvare, "  was  imported  into  Europe 
principally  by  the  Portugese,  who  gave  it  the  name  of  porce- 
lain, from  its  resemblance  to  the  nacre  or  lining  of  the  sea- 
shell  Porcellana  (C'yprea).  The  shells  of  this  species  derive 
their  name  from  their  supposed  resemblance  to  the  back  of  a 
hog  (Porcus).  It  was  at  first  su^jposed  that  porcelain  con- 
sisted of  pulverized  egg  shells,  fish  scales  and  fish  glue. 

The  first  authentic  record  we  can  find  of  porcelain  being 
used  for  dental  purposes  appears  in  the  "Art  of  Dentistry," 
published  by  Fauchard  in  17:28.  In  this  he  says:  "I  have 
thought  that  advantage  might  be  derived  from  a  regular  and 
unaltei'able  coloration  from  enamel  artificially  composed.  I 
have  also  thought  that  I  might  from  this  not  only  perfectly 
imitate  the  enamel  of  the  teeth,  but  the  gum  in  cases  where  it 
is  necessary  to  replace  the  teeth  in  whole  or  in  parts  of  sets. 
I  have  consulted  the  most  able  enamelers,  and  by  conversa- 
tions which  I  have  had  with  them  I  have  rendered  practicable 
tiiat  which  I  believe  no  one  else  has  ever  thought  of;  the  teeth 
or  dentures  made  of  enamel  will  endure  a  very  considerable 
time,  since  the  enamel  is  a  substance  scarcely  susceptible  of 
change  or  alteration." 

EARLY    APPLICATION    OF    PORCELAIN    IN   DENTURE 
CONSTRUCTION 

The  development  of  porcelain  in  its  application  to  den- 
tistry is  a  most  interesting  story,  an  outline  of  which  will  be 
found  in  the  chapter  on  the  "History  of  Prosthetic  Den- 
tistry. ' ' 

The  efforts  of  the  pioneers  in  the  porcelain  field  until 
Fonzi's  time,  1808,  were  directed  principally  to  the  produc- 
tion of  full  and  partial  dentures  in  a  single  piece,  yet  but 
little  progress  .was  made  in  this  class  of  work  until  about 
1850,  when  Dr.  John  Allen  introduced  the  continuous  gum 
denhire.  His  work  consisted  in  improving  the  character  of 
the  porcelain  then  in  use,  reducing  its  fusing  point  and  con- 

901 


902  INLAYS 

tractile  tendency,  improving  tlie  color  of  the  gum  enamel, 
and  of  baking  the  denture  on  a  platinum  base  to  which  the 
teeth  were  previously  attached  by  soldering.  The  use  of  the 
platinum  base  obviated  the  warpage,  which  invariably  oc- 
curred when  the  porcelain  was  fused  on  a  silex  and  plaster 
form. 

CORRECTION    OF   WARPAGE   IN    THE    ALL-PORCELAIN 
DENTURE 

Previous  to  Allen's  improvement,  it  was  necessary,  after 
the  denture  was  baked,  to  secure  an  accurate  cast  of  the 
mouth  in  plaster,  paint  the  areas  to  be  covered  by  the  denture 
with  red  lead  or  similar  pigment,  and  apply  the  denture  to  the 
cast ;  the  areas  of  contact  between  denture  base  and  cast  were 
colored  on  the  base  with  the  pigment,  and  on  removal  were 
ground  with  small  stones.  This  process  of  trial  and  grinding 
was  repeated  until  finally  the  entire  denture  surfaces  which 
rested  upon  the  oral  tissues  showed  color,  when  pressed  ujjon 
the  cast.  The  same  general  technic  was  followed  in  securing 
adaptation  to  the  oral  tissues,  of  the  old-time  dentures  carved 
from  the  elephant  or  hippopotamus  ivory. 

Dentures  constructed  by  this  method,  while  occasionally 
showing  good  adaptation  and  stability,  usually  recjuired  the 
aid  of  springs  for  their  retention  under  masticatory  stress. 

BASIC   INGREDIENTS   OF  PORCELAIN 

The  basic  ingredients  in  most  of  the  porcelain  bodies  of 
today  consist  of  kaolin,  silex  and  feldspar  in  proportions 
varying  according  to  the  purpose  for  which  the  material  is 
intended.  The  porcelain  used  for  tooth  bodies  is  the  highest 
fusing  of  any  used  for  dental  purposes,  the  point  of  vitrifica- 
tion ranging  from  2,440°  to  2,600°  F. 

KAOLIN    (Al,H,(SiO.)-H,0 

The  word  kaolin  is  a  corruption  of  the  Chinese  word 
Kauling,  which  means  a  high  ridge,  and  is  the  name  of  a  hill 
near  Jachau  Fu,  China,  from  which  a  great  deal  of  this  ma- 
terial is  derived.  A  tine  variety  of  clay  is  also  found  in 
Germany.  Both  of  these  varieties  of  elaj"  are  practically  free 
from  iron  oxide  and  other  deleterious  imirarities  and  are  used 
almost  exclusively  in  the  compounding  of  dental  porcelains. 

Kaolin  is  a  tine  pure  variety  of  clay,  or  aluminum  sili- 
cate.    It  is  formed  by  the  disintegration  and  decomposition 


INLAYS  903 

of  granitic  and  feldspatliic  rocks  tlirougli  weathering,  or  con- 
tinued freezing  and  thawing.  Tliese  rocks  being  granular, 
take  up  moisture,  and  this  when  expanded  by  freezing  spilts 
oft"  the  outer  surfaces  of  the  rock.  The  rain  in  time  dissolves 
out  some  of  the  constituents  and  washes  away  the  small  par- 
ticles, which,  as  they  are  carried  down  the  stream,  grind  upon 
each  other  and  become  still  more  finely  divided  until  all  sem- 
blance of  their  original  form  is  lost.  These  particles,  mixed 
with  sand,  float  or  are  washed  down  stream  and  settle  in  beds. 
Some  of  these  clay  beds  are  at  tlie  present  time  high  above 
the  water  line,  having  been  deposited  ages  ago  and  placed  in 
their  present  location  by  volcanic  upheavals. 

PREPARING  THE  CLAY   FOR  USE 

The  clay  is  prepared  for  use  by  mixing  with  water  in  a 
tank,  agitating  and  allowing  the  sand  and  heavier  particles  to 
settle,  after  which  the  water  is  drawn  otf  into  another  tank, 
while  the  finer  j^articles  of  clay  are  still  held  by  it  in  solution. 

These  finer  particles  are  allowed  to  settle  in  the  second 
tank,  and  when  the  water  becomes  clear  it  is  carefully  drawn 
off  and  the  clay  allowed  to  dry.  The  slab  of  dry  clay  is  then 
turned  over  and  the  coarser  particles  which  settled  to  the  bot- 
tom as  the  first  preciiiitate  are  scraped  off,  when  it  is  ready 
for  use. 

FELDSPAR    (KAlSi.OO 

Feldspar  is  a  double  silicate  of  aluminum  and  potassium 
known  as  Orthoclase.  It  occurs  crystallized  in  rhombic  prisms. 
There  are  many  varieties  of  this  mineral,  but  only  those  that 
are  free  from  soda  or  lime  are  used  in  compounding  porce- 
lain. It  is  yellowish  pink  in  color  in  its  natural  state,  but 
transparent  and  colorless  when  fused. 

A  variety  of  this  mineral  suitable  for  tooth  bodies  is 
found  in  many  parts  of  the  United  States.  The  principal  de- 
posits snital)le  for  the  compounding  of  porcelain  are  found 
near  Wilmington,  Del. 

PREPARING  THE  FELDSPAR  FOR  USE 

Feldspar  is  prepared  for  use  by  heating  to  redness,  drop- 
ping in  water  while  hot,  to  break  it  up  into  small  pieces, 
ground  to  powder  in  a  special  pulverizing  machine  or  with  a 
large  mortar  and  pestle,  and  under  water,  to  facilitate  the 
grinding.  The  powder  is  then  run  through  a  No.  10  bolting 
sieve,  placed  in  closed  vessels  to  keep  dry  and  free  from  im- 


purities  until  needed  for  use.    Pulverizing  too  finely  detracts 
from  the  translucency  of  the  porcelain  when  fused. 

SILICA    (SiO.) 

This  mineral  is  a  silicic  oxide,  ordinarily  known  as 
quartz.  It  is  one  of  the  constituents  of  granitic  rocks ;  it  also 
occurs  free  in  large  masses  in  many  parts  of  the  United 
States,  as  well  as  in  many  parts  of  the  Avorld. 

PREPARING  THE  SILICA  FOR  USE 

Silica  is  prepared  for  use  l),y  grinding  to  a  liue  powder 
in  a  powerful  mill  constructed  especially  for  this  class  of  work. 
It  is  extremely  hard  and  fuses  only  at  very  high  tempera- 
tures, about  .3,500°  F. 

These  three  materials,  kaolin,  silex  and  feldspar,  as  be- 
fore stated,  are  combined  in  varying  proportions  to  form 
tooth  bodies,  and  the  more  fusible  continuous  gi;m  and  inlay 
bodies. 

PROPERTIES  OF  THE  BASIC  CONSTITUENTS  OF 
PORCELAIN 

Kaolin  imparts  plasticity  to  the  tooth  body,  enabling  it 
to  be  luolded  into  the  desired  form  before  baking.  It  also 
contracts  somewhat  in  fusing,  and  as  a  result  draws  together 
the  more  infusible  constituents,  thereby  imparting  density  to 
the  mass. 

Silex,  on  account  of  its  infusible  property,  tends  to  keep 
the  form  into  which  it  is  molded,  whether  inlay,  tooth,  crown, 
bridge  or  denture,  from  melting  down  in  the  heat  of  the  fur- 
nace. 

Feldspar  imparts  translucency  and  also  acts  as  a  flux, 
closely  uniting  the  kaolin  and  silex.  By  varying  the  propor- 
tion of  this  material  in  compounding  the  l)ody,  a  number  of 
porcelains  differing  in  texture  and  fusibility  can  be  pro- 
duced. 

APPROXIMATE    PROPORTIONS    OF    INGREDIENTS    IN 
PORCELAIN 

The  manufacturers  do  not  publish  the  formulas  of  their 
tooth  or  other  porcelain  bodies  of  the  lower  fusing  types  de- 
signed to  be  used  in  continuous  gum  and  other  classes  of 
work.  Since  it  is  not  necessary  for  the  prosthetist  to  com- 
pound his  own  porcelain  materials,  as  the  pioneers  in  this 


INLAYS  905 

field  were  required  to  do,  still  it  is  essential  that  he  know 
the  elementary  constituents  and  their  physical  properties 
in  order  that  the  best  results  may  be  derived  from  their  use. 

The  names  of  Wildman,  Hunter  and  Allen  are  insepara- 
bly connected  with  the  history  of  continuous  gum  work  and 
carved  block  teeth  in  this  country,  and  to  them  the  profession 
owes  mucli  for  im^^rovements  in  porcelain  bodies  and  tech- 
nical methods.  The  period  of  greatest  activity  of  these  early 
porcelain  workers  extended  from  1835  to  1860.  Since  the 
latter  date  the  carving  and  baking  of  single  and  block  teeth 
in  the  dental  laboratory,  as  was  the  prevailing  custom  in 
their  time,  has  been  discontinued  because  of  the  continually 
advancing  improvements  in  these  lines  of  the  manufactured 
products.  Continuous  gum  dentures,  however,  cannot  be 
made  in  a  factory.  The  prosthetist,  therefore,  should  be 
capable  of  selecting  the  best  material  and  of  manipulating 
it  in  tlie  best  possible  manner  to  secure  ai'tistic  and  perma- 
nent results  in  the  construction  of  dentures  of  this  type. 

The  following  formulas  will  show,  in  a  general  manner, 
the  proportions  of  the  basic  ingredients  used  in  compound- 
ing some  of  the  many  iiorcelains : 

Dr.  Wildman's  fonnnla  for  toDth  bodi/: 

No.  1.     Kaolin   1  oz. 

Silex 3  ozs. 

Feldspar  18  ozs. 

Titanium  oxide 65  grs. 

Titanium  oxide  imparts  a  yellowish  tint  to  porcelain. 
The  oxides  of  some  of  the  other  metals  are  used  for  produc- 
ing various  tints,  as  required ;  they  are  mixed  in  and  thor- 
oughly incorporated  with  the  porcelain  in  process  of  manu- 
facture, the  latter  often,  after  the  addition  of  the  metallic 
oxide,  being  fused,  crushed  and  pulverized,  to  more  thor- 
oughly disseminate  the  tint. 

OXIDES  OF  THE  METALS  USED  IN  TINTING  PORCELAIN 

Gold  in  a  state  of  minute  subdivision Eose  red 

Oxide  of  gold Bright  rose  red 

Purple  of  Cassius  (double  oxide  of  tin  and  gold .  Purplish  red 

Sponge  platinum  and  filings Grayish  blue 

Oxide  of  cobalt.  . : Bright  blue 

Oxide  of  manganese Purple 

Oxide  of  uranium Greenish  yellow 

Oxide  of  silver Lemon  yellow 

Oxide  of  zinc Lemon  yellow 

Oxide  of  titanium Bright  yellow 


906  I^a,AYS 

The  formula  for  continuous  gum  body  is  similar  to  that 
of  the  Wildnian  tooth  hody,  previously  given,  except  that  more 
kaolin  and  feldspar  are  added  to  reduce  the  fusing  point ;  this 
is  necessary  in  order  that  the  teeth,  which  have  previously 
heen  attached  to  the  platinum  base,  will  not  be  fused  and  lose 
their  shape  or  color  while  vitrifying  the  continuous  gum  body. 

THE  CONSTITUENTS   OF  GUM   ENAMEL 

The  continuous  gum  body,  when  applied  around  the 
teeth  and  over  the  metallic  base,  gives  form  and  contour  to 
the  denture;  in  color  it  does  not  resemble  the  natural  gums, 
being  white,  or,  when  oxide  of  titanium  is  present,  slightly 
yellow;  the  denture  must  be  tinted  to  give  it  a  natural  ap- 
pearance. A  material  called  gtim  enamel,  purplish  pink  or 
red  in  color,  is  distributed  in  a  thin,  more  or  less  uniform 
layer,  over  those  surfaces  representing  the  mucous  tissues 
and  fused  to  the  continuous  gum  body,  thus  giving  the  re- 
quired color  and  the  proper  glaze,  to  the  surfaces  of  the 
denture  as  well. 

Gum  enamel  is  made  by  combining  certain  compounds  in 
definite  proportions  with  feldspar.  These  compounds  are 
known  as  frits  and  fluxes,  the  formuke  of  which  are  similar  to 
the  following: 

No.  2.     Flux. 

Carbonate  of  potassium 1  oz. 

Fused  borax  (powdered) 1  oz. 

Quartz 4  oz. 

These  materials  are  fused  together,  then  crushed  and 
ground  to  a  tine  powder,  to  prepare  them  for  combining  with 
the  following: 

No.  3.     Gum  frit. 

Purple  of  Cassius 16  grs. 

Feldspar  700  grs. 

Flux  (as  per  Formula  No.  2) . .  .175  grs. 
This  gum  frit  is  fused,  crushed  and  ground  to  a  tine 
powder,  preparatory  to  the  final  compounding  of  the  pink 
gum  enamel. 

No.  4.     Gum  enamel. 

Gum  frit  (as  i^er  Formula  No.  3)     1  oz. 

Feldspar 3  oz. 

This  also  is  fused,  crushed  and  ground,  wlien  it  is  ready 
for  use.  Fortunately,  both  continuous  gum  body  and  gum 
enamel  of  excellent  quality  are  procurable  at  the  supply 
houses,  which,  by  mixing  into  a  paste  with  water,  is  ready 


for  immediate  use.  From  the  preceding  formulas  a  vague 
idea  can  be  formed  as  to  the  amount  of  study  and  effort  it 
has  taken  to  develop  suitable  materials  for  use  in  dento- 
ceramic  art. 

CROWN,  BRIDGE  AND  INLAY  PORCELAINS 

The  porcelain  most  commonly  used  in  crown,  bridge  and 
inlay  work  closely  resembles  in  composition  and  physical 
properties  that  prepared  for  continuous  gum  work,  except 
that  it  is  ground  a  little  finer  and  fuses  at  a  slightly  lower 
temperature.  Crown,  bridge  and  inlay  porcelain  is  also  pre- 
pared in  a  variety  of  colors,  in  order  to  match  the  varying 
shades  of  teeth  in  and  next  to  which  it  may  be  placed. 

HIGH  AND  LOW  FUSING  PORCELAIN  BODIES 

The  fusibility  of  porcelain  separates  this  material  into 
two  general  classes,  the  fusing  point  of  pure  gold  being  the 
dividing  line.  Those  fusing  at  or  above  this  point  are  called 
high  fusing,  and  those  fusing  under  this  point  are  denomi- 
nated lotv  fusing  porcelain. 

The  following  table,  from  Dr.  W.  A.  Price's  tempera- 
ture scale,  gives  the  approximate  temperatures  required  to 
vitrify  the  principal  bodies  and  enamels,  also  the  fusing  point 
of  gold  and  coiDperas  registered  liy  the  same  scale: 

Consolidated  tooth  body 2630-F. 

S.  S.  White's  tooth  body 2515-F. 

Dental  protective  tooth  body 2440-F. 

Justi's  tooth  bodv 2440-F. 

Sibley's  tooth  body 2410-F. 

White's  porcelain   (crown  and  bridge)  .2300-F. 

Close's  bodv  2300-F. 

Ash's  tooth  body 2260-F. 

Whiteley's  porcelain 2210-F. 

Brewster's  bodv 2210-E\ 

Consolidated  high  fusing 2200-F. 

Brewster 's  enamel 2080  F. 

Moffitt's  porcelain   2050-F.     . 

Copper    1980-F. 

Gold 1950-F. 

Ash's  high-  fusing 1900-F. 

Downie-'s    1550-F. 

Jenkins'   1550-F. 

Ash's 1550-F. 

Brewster's  low 1500-F. 


COMPARATIVE  VALUE  OF  HIGH   AND  LOW   FUSING 
PORCELAINS 

Experience  has  shown  that  lii.uli  i'usini'-  jiorcehiin  is  a 
stronger  and  more  permanent  material  for  use  in  the  montli 
than  is  the  low-fusing  porcelain.  Foi'  this  reason,  therefore, 
it  has  almost  entirely  displaccMJ  the  latter,  especially  in 
crown  and  bridge  construction,  and  in  inlay  work  where  the 
filling  will  be  subjected  to  any  considerable  stress. 

The  principal  advantage  of  low-fusing  porcelain  for  in- 
lay work  is  in  the  ease  witli  which  it  may  be  fused,  and  in 
certain  cases  because  of  its  more  opaque  texture,  better  color 
results  in  the  matching  of  the  natural  teeth  are  possible 
than  with  high-fusing  bodies.  In  the  hands  of  the  inexpe- 
rienced it  is  doubtful  whether  the  low  fusing  will  yield  as 
good  results  as  will  the  iiigh-fnsing  ))odies. 

PORCELAIN  INLAY  WORK 

The  system  of  inlay  work  most  generally  in  vogue  at  the 
present  time  consists  in  preparing  the  tooth  cavity,  conform- 
ing a  matrix  of  platinum  or  pure  gold  to  it,  or  a  reproduc- 
tion of  it,  fusing  the  inlay  material  into  the  matrix  thus 
formed,  removing  the  matrix  from  the  fused  filling  and  set- 
ting the  latter  in  the  cavity  with  cement.  Like  all  classes 
of  filling  materials,  porcelain  has  its  advantages  and  disad- 
vantages. 

ADVANTAGES 

With  care,  skill  and  experience,  porcelain  inlays  may, 
in  many  cases,  be  so  accurately  constructed,  and  the  shades 
of  the  natural  teeth  in  which  they  are  placed  so  perfectly 
matched,  that  it  will  be  impossible  to  detect  these  restora- 
tions from  the  natural  tooth  structure,  except  by  the  closest 
scrutiny.  The  esthetic  properties  of  this  material,  there- 
fore, place  ])orcelain  above  that  of  any  other  filling  material 
for  the  artistic  restoration  of  natural  teeth.  Its  insolubility 
places  it  above  the  synthetic  cements. 

Second,  porcelain  is  a  poor  thermal  conductor,  and  for 
this  reason,  inlays  may  be  placed  in  cavities  of  teeth,  the 
pulps  of  which  are  sensitive  to  sudden  temperature  changes, 
where  metallic  fillings  could  not  be  tolerated. 

Third,  patients  are  relieved  from  long  and  tedious  sit- 
tings in  the  chair,  when  for  any  reason  they  are  physically 
unfit  for  lengthy  operations. 


Fourth,  the  strain  upon  the  operator  is  much  less  than  in 
ordinary  filling  operations. 

OBJECTIONS 

The  principal  disadvantages  resulting  from  inherent  de- 
fects in  the  material  itself,  or  from  use  in  the  mouth,  may 
be  stated  as  follows :  Friability,  constructive  difficulties, 
shadow  problem  and  retention. 

FRIABILITY 

In  thin,  attenuated  plates,  porcelain  is  frial)le  and  very 
easily  broken.  It  is  strong  only  in  bulk,  and,  therefore,  the 
utmost  care  should  he  exercised  in  the  preparation  of  cavi- 
ties to  so  shape  them  that  the  inlay,  when  set,  may  be  sub- 
jected to  but  little,  if  any,  stress.  Cavities  involving  an 
incisal  edge  or  the  proximo-occlusal  surfaces  of  a  bicuspid 
or  molar  should  be  so  formed  that  the  inlay  will  have  strong, 
well-defined  margins  and  ample  bulk  to  withstand  masti- 
catory action  without  fracturing.  When  conditions  preclude 
the  formation  of  cavities  in  this  manner,  porcelain  is  contra- 
indicated. 

DIFFICULTIES  MET  WITH  IN  CONSTRUCTION 

Among  the  most  important  difficulties  which  arise  dur- 
ing the  construction  and  in  the  a]5plication  and  use  of  porce- 
lain inlays,  the  following  deserve  careful  consideration: 

First,  inlay  retention,  or  developing  retention  form  in 
the  cavity,  so  that  the  inlay,  when  formed  and  set,  may  not 
become  displaced  under  stress. 

Second,  securing  correct  adaptation  of  tlie  matrix  to 
cavity  walls. 

Third,  avoiding  warpage  of  the  matrix  during  the  fusing 
of  the  porcelain. 

Fourth,  the  selection,  ajjplication  and  fusing  of  the  sev- 
eral tints  of  porcelain  in  proper  succession,  so  that  the 
finished  inlay  will  coincide  in  color  with  the  natural  tooth  in 
whicli  it  is  to  be  placed.  These  constructive  problems  will 
now  be  briefly  considered. 

INLAY   RETENTION 

The  walls  of  cavities  intended  for  the  reception  of  in- 
lays of  any  class  must  show  slight  divergence  from  within 
outward  in  order  that  the  matrix,  or  wax  model,  may  be 


910  INLAYS 

released  without  distortion.  This  applies  to  both  gold  and 
porcelain  inlays. 

A  cavity  should  be  so  shaped  that  when  the  inlay  is 
constructed  and  set,  the  forces  to  which  the  latter  is  sub- 
jected will  tend  to  drive  it  into  the  cavity  rather  than  out  of 
position.  Where  an  inlay  is  solely  dependent  upon  cement 
for  retention  purposes,  particularly  when  subjected  to  any 
appreciable  stress,  its  permanence  and  value  as  a  filling  are 
questionable. 

The  usual  means  of  retention  capable  of  being  developed 
in  the  formation  of  the  cavity  are:  parallel  or  slightly  di- 
vergent, opjiosing  walls,  flat  seats,  and  grooves  so  formed  as 
to  permit  not  only  the  ready  removal  of  tlie  matrix  without 
distortion,  but  to  allow  the  inlay,  when  completed,  to  go  to 
place  without  interference. 

As  a  means  of  retention  for  porcelain  inlays,  Dr.  F.  H. 
Skinner  suggests  the  following: 

Drill  one  or  more  small  retention  pits  in  gingival  wall 
or  incisal  step  of  the  cavity,  in  line  with  tlie  direction  of  re- 
moval of  the  matrix. 

When  the  matrix  has  been  conformed  to  the  cavity,  that 
over  the  retention  pits  is  pimctured  and  the  margins  turned 
into  the  opening. 

Each  pit  is  now  lined  with  a  small  cylinder  of  foil  made 
by  cutting  a  strip  slightly  wider  than  depth  of  pit  and  a  little 
more  than  three  times  longer  than  its  diameter. 

This  strip  is  formed  into  a  cylinder,  slit  at  three  or  four 
points  around  tlie  periphery,  so  that  the  sections  of  foil  be- 
tween may  be  reflected  outward. 

The  cylinder  is  passed  through  the  opening  in  the  foil,  to 
the  bottom  of  the  pit,  the  slit  sections  of  the  opposite  ends 
turned  down  on  the  foil  covering  the  gingival  wall,  or  incisal 
step  of  the  cavity,  and  there  closely  adapted  to  the  matrix. 

The  cylinder  which  lines  the  pit  should  be  pressed  out- 
ward against  its  walls  so  as  to  form  a  clear  opening  into 
which  the  porcelain  may  later  find  its  way. 

Sticky  wax  is  now  softened  and  pressed  into  the  cavity, 
against  all  matrix  walls,  and  when  hardened  the  foil  can  be 
removed  without  distortion. 

The  matrix  is  invested  in  high-fusing  investment  material, 
and  when  set  the  wax  is  removed  and  the  porcelain  applied 
for  first  bake. 

If,  in  applying  the  wax,  care  is  taken  to  fill  the  small 


cylinders  in  the  retention  pits  also,  to  exclude  the  investment, 
the  porcelain  will  flow  into  and  fill  them. 

When  the  inlaj-  is  fused,  and  the  foil  is  removed,  the  small 
projections  of  porcelain  which  are  seen  will  fit  into  tlie  reten- 
tion pits  of  the  cavity  and  prevent  displacement. 

WARPAGE  OF  THE  MATRIX 

Patinum  foil  1/1000  of  an  inch  thick  is  most  commonly 
used  for  matrix  construction  in  porcelain  work.  Thicker 
foil,  say  1/500  of  an  inch,  while  naturally  more  rigid,  when 
stripped  from  the  completed  inlay,  results  in  too  much  space 
between  the  latter  and  the  cavity  walls;  again,  it  is  more 
difficult  to  adapt  to  small  or  complex  cavities  than  the 
lighter  gauges.  On  the  other  hand,  1/2000  foil,  occasionally 
used,  is  too  easily  distorted,  both  in  handling  and  through 
contraction  of  the  porcelain  in  fusing,  to  be  depended  upon 
as  a  reliable  matrix  material. 

NECESSITY   FOR  ANNEALING  THE  FOIL 

Unless  thoroughly  annealed  before  beginning,  kept  soft 
by  occasional  reheatings  throughout  the  steps  of  adaptation, 
and  given  a  thorough  final  annealing,  followed  by  final  pres- 
sure swedging  with  spunk,  camphor  gum  or  sticky  wax,  ))e- 
fore  applying  the  porcelain,  any  of  the  platinum  foils  ordi- 
narily used  in  matrix  construction  are  very  liable  to  spring 
away  from  the  cavity  walls,  either  before  or  during  the  fusing 
process,  and  thus  present  from  the  very  start  an  imperfect 
matrix  in  whicli  to  fuse  the  porcelain. 

WARPAGE  RESULTING  FROM  IMPROPER  SUPPORT  OF  THE 
MATRIX 

Warpage  of  the  matrix  may  also  result  from  its  im- 
proper support  in  the  furnace  while  baking  the  porcelain. 
Before  final  adaptation  of  the  foil  to  the  cavity  is  secured, 
excessive  overlapping  jjeripheral  margins  and  long,  angular 
points  must  be  removed ;  otherwise  one  or  more  of  such 
points  may  prevent  the  matrix  proper,  with  the  added  weight 
of  the  porcelain,  from  resting  uniformly  upon  the  muffle  slab. 
Under  ordinary  .temperatures  no  mishap  would  occur,  but 
with  the  platinum  highly  heated  and  somewhat  soft,  con- 
traction occurring  in  the  porcelain  contained  within  it,  to- 
gether with  more  or  less  adhesion,  developed  and  active,  be- 
tween the  latter  and  the  metal,  warpage  is  most  certain  to 


occur.  A  mufflo  tray  or  slab  for  supporting  and  carrying 
tile  matrix,  having  a  slight  dejjression  in  its  npper  surface, 
can  be  used  to  advantage  in  the  fusing  of  inlays  of  compli- 
cated form.  In  the  depression  of  the  slab,  some  granular 
silex  is  placed,  building  it  higher  in  the  center,  if  necessary, 
to  meet  and  support  the  matrix.  On  this  granular  bed  the 
matrix  is  carefully  placed,  moving  it  just  sufficiently  to  de- 
veloj)  support  at  several  divergent  itoints,  particularly  in  the 
center. 

WARPAGE  DUE  TO  CARELESS  HANDLING 

In  addition  to  these  causes  of  warpage  mentioned,  a 
matrix  may  be  distorted  through  careless  handling  in  re- 
moval from  the  cavity^  or  in  any  of  the  manipulative  proced- 
ures u])  to  the  time  the  porcelain  is  fused  within  it.  The 
necessity  for  exercising  constant,  ever-watchful  care  in  the 
production  and  manipulation  of  the  matrix  and  in  applying 
and  fusing  the  materials  is  one  of  the  principal  reasons  why 
porcelain  is  not  used  more  extensively  than  it  is  at  the  pres- 
ent time. 

FAVORABLE  LOCATIONS  FOR  PORCELAIN  INLAYS 

Porcelain  inlays  are  indicated  in  all  cavities  exposed  to 
view,  Avhen  proper  retention  can  be  secured,  and  the  fillings, 
when  constructed,  will  have  sufficient  bulk  to  withstand  stress. 

The  classification  of  cavities,  ranging  from  those  in  which 
porcelain  is  most  strongly  indicated,  to  those  in  which  it  is 
least  required,  may  be  stated  as  follows : 

First — Gingival  third  cavities  in  the  anterior  teeth. 

Second — Proximal  cavities  in  the  anterior  teeth,  not  in- 
volving the  angles. 

Third — Proximal  cavities  in  the  anterior  teeth,  involving 
the  angles. 

Fourth — Cavities  in  bicuspids  and  molars,  involving  a 
visible  axial  and  occlusal  surface. 

Fifth — Occlusal  cavities  in  the  posterior  teeth. 

GENERAL   RULES   IN   REGARD   TO   CAVITY   PREPARATION 

Cavity  walls  should  be  formed  at  right  angles  to  the  sur- 
faces in  which  they  are  located. 

Opposing  axial  walls  should  be  formed  as  nearly  parallel 
as  possible,  yet  be  sufficiently  divergent  to  permit  the  matrix 
to  be  withdrawn  without  distortion. 

Gingival  and  pulpal  walls  should  be  flat,  and  at  right 
angles  to  the  long  axes  of  the  teeth. 


Cavo-surface  angles  sliould  be  planed  true,  but  not  per- 
ceptibly beveled  as  for  gold  foil  or  amalgam  tillings.  This  is 
to  avoid  the  formation  of  a  frail  margin  to  the  porcelain. 

Cavities  occurring  in  occlusal  surfaces  should,  when  prac- 
ticable, have  the  cavo-surface  angle  of  their  walls  laid  be- 
yond points  of  contact  or  occlusion  with  the  opposite  teeth. 

This  will  greatly  reduce  the  liability  of  margins  to  frac- 
ture under  stress. 

When  an  inlay  is  pro^jerly  set,  under  pressure  maintained 
while  the  cement  is  crystallizing,  the  minutest  space  between 
the  cavo-surface  angles  and  the  periphery  of  the  inlay  is  filled 
with  condensed  cement.  This  supports  both  enamel  margins 
and  those  of  the  inlay,  and  since  condensed  cement  maintains 
its  integrity  much  better  and  solution  occurs  more  slowly  than 
when  introduced  as  an  ordinary  filling,  it  is  reasonable  to  sup- 
pose, and  observation  has  shown,  that  cavity  margins,  though 
only  slightly  beveled,  will  stand  for  a  considerable  length  of 
time. 

DETAILS  OF  CAVITY  PREPARATION 

GINGIVAL  THIRD  CAVITIES  IN  THE  ANTERIOR  TEETH 

In  cavities  of  this  class,  as  well  as  in  all  others,  the  prin- 
ciples of  ertensinn  for  prevention  should  be  carried  out  as 
fully  as  possible. 

Undermined  enamel  should  be  broken  down  and  the  cav- 
ity outlines  made  s\Tnmetrical. 

The  walls  should  be  as  nearly  parallel  as  conditions  will 
permit  to  insure  retention  of  the  filling. 


SQIUUIB    END,     PAKALUa.    SIDE. 

Braia,    USEFUL    IN    CAVITY 

PBEPABATION 


\  ARIOUS  KORMS  OF  SMALL 
ARKANSAS  STONES,  SOMPTIMBS 
USED    IN    SMOOTHING    MARGINS, 


In  surfaces  where  much  curvature  exists  a  parallel  con- 
dition of  the  walls  may  be  secured,  partially  at  least,  by  squar- 
ing out  the  dentine  slightly  below  the  dento-enamel  jmiction. 

The  angle  formed  by  the  junction  of  the  axial  with  other 
walls  should  not  be  squared  out  too  definitely. 

The  cavo-surface  angles  should  be  sharp  and  well  defined 


and  Init  sliglitly  beveled,  if  at  all,  in  order  that  the  perii)heral 
margins  of  the  inlay  will  not  be  frail. 

PROXIMAL   CAVITIES   IN   THE   ANTERIOR   TEETH    NOT 
INVOLVING  THE  ANGLES 

In  cavities  of  this  class  it  is  necessary  to  separate  the 
teeth  before  beginning  operations.     Tliese  cavities  must  be 


formed  without  undercuts.  They  should  be  so  shaped  that 
the  matrix  when  burnished  in  position  can  be  removed  without 
distortion.  The  location  of  the  cavity  will  determine  the  direc- 
tion in  which  the  matrix  can  be  most  readily  removed,  whether 
labially  or  lingually.  If  the  cavity  of  decay  has  progressed 
more  to  the  labial  than  to  the  lingual,  the  cavity  preparation 
should  be  made  to  allow  the  removal  of  the  matrix  labially. 
If  decay  has  progressed  to  a  greater  extent  lingually,  the  prep- 
aration of  the  cavity  should  be  made  accordingly  to  meet  this 
condition.     (See  Cut  I.) 

The  gingival  and  incisal  walls  should  be  made  as  nearly 


INLAYS 


915 


parallel  to  each  other  as  practicable.  When  the  cavity  is 
formed  for  the  introduction  of  the  matrix  from  the  lingual 
side,  the  labial  margin  should  be  carried  far  enough  labially 
to  insure  the  porcelain  being  well  exposed  to  view.  This  will 
partially  obviate  the  shadow  problem  that  arises  in  this  loca- 
tion. The  cavo-surface  angles  should  be  prepared  as  outlined 
in  cavities  of  the  previous  class. 


BUCCAL  CAVITIES 

The  pi'eparation  of  cavities  of  this  class  is  similar  in 
most  respects  to  those  of  the  first  class  mentioned,  and  the 
rules  there  laid  down  apply  with  equal  force  to  the  class  under 
consideration. 


PROXIMAL  CAVTTIES   IN  THE  ANTERIOR  TEETH   INVOLVING 
THE  ANGLES 

The  pre]iaration  of  cavities  of  this  class  requires  much 
thought  and  skill,  since  the  completed  fillings  are  exposed  to  a 
greater  or  less  amoixnt  of  stress  in  mastication. 


916  INLAYS 

The  g'iiinixal  wall  or  seat  should  he  made  Hat  and  at  ri.u'ht 
angles  to  the  h)ng  axis  of  the  tootli. 

The  iuti'oduction  of"  inlays  in  cavities  of  this  class  must 
naturally  be  in  a  labial,  lingual  or  incisal  direction,  therefore 
tlie  labial  and  lingual  cavity  walls  must  be  formed  at  least 
parallel  with  the  long  axis  of  the  tooth. 

In  the  tijjper  anterior  teeth,  when  the  cavity  does  not 


extend  far  on  the  labial  surface,  iireparation  can  he  made  as 
follows : 

Square  the  gingival  wall.  Cut  away  the  labial  and  lingual 
walls  to  pei-mit  of  the  ready  removal  of  the  matrix.  Cut  a 
step  on  the  lingual  surface  of  the  tooth,  extending  from  the 
incisal  edge  to  the  gingival  wall. 

This  is  done  by  removing  a  section  of  the  lingual  plate 
of  enamel,  as  shown  in  Cut  II. 

Cut  a  groove  at  the  junction  of  the  linguo-axio-mesial  or 
distal  walls,  as  the  case  may  be,  extending  from  the  gingival 


wall  to  the  iiicisal  edge,  and  bevel  the  several  cavo-surfaoe 
angles  slightly. 

It  is  usually  best  to  out  away  the  labial  plate  of  enamel 
at  the  ineisal  edge  to  the  same  extent  that  the  lingual  has  been 
carried  back  (Cut  II),  to  avoid  a  long  irregular  line  of  junction 
occurring  on  the  ineisal  edge. 

Cut  III  illustrates  a  cavity  prepared  as  directed  and  tlie 
inlay  baked  around  a  post  whicli  extends  into  the  root  canal, 


thus  furnishing  additional  anchorage.     Note  that  there  is  a 
labial  shoulder  to  prevent  outward  displacement. 

CAVITIES  IN  BICUSPIDS  AND  MOLARS  INVOLVING  AN  AXIAL 
AND  AN   OCCLUSAL  SURFACE 

The  same  general  principles  followed  in  the  prepara- 
tion of  cavities  for  the  reception  of  gold  or  amalgam  fillings 
applv  in  inlav  work  with  a  few  exceptions,  which  will  be  noted. 
(See  Cut  IV!) 

First — The  cavity  must  l)e  formed  without  imdercuts. 

Second — The    axial,    buccal    and    lingual    walls    sliould 


918  INLAYS 

slightly  diverge,  from  gingival  to  occlusal,  to  allow  the  ready 
removal  of  the  matrix  in  an  occlusal  direction. 

Third — When  the  line  of  junction  of  the  cavity  wall  and 
the  periphery  of  the  inlay  comes  within  a  contact  area  of  a 
tooth  in  the  opposite  arch,  fracture  of  one  or  both  margins  is 
liable  to  occur.  Therefore  cavity  walls  should  be  laid  beyond 
such  points  of  contact  to  prevent  stress  on  the  periphery  of 
the  inlav- 


Cut  V  represents  a  method  of  restoring  the  angle  of  an 
incisor  tooth.  The  cut  shows  a  lingual  view  of  the  cavity,  with 
the  inlay  rotated  to  the  left.  The  labial  shoulder,  flat  seat  and 
slight  groove  in  both  seat  and  shoulder  furnish  needed  resist- 
ance to  displacement.  The  preparation  for  lower  incisors 
should  be  reversed. 

RESTORATION  OF  INCISAL  EDGES 

Cut  VI  illustrates  a  method  of  restoring  a  notched  incisal 
edge.  A  lingual  view  of  the  cavity  is  presented.  The  shoulder 
prevents  outward  displacement.    In  lower  incisors  the  shoul- 


der  should  be  lorepared  in  the  labial  plate  to  prevent  lingual 
displacement  by  the  iipper  teeth. 

The  preparation  of  the  cavities  as  outlined  is  similar  in 
most  respects  to  the  methods  recommended  and  taught  by  Dr. 
A.  E.  Peck,  who  deserves  much  credit  for  the  interest  he  has 


displayed  along  this  line.     Those  who  are  familiar  with  his 
system  will  note  the  points  of  difference  as  they  occur. 


PRODUCTION  OF  THE  MATRIX 

The  conformation  of  the  ])latinum  foil  to  the  cavity  is  a 
step  requiring  skill,  patience  and  experience.  Two  methods 
are  followed  at  the  present  time,  both  of  which  are  reliable  if 
proper  care  is  exercised.  The  first  consists  in  burnishing  the 
foil  directly  into  the  cavity  with  pellets  of  cotton  or  spunk 


920  INLAYS 

carried  in  the  pliers  aud  by  the  use  of  suitable  Ijiiriiishers  of 
ordinary  and  special  shapes. 

The  other  metliod  consists  in  forming  the  matrix  against 
an  impression  of  the  cavity  or  a  model  derived  from  an  im- 
jtression,  with  a  suitable  swaging  device. 

BURNISHING  THE   MATRIX 

The  rubber  dam  should  be  applied  in  all  cases  and  the 
cavity  dusted  with  soapstoue  to  prevent  tearing  the  foil. 

A  piece  of  platinum  foil,  thoroughly  annealed,  should  be 
cut  of  sufficient  size  to  extend  beyond  the  cavity  margins  when 
pressed  into  place.  This  is  centered  over  the  cavity  and  held 
in  position  with  the  fingers,  while  a  small  piece  of  spunk  car- 
ried in  a  pair  of  ball-pointed  pliers  is  pressed  against  the  cen- 
ter of  the  foil  to  force  it  against  the  floor  of  the  cavity. 

Special  care  should  be  taken  to  obviate  the  wrinkling 
of  the  foil  against  the  cavity  walls,  to  prevent  its  tearing  while 
being  forced  to  place,  or  its  perforation  by  the  pliers  or  burn- 
ishers. Wherever  a  wrinkle  or  fold  appears  it  represents 
three  thicknesses  of  foil  at  that  point,  and  while  the  bulk  of 
material  may  be  thinned  down  somewhat  in  burnishing,  it 
cannot  be  reduced  to  any  great  extent.  The  result  is  that 
when  the  inlay  is  completed  a  very  perceptible  space  exists 
where  the  fold  occurred,  which  must  be  filled  with  cement.  This 
is  objectionable  on  account  of  the  color  of  the  cement  and  be- 
cause of  its  ready  dissolution  under  such  conditions. 

The  foil,  having  been  carefully  forced  to  the  floor  of  the 
cavity,  is  held  there  by  a  burnisher  resting  on  a  pellet  of 
spimk.  Another  pellet  is  taken  up  with  the  pliers  and  forced 
into  the  cavity,  carefully  adapting  the  foil  to  the  entire  floor 
first,  before  making  any  attempt  to  adapt  it  to  the  walls. 

A  ligature  or  strip  of  thin  tape  passed  through  the  inter- 
proximate  spaces  and  against  the  matrix  will  oftentimes  assist 
in  holding  it  in  place  while  securing  adaptation  of  the  foil  to 
the  various  surfaces. 

The  adaptation  to  the  walls  is  secured  by  pressing  a  small 
pellet  into  the  cavity  near  the  floor  and  drawing  it  outward, 
producing  pressure  toward  the  wall  at  the  same  time.  The 
entire  floor  of  the  cavity  should  be  covered  with  spunk,  held 
with  some  suitable  instrument  during  the  operation. 

Some  prefer  to  use  various  shapes  of  rubber  points  for 
this  i^urpose,  and  very  good  results  are  secured  in  this  way, 
but  as  the  spunk  and  cotton  are  always  conveniently  at  hand 
and  pellets  of  any  size  can  be  formed  quickly,  these  materials 
are  perhaps  more  commonly  used  than  the  rubber  points. 


INLAYS 


& 


BALL-POINTED    PLIERS    FOR 

APPLYING  COTTON  OR  SPUNK 

TO   THE  MATRIX 


CARVING  TOOL  WITH  COR- 
RUGATED SIIA^^<.  WHICH. 
BV  DRAWING  ACROSS  THE 
TWEEZERS,  VIBRATES  AND 
CONDENSES  THE  PORCELAIN 
BODY 


SJIALL  SPATULA  FOR  MIX- 
ING AND  APPLYING  THE 
PORCELAIN  TO   THE  MATRIX 


922  INLAYS 

Buruishers  of  various  forms,  as  tlie  Thompson  or  Reeves 
selections,  may  be  used  to  advantage  in  securing  adaptation 
of  the  foil  to  the  cavity  walls  and  angles. 

When  fairly  close  general  adaptation  has  been  secured 
tlie  entire  matrix  is  filled  with  spunk  and  pressure  applied  with 
an  instrument  which  will  force  the  foil  against  the  floor  and 
walls  of  the  cavity  at  the  same  time. 

The  adaptation  of  the  foil  to  the  outer  surfaces  of  the 
tooth  can  be  accomplished  with  spunk  in  the  manner  outlined, 
drawing  the  pellet  from  the  cavo-surface  angle  outward  in  all 
direction  until  the  foil  lies  flat  upon  the  tooth  surface. 

The  adaptation  of  the  foil  to  the  cavo-surface  angle  yet 
remains  to  be  done.  This  is  one  of  the  most  important  steps 
in  the  whole  operation.  Securing  perfect  adaptation  at  this 
point,  with  sharp  angle  definition,  without  folds  in  the  foil,  in- 
sures practically  perfect  margins  to  the  inlay. 

The  entire  interior  of  the  matrix  should  now  be  filled 
with  spunk  and  a  piece  larger  than  the  cavity  applied  over  all. 
Pressure  with  a  suitably  shaped  instrument  slightly  larger 
than  the  cavity  or  with  the  finger,  when  this  is  possible,  is 
made  against  the  spunk  to  force  the  matrix  into  all  parts  of 
the  cavit.y,  against  the  cavity  margins  and  the  tooth  surfaces 
at  the  same  time. 

REMOVAL  OF  THE  MATRIX 

The  spunk  should  then  be  removed  and  the  matrix  lifted 
out.  the  surplus,  if  excessive,  trimmed  away  and  the  foil  thor- 
oughly annealed  and  returned  to  tlie  cavity  for  adaptation. 

NECESSITY  FOR  FINAL  ANNEALING 

When  metal  plate  is  swaged,  hammered  or  burnished  the 
relation  of  the  molecules  to  each  other  is  changed.  This  is 
especially  true  of  platinum  foil  used  in  matrix  construction. 
By  repeatedly  annealing  and  returning  the  matrix  to  the  cav- 
ity for  final  adaptation  the  foil  can  he  made  to  lie  "dead  flat" 
without  change  under  high  temperature. 

SELECTION,    APPLICATION    AND    FUSING    OF   THE 
PORCELAIN 

SELECTION  OF  SHADE 

As  porcelain  powders  are  now  supplied  by  the  manufac- 
turers they  appear  to  be  white,  or  but  slightly  tinted  with 
yellow  or  brown.  No  definite  idea  can  be  formed  from  looking 
at  the  powder,  or  when  made  into  a  paste  with  water,  as  to 


INLAYS  923 

what  its  tint  will  be  when  fused,  as  its  true  color  is  only  de- 
veloped by  vitrifying. 

To  select  a  suitable  porcelain  for  an  inlay  to  match  the 
shade  of  a  natural  tooth  small  sticks  of  fused  porcelain,  each 
made  of  a  particular  single  shade,  are  supplied  by  the  manu- 
facturers. These  sticks  are  made  from,  and  numbered  to  cor- 
respond with,  the  numbers  of  the  powders  supplied.  In  de- 
termining the  shade  of  porcelain  to  use  in  a  given  case,  one 
of  these  fused  j^ieces  is  placed  alongside  of  the  tooth  for 
which  the  inlay  is  to  be  constructed  and  the  similarity  or  dif- 
ference in  shade  noted.  This  process  is  repeated  until  a  satis- 
factory shade  has  been  found  to  match  the  tooth,  or  some 
portion  of  it,  against  which  the  inlay  is  to  rest. 

It  is  fro(inently  necessary  to  select  two,  sometimes  three, 
shades  of  porcelain  for  a  proximo-incisal  inlay  when  the  tooth 
presents  marked  variation  in  shade  from  gingival  to  incisal 
areas.  In  ai)plying  these  vari-shaded  porcelains  to  the  matrix 
they  are  not  blended  on  the  slab  but  are  applied  in  the  matrix 
in  the  particular  location  where  indicated.  By  drawing  a 
rough  instrument  across  the  pliers  with  which  the  matrix  is 
held  the  vibration  so  caused  will  blend  the  several  colors  at 
their  margins  sufficiently  to  obviate  a  sharp  line  of  demarka- 
tion  of  tints.  Usually  after  fusing  the  primary  colors  selected 
a  neutral  shade  of  porcelain  is  applied  and  fused  to  complete 
the  contour  and  still  further  soften  and  blend  the  more  pro- 
nounced underlying  tints. 

MIXING  THE  PORCELAIN 

The  proper  colors  having  been  selected  corresponding 
l^owders  are  placed  separately  on  a  clean  glass  slab  and  with 
a  drop  tube,  sufficient  distilled  water  is  added  to  form  each 
into  a  mass  of  medium  plasticity.  The  powder  and  water 
should  be  well  spatulated  to  thoroughly  incorporate  the  sev- 
eral ingredients  in  each  shade.  To  prevent  the  heavier  from 
settling  and  forcing  the  lighter  particles  to  the  top  of  the 
mass  when  well  mixed,  a  linen  napkin,  or  piece  of  bibulous 
paper,  should  be  pressed  against  the  paste  to  take  up  the  ex- 
cess moisture. 

APPLICATION  OF  THE  PORCELAIN  TO  THE  MATRIX 

The  matrix  is  grasped  with  a  pair  of  K  tweezers  at  some 
point  on  the  surplus  margin  in  such  manner  as  not  to  distort 
it,  yet  with  sufficient  hold  to  sustain  not  only  the  matrix  but 
the  porcelain  to  be  added  as  well.     A  small  amount  of  the 


924  INLAYS 

paste,  usuallv  of  a  yellowish  liii,i;;e.  1o  serve  as  a  foundation 
body,  is  transferred  from  the  shib  to  the  matrix,  api)lied  to 
the  hitter  without  ijressure  and  the  serrated  surface  of  the 
earving  tool  drawn  over  the  tweezer  beaks  to  vibrate  the 
porcelain  in  position.  More  is  added  in  like  manner  until  the 
matrix  is  from  one-half  to  two-thirds  full,  leaving  the  labial 
portion  deficient  in  order  to  add  the  proper  colors  later.    The 


partially  filled  matrix  is  now  carefully  passed  above  a  Bnnsen 
flame,  or  placed  near  the  entrance  of  the  furnace,  to  gradually 
expel  the  moisture,  after  which  it  is  placed  on  a  muffle  tray, 
introduced  and  fused. 

When  removed,  the  various  tints  are  applied  in  their  re- 
spective locations,  this  time  filling  the  matrix  to  its  margins 
and  vibrating  as  before  so  as  to  blend  the  sevei-al  colors. 
Any  excess  paste  which  overflows  is  carefully  brushed  off  with 
a  dampened  sable  brush,  thus  avoiding  thin  overhanging 
margins  in  the  finished  inlay. 

Should  the  colors  be  too  pronounced  when  fused,  a  thin 
layer  of  gray  or  neutral  tint  may  be  overlaid  and  fused,  as 
before  suggested,  to  tone  them  down. 

Usually  in  simple  cavities  two  applications  of  the  body 
and  two  fusings  will  be  sufficient  to  produce  a  satisfactory 
inlay.  In  complicated  cases,  however,  three,  or  possibly 
four,  fusings  may  be  required.  It  must  be  kept  in  mind,  how- 
ever, that  each  additional  fusing  not  only  produces  contrac- 
tion in  the  porcelain  last  added,  but  in  the  entire  mass,  thus 
increasing  the  danger  of  warpage  and  a  misfit.  The  fewer 
times  required  for  fusing  and  finishing  a  piece  of  porcelain 
of  any  class,  the  better  the  quality  of  the  material  and  the  less 
contraction  and  warpage  will  occur. 

When  slightly  overfused,  or  when  the  vitrifying  process 
is  continued  too  long,  both  the  texture  of  the  porcelain  and  its 
color  is  impaired.  Long  continued  low  temperature,  just  suf- 
ficient to  vitrify  porcelain,  will  produce  better  results  as  to 
texture  and  color  than  when  the  process  is  carried  on  rapidly 
and  at  a  higher  temperature. 


FURNACES    FOR    FUSING    PORCELAIN 

Various  tj'pes  of  furnaces  are  used  for  fusing  or  "bak- 
ing" porcelain,  as  this  process  is  usually  termed.  The  most 
common  method  of  developing  the  required  temperature  is 


MUFFLE    TKAY    TONGS,     FOR    INTRODUCTION    AND 

REMOVAL,    OF    THE    TRAY    DURING    THE    STEPS 

OP   FUSION    OF    THE   PORCELAIN 

by  passing  an  electric  current  through  a  fine  platinum  wire 
imbedded  to  a  slight  depth  within  the  fine  clay  muffle  walls. 
The  resistance  of  the  wire  to  the  passage  of  the  current  de- 


926  INLAYS 

velops  an  intense  heat  within  tlie  wire  when  fine,  which  in  tiirn 
is  transmitted  to  the  fire-clay  lining  of  the  furnace. 

The  amount  of  heat  capable  of  being  developed  within  a 
mufJie  is  dependent  upon  the  length  and  sectional  area  of  the 
wire,  the  depth  it  is  imbedded  in  the  fire-clay  lining  and  the 
intensity  of  the  current  which  flows  through  it.  Furnaces  of 
tills  type  are  called  "electric  furnaces,"  and  as  a  rule  are 
capable  of  developing  a  considerably  higher  temperature  than 
that  required  to  fuse  the  common  porcelain  bodies.  In  most 
cases  a  rheostat  is  employed  to  control  the  flow  of  the  cur- 
rent and  keep  the  temperature  within  working  range.  In  some 
cases  furnaces  are  fitted  with  pyrometers  for  indicating  the 
point  of  fusion  of  the  porcelain. 

To  Dr.  L.  E.  Custer  belongs  the  credit  of  having  first  con- 
structed a  practical  electric  furnace  suitable  for  fusing  porce- 
lain (1894).  At  the  pi-esent  time  a  number  of  excellent  electric 
furnaces  are  procurable.  Gas,  gasoline,  oil  and  coke  furnaces 
are  also  manufactured  which,  from  a  practical  standpoint,  are 
applicable  to  porcelain  work.  The  electric  furnace  is  prefer- 
able in  dental  opei"ations  because  of  its  compactness,  ease  of 
manipulation  and  freedom  from  gases  which  always  accom- 
pany the  use  of  the  fuels  mentioned. 

The  temperature  usually  required  to  fuse  the  various 
inlay,  crown  and  bridge,  porcelain  bodies  is  given  under  the 
heading  of  "High  and  Low  Fusing  Porcelain  Bodies." 

FUSING  THE  PORCELAIN 

The  moisture  having  been  expelled  from  the  porcelain, 
the  matrix  is  placed  upon  the  muffle  slab  and  introduced  in 
the  furnace.  Care  should  be  taken  to  see  that  the  body  of  the 
matrix  rests  upon  the  fire-clay  slab,  or  that  a  sufficient  number 
of  marginal  points  touch  to  afford  ample  support  and  prevent 
warpage.  When  the  form  of  the  matrix  is  complicated  some 
granular  silex  should  be  placed  upon  the  slab  and  the  matrix 
settled  carefully  down  upon  it. 

When  a  furnace  having  no  pyrometer  is  used,  a  pellet  of 
pure  gold  is  usually  placed  alongside  of  the  matrix  to  serve 
as  a  guide  in  determining  the  point  of  vitrification.  A  little 
device  made  of  soapstone  or  fire  clay,  having  a  small  imder- 
cut  groove  with  slightly  enlarged  extremities,  is  cut  in  the 
concave  face  of  the  block.  In  the  upper  extremity  of  the 
groove  a  pellet  of  gold  is  placed  and  when  fusion  of  the  latter 
occurs  it  disappears  by  falling  to  the  lower  extremity,  much 
as  the  sand  in  an  hour  glass  flows  from  upper  to  lower  com- 


INLAYS  927 

partment.  When  the  temperature  is  reduced  and  the  gold  solid- 
ifies, by  inverting  the  block  the  gold  is  again  at  the  upper  ex- 
tremity of  the  groove  and  in  position  for  another  test. 

The  matrix  and  test  block  being  in  position,  the  current 
is  turned  on  by  moving  the  rheostat  arm  from  its  initial  po- 
sition of  rest  to  the  first  contact,  where  it  should  be  allowed 
to  remain  for  five  minutes,  when  it  can  be  moved  to  the  second 
contact.  Tlie  arm  should  remain  on  each  contact  about  the 
same  length  of  time  before  moving  to  the  next  in  order  to  re- 
duce to  the  minimum  ihe  strain  on  both  platinum  wire  and 
fire-clay  lining,  and  also  so  that  the  porcelain  may  not  be 
subjected  to  sudden  increase  of  temperature.  In  most  fur- 
naces the  rheostats  are  supplied  with  five  or  six  contacts. 
When  the  arm  is  moved  at  five-minute  intervals  the  iDorcelain 
will  usually  bo  near  the  point  of  fusion  by  tlie  time  the  arm  is 
transferred  to  the  last  contact.  The  gold  must  be  closely 
watched  and  the  instant  it  fuses  the  time  should  be  noted. 

By  iireviously  determined  tests,  the  difference  in  time 
between  the  melting  of  the  gold  and  the  biscuiting,  as  well  as 
glazing  of  the  porcelain,  is  known,  and  this  time  should  be 
allowed  according  to  the  degree  of  fusion  required.  This 
period  varies  usually  from  forty  seconds  to  six  or  seven 
minutes,  depending  on  the  intensity  of  the  current,  the  class 
of  porcelain  used  and  the  type  of  furnace  employed. 

The  first  bake  should  be  carried  to  the  "biscuit"  stage, 
i.e.,  where  vitrification  has  occurred  but  the  granular  surface 
has  not  disappeared. 

The  rheostat  arm  is  now  returned  to  the  second  contact 
to  conserve  time,  and  heat  as  well,  by  not  allowing  the  furnace 
to  become  cold,  the  muffle  opened  and  the  slab  partially  with- 
drawn, allowed  to  cool  somewhat  and,  finally,  the  matrix  is 
picked  up  with  tlie  K  tweezers  and  the  result  of  the  first  liake 
noted.  If  free  from  porosity,  of  good  color  and  not  overfused 
the  second  application  of  body  is  made  as  at  first.  When  an 
effort  is  made  to  complete  the  inlay  in  two  liakes  the  second 
application  of  porcelain  should  be  very  carefully  executed, 
developing  very  slightly  fuller  contour  than  required  to  com- 
pensate for  final  contraction  that  always  occurs  on  fusing. 

When  two  or  more  colors  are  required  to  match  the  tooth 
shade  they  are  applied  at  this  time  and  blended  as  before  de- 
scribed. 

SECOND    BAKING 

The  contour  of  the  second  application  of  body  having 
been  completed,  surplus  removed  from  the  margins  and  the 


928  INLAYS 

moisture  expelled,  the  matrix  is  again  returned  to  the  furnace. 
The  temperature  is  gradually  raised  as  before  until  the  sur- 
face of  the  inlay  is  glazed  and  perfectly  free  from  granules, 
the  idea  being  to  give  it  such  a  surface  as  will  not  require  the 
application  of  discs  or  polishing  powders.  Porcelain  inlays 
baked  under  ordinary  conditions  are  liable  to  be  slightly 
porous  under  the  glazed  surface,  and  these  porous  sjjaces  are 
frequently  disclosed  on  grinding.  Since  reglazing  does  not 
always  remove  the  ])its.  and  if  more  is  added  to  correct  the 
defects  the  additional  fusion  will  induce  further  dimensional 
changes  in  the  inlay  itself,  it  is  best  to  avoid  grinding  and 
polishing   if   possible   to   do    so. 

DELETERIOUS  EFFECT  OF  OVERFUSING  THE  PORCELAIN 

Special  care  should  be  taken  to  not  overfuse  the  jiorce- 
lain.  Some  of  tlie  defects  arising  from  this  mishap  are  bleach- 
ing of  the  porcelain,  friability,  undue  contraction  and  warp- 
age  and  the  development  of  porosity — sometimes  to  such  an 
extent  as  to  render  the  inlay  useless. 

THE   SHADOW   PROBLEM 

Comparatively  little  difficulty  is  encountered  in  selecting 
porcelain  of  suitable  translucency  and  color,  which  when  fused 
to  proper  form  and  introduced  in  the  cavity  without  cementa- 
tion will  harmonize  with  tooth  structure. 

The  discouraging  feature  connected  with  porcelain  inlay 
work,  however,  is  in  the  variation  in  shade  observed  between 
the  natural  teeth  and  inlay  when  the  latter  is  finished  and 
set  with  cement.  All  varieties  of  cement  used  in  the  setting 
of  inlays  are  opaque.  Light  will  not  readily  pass  through 
even  thin,  attenuated  layers  of  this  material.  Therefore,  un- 
less the  light  which  falls  upon  a  tooth  filled  with  a  cemented 
inlay  is  directly  parallel  with  the  exposed  cavity  walls  a 
shadow  will  be  cast  upon  either  tooth  or  the  inlay,  de]:)ending 
upon  which  is  nearest  the  source  of  light. 

For  example,  in  a  distal  cavity  in  a  central  incisor  involv- 
ing the  angle,  when  the  light  falls  upon  the  tooth  first — the 
direction  of  the  rays  slanting  toward  the  inlay — a  shadow 
will  be  observed  in  the  latter  next  to  the  line  of  junction, 
owing  to  the  cutting  off  of  the  light  by  the  film  of  interposed 
cement.  When  the  light  comes  from  the  opposite  direction, 
striking  the  inlay  first,  the  shadow  will  appear  in  the  tooth, 
but  to  a  less  extent  because  of  a  more  or  less  general  diiifasion 


of  light  in  the  greater  l)ulk  of  tooth  structure.  lu  the  upper 
teeth  the  overhang  of  the  upper  lip  will  often  oast  a  shadow 
in  the  gingival  portion  of  an  inlay,  though  the  light  may  be 
comparatively  direct  and  well  diffused. 

To  overcome,  or  at  least  reduce  somewhat,  the  shadow 
caused  by  indirect  rays  of  light  on  an  inlay,  the  labial  walls  of 
cavities  in  the  anterior  teeth  sliould  be  carried  well  to  the 
labial.  The  result  of  such  cavity  formation  is  to  increase  the 
bulk  of  porcelain  in  the  inlay  and  permit  diffused  light  to 
enter  through  the  porcelain,  thus  reducing  the  depth  of  shadow 
cast  in  inlays  of  limited  labial  exposure.  The  necessity  for 
this  line  of  procedure  is  evident  when  the  form  and  position 
of  an  inlay,  in  proximal  cavities,  is  considered.  On  one  side 
the  inlay  is  limited  by  an  ojiaque  layer  of  cement,  and  on 
the  other  by  the  proximating  tooth,  both  of  which  tend  to 
restrict  the  uniform  diffusion  of  light  through  the  porcelain 
except  under  the  most  favoralile  circumstances. 

Again,  the  color  of  the  cement  used  in  setting  an  inlay 
may  modify  the  shade  of  both  the  restoration  and  the  tooth 
next  to,  and  for  a  short  distance  away  from,  the  cavity  walls, 
lightening  or  darkening  both  according  to  the  inherent  tinge 
of  the  cement.  The  remedy  for  tlie  latter  defect  is  overcome 
to  a  great  extent  by  using  a  cement  which  in  color  coincides 
as  nearly  as  possible  with  the  shade  of  the  natural  tooth. 

It  has  been  suggested  that  the  use  of  an  opaque,  low- 
fusing  porcelain  of  the  Jenkins  tyjie,  in  which  color  effects  are 
not  so  much  dependent  upon  translucency  as  is  the  case  in  the 
higher  fusing  porcelains,  may  be  applied  to  overcome  the 
shadow  effects  noted.  An  inlay  constructed  of  an  opaque 
porcelain  having  the  essential,  component  colors  of  the  tooth 
brought  to  the  labial  surface  is  but  slightly  affected  by  light 
striking  it  at  various  angles.  The  tooth  in  which  it  is  placed, 
however,  is  subjected  to  shadow  variations  to  the  same  ex- 
tent as  wlicn  higli  fusing  i)orce]ains  are  employed. 

REMOVING    THE    MATRIX 

Wlien  the  fusing  of  the  inhiy  is  comi)leted  the  platinum 
foil  matrix  must  be  removed.  This  may  lie  accomplished  by 
carefully  grasping  the  surplus  margin  with  the  beaks  of  the 
K  tweezers  and  with  a  rotary  movement  roll  the  foil  awav 
from  the  margins  of  the  porcelain,  using  special  care  to  avoid 
fracturing  the  latter.  By  wetting  the  inlay  and  matrix  the 
danger  of  fracture  is  greatly  reduced.  Usually  the  matrix 
can  be  peeled  off  by  grasping  the  surplus  margin  between 


930  INLAYS 

the  thumb  nail  and  the  ball  of  the  index  finger,  the  latter 
acting  as  a  resilient  cushion  on  which  to  rotate  the  inlay. 
In  case  the  matrix  tears,  the  adherent  portion  being  devoid 
of  free  margins,  it  must  be  chiseled,  scraped  or  ground  away, 
as  when  allowed  to  remain  it  will  interfere  with  the  correct 
seating  of  the  inlay. 

ETCHING  THE  CAVITY  SURFACES  OF  THE  INLAY 

To  break  up  the  glaze  and  afford  better  retention  of  the 
cement  to  the  porcelain  the  cavity  surfaces  shoiild  be  etched 
with  hydrofluoric  acid.  The  labial,  and,  in  fact,  all  the  exposed 
surfaces  of  the  inlay,  must  be  protected  from  the  action  of  the 
acid  by  covering  them  with  wax,  the  acid  having  no  effect  on 
the  latter  material.  The  wax  should  be  formed  into  a  roll, 
the  end  heated  and  the  inlay  pressed  against  it,  being  careful 
to  see  that  all  surfaces  on  which  the  glaze  is  to  be  preserved 
are  perfectly  covered. 

With  a  pencil  of  wax,  or  a  toothpick,  the  acid  is  applied 
to  the  cavity  surfaces,  the  application  renewed  once  or  twice 
until  the  glaze  is  removed.  The  acid  is  then  washed  otf  with 
water  and  neutralized  with  a  solution  of  bicarbonate  of  soda, 
again  washed  and  dried,  when  it  is  ready  to  set. 

SETTING  THE  INLAY  WITH  CEMENT 

The  rubl)er  dam  should  be  applied  to  the  tooth  involved, 
and  the  proximating  teeth  as  well,  and  the  cavity  thoroughly 
cleansed  and  dehydrated. 

Cement  of  suitable  shade  mixed  to  medium  consistency  is 
quickly  applied  to  both  inlay  surfaces  and  cavity  walls,  the 
inlay  introduced  and  forced  to  place  under  gradual, 
heavy,  maintained  pressure.  In  proximal  cavities,  this  pres- 
sure may  he  applied  by  forcing  between  the  inlay  and  the 
proximating  tooth  a  ]ireviously-prepared  wedge  of  orange 
wood.  Care  should  be  taken  to  see  that  in  forcing  the  wedge 
in  place  the  inlay  is  not  displaced  or  unseated  at  any  point. 

The  force  capable  of  being  exerted  by  a  thinly-tapered 
wedge  is  enormous,  therefore  caution  must  be  exercised  to 
avoid  undue  force  in  its  application.  The  mallet  should  never 
be  used  in  setting  a  porcelain  inlaj',  as  the  instantaneous  blow 
will  scarcely  produce  flow  in  cement  of  medium  consistency, 
while  the  impact  is  liable  to  fracture  the  porcelain. 

A  piece  of  pine  stick  a  little  larger  than  a  lead  pencil, 
with  one  end  trimmed  to  suitable  size  and  slightly  concaved  to 


fit  snugly  against  the  inlay,  affords  a  most  convenient  means 
of  producing  and  maintaining  pressure  upon  the  restoration 
until  the  excess  cement  has  heen  expelled  and  crystallization 
has  set  in.  Pressure  on  the  inlay  should  usually  be  main- 
tained from  five  to  eight  minutes,  dei)ending  on  the  rapid 
setting  qualities  of  the  cement  used. 

In  setting  inlays  in  proximal  cavities,  a  strip  of  rubber 
dam  about  six  inches  long  and  one-fourth  inch  wide  can  be 
passed  between  the  inlay  and  the  proximating  tooth,  the  two 
ends  of  the  strip  placed  together  and  the  ruljber  stretched 
almost  to  its  limit,  in  a  direction  at  right  angles  to  the  long 
axis  of  the  tooth.  The  resilient  rubber  forces  the  inlay  into 
the  cavity  and  condenses  the  cement  in  the  joint  line  as 
well. 

When  hardened,  the  excess  cement  is  removed  from  the 
joint  and  adjacent  surfaces,  the  rubber  dam  removed,  the  parts 
syringed  with  warm  water,  and  the  occlusion  verified  to  see 
that  in  setting  it  has  not  been  modified  by  the  cementing  me- 
dium. If  so,  it  should  be  corrected  by  grinding  and  polishing 
until  clearance  space  is  gained,  to  avoid  fracture  from  stress 
of  oijposing  teeth. 

GOLD  INLAYS 

The  production  of  gold  inlays  may  be  occomplished  in 
various  ways.  With  one  or  two  exceptions,  all  of  the  many 
methods  in  vogue  may  be  groiiped  into  two  general  classes, 
viz.,  the  matrix  method  and  the  casting  process.  A  descrip- 
tion of  both  methods  will  follow  cavity  preparation. 


CAVITY  PREPARATION  FOR  GOLD  INLAYS 

The  general  princij)les  followed  in  cavity  formation  for 
gold  foil  or  amalgam  fillings  apply  with  equal  force  to  those 
designed  for  the  reception  of  inlays  of  any  class.  Briefly 
stated,  these  princi])les,  as  laid  down  in  Black's  Operative 
Dentistry,  are  as  follows  : 

First — Obtain   the   required  outline   form. 

Second — Obtain  the  required  resistance  form. 

Third — Olitain.the  required  retention  form. 

Fourth — Obtain  the  required  convenience  form. 

Fifth — Remove  any  remaining  carious  dentin. 

Sixth— Finish  the  enamel  wall. 

Seventh — Make  the  toilet  of  the  cavity. 


OUTLINE   FORM 

To  secure  the  ooncct  outline  i'oi-ui  involves  the  breaking 
down  of  unsound  overhiingiiig  enamel  walls,  the  removal  of 
practically  all  undercuts,  the  opening  up  of  tissures  when  re- 
quired, extension  for  prevention  of  all  margins  to  immune 
areas,  and  further  extension  of  margins,  if  necessary,  for 
convenience  of  introduction  and  removal,  without  distortion, 
of  tlie  wax  model,  or  the  I'dil  matrix. 

RESISTANCE  FORM 

Resistance  form  refers  to  the  development  of  flat  gingival 
and  jtulpal  walls  so  as  to  withstand  the  stress  of  mastication, 
thus  obviating  the  tendency  of  the  inlay  to  slide  from  or  rotate 
out  of  position  under  direct  stress. 

RETENTION    FORM 

In  the  preparation  of  a  cavity  for  an  inlay,  the  walls  that 
lie  parallel  with  the  line  of  direction  of  introduction  of  the 
inlay  should  be  formed  at  an  angle  of  divergence  of  at  least 
one  degree  from  perpendicular  to  the  base,  to  obviate  distor- 
tion of  the  wax  model  in  removing  from  the  cavity.  A  greater 
amount  of  divergence  may  be  permissible  in  some  cases,  but 
firmer  and  better  retention  follows  with  slight  than  with  ex- 
cessive divergence  of  the  walls. 

AVliile  cement  is  employed  for  the  retention  of  all  classes 
of  inlays,  this  means  alone  will  prove  ineffectual  against  side 
stresses  and  strains,  particularly  when  the  inlays  are  to  be 
utilized  as  abutments  in  biidgework. 

Since,  for  obvious  reasons,  neither  undercuts  nor  parallel 
walls  are  permissible  in  the  finished  cavity,  and  since  cement 
is  unreliable  under  heavy  stress,  some  more  positive  means 
of  retention  must  be  developed  in  practically  all  cases;  this 
may  be  accomplished  in  several  ways,  depending  on  the  form 
and  location  of  the  cavity. 

In  cavities  involving  an  axial  and  an  occlusal  surface, 
flat  pidpal  and  gingival  seats  afford  resistance  to  direct  stress, 
while  a  dovetail  on  the  occlusal  surface  will  prevent  the  tip- 
ping stress. 

When  more  than  one  axial  surface  is  involved,  and  it  is 
deemed  advisable  to  connect  the  cavities  and  thus  construct 
the  inlay  in  one  piece,  the  proper  flare  of  the  walls,  to  avoid 
undercuts,  should  be  constantly  kept  in  view,  so  as  to  obviate 
distortion  of  the  wax  model  in  removal  from  the  cavity. 


INLAYS  933 

Frequently  when  two  or  more  axial  surfaces  are  involved, 
and  the  preparation  of  the  cavity  so  as  to  permit  the  release 
of  the  matrix  would  recjuire  excessive  sacrifice  of  good  tooth 
structure,  an  interlocking  inlay  constructed  in  two  pieces  can 
be  used  to  advantage.  In  such  case  one  inlay  having  a  dove- 
tailed sjiace  to  receive  the  interlocking  spur  of  the  adjacent 
piece  or  complement,  is  first  cast  and  set,  after  which  the  wax 
model  of  the  other  is  formed  and  cast  in  like  manner.  By 
this  sectional  method  of  construction,  maximum  resistance  to 
displacement  of  the  inlay  is  gained,  with  the  sacrifice  of  tlie 
mininuun  amount  of  tooth  structure. 

Oftentimes  a  slightly  divergent  groove  can  be  formed  in 
the  puli)al  wall  of  the  cavity  in  such  manner  as  to  release  the 
wax,  the  resulting  shoulder  of  which  on  the  inlay  will  effectu- 
ally prevent  it  from  tipping. 

In  obtaining  retention  form  in  cavities  in  the  anterior 
teeth,  an  incisal  step  with  a  notch  in  the  lingual  plate  of  en- 
amel will  etfectually  counteract  the  tendency  to  displacement 
from  tipping  stress. 

Frequently,  by  stripping  both  labial  and  lingual  plates 
of  enamel  away  so  as  to  ex])oso  the  dentine,  the  latter  may  be 


VARIOUS   FORMS   OF   CAVITIES    IN   WHICH   DENTIN    SHODLDERS   AND   LINGUAL   GROOVES 
ARE  DEVELOPED   FOR   RETENTION  I"ITRI'0SE.S    (ST.    .TOHNI 

used  as  a  shoulder  or  hook,  as  it  were,  ovei'  which  the  inlay 
may  be  formed,  and  which  will  e1Te<-tually  counteract  the 
tendency  to  tip.    This  form  of  cavity  iirei)aration  was  recom- 


mended  many  years  ago  by  Dr.  I.  ('.  St.  John  of  St.  Paul,  for 
the  reception  of  gold  foil  fillings.  In  eeitain  eases  it  lias 
proven  very  serviceable  for  inlays. 

PIN  ANCHORAGE   FOR   INLAYS 

The  application  of  pins  for  the  retention  of  inlaw's,  and 
in  obviating  displacement  under  heavy  stresses,  has  proven 
of  great  value,  particularly  when  the  inlays  are  utilized  as 
abutments  for  bridges. 

The  form  and  location  of  the  cavity  and  the  condition  of 
the  tooth,  whether  vital  or  pulpless,  govern  the  size  and  length 
of  the  pin. 

The  usual  manner  of  developing  a  pin  anchorage  consists 
in  drilling  a  hole  in  the  gingival  or  pulpal  wall  of  the  cavity 
entirely  within  the  dentine,  in  such  location  as  not  to  inter- 
fere with  the  pulp.  The  direction  of  the  hole  should  corre- 
spond with  the  line  of  removal,  or  at  least  not  interfere  with 
the  release  of  the  wax  model  from  the  cavity.  The  diameter 
of  the  hole  should  be  but  slightly  larger  than  the  pin  to  be 
employed.  Before  introducing  the  wax,  the  pin,  cut  slightly 
longer  than  the  depth  of  the  hole,  is  inserted  and  as  the  wax 
presses  to  ])lace  it  surrounds  the  projecting  end  of  the  pin. 
When  the  wax  model  is  removed,  the  pin  is  removed  with  it 
and  caught  in  the  investment  and  the  gold  cast  around  it. 

CONVENIENCE  FORM 

Convenience  form  relates  to  such  modifications  in  pre- 
pared cavities  as  will  admit  of  the  most  perfect  as  well  as  con- 
venient placing  of  the  filling.  In  gold  foil  operations  this  re- 
fers to  cutting  away  a  wall  or  some  area  that  interferes  with 
proper  instrumentation  or  the  development  of  slight  under- 
cuts in  certain  locations  to  aid  in  holding  the  filling  material 
until  the  general  retention  form  can  be  made  effective. 

These  points  do  not  directly  apply  to  inlay  work,  but 
indirectly  the  shaping  of  the  cavity  so  as  to  permit  the  ready 
removal  of  the  wax  model  and  the  introduction  of  the  inlay 
come  under  this  head.  When  the  general  form  of  a  cavity  has 
been  developed,  it  is  frequently  found  that  some  slight  under- 
cut within  the  dentine  will  seriously  interfere  with  removal  of 
the  wax  model.  The  removal  of  the  undercut  by  reshaping 
the  cavity  may  result  in  weakening  an  otherwise  firm  cavity 
wall  when  by  carefully  filling  the  depression  with  cement,  the 
difficulty  may  be  overcome.    As  a  general  rule,  however,  the 


best  plan  is  to  eliminate  all  nndercuts  in  the  development  of 
the  ontline  form,  and  not  depend  upon  cement  for  such  pur- 
pose. 

REMOVAL  OF  ANY  REMAINING  CARIOUS  DENTINE 

It  is  just  as  important,  in  cavity  preparation  for  inlays 
as  for  other  classes  of  fillings,  that  all  decayed  dentine  be 
removed  to  obviate  recurrent  caries. 

Some  prefer  to  leave  a  layer  of  leathery,  decayed  dentine 
in  the  pulpal  or  axial  walls  of  deep  cavities,  under  the  mis- 
taken idea  that  tlie  transmission  of  thermal  changes  will  be 
impeded  and  the  vitality  of  the  pulp  be  conserved. 

This  is,  in  nearly  every  instance,  an  incorrect  procedure, 
for  in  cavities  which  encroach  so  closely  on  the  pulp  as  to 
need  a  protection  of  this  character,  the  varjnng  thermal 
changes  transmitted  by  a  large  gold  inlay  will  very  soon  set 
up  hyperemia  conditions,  and  the  pulp  will  die. 

FINISH    OF   THE   ENAMEL   WALLS 

In  gold  inlay  as  well  as  in  gold  foil  operations,  the  cavo- 
surface  angles  should  be  beveled  for  the  protection  of  the 
exposed  enamel  rods.  This  is  carried  out  as  in  general  opera- 
tive jirocedures  by  carefully  planing  outer  cavity  margins 
with  sharp  chisels  and  gingival  margin  trimmers. 

The  method  of  using  stones  on  the  margin  and  in  smooth- 
ing up  the  walls  of  cavities  is  bad  practice  and  to  be.  deplored. 
The  method  cannot  be  made  effective  in,  nor  is  it  universally 
applicable  to,  all  classes  of  cavities,  and  where  applicable  the 
tendency  is  to  weaken  frail  walls  and  obliterate  definite  re- 
tention surfaces.  The  only  possible  advantage  resulting  from 
this  method  is  in  reducing  to  a  slight  degree  the  discomfort 
to  the  patient,  in  those  cases  where  the  tooth  structure  is  sen- 
sitive to  the  application  of  the  bur. 

TOILET  OF  THE  CAVITY 

The  removal  of  all  chips  and  debris,  not  only  from  the 
cavity  but  from  the  mouth  as  well,  is  important  and  can  best 
be  accomplished  by  use  of  the  water  syringe  and  wiping  the 
cavity  thoroughly  with  pellets  of  cotton  before  forming  the 
wax  model. 

In  forming  the  wax  model,  as  will  be  seen  later,  a  lu))ri- 
cant  is  used  to  facilitate  the  ready  application  and  adaptation 
of  the  wax  to  all  cavity  surfaces.  This  lubricant,  whatever  its 
class,  should  be  thorouglily  removed,  the  cavity  dried  and 


936  INLAYS 

packed  willi  a  .n'ooil  (|iialit>'  of  .i^ntta  jXTclia  until   tlic  time 
of  setting-  of  tlic  inlay. 

SOME   SPECIAL   METHODS  OF  CAVITY   PREPARATIONS 

I'rnxiinal  caNirics  in  the  anterior  teetli,  in  which  gold 
inlays  are  to  b(^  placed,  require  special  attention.  In  case  a 
tooth  proximates  tlie  one  in  which  the  cavity  occurs  and  the 
angle  is  involved,  the  cavity  must  be  formed  so  as  to  release 
the  wax  model  usually  lingually  or  incisally. 

Provision  must  he  made  to  prevent  the  inlay  when  set, 
from  becoming  dislodged  under  ti]:)ping  stress.  Several  meth- 
ods are  resorted  to  for  accomplishing  this  object.  These  usu- 
ally consist  of  a  dovetail  or  some  form  of  step  in  the  lingual 
surface  of  the  tooth  involved,  some  of  wliich  will  be  illustrated. 


TUO  VIEWS  OF  TOOTH  IMlErAREO  WITH    AN   INCISAL   HOOK  OF   DENTIN 
(ST.    JOHN) 

The  first  of  these,  the  St.  John  method  of  cavity  prepara- 
tion, jireviously  alluded  to,  consists  in  stripping  off  the  plates 
of  enamel  so  as  to  expose  sufficient  solid  dentine  to  form  a 
hook  for  incisal  anchorage.  A  gingival  seat  takes  up  the  in- 
cisal  stress. 

A  method  of  forming  a  dovetailed  space  in  the  lingual 
surface  of  the  tootli  as  near  the  incisal  edge  as  possible,  to 
provide  for  tipping  as  well  as  outward  displacement. 

A  method  of  forming  a  step  along  the  linguo-incisal  edge, 
involving  principally  the  lingual  ])late  of  enamel.  The  bottom 
of  the  steji  may  be  grooved  slightly,  and  near  its  farthest 
extremity  from  the  cavity  a  small  hole  is  drilled  in  tlie  dentine 
to  receive  an  iridio-platinum  post.  The  line  of  junction  of 
the  inlay  with  the  labial  ]ilate  of  enamel,  occurring  on  the  in- 


937 


eisal  edge,  invites  displaeenient  of  the  inlay  as  well  as  frac- 
ture of  the  labial  plate  of  enamel  under  stress. 

A  method  of  step  preparation,  similar  to  the  above,  but 
with  the  labial  plate  rediu>ed  sliojitly  so  that  tlie  inlay  will 


PR0X1M.VL   VIEW  OF  DISTAL 

CAVITY    IN    CUSPID    TOOTH. 

SHO«nNG   I.IXGUAL   STEP 


LINOUAL      VIEW.      SHOWING 
DOVETAIL,    OP    STEP 


LINGDAL  VIEW  OP 
BOTH,  SHOWING  IN 
CISAI,  STEP  CAVITY 
WITH    PIN     IN     STEP 


UISTO-I.IXOUAL  VIEW 

OF    PRECEDING 

TOOTH 


LABIAL        VIEW        OP 

TOOTH      WITH      INI.AY 

JX     POSITION 


I-INGUAI,  VIEW  OF 
INCISAL  STEP  CAV- 
I  T  V  ,  S  H  O  W  I  N  G 
GROOVE       RETENTION 


LABIAL        VIEW        OP 

TOOTH     WITH     INI.AY' 

IN    POSITION 


LABIAL.     DISTAL    ANt)     INCISAL     VIEW     OF 

CAVITY       IN       CUSPID       PREPARKO       WITH 

DO\ETAILED  ANCHORAGE  COMBINED   WITH 

PIN. 


form  a  tip  of  gold  over  the  two  plates  of  enamel.    This  form 
of  cavity  preparatipu  is  preferal)le  to  the  preceding. 

A  method  ef  forming  a  step  similar  to  the  above,  but  in- 
stead of  the  pin  anchorage,  a  drop  of  the  step  gingivally,  in 
the  lingual  plate  of  enamel  and  the  dentine  as  well,  furnishes 
the  resistance  to  tipping  stress. 


A  method  of  auelioriug  a  large  contour  filling  in  a  pulp- 
less  tooth  by  means  of  a  pin  extending  into  the  root  canal. 

A  method  of  forming  in  the  labial  or  buccal  surface  of 
the  wax  model,  a  cavity  with  undercuts,  in  which,  after  the 
inlay  is  set,  a  synthetic  cement  filling  is  placed  to  avoid  the 
display  of  gold. 


I'ROXIMAI.    VIEW    OF      LINGUAL      VIEW      O 
TOOTH    WITH    MESIO-  THE    PRECEDING 

INl'lSO-DISTAL      CAV- 
ITY   PKEPiVBED 


LINGUAL       VIEW       OF 

TOOTH  WITH  FILLING 

IN    POSITION 


LABIAL        VIEW        OF 

TOOTH  WITH  FILLING 

IN    POSITION 


A  method  of  preparation  for  a  mesio-inciso-distal  cavity 
in  an  anterior  tooth,  formed  with  a  grooved  step,  cut  princi- 
pally at  the  expense  of  the  lingual  plate  of  enamel.  The  in- 
cisal  edge  of  the  tooth  is  rediiced  so  that  it  may  be  tipped  with 
gold  for  its  protection. 


THBEE  VIEWS  OF  THE  WAX  MODEL  FOR  A  MESIO-INCISO-DISTAL  INLA\' 

In  casting  fillings  of  this  type,  a  piece  of  iridio-platinum 
wire  should  be  bent  so  that  it  will  not  interfere  with  the  mar- 
gins of  the  inlay.  This  is  inserted  in,  and  as  close  to  the 
cervical  terminal  of  the  wax  model  as  possible  to  prevent 
change  of  relation  due  to  contraction. 


INLAYS  939 

A  straight  piece  with  square  ends  will  serve  this  purpose 
equally  as  well,  if  inserted  between  the  axial  surfaces  of  the 
mesial  and  distal  sections. 

A  mesio-oeclusal,  grooved  cavity  in  an  upper  molar.  The 
pulpal  wall  is  grooved  to  provide  against  tipping  stress.   This 


THEEE  \IE\VS    OF   TTIE    CO^!^LETED    IXLAY 


form  of  cavity  preparation  is  frequently  employed  when  the 
inlay  is  to  serve  as  a  bridge  abutment. 

A  loose  pin  anchorage  for  an  inlay  to  lie  used  as  an  abut- 
ment for  a  bridge.     A  square  iridio-platinum  bar,  from  32  to 


SECTIONAL    VIE\V    OF    A    MOLAB. 

SHOWING     GROOVED     STEP     FOB 

(ItlARDING       AGAINST       TIPI'ING 

STRESS 


SIMPLE      MESIO-Ot'CH'SAL. 

DOVETAIL      STEP      CA\ITy 

IN    MOLAR 


14  gauge,  is  imiformly  tapered  on  the  four  sides,  extending 
back  about  three-fourths  of  an  inch  from  one  end,  and  reduced 
sufficiently  to  enter  the  enlarged  root  canal  the  required  depth 
for  anchorage  purposes.    Around  the  tapered  portion  and  in- 


volviiii;-  tlic  ai'cn  wliicli  will  rest  within  1lic  inlay,  is  wrapped 
a  band  of  1  100(1  platiinnn  foil  wliieli  slionid  lap  on  itself  about 
one-half  tnin  of  the  wire.  The  taper  pin  is  withdrawn  and 
the  square  tube  of  foil  is  tacked  with  a  little  pure  gold  solder 
to  prevent  it  from  opening.  It  is  returned  to  the  pin  and  re- 
ada])ted  to  coi-reet  any  change  that  may  ha\(!  occurred  in 
soldei'ing. 

The  wax  model  is  carved  to  proper  contour,  and  the  pin 
without  the  sleeve  is  warmed,  passed  throTigh  the  wax  and  to 
position  in  the  root  canal  and  withdrawn.  It  is  now  heated  to 
burn  off  the  adherent  wax  and  oiled  to  ])re\'ent  the  sleeve  be- 


coming fast.  The  sleeve  is  again  returned  to  position,  pin 
warmed  and  the  two  are  passed  through  the  opening  in  the  in- 
lay and  into  the  canal  to  projier  position.  A  small  heated  in- 
strument is  passed  around  the  sides  of  the  tube  so  as  to  cause 
the  wax  to  adhere  to  it,  but  not  to  the  pin.  The  latter  is  now 
withdrawn,  wdiile  the  tube  remains  in  the  wax.  The  tube  should 
be  long  enough  to  project  beyond  the  upper  and  lower  sur- 
faces of  the  wax,  so  as  to  become  inclosed  in  the  investment. 
On  removal  of  the  wax  model,  the  tube  is  first  filled  with  in- 
vestment, after  which  the  model  is  invested  in  the  usual  man- 
ner. When  cast,  the  projecting  ends  of  the  tube  are  reduced 
to  the  level  of  the  inlay  surfaces,  the  opening  cleared  for  the 


reception  of  the  i^in,  the  inlay  finished  and  set  and  while  the 
cement  is  still  soft  the  pin  is  forced  to  place.  Care  should  be 
taken  to  avoid  the  excessive  use  of  cement  which  might  be 
forced  into  the  canal  from  which  it  would  bo  difficult  to  expel 
it. 

This  attacliment  is  intended  to  be  used  in  conjunction  with 
bridge  work,  and  as  the  setting  of  the  bridge  is  of  itself  a 
particular  operation,  the  following  plati  could  be  adopted : 

Fill  the  root  canal,  or  the  outer  portion  of  it,  with  tem- 
porary stopping,  being  careful  not  to  encroach  on  the  base 
of  the  cavity.  Set  the  bridge  in  the  usual  manner,  and  when 
the  cement  has  hardened,  with  a  small,  rough,  heated  instru- 
ment remove  the  temporary  stopping,  and  free  the  canal  from 
all  debris,  after  which  the  pin  may  be  set  independently  and 
the  ijrojecting  end  reduced  with  stones  to  the  level  of  the  in- 
lay. This  method  was  suggested  anci  has  been  successfully 
used  ])y  Dr.  A.  L.  Le  Gro  of  Detroit,  Mich.,  who  has  demon- 
strated it  at  various  times  within  the  past  few  years. 

A  metliod  of  utilizing  short  pins  for  anchorage  purposes, 
placed  in  various  locations  in  cavities  prepared  in  vital  teeth, 
has  been  extensively  applied  by  Dr.  M.  L.  Ward  of  Ann 
Arbor.  Mich.  In  this  system  he  makes  use  of  one  or  more 
pins  or  a  two-point  staple,  the  bent  ])ortion  of  which  is  en- 
closed in  the  inlay. 

The  main  points  to  keep  in  mind  in  api>lying  this  system 
of  anchorage  to  inlays  are  to  arrange  the  pins  parallel  with 
the  line  of  direction  in  which  the  wax  model  is  withdrawn 
from  the  cavity,  and  in  drilling  the  holes  to  avoid  encroaching 
on  the  pulp. 

A  method  of  shoulder  anchorage,  applicable  to  axio-occlu- 
sal  cavities  in  vital  bicuspid  and  molar  teeth..  In  this  system 
a  groove  is  cut  at  the  extremity  of  the  steyi  farthest  from  the 
axial  wall  involved  and  of  sufficient  deptii  to  prevent  radial 
rnovement  of  the  inlay  outward.  Usually  from  one  to  one  and 
one-half  millimeters  in  width  and  depth  will  be  ample  dimen- 
sions for  the  groove. 

A  simple  method  of  dovetailed  anchorage,  applicable  to 
axio-occlusal  cavi-ties  in  vital  teeth.  This  cavity  preparation 
ditifers  but  little  from  that  followed  in  gold  foil  operations, 
except  that  all  axial  walls  must  flare  slightly  from  gingival 
and  ])ul]ial  surfaces,  from  one  to  two  degrees. 


942  INLAYS 

THE  MATRIX  METHOD  OF  INLAY  PRODUCTION 

The  preparation  of  cavities  intended  for  the  reception  of 
inlays  formed  in  a  matrix  is  essentially  the  same  as  for  in- 
lays of  any  class,  viz.,  the  development  of  flat  seats,  and 
slightly  flaring  walls,  to  permit  release  of  tlie  matrix  without 
distortion.  The  subject  of  cavity  preparation  will  lie  found 
on  page  931. 

The  matrix  of  gold  or  platinum  may  l)e  formed  in  two 
ways,  by  the  dirrrf,  or  by  the  indirect  method. 

DIRECT  METHOD  OF  PRODUCING  A  MATRIX 

The  direct  method  consists  in  adapting  a  piece  of  24- 
carat  gold,  or  platinum  foil,  to  and  against  the  cavity  sur- 
faces of  the  natural  tooth.    The  steps  are  as  follows : 

Cut  a  piece  of  foil  somewhat  larger  than  the  cavity  and 
from  1  1000  to  1-500  of  an  inch  thick,  the  thicker  foils,  while 
being  more  difficult  to  adapt,  are  less  liable  to  distort  in  sub- 
sequent steps. 

Anneal  the  piece,  center  it  over  the  cavity,  and  with  spunk 
or  pellets  of  cotton,  in  the  ball-pointed  pliers,  press  it  against 
the  cavit\'  floor  and  gradually  adapt  it  to  the  cavity  walls  and 
margins. 

Since  the  steps  are  practically^  the  same  as  in  forming  a 
platinum  matrix  for  a  porcelain  inlay  further  details  may  be 
found  on  page  920. 

When  general  adaptation  of  the  foil  to  the  cavity  surfaces 
has  been  secured,  the  peripheral  excess  is  trimmed  away,  a 
narrow  margin,  however,  being  left  to  outline  the  cavity  mar- 
gins and  prevent  the  gold,  in  fusing,  from  being  drawn  out- 
side to  the  cavity  surfaces  of  the  matrix. 

Finally,  the  matrix  should  be  annealed  and  readapted  to 
the  cavity  with  spunk  or  cotton,  applied  under  heavy  pressure, 
to  correct  warpage. 

In  simple  cases  the  matrix  is  carefully  removed,  laid  on 
the  solder  block,  some  small  squares  of  plate  or  pellets  of  pure 
gold,  previously  spheroided  and  fluxed,  placed  in  the  interior, 
and  high-grade  solder  fused  iiitd  the  matrix  and  around 
them. 

During  the  fusing  of  the  solder  the  pure  gold  pellets  or 
pieces  are  not  fused,  consequently  there  will  be  less  contrac- 
tion and  less  danger  of  warpage  of  the  matrix  than  when 
solder  alone  is  used. 

Sufficient  gold  is  added  and  fused  to  develop  desired  con- 


tour,  the  inlay  pickled  in  acid,  washed  and  returned  to  the 
cavity  for  final  reduction  with  stones  and  discs. 

It  is  then  cemented  in  position  and  the  final  polish  applied 
as  vvith  a  gold  foil  filling. 

VARIATION  IN  METHOD 

In  compound  cavities,  it  is  frequently  advisable  to  force 
slightly  softened  wax  in  the  matrix  while  in  the  cavity,  being 
particularly  careful  to  adapt  it  to  the  margins. 

The  matrix  is  then  removed  and  its  cavity  surfaces  im- 
bedded in  some  good  investment  material.  When  hardened, 
the  wax  is  removed,  the  matrix  fluxed,  case  heated,  and  solder 
applied  as  above  described. 


FORMING  THE  MATRIX  BY  THE  INDIRECT  METHOD 

An  impression  of  the  tooth  is  secured  in  modeling  com- 
pound. One  of  the  cup  pattern  trays,  suggested  by  Dr.  Eoach, 
may  be  used  or  one  can  be  improvised  from  thin  aluminum 
plate  by  the  method  described  by  Dr.  Van  Woert.  (Items  of 
Interest,  1913.) 

The  impression  is  dusted  witii  talcum  powder  and  the 
surplus  carefully  brushed  from  the  deeper  portions.  This  is 
to  serve  as  a  separating  medium. 

Modelite  or  a  good  quality  of  cement  is  mixed  to  medium 
thick  consistency,  applied  and  forced  into  every  joortion  of  the 
impression,  building  it  up  in  sufficient  bulk  to  withstand  the 
stress  of  matrix  adaptation,  without  fracturing. 

When  the  cement  has  hardened,  the  modeling  compound 
is  removed,  and  the  cement  tooth  partially  imbedded  in  model- 
ing compound  for  support,  or  it  may  be  set  in  a  ring  of  the 
swaging  device. 

In  either  case,  the  cement  reproduction  of  the  tooth  should 
be  so  placed  that  its  axial  walls  will  be  supported  to  resist  side 
stress.  Most  of  the  force  of  matrix  adaptation  should  be  ap- 
plied vertically,  downward. 

The  matrix  may  be  adapted,  either  by  burnishing  or 
swaging,  or  by  both  methods  combined. 

When  possible  to  do  so  it  is  advisable  to  test  the  adapta- 
tion of  matrix -to  tooth  cavity  before  contouring  with  gold. 

When  the  matrix  method  is  carried  out  accurately,  com- 
paratively perfect  adaptation  of  an  inlay  to  tooth  and  cavity 
surfaces  can  be  secured. 


CAST  GOLD  INLAYS 
GENERAL  REMARKS 

To  be  reasonably  siiecesst'iil  iu  the  easting  of  inlays  and 
of  prosthetic  restorations  in  general,  it  is  necessary  to  know 
something-  of  tlie  physical  properties  of  the  materials  em- 
ployed. 

Casting  operations  involve  the  nse  of  waxes,  investments, 
and  the  metal  of  whicli  the  restorations  are  to  be  made,  usu- 
ally gold.  These  materials,  within  certain  limits,  are  subject 
to  the  same  law  as  are  nearly  all  solid  substances,  viz.,  that 
heat  expands  and  cold  contracts,  the  amount  of  dimensional 
change  being  generally  dependent  on  temperature  varia- 
tions. 

In  the  various  steps,  from  the  formation  of  the  wax  model 
to  its  reproduction  in  metal  by  casting,  the  materials  under 
consideration  are  subjected  to  widely  varying  temperature 
changes.  These  changes,  as  the  work  is  carried  forward,  tend 
to  produce  errors,  by  increasing  or  decreasing  the  size  of  the 
model,  the  form  of  the  investment,  and,  finally,  reduction  in 
size,  or  in  warpage  of  the  metal  casting  itself,  which  changes 
are  oftentimes  sufficient  to  render  it  worthless. 

AVhile  no  absolute  line  of  procedure,  for  avoiding  error  in 
the  casting  process  has  been  determined,  certain  facts  of  im- 
portance are  known,  wliich,  if  observed,  will  minimize  the  tend- 
ency to  error. 

PHYSICAL    PROPERTIES    OF   THE    MATERIALS    EMPLOYED 
IN  CASTING 

With  few  exceptions,  the  physical  law,  as  previously 
stated,  that  heat  expands  and  cold  contracts,  ajjplies  to  solids, 
liquids,  and  gases  alike.  The  standard  of  measurement  of  the 
linear,  superficial,  or  cubical  change,  occasioned  by  raising 
the  temperature  of  a  given  substance,  is  based  on  the  increase 
noted  in  elevating  the  temperature  of  that  substance  from 
0  to  1°  C.  The  amount  of  such  increase  is  termed  the  co-effi- 
cient of  expansion. 

Between  0  and  100°  C,  the  co-efficient  of  expansion  in  a 
metal,  an  alloy,  or  any  substance  of  standard  character,  is 
comi^aratively  constant  for  that  or  any  like  class  of  substances. 
When  metals  are  alloyed,  or  when  the  composition  of  sub- 
stances is  modified,  their  co-efficients  of  expansion  change, 
sometimes  to  a  remarkable  degree.    The  following  four  alloys 


INLAYS  945 

of  nickel  and  iron,  although  instances  of  the  extreme  type, 
serve  to  illustrate  this  fact. 

Mean  co-efficient  of  expansion 
Nickel.       Iron.         between  O  and  100  deg.  C. 

No.   1 28  72  .000015 

No.  2 36     64     .0000015  (Known  as  "invar") 

No.  3 .45      55      .0000088 

No.  4 GO     40      .000012 

Varying  the  proportion  of  nickel  and  iron  only  8  per  cent 
reduces  the  co-efficient  of  expansion  of  the  invar  to  one-tenth 
that  of  the  first  alloy.  Combining  the  same  two  metals  in  the 
proportions  as  shown  in  the  fourth  alloy,  results  in  increas- 
ing the  expansive  index  to  within  .OOOOOo  that  of  the  first. 

EXPANSIVE  AND  CONTRACTILE  FORCES 

When  metal  is  expanded  by  heat,  a  certain  amount  of 
energy  is  develojjed  which  becomes  apparent  on  restricting  its 
free  movement.  According  to  Joule's  data,  when  a  pound  of 
iron  is  raised  in  temperature  from  0  to  100°  C,  it  expands  one- 
two-humlred-and-eightieth  of  its  bulk.  The  energy  or  force 
of  this  expansion  is  sufficient  to  raise  seven  tons  one  foot  in 
height. 

A  bar  of  iron  10  inches  long  will  expand  1/200  of  an  inch 
with  a  raise  in  temperature  of  45°  C.  The  force  of  this  ex- 
pansion is  equivalent  to  50  tons. 

A  bar  of  malleable  iron,  of  one  inch  sectional  area,  is 
stretched  1/10000  of  its  length  by  a  weight  of  one  ton.  Raising- 
its  temperature  about  9°  C.  will  elongate  it  to  the  same 
extent. 

When  bodies  have  been  heated  to  a  high  temperature,  the 
force  produced  by  their  contraction  in  cooling  is  equivalent 
to  the  force  wliich  is  needed  to  compress  them  to  the  same 
extent  by  mechanical  means.     (Ganot's  Physics.) 

The  relation  of  these  examples  of  expansive  and  con- 
tractile forces  to  inlay  work,  particularly  to  investments,  will 
be  brought  out  later. 

PRINCIPAL  SOURCES  OF  ERROR  IN  INLAY  CONSTRUCTION 

The  three  principal  classes  of  materials  used  in  inlaj'  con- 
struction, as  previously  stated,  are  waxes,  refractory  invest- 
ments and  gold  of  varying  carats.  In  manipulative  proced- 
ures these  materials  are  subjected  to  dimensional  changes 
which  vary  according  to  the  composition  of  the  substances 
used,  and  the  technical  methods  employed.  The  many  varie- 
ties of  wax  exhibit  a  wide  range  of  difference  in  their  hard- 


946  INLAYS 

ness,  adhesivoiioss,  cohcsiveness,  expansive  tendenoy,  liabilit.y 
to  warp,  and  general  susceptibility  to  thermal  changes. 

Investment  materials  vary  greatly  in  composition,  density 
and  porosity.  Some  maintain  their  integrity  at  high  tempera- 
tures without  crumbling,  crushing,  or  flaking,  while  others  are 
more  or  less  disintegrated. 

Gold  of  varying  carats  and  compositions  show  different 
exjaansive  indices,  and  more  or  less  variation  in  fluidity,  as  a 
general  rule,  when  fused.  The  higher  the  carat  of  gold  used, 
the  sharper  will  be  the  casting,  while  less  contraction  will 
occur  in  cooling.  There  are,  however,  exceptions  to  this  in 
some  of  the  more  recent  alloys  of  gold. 

Two  or  more  men  using  identically  the  same  materials,  fol- 
lowing the  same  technic,  and  working  under  as  nearly  the 
same  conditions  as  possible,  will  not  produce  identical  results. 
Duplicate  pieces  produced  by  the  same  individual,  even  when 
extreme  care  is  taken  to  follow  the  same  methods,  vary  more 
or  less. 

This  fact,  together  with  variations  in  the  physical  prop- 
erties of  materials  employed,  render  impossible  the  produc- 
tion of  perfect  inlays.  A  near  approach  to  good  adaptation 
and  general  requirements,  however,  may  be  secured  by  using 
carefully  selected  materials,  and  by  exercising  care  in  tech- 
nical details. 

WAXES 

The  basis  of  most  of  the  inlay  waxes  is  beeswax.  In  its 
natural  condition  beeswax  is  not  siiitable  for  inlay  models.  It 
is  too  soft  and  bends  too  easily  to  retain  its  form  in  handling. 
Beeswax  consists  of  three  principal  substances,  first,  Myricyl 
palmitate,  CauH„i  CjoHsiOo;  second,  Cerotic  acid,  C^jHsiOo,  and 
Cerolein,  a  waxy  organic  compound. 

Beeswax  melts  at  63°  C.  (145°  F.),  Sp.  Gr.  .960.  Wlien 
melted  on  a  plaster  slab  it  is  gradually  absorbed,  and  if  pure 
leaves  no  residue.  On  applying  increased  heat  it  is  volatil- 
ized. It  is  quite  adhesive  when  pressed  firmly  against  an 
object.  This  is  a  detrimental  quality,  as  it  tends  to  stick  to 
cavity  walls.  Beeswax  lacks  cohesiveness  and  consequently 
its  molecules  do  not  cling  together  firmly.  For  this  reason  it 
is  brittle,  and  in  carving,  thin  margins  tear  away  easily. 

PARAFFIN 

Paraffin  is  a  natural,  wax-like  substance,  usually  com- 
posed of  two  or  more  members  of  the  paraffin  series  of  hydro- 


INLAYS  947 

carbons.  Its  formula  varies  soniewiiat,  dppcndiug  on  its  der- 
ivation, but  corresponds  generally  with  the  following: 
C.jr.,s  C..H„o  a„H„..  It  melts  between  li:'.  to  149°  F.,  depend- 
ing on  the  source  from  which  procured,  and  on  cooling  forms 
a  white,  rather  hard,  compact  crystalline  mass.  It  is  quite 
cohesive,  but  not  very  adhesive  in  a  cold  state. 

EFFECT   OF   COMBINING  WAX   AND   PARAFFIN 

By  combining  beeswax  with  iniraffin,  frequently  having 
a  very  considerable  excess  of  the  latter,  the  product  is  less 
adhesive,  more  cohesive,  and  somewhat  harder  than  when 
uncombined.  Some  of  the  resins  are  frequently  added  to  the 
foregoing  combination,  to  give  increased  liardness.  Such 
])rodncts  sometimes  fail  to  volatilize,  leave  a  residue  in  the 
matrix,  and  are  usually  detrimental. 

ESSENTIAL  REQUISITES  OF  A  WAX 

Briefly  stated,  the  necessary  qualities  of  an  inlay  wax  are 
as  follows : 

First,  it  must  have  a  low  coefficient  of  expansion. 

Second,  it  should  l)e  strongly  cohesive,  but  not  percept- 
ibly adhesive. 

Third,  when  cold,  it  should  break  before  bending. 

Fourth,  it  should  be  hard  enough  at  body  temperature  to 
carve  well. 

Fifth,  it  should  become  plastic  at  a  reasonably  low  point 
above  body  temperature. 

Sixth,  it  should  be  dark  in  color  and  translucent,  so  that 
in  carving,  tooth  surfaces  may  be  seen  through  thin  layers  of 
it.  " 

In  practice,  a  wax  should  be  selected,  as  previously  stated, 
which,  on  testing,  leaves  no  residue.  If  so,  it  should  be  dis- 
carded, as  its  use  would  result  in  rough  and  imperfect  sur- 
faces to  the  inlay.  The  next  most  important  quality  in  a  wax 
is  a  low  range  of  expansion.  It  must  be  borne  in  mind  that 
the  wax  is  forced  into  the  cavity  in  its  most  expanded  condi- 
tion The  higher  the  temperatui'e  required  to  render  it  plastic, 
the  greater  its  expansion,  and,  conseciuently,  the  more  con- 
traction will  occur  in  cooling  to  room  temperature.  While  in 
this  contracted  state,  the  investment  of  the  model  is  usually 
accomplished.  It  is  therefore  smaller  than  when  first  adapted 
to  the  cavity  walls.  "While,  in  the  subsequent  steps  of  cast- 
ing, the  investment  and  ring  expand  under  heat,  and  i^ossibly 


948  INLAYS 

the  matrix  itself  may  become  sliglitly  enlarged,  such  changes 
are  beyond  control.  They  may  correct,  partially  or  wholly, 
the  error  of  contraction  in  the  wax,  or  they  may  lead  to  still 
greater  error,  through  unequal  expansion,  since  the  crucible 
portion  of  the  ring  is  much  hotter  than  the  bottom,  at  the 
moment  of  casting. 

ELASTIC  PROPERTIES  OF  WAX 

When  a  roll  of  wax  is  rendered  plastic  by  heat,  bent  in 
the  form  of  a  ring,  and  chilled,  the  ends  being  unattached,  it 
will  remain  in  that  form  so  long  as  the  temperature  is  not 
raised.  In  bending,  the  molecules  on  the  outer  periphery  of 
the  ring  are  elongated,  while  those  along  tlie  inner  y)eripliery 
are  compressed. 

In  most  materials,  and  in  wax  as  well,  the  tendency  of 
molecules,  when  stretched  or  distorted,  is  to  return  to  norma! 


n  I  A  G  R  A  M  M  A  T  I  ('    DRAWING 
SHOWING     MOLECULAR    AB- 

RANGEMENT  OF  WAX  WHEN 
MELTED  ASn  RIN  IN  BAR  FORM. 
DIAGRAM  OF  TOOTH  WITH  liAR 
BEXT  INTO  A  MESIO-OIVHiSO- 
DISTAL  CAVITY-  NOTICE  THE 
BI.ONGATION  OF  THEORETIl^iL 
MOLECrLE.S  ON  THE  OUTER 
PERIPHERY  AND  THE  COM- 
PRESSED CONDITION  OF  THOSE 
IN    THE    INNER    PERIPHEHY" 


form  and  relation  to  each  other,  when  the  stress  which  dis- 
torted them,  or  the  force  which  holds  them  in  abnormal  form 
and  position,  is  removed.  Chilling  the  wax  hardens  it,  and 
renders  inert  the  tendency  of  the  molecules  to  return  to  nor- 
mal form.  By  subsequently  raising  the  temperature  of  the 
wax,  the  force  which  locks  the  molecules  in  their  strained  rela- 
tion is  partially  overcome,  and,  to  a  limited  extent,  they  re- 
turn to  their  original  form,  causing  the  ends  of  the  wax  ring 
to  separate.  The  temperature  at  which  the  inherent  tendency 
of  the  molecules  of  wax  to  recover  their  form  becomes  per- 


INLAYS  949 

ceptible  varies  according-  to  the  comiiosition  of  the  material. 
It  is  evident  that  some  waxes,  hard  enough  to  carve  at  body 
temperature,  change  form  on  removal  from  the  mouth,  while 
others  apparently  do  not  exhibit  such  tendency.  Time,  and 
fluctuating  temperature,  without  doubt,  encourage  warpage, 
therefore,  to  avoid  excessive  dimensional  change  and  warpage, 
the  wax  model  should  be  invested  as  soon  as  possible. 

INVESTMENT    MATERIALS 

The  refractory  basis  of  most  investment  materials,  used 
for  casting  purposes,  is  pulverized  silex,  of  varying  degrees 
of  fineness,  and  in  some  cases  graphite.  Plaster  of  paris 
serves  as  a  binder,  or  cementing  medium,  and  fills  the  voids 
between  the  granules  of  silex.  Various  other  substances  are 
added  to  control  the  time  of  setting,  prevent  contraction,  and 
impart  smoothness  and  density  to  the  mass  when  mixed. 

EXPANSION  OF  INVESTMENT   RING  AND  INVESTMENT 
MATERIAL 

The  coefficient  of  expansion  of  l)rass  of  which  most  casting 
rings  are  made  is  .000018,  between  0  and  100°  C,  that  of  quartz 
between  0  and  1000°  C,  .00000055.  (Ganot's  Physics.)  The 
expansion  of  the  brass  is  therefore  thirty-three  times  greater 
at  only  one-tenth  the  temperature,  than  that  of  quartz.  The 
coefficient  of  expansion  of  graphite  is  .0000078  (Ganot's 
Physics),  or  about  14  times  greater  than  that  of  quartz,  but 
perce];)tibly  less  than  brass.  Its  effect,  when  combined  with 
quartz  in  an  investment,  is  to  increase  the  coefficient  of  ex- 
pansion. Some  of  the  liest  investments  procurable  contain  a 
considerable  percentage  of  graphite  incor])orated  for  this  pur- 
pose. The  coefficient  of  expansion  of  the  materials  mentioned 
is  variable,  according  to  composition,  variety,  etc. 

Since  the  investment  ring  ex]iands  on  heating,  the  invest- 
ment itself  should  also  expand  and  follow  the  walls  as  closely 
as  possible,  first,  to  counteract  the  internal  force  brought  upon 
the  matrix  walls  in  casting  the  gold  under  pressure,  thus  pre 
venting  the  investment  from  cracking  or  Inilging  outward  in 
thin  places,  and  second,  to  prevent  the  investment  dropping 
from  the  ring  in  handling;  third,  to  enlarge  the  mold  slightly, 
thus  compensating  to  a  slight  extent  for  contraction  of  the 
gold.  Expansion  of  the  investment,  therefore,  is  a  neces- 
sary quality. 

Some  investment  materials  show  a  tendency  to  contract 
toward  several  common  centers  when  overheated.    When  this 


occurs,  ci-ack'iiii;'  of  the  investment    follows  and   the  si:eneral 
surfaces  of  the  matrix  are  warped. 

Some  investment  materials  are  sul),)ect  to  varyin.i;'  dimen- 
sional changes  on  the  apitlication  of  heat,  depending  on  the 
quantity  of  water  used  in  mixing.  Thin  mixes,  as  a  rule,  show 
a  greater  tendency  to  contract  and  warp  than  thick  mixes  of 
the  same  material.  Taggart's  investment  is  an  exception  to 
this  rule,  as  it  has  a  high  coefficient  of  expansion  when  mixed 
thin  enough  to  l)e  poured. 

ESSENTIAL   PROPERTIES   OF  AN    INVESTMENT   MATERIAL 

'J'lie  essential  ])roi)erties  of  an  inlay  investment  material, 
briefly  stated,  are  as  follows: 

First,  it  should  not  contract  in  setting,  even  when  mixed 
thin. 

Second,  it  should  be  dense  and  free  from  perceiitible 
porosity  when  set. 

Third,  it  should  be  hard,  resistant  to  stress,  and  show  no 
tendency  to  crack  when  heated  to  casting  temperature. 

Fourth,  it  should  possess  a  high  expansive  index,  and  a 
low  co-efifieient  of  conductivity  under  heat. 

Fifth,  it  should  not  be  fused,  by  the  molten  gold,  in  cast- 
ing the  latter. 

Since  there  is  no  cohesion  whatever  between  the  granules 
of  refractor^'  materials  themselves,  a  binder  must  be  incor- 
porated, which  in  practically  all  cases  is  plaster  of  Paris.  As 
has  previously  been  shown,  this  material  is  a  crystallized, 
di-hydrate  of  calcium  sulphate,  which  decomposes  to  a  greater 
or  less  extent  at  190°  C.  The  crystals  do  not  immediately 
crumble  on  being  heated,  but  are  greatly  weakened,  so  that 
the  application  of  slight  force  is  sufficient  to  disintegrate 
them.  That  the  matrix  walls  of  overheated  cases  do  not  flake 
away  more  readily  than  would  at  tirst  api:)ear  from  the  disin- 
tegration of  plaster  is  due  to  the  mechanical  interlocking  of 
the  granules  of  the  various  materials  of  which  the  invest- 
ment is  composed,  and  which  lie  in  more  or  less  close  contact. 
Decomposition  of  the  binder  from  overheating  is  largely  re- 
sponsible for  the  roughening  and  bulging  outward  of  the 
matrix  walls  under  the  ]3ressure  of  casting. 

As  an  example,  casts  and  investments  composed  of  plaster 
alone,  although  at  first  expanded  with  slight  rise  in  tempera- 
ture, when  heated  to  high  temperatures,  contract,  crack  and 
distort  very  quickly.    Plaster,  therefore,  should  not  be  used  to 


excess  in  inlay  investments  or  tlie  qnality  of  tlie  latter  will  be 
impaired  in  proi)ortion  to  the  excess  of  this  material  present. 
By  using  but  little  more  than  an  amount  sufficient  to  till  the 
voids  between  the  granules  of  refractory  materials,  contrac- 
tion is,  to  a  great  extent,  obviated  and  the  tendencj^  to  crack 
and  warp  is  greatly  reduced.  Roughly  estimated,  the  propor- 
tion of  plaster  to  refractory  materials  ranges  from  25  to  -iO 
per  cent. 

Further  valuable  discussion  of  this  subject  will  be  found 
under  the  heading,  "Refractory  Materials,"  by  Dr.  Wein- 
stein,  page  1040. 

DIMENSIONAL    CHANGES    IN    GOLD,    DUE    TO    TEMPERATURE 
CHANGES 

When  gold  changes  from  a  fused  to  solid  state  and  normal 
temi)erature,  its  cubical  contraction,  according  to  Dr.  W.  A. 
Price's  tindings,  is  about  6.75  per  cent  of  volume. 

Linear,  being  one-third  that  of  cubical  contraction,  is, 
therefore,  about  2.25  per  cent.  In  an  inlay  one-fourth  inch 
wide,  or  long,  the  linear  contraction  of  that  surface  would 
show  a  deficiency  of  about  .005  of  an  inch. 

While  heavy  pressure,  api)lied  during  and  after  injection 
of  the  molten  gold  into  the  mold,  might,  by  the  compressive 
force  exerted,  reduce  to  a  slight  extent  the  percentage  of 
contraction  noted,  such  method  is  impracticable,  because  of  the 
comparative  non-resistance  of  the  investment  materials  to 
heavy  pressure. 

Contraction  of  the  gold,  therefore,  is  a  constant  source  of 
error  in  the  production  of  castings  of  exact  dimensions. 

COMPENSATING  FOR  ERRORS  DUE  TO  CONTRACTION  OF 
GOLD 

Various  means  have  been  suggested  for  minimizing  the 
errors  arising  from  the  contraction  of  gold  in  cooling,  a  few 
of  which  will  now  be  mentioned. 

First,  the  use  of  an  investment  which  will  expand  on  heat- 
ing, thus  enlarging  the  matrix  to  a  slight  extent.  This  method, 
however,  is  subject  to  error,  for  unless  the  investment  is  lani- 
formly  heated  it  will  not  be  equally  expanded,  and  as  a  result 
the  mold  walls  will  be  distorted. 

Second,  heating  the  wax  model  somewhat  above  body  tem- 
perature by  investing  in  warm,  instead  of  cold,  investment, 
thus  expanding  it  slightly  before  the  investing  medium  hard- 
ens.   Error  may  or  may  not  occur  when  this  method  is  fol- 


952  INLAYS 

lowed;  if  the  wax  is  under  niolcciilar  slraia,  yet  rigid  at  room 
or  body  temperature,  investing  it  in  a  warm  medium  may  re- 
lease the  tension  and  result  in  warpage  of  the  model  before  the 
investment  hardens.  When  not  subjected  to  molecular  tension, 
expansion  without  distortion  will  occur,  thus  favorably  in- 
creasing the  dimensions  of  the  matrix. 

Third,  tlie  use  of  sufficient  gold  to  insure  a  considerably 
larger  residual  button  in  the  crucil)le  than  the  bulk  of  gold  in 
the  casting.  Naturally,  the  casting,  being  smaller,  and  the 
matrix  walls  in  a  less  heated  state  than  the  crucible,  the  con- 
tents of  the  mold  will  solidify  first.  When  the  sprue  is  of 
sufficient  size  and  its  length  not  excessive,  as  contraction  of 
the  gold  within  the  matrix  sets  in,  the  pressure  on  the  more 
highly  heated  residual  gold  in  the  crucible  forces  it  in  and 
feeds  the  contracting  mass  within  the  mold  until  it  solidifies. 

The  necessity  for  the  unequal  balancing  of  the  gold  as 
suggested  is  apparent  for  the  following  reasons: 

To  produce  sharp  castings  it  is  necessary  that  the  gold  be 
in  a  su]3erheated  condition,  considerably  above  its  actual  fus- 
ing point.  The  contraction  of  superheated  gold  may  be 
divided  into  two  stages,  first,  that  which  occurs  in  passing 
from  its  highest  heated,  and  most  expanded  condition  to  the 
freezing  state,  and  second,  from  the  point  of  congealing  to 
normal  temperature. 

Now,  if  gold,  in  a  superheated  condition,  be  cast  into 
either  a  hot  or  cold  matrix,  and  no  provision  is  made  for  re- 
plenishing the  contracting,  fluid  mass,  the  casting  will  be  de- 
fective, and  in  case  of  inlays  the  margins  will  be  rounded. 

RESULT  OF  CONTRACTION  OF  GOLD  IN  INLAY  ADAPTATION 

The  result  of  contraction  of  gold  in  inlay  construction  is 
that;  in  a  simple  cavity,  the  inlay  will  fail  to  fill  the  cavity  per- 
fectly, a  more  or  less  open  space  showing  around  the  margins, 
while  the  axial  surface  usually  sinks  slightly  below  that  of  the 
tooth. 

Since,  as  has  been  previously  shown,  the  contractile  force 
exerted  by  a  casting,  in  cooling,  is  equivalent  to  the  mechanical 
force  required  to  compress  gold,  of  similar  bulk,  an  equal 
amount  by  mechanical  means,  it  therefore  follows  that  in 
mesio-occluso-distal  inlays  the  investment  interposed  between 
the  mesial  and  distal  flanges  of  the  inlay  will  be  compressed 
and  distorted  to  a  greater  or  less  extent. 

As  a  result  of  such  contraction,  the  inlay  frequently  fails 
to  go  to  place.    To  seat  it,  the  tooth  may  be  reduced,  the  inner 


walls  of  the  matrix  enlarged  or  the  oeelusal  portion  of  the  in- 
lay stretched  snffieieutly  to  permit  its  being  driven  to  place. 

Dr.  Price  suggests  two  means  for  overcoming  the  diffi- 
culty; first  to  cast  the  inlay  against  a  reproduction  of  the 
tooth,  develoi^ed  in  a  special  artificial  stone,  or  to  cast  the  in- 
lay around  a  threaded  iridio-platinuni  liar,  extended  through 
and  beyond  the  occlusal  body  of  the  inlay,  sufficiently  to  gain 
a  firm  hold  in  the  investment. 

Still  another  method,  suggested  by  a  member  of  the  pro- 
fession in  Wisconsin,  whose  name  the  writer  cannot  recall, 
consists  in  drilling  a  hole  through  the  occlusal  portion  of  the 
inlay,  inserting  a  fine  saw  and  cutting  l)uccally  and  lingually 
almost,  but  not  quite,  to  the  walls  to  weaken  the  gold,  introduc- 
ing the  inlay  and  driving  it  to  i)lace.  As  a  result  the  gold  is 
stretched  and  the  inlay  lengtheneti.  Care  should  be  taken  to 
see  that  the  gingival  ends  are  not  bent  outward,  or,  if  so,  to 
readjust  them,  after  which  wax  is  filled  in  the  hole  and  saw 
cut,  the  inlay  invested  and  the  opening  filled  with  solder. 

Since  ordinary  investments,  used  in  casting,  are  unable 
to  resist  the  force  of  contraction  of  the  gold,  practically  the 
only  means  left  is  to  select  a  material  that  expands  perceptibly 
during  the  heating  and  casting  process. 


TECHNIC  OF  CAST  GOLD  INLAY  CONSTRUCTION 
FORMING  THE  WAX  MODEL 

Tnlay  waxes  are  prepared  in  stick  form  and  are  also  sup- 
plied in  the  form  of  cones  and  various  irregular  shapes  suit- 


••Attll«t 


VARIOUS   FdRMS  OF    IN'l.AV.    WAX   JU.OI'KS 


able  for  introduction  into  different  classes  of  cavities,  with- 
out bending.   - 

These  blocks  and  sticks  are  formed  by  melting  the  wax 
and  casting  into  molds.  They  are,  therefore,  free  from  mole- 
cular tension. 


954  INLAYS 

Select  a  wax  form  of  approximately  the  sliape,  Init  larger 
than  is  required  to  fill  the  cavity. 

If  the  cavity  is  irregular  as  one  of  the  mesio-occluso-dis- 
tal  class,  a  form  should  be  carved,  of  the  desired  shape,  from 
a  large  block,  or  two  forms  may  be  joined  by  melting  their 
contact  surfaces,  and  the  reqiiired  form  carved  from  the 
united  pieces. 

Soften  by  placing  in  hot  water,  the  temperature  of  which 
should  range  from  US'"  to  139°  F.,  according  to  the  variety 
of  wax  used. 

Price's  wax  becomes  workable  at  115°  P.,  Peck's  at  120° 
F.,  Cleveland  Dental  at  127°  F.,  S.  S.  Wliite  at  128°  F.,  Con- 
solidated at  130°  F.,  Goslee's  at  135°  F.  and  Taggart's  and 
Klewe's  at  139°  F. 

The  wax  should  be  entirely  immersed  in  the  water,  re- 
maining there  a  sufficient  time  to  become  uniformly  heated 
throughout.  Dry  the  cavity  and  apply  a  thin  film  of  oil  to 
l^revent  wax  adhesion.  Introduce  wax  in  the  cavity,  and  with 
ball  of  the  thumb  or  finger  apply  steady,  positive  pressure  in 
such  direction  as  will  force  the  wax  info  and  affohhst  cavity 
walls  and  margins. 

Avoid  changing  direction  of  pressure,  or  rolling  the  ball 
of  the  finger  over  the  wax.  When  change  of  direction  of 
pressure,  from  any  cause,  occurs,  the  wax  is  liable  to  be- 
come unseated,  or  moved  away  from  the  cavity  walls.  Then, 
when  contraction  of  the  wax  occurs,  as  is  invariably  the  case, 
errors  in  adaptation  are  still  further  increased. 

Continue  pressure  until  wax  has  cooled  to  body  tempera- 
ture. Heat  a  spatula  and  soften  the  occlusal  surfaces.  Instruct 
patient  to  subject  the  wax  to  the  action  of  opposing  teeth, 
not  only  in  full  occlusion,  but  to  lateral  movements  as  well. 

Remove  peripheral  surplus  of  wax  and  carve  to  desired 
form.  The  carving  tool  should  be  applied  so  as  to  cut  parallel 
with  the  line  of  junction  of  wax  with  cavity  margin  or  be 
drawn  diagonally  across  the  junction  from  wax  to  tooth. 
When  drawn  from  tooth  to  wax,  the  latter  is  liable  to  be  torn 
or  drawn  away  from  the  cavity  margin  and  thus  result  in  a 
defective  margin  of  the  wax  model. 

A  smooth  finish  may  Iie  given  axial  surfaces  by  means  of 
silk  strips,  moistened  with  oil  of  cajeput.  Flat  surfaces  may 
be  smoothed  with  pellets  of  cotton,  slightly  moistened  with 
the  oil. 

Remove  the  wax  model  carefully  with  small  instrument, 
and  attach  sprue  former. 


In  all  cases  the  attacliinent  of  the  sprue  to  the  wax  should 
be  at  the  highest  point  of  the  matrix,  when  the  ring  is  set  in 
projier  position  for  casting. 

AVhen  any  portion  of  the  matrix  is  higher  than  the  point 
of  entrance  of  the  gold  into  the  latter,  air  frequently  becomes 


WAX    MODEL    OP    INI.AY    ATTACHED 

TO    SI'RUE    FORMER.    READY 

FOR  INVESTMENT 


WAX  MODEL  OF  SMALL  SADDLE. 
READY  FOR  INVESTMENT.  THREE 
WAX  SPRIE  FORJIERS  LEAD  FROM 
METAL  SPRUE  FORMER  TO  EX- 
TREMITIES  AND   CENTER  OF   MODEL 


confined  or  the  gold  becomes  chilled  and  fails  to  perfectly  fill 
such  high  areas. 

A  small  strip  of  gold  plate  may  be  heated  sufficiently  to 
melt  its  way  into  the  wax,  and  when  cold  this  will  serve  as  a 
plier  grasp  in  removing  the  model.  It  may  be  allowed  to 
remain  in  the  wax  when  invested,  and  when  the  inlay  is  cast, 
the  projecting  end  will  facilitate  handling  the  inlay  while 
fitting-  After  serving  its  purpose  it  may  be  removed  by  cut- 
ting and  the  surfaces  polished  smoothly.  Suggested  by  Dr. 
T.  L.  Pepperling. 

The  sprue  former  is  now  heated  and  applied  at  the  point 
of  proximate  contact.  It  must  be  imbedded  sufficiently  to  ob- 
tain a  firm  hold  upon  the  model  so  that  displacement  will  not 
occur  during  investment. 

The  wax  around  the  sprue  former  should  be  smoothed 
properly  and  a  slight  amount  added,  if  necessary,  to  insure 
strong  proximate  contact. 


INVESTMENT  OF  THE  WAX   MODEL 

The  sprue  former  with  wax  models  attached,  is  now  set  in 
the  opening  of  the  crucible  former  and  the  wax  washed  with 
a  soap}'  water  solution  and  afterward  clear  water,  applied 
with  fine  brush,  to  remove  the  oil. 

A  mix  of  investment  of  medium  consistency  is  now  made 
and  with  a  fine  brush  the  surfaces  of  the  wax  are  carefully 
coated  with  a  film  of  it.     The  investment  ring  is  now  set  in 


956  INLAYS 

])ositi()ii,  the  rounded  iiuirgiii  down,  ajitl  ilic  space  around  tlie 
model  entirely  iillod  with  investment. 

(!are  sliould  be  taken,  both  in  coating  the  wax  and  in  till- 
ing tlie  ring  with  investment,  to  avoid  tlie  fornuition  of  air 
spaces. 

When  the  investment  has  hardened,  the  surplus  project- 
ing from  the  open  end  of  the  ring  is  squared  off,  the  crucible 
former  removed,  the  sprue  former  heated  sufficiently  to  melt 
tlie  wax  at  its  inclosed  end,  after  which  it  is  carefully  removed. 

Remove  from  the  crucible  and  the  spru.e  any  particles  of 
investment  that  may  be  present,  so  that  when  ready  to  cast 
the  mold  may  lie  clear. 

DRYING  OUT  THE  INVESTMENT  AND  ELIMINATING  THE  WAX 

Place  the  investment  ring  al)out  three  inches  above  a  low 
Bunsen  flame  for  five  minutes,  that  it  may  become  gradually 
heated. 

Lower  the  ring  and  raise  the  flame  imtil  the  latter  touches 
the  investment,  and  continue  the  heating  process  for  five  or 
ten  minutes  longer. 

Increase  the  flame  until  it  passes  up,  surrounding  the 
sides  of  the  ring.  Continue  the  heat  at  this  higher  tempera- 
ture until  the  investment  is  freed  from  all  moisture  and  the 
gas  has  been  driven  off.  At  no  time  should  the  heat  be  applied 
so  rapidly  as  to  boil  the  wax  and  force  it  through  the  sprue. 

Test  by  holding  a  piece  of  cool  glass  close  to  upper  end 
of  ring. 

When  all  gas  has  been  expelled,  the  ring  is  set  aside  and 
allowed  to  cool  before  casting. 

VARIATION  IN  THE  METHOD  OF  PREPARING  THE  MOLD  FOR 
CASTING 

When  investment  has  hardened,  the  ring  is  placed  about 
six  inches  above  a  medium-sized  Bunsen  flame  and  allowed 
to  remain  in  the  current  of  heated  air  until  all  moisture  is 
expelled. 

This  may  require  from  ten  to  twenty  minutes,  and  during 
the  process  the  temperature  will  be  raised  somewhat  above 
212°  F.  It  should  not  at  any  time  be  raised  much  above  that 
point. 

Now,  since  wax  melts  at  about  150°  F.,  it  will  be  absorbed 
by  the  investment  as  the  moisture  is  expelled  from  the  latter. 
A  film  of  wax,  however,  will  remain  on  the  matrix  walls. 

The  ring  may  be  set  aside  to  cool,  before  casting  the  gold, 


INLAYS  957 

or  the  button  of  gold  may  be  placed  in  the  crucible,  fused  and 
cast  immediately,  if  desired. 

The  film  of  wax  in  no  way  interferes  with  the  production 
of  a  sharp  casting.  In  fact,  when  the  gold  is  sufficiently  super- 
heated and  injected  into  the  mold,  under  proper  conditions, 
a  sharper  and  cleaner  casting  can  be  produced  by  this  than  by 
the  former  method. 

The  instant  the  gold  is  forced  into  the  matrix  its  tempera- 
ture is  considerably  above  2000°  F.  All  gas  and  air  in  the 
matrix  is  forced  outward  through  the  walls  into  the  invest- 
ment, the  film  of  wax  is  instantly  carbonized  and  prevents  the 
oxygen  in  the  air,  forced  out,  from  coming  in  contact  with  the 
gold,  the  result  being  a  clean,  bright  casting. 

The  greatest  advantage,  however,  is  that  the  binder  in 
the  investment  has  not  been  disintegrated  by  previous  heat- 
ing, and  as  a  result  the  matrix  walls  are  firm  and  compara- 
tively unyielding.  The  roughness,  therefore,  so  frequently 
seen  on  cast  gold  surfaces,  when  the  investment  is  previously 
highly  heated,  is  not  noticeable  in  a  casting  produced  by  the 
method  just  described. 

Credit  for  this  method  of  treatment  of  the  invested  case 
belongs  to  Dr.  Chas.  B.  Meade  of  Rockford,  111.,  who  first  dem- 
onstrated it  at  a  clinic  of  the  Chicago  Dental  Society. 

THE  CASTING   OF  GOLD 

Under  the  most  favorable  circumstances  a  certain  amount 
of  time  unavoidably  elapses  between  the  discontinuance  of  the 
heat  applied  in  fusing  the  gold  and  its  injection  into  the  mold. 

The  instant  the  flame  is  discontinued  the  temperature  of 
the  gold  begins,  and  continues  to  drop,  resulting  in  change 
from  a  fluid  to  a  pasty  and  finally  a  solid  state. 

When  gold  is  brought  to  a  fused  condition  only,  and  the 
flame  is  discontinued,  these  changes  occur  very  quickly,  so 
rapidly,  in  fact,  that  in  introducing  it  in  the  mold,  even  under 
heavy  pressure,  the  latter  will  seldom  be  filled  perfectly,  be- 
cause of  the  changes  mentioned. 

Therefore,  to  insure  sharp  castings,  gold  must  be  super- 
heated considerably  above  its  actual  fusing  ijoint  in  order 
that  it  may  not  only  enter  the  mold,  but  be  sufficiently  fluid, 
after  injection,  to  conform  to  all  irregular  surfaces  of  the 
matrix  under  the  compressive  force  applied. 

The  most  imi^ortant  contribution  of  Dr.  Taggart  to  the 
casting  process  was  the  discovery  that  in  order  to  cast  sharply, 
gold  must  be  superheated  considerably  above  its  fusing  point. 


Tliis  lie  aceonii)lisli('(l  icmlily  liy  iiiciiiis  of  a  slij.;lit  iiiodilica- 
tion  of  tlie  Kua]!))  nitrous  oxide  and  gas  l)lowpipe. 

When  all  moistnre  has  been  eliminated,  the  ring  is  placed 
in  the  casting  device,  a  button  of  gold  considerably  larger  than 
required  is  placed  in  the  crucible,  brought  to  a  superheated 
condition  and  as  quickly  as  i^ossible  forced  into  the  matrix 
under  pressure. 

With  the  Taggart  a])pliances  tlie  gold  may  he  quickly 
brought  to  a  suix'rhcafed  condition  ))y  means  of  the  nitrous 


oxide  and  gas  blowpij^e  and  the  casting  quickly  accomplished 
by  forcing  the  sealing  cap  down  tightly  upon  the  ring  margins. 

With  the  R.  &  K.  vacuum  machine,  the  chamber  should 
be  emptied  of  air  before  fusing  the  gold,  when,  after  this  has 
been  accomplislied,  by  opening  the  valve,  the  gold  is  drawn 
into  the  matrix  by  suction. 

Further  details  of  gold,  reducing  fluxes,  investments,  etc., 
of  practical  value  will  be  fcnuul  in  the  section  on  metallurgy, 
under  the  general  topic,  "Alloys  of  Gold,"  etc.,  by  Dr.  Wein- 
stein. 

ROUGH  FINISHING  THE  CASTING 

On  removal  of  the  casting  from  the  investment,  it  should 
be  washed,  boiled  in  acid,  and  again  washed,  to  remove  the 
acid. 

The  button  is  now  removed  from  the  casting,  the  rough 
points  removed  with  discs,  being  careful  while  doing  so  not 


959 


to  mar  the  margins,  and  in  proximo-occlusal  inlays  to  pre- 
serve a  strong  contact  point. 

Should  nodnles  be  present  in  any  of  the  inlay  surfaces 
which  proximate  cavity  walls,  they  should  he  smoothed  down 


THE   RANSOM    &   RAXDOI.I'H    \ACUUM    CASTING    MACHINE 

with  chisels;  discs  or  stones  or  reduced  in  any  manner  most 
convenient.  Wlien  present,  they  prevent  proper  seating  of 
the  inlay. 

SETTING  THE  INLAY 

When,  b}'  test,  the  inlay  can  be  perfectly  seated,  it  is  re- 
moved, the  cavity  rendered  thoroughly  dry,  cement  mixed  and 
applied  in  the  usual  manner,  and  the  filling  set  imder  con- 
tinued, heavy  pressure. 

FINISHING 

Wlien  the  cement  has  thoroughly  hardened,  the  margins 
of  the  inlay  are  now  given  their  final  finish  with  discs,  strips, 
and  polishing  powders. 

Previous  to  the  final  setting,  however,  the  contact  and 
adjacent  areas  of  the  filling  are  polished,  thereby  reducing 
danger  of  loss  of  proximate  contact,  which  frequently  occurs 
in  final  finishing,  unless  separation  of  the  teeth  is  previously 
made. 


CHAPTER    XXXII 

AN  OUTLINE  OF  METALLURGY 

The  science  of  metallurgy  deals  with  the  extraction  of 
metals  from  their  ores,  with  their  physical  properties  when 
free  and  nncoral)ined,  and  with  the  changed  conditions 
brought  about  by  alloying  the  individual  metals,  or  by  the 
presence  of  some  other  substances,  either  in  the  form  of  im- 
purities or  that  maj^  have  been  added  for  some  definite  jiur- 
l^ose. 

Metallography  deals  more  particularly  with  the  structural 
form  of  metals  and  their  alloys,  the  study  in  this  compar- 
atively new  field  in  physics  being  carried  on  chiefly  with  the 
microscope.  It  is  closely  related  to  the  chemistry  of  metals, 
and  yet  it  covers  a  field  not  occupied,  and  yields  information 
not  obtainable,  In^  ordinary  chemical  analysis. 

In  the  i^ractice  of  prosthetic  dentistry,  aliout  fifteen  of 
the  metals  are  used  to  a  greater  or  less  extent,  either  in  their 
pure  state,  or  in  the  form  of  alloys.  To  handle  these  various 
metals  intelligently  and  economically,  so  as  to  secure  the  best 
results,  the  prosthetic  dentist  sliould  have  an  intimate  knowl- 
edge of  general  and  metallurgical  chemistry,  as  well  as  of  the 
collateral  sciences.  In  the  description  of  the  metals  now  about 
to  be  considered  an  effort  will  be  made  to  point  ont  those 
essential  physical  and  chemical  ijroperties  and  peculiarities 
which,  if  overlooked  or  misunderstood  by  the  prosthetist,  may 
result  in  mishaps  of  a  more  or  less  serious  character. 

All  of  the  material  substances  of  the  universe  with  which 
we  are  acquainted  consist  of  elements  alone  or  in  combinaticm 
with  each  other. 

An  element  is  a  substance  which  cannot  be  siilit  uj)  or 
decomposed  into  dissimilar  substances  by  any  means  now 
known,  and  differs  from  a  compound,  which  may  be  split  up 
or  separated  into  dissimilar  substances. 

At  this  time  there  are  about  eighty  elements  known, 
fifty-two  of  which  are  metals.  It  is  possible  that  some  of  these 
substances  which  are  now  considered  elements  may  prove  to 
be  compounds. 

960 


AN    OUTLINE    OF    METALLURGY  961 

FACTS,  HYPOTHESES,  THEORIES  AND  SPECULATIONS 
ELEMENTS 

An  element  is  a  substance  which  cannot  be  decomposed 
into  simpler  substances  by  any  method  now  known.  Stated 
differently,  "an  element  is  a  distinct  species  of  matter  which 
has  not  been  shown  to  be  composite." 

At  the  present  time,  so  far  as  is  known,  there  are  about 
eighty  elements  in  the  universe.  The  physical  properties  of 
most  of  these  are  well  understood,  but  a  few,  because  of  their 
scarceness  and  the  difficulties  attending  their  examination, 
have  but  sparse  accumulated  data.  It  is  not  only  possible  but 
quite  probable  that  other  elements  now  unknown  may  be  dis 
covered,  and  that  some  of  those  now  classed  as  elements  may 
prove  to  be  compounds. 

DISCOVERY  OF  ELEMENTS  BY  MEANS  OF  THE  SPECTROSCOPE 

The  spectroscope  has  aided  materially  in  the  detection 
of  some  of  the  elements,  and  by  means  of  it  their  presence  in 
the  universe  was  recognized  before  they  themselves  were  iso- 
lated. As  an  illustration,  in  1868  a  bright  line  was  noticed 
in  the  spectrum  of  the  sun's  atmosphere  which  differed  from 
that  of  any  element  then  known.  Lockyer  and  Frankland,  be- 
lieving it  to  be  a  new  element  in  the  sun,  called  it  helium,  from 
the  Greek,  meaning  the  sun.  Twenty-seven  years  later  Sir 
William  Ramsey  discovered  in  the  spectrum  of  cleveite,  a  line 
corresponding  to  that  of  helium,  which  was  still  unknown 
except  by  its  spectrum.  On  further  examination  this  new 
element  proved  to  be  a  gas,  a  constant  component  of  the 
earth's  atmosphere,  and,  as  will  be  shown  later,  an  end 
product  of  radio  active  substances  under  certain  conditions. 
Because  of  its  spectroscopic  position  it  received  the  name  of 
helium.  For  many  years  the  spectrum  of  the  Aurora  Borealis 
was  a  subject  of  puzzling  investigation.  This  light  shows  in 
it  a  peculiar,  greenish  yellow  line,  unlike  that  of  any  other 
element  known.  The  discoverey  of  krypton  solved  the  prob- 
lem, its  spectrum  showing  the  identical  line  found  in  that  of 
the  "Northern  Lights." 

THE  MUTABILITY  OF  MATTER 

There  is  a  growing  belief  among  physicists  that  some, 
possibly  all  substances  now  known  as  elements,  may  be  trans- 
mutable  or  capable  of  being  changed  from  one  to  the  other. 
The  change,  however,  appears  to  be  one  of  degradation. 


9G2  AN    OUTLINE    OF    METALLURGY 

No  laws  have  been  discovered  by  which  this  mutability  of 
matter  can  be  brought  about  at  will  or  among  the  elements 
indiscriminately.  Certain  facts,  however,  have  been  observed 
and  verified  time  and  again,  beyond  the  question  of  doubt, 
that  under  definite  conditions  degradation  of  elements  occurs. 
The  character  of  the  element  before  such  change  occurs  can 
be  recognized,  the  intense  energy  exhibited  while  decomposi- 
tion is  going  on  can  be  noted  and  even  measured  to  a  certain 
degree,  and  the  character  of  the  substance  into  which  the 
original  element  is  finally  resolved  can  1)0  determined. 

BRIEF   OUTLINE    OF   RECENT    DISCOVERIES 

To  make  these  facts  more  plainly  ai)i>ar<'iit,  a  statement 
of  some  of  the  discoveries  in  physical  and  chemical  fields  in 
the  last  twenty  years,  together  with  their  bearing  on  the  sub- 
ject under  discussion,  will  be  in  order. 

ELEMENTAL  GASES 

In  1894  Lord  Eayleigh  discovered  in  the  atmosphere  a 
new  and  hitherto  unsuspected  gaseous  element.  Because  it 
would  not  combine  chemically  with  any  other  substance  except 
at  intensely  high  temperatures,  and  in  other  ways  seemed 
generally  inert,  it  was  named  "argon"  which  means  "lazy." 
It  closely  resembles  nitrogen  in  its  physical  i^roperties,  is 
slightly  heavier  and  extremely  difficult  to  separate  from  the 
latter  gas  witli  which  it  is  associated  in  the  atmosphere. 

In  1895,  Sir  AVm.  Ramsey  discovered  four  other  elemental 
gases  in  the  air,  viz.,  helium,  neon,  krypton,  and  xenon,  all  of 
which  have  similarly  inert  i^roperties  to  argon.  These  five 
gases  have  all  been  "won  out  of  the  hidden  places  in  the  air," 
and  as  will  be  seen  later,  the  presence  of  most  of  them  in  this 
medium  can  he  accounted  for. 

DISCOVERY  OF  THE  X-RAYS 

In  the  same  year  Prof.  William  Konrad  Roentgen  dis- 
covered the  peculiar  penetrating  power  of  the  rays  from  an 
induced  electric  current  when  passed  through  a  vacuum. 
These  rays  are  now  known  as  Roentgen,  or  X-rays,  and  their 
power  of  penetrating  opaque  substances  and  affecting  light 
proof  photographic  plates  is  well  understood  and  made  use  of 
in  innumerable  ways,  particularly  in  the  medical  and  dental 
fields,  for  diagnostic  purposes. 


AN    OUTLINE    OF    METALLURGY  963 

DISCOVERY  OF  RADIO-ACTIVE  SUBSTANCES 

In  1896,  Becqnerel  discovered  that  all  compounds  of 
uranium  emitted  a  radiation  capable  of  penetrating  opaque 
objects  similar  to  Init  not  with  the  same  energy  or  rapidity 
displayed  by  the  X-ray.  Uranium  com])(nmds  are  derived 
from  pitchlilende,  a  complex  mineral  containing  many  other 
elements.  The  residue  left  after  extracting  practically  all  of 
the  uranium  is  the  source  from  which  radium  is  derived. 
The  Curies  noticed  that  this  residue  possessed  considerable 
radio-activity.  In  an  effort  to  locate  the  true  source  of  the 
emanations,  they  found  that  after  separating  the  residue  into 
its  constituent  parts,  so  far  as  could  be  done  at  that  time,  that 
most  of  the  radio-activity  was  concentrated  in  the  chloride  of 
barium.  On  sul)jecting  the  barium  chloride  to  further  reduc- 
tion, the  barium  was  finally  eliminated  and  a  substance  which 
proved  to  be  radium  chloride  was  secured.  Radium,  the 
element,  has  only  recently  been  isolated  by  Madame  Curie.  Its 
salts  RaCL  and  EaBr^  are  commonly  prepared  and  employed 
for  experimental  and  other  jiurposes.  The  spectrum  of 
radium  and  its  chemical  relations  to  other  elements  indicate 
that  it  should  be  classed  among  the  metals  of  the  alkaline 
earths. 

There  are  about  twenty-five  substances  which  possess, 
in  varying  degrees,  distinct  radio-active  properties.  The  salts 
of  radium  mentioned  exhiliit  this  property  more  strongly 
than  any  of  the  others. 

DECOMPOSITION    OF    RADIUM    COMPOUNDS 

The  peculiar  feature  of  the  radium  compounds  is  that 
they  decompose,  rapidly  at  first,  then  more  slowly,  until  finally 
practically  nothing  remains  of  the  original  salt.  The  intense 
energy  displayed  in  their  decomposition  is  half  spent  in  the 
first  four  days  after  the  preparation  of  the  salt,  but  in  that 
time  there  has  been  emitted,  proportionately,  three  million 
times  inore  heat  than  will  result  from  any  other  chemical  ac- 
tion known. 

There  are  three  principal  types  of  rays  emitted  by  radio- 
active substances,  designated  as  alpha,  beta,  and  gamma  rays. 
The  ali)ha  raj's  are  electro-positive  particles  or  electrons  of 
atomic  size  which  fly  through  space  at  the  amazing  velocity  of 
twenty  thousand  miles  per  second.  A  little  radium  brought 
near  a  screen  of  zinc  sulphide  produces  brilliant,  scintillating 
stars  of  light.    Each  star  is  the  result  of  impact  of  an  alpha 


i)B4  AN    OUTLINE    OP    METALLURGY 

particle  or  atom  against  the  screen.  The  beta  rays  act  most 
readily  on  photographic  plates.  The  gamma  rays  possess 
the  greatest  penetrating  power,  readily  passing  through  a 
lead  jjlate  seven  centimeters  thick.  The  principal  dilTerenee 
aside  from  the  effect  of  the  several  rays  seems  to  be  one  of 
velocity,  the  alpha  rays  having  the  greatest  and  the  gamma 
rays  the  least  speed. 

CHARACTER  OF  THE  EMANATION   FROM   RADIO-ACTIVE 
SUBSTANCES 

Dorn  has  proven  that  the  emanations  from  radio-active 
substances  is  a  gas,  which,  under  dry  atmospheric  conditions, 
eventually  breaks  down  or  decays  into  helium. 

Later  Ramsey,  in  an  effort  to  utilize  or  conserve  some 
of  the  enormous  energy  which  is  manifested  during  and  is 
apparently  the  result  of  its  debasement,  placed  the  radium 
compound  in  water.  Instead  of  decaying  into  helium  as  it 
does  in  dry  atmosphere,  it  is  finally  resolved  into  neon,  the 
second  of  the  elemental  gases  mentioned. 

When  copper  sulphate  is  dissolved  in  the  water  in  which 
the  radio-active  substance  is  placed  neither  helium  nor  neon 
are  found,  but  argon  is  the  final  product. 

Prof.  Duncan  sums  up  these  facts  as  follows:  "It  ap- 
pears then,  that  this  gas,  this  radium  emanation,  whicli,  it 
must  be  said,  has  a  good  claim  to  the  name  of  element,  decays 
or  becomes  transmuted,  not  into  one  other  element,  but  into 
three,  according  to  its  surrounding  circumstances." 

THE    DEGRADATION    OF    COPPER 

Ramsey's  researches  further  led  him  to  believe  that  the 
action  of  the  radium  emanations  on  the  copper  sulphate  broke 
down  or  changed  some  of  the  copper  into  lithium.  He  bases 
his  deduction  on  the  following:  At  the  beginning  of  his  ex- 
periments lithium  was  not  present  in  the  water,  in  the  copper, 
in  the  emanations,  in  the  air,  nor  in  the  glass  apparatus  with 
which  the  experiments  were  conducted,  but  the  final  results 
showed  loss  of  copper  and  the  presence  of  lithium.  Every- 
thing else  could  be  accounted  for  but  the  loss  and  additions 
noted,  and  those  only  on  the  basis  of  the  degradation  of  cop- 
per into  lithium  through  the  influence  of  radio-activity. 

DEBASEMENT    OF    VARIOUS    SUBSTANCES    INTO    HYDROGEN 

Still  another  fact  of  extreme  interest  was  observed,  viz. : 
that  water  in  the  presence  of  radium  emanations  breaks  up 


AN    OUTLINE    OF    METALLURGY  965 

into  oxygen  and  hydrogen,  not  in  the  usual  proportions  of  two 
volumes  of  hydrogen  to  one  of  oxygen,  but  the  resulting  un- 
combiued  gases  show  from  10  to  20  per  cent  too  much 
hydrogen. 

Prof.  J.  J.  Thompson  has  shown  that  in  the  energetic  elec- 
trical field  generated  in  a  Crookes  tube,  various  substances 
give  off  particles  charged  with  positive  electricity,  that  these 
particles  are  independent  of  or  differ  in  character  from  the 
gas  from  which  they  originate,  that  they  are  of  two  kinds,  one 
to  all  appearances  identical  with  the  hydrogen  atom,  the 
others  resembling  in  every  respect  the  alpha  particles  which 
emanate  from  radio-active  svibstances.  All  of  the  substances 
with  which  he  experimented  were  decomposed,  in  part,  into 
the  element  hydrogen. 

These  experiments  of  Thompson's,  conducted  in  a  differ- 
ent field  with  unlike  apparatus  without  employing  any  of  the 
so-called  radio-active  substances,  serve  to  confirm  most  forci- 
bly the  work  of  Ramsey  and  others,  and  establish  the  fact  that 
hydrogen  results  from  the  debasement  of  other  elements  when 
conditions  are  favorable. 

SUMMARY    OF    THE    STATEMENTS    PRESENTED 

From  present  knowledge  it  appears  evident  that  uranium 
is  transmuted  into  radium;  that  radium  may  be  transmuted 
into  helium,  neon,  or  argon,  depending  on  surrounding  condi- 
tions ;  that  copper,  under  the  influence  of  the  alpha  rays,  may 
be  debased  into  lithium;  that  the  energizing  influence  of  the 
alpha  as  well  as  the  X-rays,  acting  on  inert  substances,  cause 
them  to  break  down  into  hydrogen,  and  finally,  that  the 
radium  emanations  are  themselves  the  product  and  evidence 
of  elemental  change  and  decay. 

The  atomic  weight  of  copper  is  63.6  and  that  of  lithium 
is  7.03.  In  every  case  the  substance  resulting  from  the  deg- 
radation of  an  element  stands  lower  in  the  atomic  scale  than 
that  from  which  it  was  derived,  copper  and  lithium  being 
examples  of  what  is  seen  in  all  of  the  other  elements  in  which 
such  changes  have  been  noted. 

In  reference  to  ' '  The  decay  of  an  element, ' '  Prof.  Alexan- 
der Smith,  Directoi:  of  General  and  Physical  Chemistry,  Uni- 
versity of  Chicago,  says:  "The  phenomena  of  radio-active 
substances  lead  undeniably  to  the  startling  conclusion  that 
some,  if  not  all,  of  the  element  are  capable  of  spontaneous 
decofnposition." 


itCC  AN    OUTLINK    OK    METALLURGY 

The  following  table  from  "Scientific  Ideas  of  Today,"  by 
Charles  E.  Gibson,  shows  the  progress  of  chemical  discovery 
of  the  elements  in  the  last  4(i4  years. 

THE  ELEMENTS  IN   ORDER  OF  THEIR  DISCOVERY 

A.D.         Elements  Discovered  by 

1450  Antimony    Valentino  (German  alchemist) 

1450  Bismnth    \^alentiue  (German  alchemist) 

1520  Zinc    Paracelsus  (Swiss  chemist) 

1694  Arsenic    Schroder  (German) 

1733  Cobalt    Brandt  (German) 

1738  Phosphorus    Brandt  (German) 

1751  Nickel    Cronstadt  (Russian) 

1766  Hydrogen   Cavendish  (English) 

1772  Nitrogen   Rutherford   (English) 

1774  Manganese   Gahu  (Swedish) 

1774  Oxygen    Priestley   (English) 

1780  Uranium  Kla])roth  (German) 

1781  Timgsten d'Elihujar  (Spanish) 

1782  Molyodenum    Hjelm  (Swedish) 

1782  Tellurium    Reiclienstein  (German) 

1785  Titanium Klaproth    (German) 

1798  Chromium    Vauquelin  (French) 

1901  Tantalum    Hatchett  (English) 

1801  Cerium    Berzelius  and  Hisinger 

(Swedish) 

1801  Vanadium  Del  Rio  (Spanish) 

1803  Osmium Tennant  (English) 

1803  Palladium  Wollaston  (English) 

1804  Iridium    Tennant  (English) 

1804  Rhodium   Wollaston  (English) 

1807  Potassium Daw  (English) 

1807  Sodiimi    Davy  (English) 

1808  Barium    Davy    (English)    and    Berzelius 

(Swedish) 

1808     Strontium    Davy  (English) 

1808     Boron    Davy    (EngUsh)    and  Gay-Lusac 

(French) 

1808     Magnesium Davy  (English) 

1808     Calcium  Davy    (English)    and    Berzelius 

(Swedish) 

1810     Chlorine    Davy   (English) 

1810     Fluorine    Ampere  (French) 


AN    OUTLINE    OF    METALLURGY  967 

A.D.         I]lenients  Discovered  by 

1811  Iodine    Conrtois  (French) 

1817  Selenium  Berzelius  (Swedish) 

1817  Lithium   Arfvedson  (Swedish) 

1817  Cadinm    Herman  and  Stromyer  (Grerman) 

1823  Solicon    Berzelius  (Swedish') 

1824  Zirconium   Berzelius  (Swedish) 

1826  Bromine    Balard   (French) 

1827  Berylium Wohler  (German) 

1828  Alumium Wohler  (German) 

1828  Thorium    Berzelius  (Swedish) 

1828  Yttrium    Wohler  (German) 

1841  Lanthanum  .Mosander  (Swedish) 

1843  Terbium    Mosander  (Swedish) 

1843  Erbium    Mosander  (Swedish) 

1844  Ruthenium    Clans  (German) 

1846  Columbium  Rose  (English) 

1860  Caesium   Bunsen  and  KirchlotT  (German) 

1862  Thallium  Crookes  (English) 

1863  Indium    Reich  and  Richter  (German) 

1868  Helium  (in  tlie  Sun).Lockyer  (English) 

1868  Rubidium    Bunsen  (German) 

1875  Gallium   Boisbaudran  (French) 

1878  Ytterbium Marignac  (French) 

1879  Thulium    Cleve  (Swedish) 

1879  Scandium    Nilson  (Swedish) 

1879  Samarium Boisbaudran  (French) 

1885  Praseodymium    Welsbach  (German) 

1885  Neodymium    Welsbach  (German) 

1886  Gadolinium Marignac  (French) 

1886  Germanium    Winkler  (German) 

1894  Argon    Rayleigh  and  Ramsay  (English) 

1895  Helium  (On  Earth) ..  Ramsay  (English) 

1897  Krypton    Ramsay  and  Travers  (English) 

1898  Xenon    Ramsay  (English) 

1898  Neon    Ramsay  and  Travers  (English) 

1898  Radium    Curie  (French) 

THE  ELEMENTS  IN  THE  ORDER  OF  THEIR  ATOMIC 
WEIGHTS 

1.  Hydrogen    1.008       4.     Glucinuni 9.1 

2.  Helium    4.00         5.     Boron    ILO 

3.  Lithium   7.03         6.     Carbon    12.0 


AN    OUTLINE    OP    METALLURGY 


7.  Nitrogen    14.04 

8.  Oxygen    16.0 

9.  Fluorine    19.0 

10.  Neon    20.0 

11.  Sodium    23.05 

12.  Magnesium   24.36 

13.  Aluminum 27.1 

14.  Silicon   28.4 

15.  Phosphorus    ....  31.0 

16.  Sulphur  32.06 

17.  Chlorine    35.45 

18.  Potassium 39.15 

19.  Argon    39.90 

20.  Calcium  40.1 

21.  Scandium 44.1 

22.  Titanium 48.1 

23.  Vanadium  51.2 

24.  Chromium 52.1 

25.  Manganese    55.0 

26.  Iron" 55.9 

27.  Nickel    58.7 

28.  Cobalt    59.0 

29.  Copper    63.6 

30.  Zinc    65.4 

31.  Gallium   70.0 

32.  Germanium    ....  72.5 

33.  Arsenic    75.0 

34.  Selenium 79.2 

35.  Bromine    79.96 

36.  Krypton    81.8 

37.  Rubidium    85.4 

38.  Stroutimn 87.6 

39.  Yttrium  89.0 

40.  Zirconium   90.6 

41.  Columbium  94.0 

42.  Molvbdium    96.0 


43. 
44. 
45. 
46. 
47. 
48. 
49. 
50. 
51. 
52. 
53. 
54. 
55. 
56. 
57. 
58. 
59. 
60. 
61. 
62. 
63. 
64. 
65. 
66. 
67. 
68. 
69. 
70. 
71. 


74. 

75. 
76. 

77. 

78. 


Ruthenium    101.7 

Rhodium   103.0 

Palladium   106.5 

Silver    107.93 

Cadmium 112.4 

Indium    114.0 

Tin   119.0 

Antimony    120.2 

Iodine    126.85 

Tellurium    127.6 

Xenon    128.0 

Ca?sium    132.9 

Bariimi    137.4 

Lanthanum 138.9 

Praseodvmii;m    .  140.5 

Cerimu  ' 140.25 

Neodymium    ....  143.6 

Samarium 150.0 

Gadolinium 156. 

Terbium    160.0 

Erl)ium    166.0 

Thulium  171.0 

Yitterbium    173.0 

Tantalum    183.0 

Tungsten    184.0 

Osmium  191.0 

Iridium    193.0 

Platinum 194.8 

Gold   197.2 

Mercury    200.0 

Thallium   204.1 

Lead 206.9 

Bismuth    208.5 

Radium    225.0 

Thorium    232.5 

Uranium    238.0 


THE  KINETIC  CONSTITUTION  OF  MATTER 

Matter  is  composed  of  or  at  least  presents  itself  to  our 
senses  in  three  distinct  forms,  viz.,  solids,  liquids  and  gases. 
The  molecular  theory  of  matter,  as  believed  in  and  taught 
by  the  physicists  of  today,  may  be  briefly  stated  as  follows: 

Matter  consists  of  units  called  molecules;  these  in  turn 


AN    OUTLINE    OF    METALLURGY  969 

are  composed  of  still  smaller  units  of  elements  called  atoms; 
atoms  are  made  up  of  still  smaller  units  consisting  of  ele- 
mentary charges  of  negative  electricity,  called  electrons,  each 
of  which  probably  has  a  nucleus  or  center  of  positive  elec- 
tricity. 

THE  VIBRATION  OF  MATTER 

It  is  believed  that  the  electrons  move  about  or  vibrate 
within  the  atom;  that  the  atoms  vibrate  within  the  molecule, 
to  a  lesser  degree ;  and  that  the  molecules  move  about  within 
the  mass  of  matter,  freely  when  the  matter  is  gaseous,  re- 
stricted in  movement  when  solid  or  liquid,  but  still  possess- 
ing movement. 

The  infinitesimal  particles  of  gold  in  a  colloidal  state,  al- 
though much  larger  than  the  estimated  size  of  electrons,  when 
viewed  through  that  wonderfully  sim^jle  but  simply  wonder- 
ful instrument,  the  ultra-microscope  of  Zsigmondy,  enables 
one  to  form  some  slight  conception  of  the  vibration  of  mat- 
ter.   Here  is  his  own  desci'iption  of  what  may  be  seen: 

"  *  *  *  The  small  gold  particles  no  longer  float,  they 
move — and  that  with  astonishing  rapidity.  A  swarm  of  danc- 
ing gnats  in  a  sunbeam  will  give  one  an  idea  of  the  motion  of 
the  gold  particles  in  the  hydrosol  of  gold.  They  hop,  dance, 
jump,  dash  together  and  fly  away  from  each  other,  so  that  it  is 
difficult  in  the  whirl  to  get  one's  bearings. 

"This  motion  gives  an  indication  of  the  continuous  mix- 
ing up  of  the  fluid;  and  it  lasts  for  hours,  weeks,  months,  and, 
if  the  fluid  is  stable,  even  years. 

"Sluggish  and  slow  in  comparison  is  the  analogous 
Brownian  movement  of  the  larger  gold  particles  in  the  fluid, 
which  are  the  transition  forms  of  ordinary  gold  that  settles. 

' '  The  smallest  particles  which  can  be  seen  in  the  hydrosol 
of  gold  show  a  combined  motion,  consisting  of  a  motion  by 
which  the  particle  moves  from  100  to  1,000  times  its  own 
diameter  in  one-sixth  to  one-eighth  of  a  second,  and  a  motion 
of  oscillation  of  a  considerabh^  shorter  period,  because  of 
which  the  possibility  of  the  presence  of  a  motion  of  oscillation 
of  a  higher  frequency  and  smaller  amplitude  could  not  be  de- 
termined, but  is  probable."  (Colloids  and  the  Ultra-Micro- 
scope, Zsigmondy).. 

The  foUowir.g  comparison  will  give  an  idea  of  the  size  of 
the  smaller  gold  particles: 

The  limit  of  visibility  of  an  ordinary  high  power  micro- 
scope is  about  one-fourth  micron,  or  one-four-thousandth  of  a 


!)70  AN    OUTLINP:    op    METALLURGY 

luilliiiictci',  a  iiiicroii  hciiij;'  oiic-oiie-thoiisaiKltli  ot"  a  milli- 
meter, or  about  one-twenty-Hve-tliousandtli  of  an  inch. 

Under  favoral>le  conditions,  particles  of  one  one-mil- 
lionth millimetei's  in  diameter  can  readily  be  seen  with  the 
nltra-microscope.  Some  of  the  smaller  particles  of  gold  are 
barely  visible  with  this  instrument,  and  it  is  believed  that 
still  smaller  particles  exist. 

When  planed  surfaces  of  gold  and  lead  are  brought  in 
contact  and  held  together  firmly  for  several  weeks,  on  ex- 
amination it  will  be  found  tliat  particles  of  gold  have  made 
their  way  into  the  lead,  likewise  particles  of  lead  can  be  found 
within  the  gold,  thus  showing  that  molecules  of  solid  sub- 
stances vibrate  or  move  about  not  only  in  the  mass  of  like 
material,  but  wander  away  into  unlike  substances. 

Prof.  A.  Wilmer  Duff,  of  the  Worcester  Polytechnic  In- 
stitute, after  citing  this  and  similar  instances  of  dift'nsion, 
states:  "There  are  many  other  reasons  for  believing  that 
the  particles  of  matter  are  in  all  cases  in  motion.  This 
hypothesis  is  called  the  hypothesis  of  the  kinetic  constitution 
of  matter." 

In  reference  to  electrons,  Sir  William  Ramsey  has  ex- 
pressed himself  as  follows:  "Electrons  are  atoms  of  the 
chemical  element  electricity;  they  possess  mass;  they  form 
compounds  with  other  elements;  they  are  known  in  the  free 
state,  that  is,  as  molecules."  (Trans.  Chemical  Society, 
Great  Britain,  1908.) 

THE  UNEQUAL  DISTRIBUTION   OF  ELEMENTS 

"More  than  99  per  cent  of  terrestrial  material  is  made  up 
of  eighteen  or  twenty  elements,  of  which  the  quantities  of  the 
first  eleven,  as  estimated  by  F.  W.  C-larke,  are  given  in  the 
following  table: 

Oxygen  49.98     Sodium  2.28 

Silicon 25.30     Potassium 2.23 

Aluminum  7.26     Hydrogen 0.94 

Iron 5.08     Titanium  0.30 

Calcium  3.51     Carbon   0.21 

Magnesium  2.50  

99.59 

"The  evidence  of  the  spectroscope  shows  that  the  sun  and 
stars  contain  many  of  the  very  same  elements  as  does  the 
earth." — Alexander  Smith. 

"Recent  researches  have  thrown  a  flood  of  light  upon 
these  questions  (the  unequal  distribution  of  elements).    It  is 


AN    OUTLINE    OF    METALLURGY  971 

now  believed  that  the  elements  are  not  tlie  changeless  sys- 
tems that  they  were  once  thouglit  to  be,  bnt  rather  systems 
in  slow  but  incessant  mutation. 

"According  to  Prof.  J.  J.  Thompson,  all  of  the  elements 
represent  successive  condensations  of  one  primary  stuff, 
whose  atoms,  called  electrons  or  corpuscles,  weigh  less  than 
the  1/1,000  part  of  an  atom  of  the  lightest  known  terrestrial 
element,  namely  hydrogen.  This  primary  stuff  is  negative 
electricity,  which  is  therefore  a  true  chemical  element." — 
Geoffrey  Martin,  in  Triumphs  and  Wonders  of  Modern 
Chemistry. 

ELEMENTS  AND  THEIR  ATOMIC  RELATION  TO  EACH 
OTHER 

Tile  elements  when  studied  collectively,  although  differ- 
ing in  many  respects  from  each  other,  as,  for  instance,  in 
their  atomic  weight,  specific  gravity,  valence  and  physical 
appearance,  have  many  peculiar  properties  in  common. 

(Jbservation  has  shown  that  certain  definite  relations 
exist  between  the  elements,  particularly  when  arranged  in 
series  or  groups.  The  gradual  and  almost  uniform  increase 
in  the  atomic  scale,  beginning  with  hydrogen,  the  lowest,  and 
progressing  up  to  uranium,  the  highest,  in  the  atomic  series, 
has  long  attracted  attention  and  given  rise  to  the  idea  that 
such  orderly  progression  is  not  the  result  of  chance,  but  of 
some  so  far  undiscovered  law. 

Hydrogen,  discovered  by  Cavendish  in  1776,  is  the  light- 
est known  terrestrial  element.  Until  recently  its  atom  has 
been  rated  as  1  of  the  atomic  scale,  but  for  reasons  subse- 
quently to  be  stated,  it  is  now  accorded  the  value  of  1.008. 
When  the  atomic  weights  of  the  other  elements  are  computed 
on  the  basis  of  1  for  hydrogen,  it  is  found  that  several  are 
whole  numbers  and  many  more  a]i]iroximate  whole  numbers. 

PROUT'S    HYPOTHESIS 

Just  one  hundred  years  ago  William  Prout,  an  English 
physician,  observing  that  the  atomic  weights  of  many  of  the 
elements  were  either  exactly  or  approximately  whole  num- 
bers, advanced  the  idea  that  all  of  the  other  elements  were 
composed  of  hydrogen  atoms  in  various  stages  of  condensa- 
tion, and  that  therefore  their  atomic  weights  must  be  even 
multiples  of  that  of  hydrogen.     Th(>  fact  that  some  of  the 


972  AN    OUTLINE    OF    METALLURGY 

atomic  weights  as  then  determined  terminated  in  decimals, 
he  regarded  as  the  result  of  errors  in  calculation. 

Chemists  lined  up  in  support  of,  or  in  an  effort  to  dis- 
prove, Front's  theory,  and  for  a  time  great  diversity  of 
opinion  prevailed,  due  largely  to  the  fact  that  the  atomic 
weights  of  some  of  the  various  elements  had  not  been  deter- 
mined accurately. 

The  brilliant  work  of  Stas,  a  Belgian  chemist,  in  the 
period  between  1855  and  1865,  in  accurately  computing  the 
atomic  weights  of  many  of  the  elements,  cleared  up  much 
of  the  existing  confusion.  As  a  result  of  his  etforts,  the  even 
multiple  theory  of  Prout  was  proven  incorrect.  Later  it  was 
shown  that  the  atomic  weight  of  oxygen  was  not  16,  as  Prout 's 
hypothesis  called  for,  but  15.879,  which,  however,  was  within 
Ys  of  1  per  cent  of  a  whole  number. 

Further,  it  was  foimd  that  by  allotting  to  oxygen  the 
atomic  weight  of  16,  and  computing  the  atomic  weights  of  all 
of  the  other  elements  on  this  basis,  a  much  larger  percentage 
of  them  were  resolved  into  whole  numbers  than  when  calcu- 
lated on  the  basis  of  1  for  hydrogen.  By  this  system  of  com- 
putation, which  is  the  accepted  one  at  present,  the  atomic 
weight  of  hydrogen  is  1.008,  as  before  stated.  Considering 
the  atomic  weight  of  oxygen  as  16,  the  atomic  weights  of 
fifty-five  elements  are  foimd  to  be  either  whole,  or  within 
1/10  of  1  per  cent  of  whole  numbers. 

Now  since  it  is  clearly  shown  that  the  atomic  weights  of 
more  than  five-eighths  of  all  Imown  elements  are  approxi- 
mately whole  numbers,  much  interest  in  chemical  and  phys- 
ical fields  has  been  aroused,  and  efforts  have  been  made  to 
determine,  if  possible,  the  laws  governing  the  atomic,  as 
well  as  other  interesting  relations  discernible  in  the  ele- 
ments. This  interest,  which  is  greater  at  present  than  ever 
before,  first  found  tangible  expression  in  the  hypothesis  of 
Prout,  although  the  theory  of  the  unity  of  matter  is  one  of 
very  ancient  origin. 

THE  TRIADS  OF  DOBEREINER 

In  1827  Dobereiner  called  attention  to  the  fact  that 
among  the  elements  then  known,  there  occurred  here  and 
there  groups  of  three  having  remarkably  similar  chemical 
properties.  These  groups  have  since  been  termed  the 
"Triads  of  Dobereiner." 


AN    OUTLINE    OF    METALLURGY 


The  following  will  serve  to  illustrate  some  of  the  vari- 
ous triads  observed : 


Atomic  Weight. 

Calcium 40.1 

Strontium  .  .  .   87.7 
Barium   137  4 


Atomic  Weight. 

Sulphur 32.1 

Selenium 79.2 

Tellurium  .  .  .127.5 


Atomic  Weight. 
Chlorine   ....   35.4 
Bromine   ....   80.0 
Iodine   126.8 


The  first  group  is  composed  of  alkaline  earth  metals. 
They  are  white  in  color,  about  as  soft  as  lead,  and  decompose 
water  at  ordinary  temperatures,  resulting  in  the  formation 
of  hydroxides  with  the  liberation  of  hydrogen.  In  most  com- 
pounds these  metals  are  divalent. 

The  second  group,  consisting  of  Sulphur,  which  is  very 
abundant,  and  Seleniinn  and  Tellurium,  which  are  compara- 
tively rare,  forms  a  series  of  similar  compounds. 

The  third  group  are  sometimes  called  the  halogens  (pro- 
ducers of  sea  salt),  because  they  are  found  in  sea  water.  The 
first  is  a  greenish-yellow  gas,  the  second  is  a  red  liquid  and 
the  third  is  a  purplish-black  solid.  They  are  monovalent  in 
their  compounds  with  hydrogen,  and  when  combined  with  the 
latter,  form  acid  gases  soluble  in  water. 

The  most  remarkable  characteristic  noted,  however,  was 
in  the  ratio  existing  between  their  atomic  weights.  Dobe- 
reiner  noticed  that  when  the  atomic  weights  of  the  first  and 
third  element  of  anj'  triad  were  added  and  the  sum  divided  by 
two,  the  resulting  mean  coincided  very  closely  with  the  atomic 
weight  of  the  intermediate  element  of  the  triad,  as  is  shown 
below : 

Calcium      .  .Atomic  Weight.  .       40.1 
Barium  .    .  .Atomic  Weight.  .     137.4 


Strontium  ..Atomic  Weight. 


Sulphur  ..  .  .Atomic  Weight. 
Tellurium  ..Atomic  Weight. 


Selenium  . . .  Atomic  Weight . 


2/177.5 

88.7 
87.7 

■.V2.1 
127.5 

mean 

2/159.6 

79.8 
79,3 

mean 

AN    OUTLINE    OF    METALLURGY 

Chlorine   ..  .Atomic  Woiii,lit.  .       '.]^)A 
Iodine Atomic  Weight .  .     liiG.H 


2/162.2 


81.1  mean 
Bromine   ...Atomic  Weight..        80.0 

While  in  no  ease  is  the  resulting  mean  exactly  equal  to 
the  atomic  weight  of  the  second  memlier  of  the  triad,  it  is  so 
close  in  each  instance  as  to  suggest  the  possibility  of  an  un- 
discovered law  which,  if  known,  might  clear  up  the  discrep- 
ancies. The  work  of  Dobereiner  and  others  since  his  time 
has  resulted  in  the  discovery  of  many  other  interesting  and 
peculiar  correlated  properties  of  the  elements. 

THE  OCTAVES  OF  NEWLAND 

In  1863  Newlands  called  attention  to  the  fact  tiiat  when 
the  elements  were  arranged  in  the  order  of  their  atomic 
weights,  beginning  with  the  lowest,  hydrogen  1,  running 
through  the  entire  list  of  the  elements  then  known  and  ending 
with  uranium  240,  at  regular  intervals,  every  eighth  element, 
in  most  instances,  bore  a  striking  resemblance  in  certain 
Ijroperties  to  the  preceding  eighth  below,  or  the  succeeding 
eighth  element  above.  This  method  of  classification  is  known 
as  the  Octaves  of  Newlands.  While  the  discovery  of  New- 
lands  was  remarkable,  be  failed  to  realize  its  great  impor- 
tance, or  work  out  the  full  details  of  it,  being  unable  to  clas- 
sify all  of  the  elements  satisfactorily. 

THE  PERIODIC  SYSTEM  OF  MENDELEEFF 

In  1869  two  chemists,  Dimitri  Mendeleeff,  a  Russian,  and 
Lothar  Meyer,  a  German,  working  independently,  presented 
almost  simultaneously  what  is  known  as  the  Periodic  System 
of  the  Elements.  Priority  in  this  manner  of  classifying  the 
elements  has  been  accorded  Mendeleeff,  although  Meyer's 
work,  which  was  almost  identical,  was  performed  without 
knowledge  of  Mendeleeff 's  efforts.  The  periodic  system,  as 
presented  by  Mendeleeff  and  Meyer,  was  based  on  the  Octaves 
of  Newlands,  but  differed  from  the  work  of  the  latter  by  in- 
cluding all  of  the  then  known  elements.  Previous  to  his 
death  in  1907,  MeudeleelT  revised  the  periodic  table,  modify- 
ing it  to  include  all  of  the  more  recentlv  discovered  elements 
(1903). 


AN    OrXLIXE    OF    METALLURGY 


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Ru  =  101,7           Rh  =  103.0         Pd  =  106.5  (Ag) 

Osmium             Iridium             Platinum 
Os=191              Ir  =  193              Pt=194.9(Au> 

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y76  AN    OUTLINE    OF    METALLURGY 

A  fliart  of  the  periodic  system  of  the  elements  consists 
of  13  horizontal  columns  called  series,  numbered  from  zero  to 
12,  inclusive,  subdivided  into  9  perpendicular  columns  called 
groups,  numbered  from  zero  to  8,  inclusive.  The  elements 
are  arranged  in  the  series  from  left  to  right  in  the  order  of 
their  atomic  weiglits,  and  in  the  perpendicular  grouji  col- 
umns according  to  their  chemical  properties. 

It  will  be  noticed  that  certain  spaces  are  unoccupied  by 
elements  because  of  breaks  in  the  regular  progression  of  the 
atomic  weights,  and  which,  if  closed  up,  would  throw  the  re- 
maining elements  out  of  their  natural  groups.  I'rom  this 
the  inference  is  drawn  that  elements  may  yet  be  discovered 
to  fill  these  vacant  spaces. 

When  Mendeleeff  first  devised  the  table  there  was  a 
space  in  series  4,  group  III,  another  in  series  5,  group  III, 
and  still  another  in  series  5,  group  IV.  Two  years  later,  in 
1871,  he  declared  his  belief  that  elements  would  be  found  to 
occupy  these  spaces.  He  described  their  properties  and 
atomic  weights,  and  named  them  eka-alumiuum,  eka-boron 
and  eka-silicon.  In  1878  Boisiiaudrau,  a  French  chemist,  dis- 
covered gallium,  eka-boron;  in  1879  Nilson,  a  Swedish  chem- 
ist, discovered  scandium,  eka-aluminum,  and  in  1886  Winkler, 
a  German  chemist,  discovered  germanium,  eka-silicon,  all  of 
which  corresponded  to  Mendeleeff 's  predictions  as  to  proper- 
ties, and  fit  exactly  in  the  vacant  spaces. 

NEW   ELEMENTS 

In  Mendeleeff 's  latest  table  he  includes  two  new  ele- 
ments, neither  of  which,  so  far  as  is  known,  have  a  place 
among  the  terrestrial  elements.  These  two  head  the  list  and 
are  designated  as  x  and  y,  both  supposed  to  be  gases  and 
lighter  than  hydrogen. 

Coronium,  found  in  the  spectrum  of  the  sun's  highest  at- 
mosphere, beyond  the  tips  of  the  sun's  flames  and  highest 
protuberances,  is  believed  to  coincide  with  y,  whose  atomic 
weight  is  estimated  by  Mendeleeff  at  0.4,  or  possibly  less. 

X  is  called  Newtonium,  after  the  famed  English  physicist. 
This  gas  element,  according  to  Mendeleeff 's  calculations,  has 
an  atomic  weight  of  probably  0.000001.  Arrhenius  states 
that  "its  atoms  ought,  therefore,  to  be  about  500  times  lighter 
than  electrons."  Now  since  electrons  are  1,000  times  smaller 
than  the  hydrogen  atom,  it  naturally  follows  that  it  would  re- 
quire 500,000  Newtonium  atoms  to  equal  one  of  hydrogen. 

Mendeleeff  further  believed  that  the  element  x,  or  New- 


AN    OUTLINE    OF    METALLURGY  977 

tonium,  is  the  substance  from  which  the  luminit'erous  ether, 
which  pervades  all  space,  is  formed. 

THE   ELEMENTS   CONSIDERED   IN   GROUPS 

The  zero  group  of  elements  is  composed  of  the  gases  of 
the  helium  family.  These  are  all  mouoatomic  and  generally 
inert,  forming  no  compounds  with  other  elements.  On  ac- 
count of  their  scarcity,  obscure  nature  and  lack  of  combining 
power,  their  presence  among  the  terrestrial  elements  was  for 
a  long  time  unknown.  It  is  only  within  recent  years  that 
they  have  been  isolated.  The  original  periodic  table,  there- 
fore, contained  no  zero  group,  because  all  but  one  of  the  ele- 
ments now  embraced  in  it  had  at  that  time  not  yet  been  dis- 
covered. Helium  was  known  by  its  spectrum  only  as  a  sun 
element.  Because  of  their  atomic  weights,  they  naturally 
precede  Group  1,  but  their  presence  in  nowise  invalidates  the 
periodicity  of  the  other  elements.  In  fact,  their  discovery  and 
position  only  confirms  the  previous  findings. 

Take,  for  instance  the  first  triad  of  Series  4,  argon,  at. 
wt.  38,  calcium,  at.  wt.  40.1  =  78.1  divided  by  2  =  39.5.  The 
atomic  weight  of  potassium,  the  middle  factor  of  the  triad, 
is  39.1.  Observe,  again,  the  first  triad  of  Series  8,  xenon, 
at.  wt.  128,  bariimi,  at.  wt.  137.4  =  265.4  divided  by  2  =  132.7. 
The  atomic  weight  of  caesium,  the  middle  factor,  is  132.9. 

When  the  elements  in  any  group  are  considered  closely 
it  will  be  seen  that  while  their  atomic  weights  increase  rap- 
idly from  above  downward,  and  they  differ  in  other  respects, 
yet  there  is  in  most  cases  a  marked  resemblance  as  to  chem- 
ical properties. 

Prof.  Duncan  calls  attention  to  the  fact  that  each  group 
may  be  arranged  in  two  sub-groups,  the  elements  embraced 
in  each  of  which  are  very  closely  related.  G-roup  2  is  taken 
as  an  example. 

The  elements  in  the  order  of  their  atomic  weights  are: 
Beryllium,  magnesium,  calcium,  zinc,  strontium,  cadmium, 
barium,  mercury  and  radium.  By  the  sub-group  arrange- 
ment the  elements  having  the  greatest  number  of  common 
pro})erti(>s  are  l>rought  together  as  follows: 

Siih-f/ioup  A.      _  Siih-group  B. 

Calcium.  Beryllium. 

Strontium.  Magnesium. 

Barium.  Zinc. 

Radium.  Cadmium. 

Mercury. 


978  AN    OUTLINIO    OF    MKTALLURGY 

THE  ELEMENTS  CONSIDERED  IN   SERIES 

As  before  stated,  the  clciiiciits  ai-ianged  in  liorizontal 
rows  are  termed  series. 

Hydrogen  is  unlike  any  otlier  element,  because  it  is  an 
essential  component  of  all  acids,  and  it,  therefore,  forms  a 
series  by  itself. 

While  there  is  a  general  similarity  between  the  elements 
in  one  series  to  tliose  in  another,  there  is  a  marked  and  pro- 
gressive variation  between  the  elements  in  the  same  series. 
First,  the  atomic  weights  rise  from  left  to  right,  or  from  1 
to  7,  in  comparatively  regular  gradations.  Second,  in  each 
horizontal  row  the  first  element  of  the  series  is  a  well-marked 
metal  or  base-forming  element,  while  the  succeeding  ones 
gradually  merge  from  metallic  into  the  non-metallic  class,  or 
acid-forming  elements,  with  the  exception  of  manganese,  the 
seventh  element  of  the  fourth  series. 

Third,  in  every  series  the  valence  toward  oxygen  ascends 
from  1  to  7,  while  the  valence  toward  hydrogen  or  chlorine 
ascends  from  1  to  4,  and  then  uniformly  descends  to  1. 

The  elements  in  Group  8  belong  to  the  metallic  class, 
have  similar  properties  to  each  other,  but  do  not  fit  in  the 
scheme  of  the  octaves,  as  their  presence  in  the  beginning  of 
the  succeeding  series  would  disarrange  the  grouping  of  the 
remaining  elements,  according  to  their  chemical  group  simi- 
larities. They  are,  therefore,  placed  in  Group  7,  outside  of 
the  octave  system,  although  their  valences  are  continuous 
with  those  of  the  regular  table. 

From  the  many  correlated  facts  observed,  the  periodic 
latv  has  been  formulated  as  follows:  The  properties  of  ele- 
ments are  periodic  functions  of  their  atomic  weights. 

Many  other  interesting  relations  have  been  disclosed,  the 
details  of  which  can  be  found  in  various  works  on  advanced 
chemistry,  particularly  Dr.  Gordin's  Inorganic  Chemistry, 
in  which  will  be  found  a  clear  and  concise  statement  of  the 
periodic  correlations  of  the  elejnents  and  of  the  imperfec- 
tions of  the  system  as  well.  These  few  crudely-stated  facts 
have  been  introduced  with  the  idea  of  creating  a  desire  for 
further  knowledge  in  this  most  interesting  field. 

The  following  works  have  been  consulted  and  largely 
utilized  in  the  presentation  of  the  foregoing  facts: 

Gordin's  Inorganic  Chemistry. 

Smith's  General  Chemistry  for  Colleges. 

Levy  and  Willis,  Radium. 

Arrhenius'  Theories  of  Chemistry. 


AN    OUTLINE    OF    METALLURGY  979 

Gribson's  Scientific  Ideas  of  To-day. 
Martin's  Trimnphs  and  Wonders  of  Modern  Chemistry. 
Kennedy  Duncan's  Some  Chemical  Problems  of  To-day 
and  the  New  Knowledge. 
Duff's  Physics. 
Ganot's  Physics. 

METALS 

Of  the  fifty-two  metals,  al^out  fifteen  are  used  in  the  arts 
and  sciences  in  their  true  metallic  condition,  as  well  as  in  com- 
bination with  each  other  and  with  the  non-metallic  elements. 

A  metal  is  an  opacjue  elementary  substance  which,  with 
the  single  exception  of  mercury,  is  solid  at  ordinary  tempera- 
ture ;  is  a  good  conductor  of  heat  and  electricity ;  has  a  metallic 
luster;  has  the  property  of  replacing  hydrogen  in  acids  form- 
ing salts,  and  is  electropositive  as  compared  with  the  non- 
metallic  elements. 

METALLOIDS 

Certain  of  the  non-metallic  elements,  iodine,  arsenic, 
jihosphorous,  silicon,  sulphur  and  carbon,  possess  to  a  greater 
or  less  degree  the  properties  attributed  to  metals,  especially 
the  power  of  reflecting  light,  and  which  is  known  as  metnUic 
lustre. 

They  are  all  more  or  less  opaque,  while  carbon  is  a  conduc- 
tor of  both  heat  and  electricity,  which  properties,  with  the  ex- 
ception just  noted,  are  confined  exclusively  to  the  metals.  This 
group  of  elements,  therefore,  while  not  metals,  are  called 
Dicfalluids,  from  their  resemblance  in  some  respect  to  the 
metals. 

FORMS  OF  MATTER 

Matter,  as  previoi;sly  stated,  presents  itself  to  our  senses 
in  three  distinct  forms,  as  solids,  liquids,  or  gases.  These 
forms,  in  most  instances  and  under  proper  conditions,  are 
snscei^tible  of  change. 

For  example,  a  metal  liquifies  when  subjected  to  heat. 

Water  vaporizes  under  heat  and  solidifies  at  low  temper- 
atures. 

Hydrogen  at  extremely  low  temperature  and  under  high 
pressure  liquifies  and  can  be  solidified  on  further  reduction  of 
temperature  and  increase  of  pressure. 

OCCURRENCE    OF   METALS   IN    NATURE— MINERALS 

Most  of  the  metals  are  found  in  combination  with  some  of 
the  non-metallic  elements,  as  oxides,  sulphides,  or  carbonates, 
etc. 


AN    OUTLINE    OF    METALLURGY 


Usually  the  combinations  are  of  such  nature  as  to  entirely 
mask  their  metallic  character  and  render  them  unrecognizable 
as  metals,  and,  when  so  occurring,  are  called  minerals. 

NATIVE  METALS 

Gold,  silver,  coj^per,  platinum,  mercury,  bismuth,  anti- 
mony and  iron  frequently  occur  in  nature  in  their  true  metallic 
condition,  and  are  known  as  native  metals.  Those  just  men- 
tioned are  about  the  only  ones  so  occurring. 

ORES 

When  a  mineral  is  found  which  contains  a  particular 
metal  in  sufficient  quantity  to  pay  for  its  extraction  on  a  com- 
mercial basis,  it  is  called  an  ore  of  that  metal. 

NOBLE   METALS 

Metals  included  under  this  head  are  those  whose  com- 
jDounds  with  oxygen  are  decomposable  by  heat  alone  at  a  tem- 
perature not  exceeding  redness.  The  following  comprise  the 
list  of  noble  metals : 

Grold,  silver,  platinum,  palladium,  rhodium,  ruthenium,  os- 
mium iridium,  mercury. 

BASE  METALS 

Under  this  classification  are  included  the  metals  whose 
comi^ounds  with  oxygen  are  not  decomposable  by  heat  alone, 
but  retain  oxygen  at  high  temperatures. 

PHYSICAL  PROPERTIES  OF  METALS 

Since  there  are  properties  common  to  all  metals,  these 
properties  will  be  briefly  explained  before  taking  up  the  study 
of  the  individual  metals. 

Some  of  these  propei'ties,  common  to  all,  but  which,  of 
course,  vary,  according  to  the  individual  metal,  are  atomic 
weight,  specific  gravity,  melting  point,  malleability,  ductility, 
tenacity,  conductivity  of  heat,  and  electricity,  specific  heat, 
color,  etc. 

ATOMIC    WEIGHT 

The  atomic  weight  of  an  element  is  the  weight  of  one 
of  its  atoms  compared  with  the  weight  of  an  atom  of  hydrogen. 

Hydrogen  is  the  lightest  of  all  known  substances,  and  is 
taken  as  the  unit  or  1  of  the  atomic  scale.    Atomic  weight. 


AN    OUTLINE    OF    METALLURGY  981 

therefore,  may  be  considered  as  the  proportion  by  weight  in 
which  elements  unite  chemically. 

SPECIFIC  GRAVITY 

The  sjjecihc  gravity  of  any  substance,  whether  solid, 
liquid  or  gas,  is  the  measure  of  its  density.  The  standard  or 
unit  of  measurement  of  solids  and  liquids  is  water,  and  that 
of  gases  is  hydrogen. 

The  specific  gravity  of  a  solid  or  a  liquid  of  a  given  bulk 
is  its  relative  weiglit  to  a  like  bulk  of  water  under  like  condi- 
tions of  temperature  and  pressure. 

In  order  to  find  the  specific  gravity  of  any  solid,  it  is  first 
weighed  in  air,  then  in  water,  and  its  weight  in  water  deducted 
from  its  weight  in  air.  The  weight  in  air  is  then  divided 
by  the  difference  thus  obtained,  and  the  result  represents 
the  specific  gravity  of  the  substance.  A  convenient  formula 
for  determining  the  specific  gravity  of  solids  and  liquids  is 
as  follows : 

■  Let  W=weight  of  substance  in  air. 

Let  Wi^weight  of  substance  in  water. 

Let  sp.  gr.=specific  gravity. 
W 

Then  ^r_-^Y~  "=  ^P'  ^^'• 

The  specific  gravity  of  most  metals  can  be  somewhat 
increased  by  hammering,  rolling,  wire  drawing  or  cold  pres- 
sure. 

The  specific  gravity  of  aluminum,  it  being  the  lightest 
metal  of  commercial  importance,  is  2.5,  while  osmium,  which 
is  the  heaviest,  is  22.47. 

Comparing  two  cubes  of  equal  size  of  aluminum  and  os- 
mium, the  first  would  weigh  2.5  and  the  latter  22.47  times 
more  than  an  equal  bulk  of  water. 

MELTING  POINT 

When  an  element  or  substance  is  changed  from  a  solid 
to  a  liquid  state  as  the  result  of  thermal  increase,  the  point 
at  which  such  change  occurs  is  called  its  "melting"  or  "fus- 
ing" point. 

When  a  liquid  is  reduced  to  a  solid  state  by  lowering  its 
temperature,  the  point  where  such  change  occurs  is  called 
its  "freezing"  point. 

The  melting  point  and  the  freezing  point  of  a  metal 
usually  approach  each  other  very  closely,  but  are  never  quite 


»82  AN    OUTLINE    OF    METALLURGY 

tlie  same.     Tliey  are  so  close  at  times  as  to  be  incapable  of 
registration  by  tbe  tlierinonieter. 

Some  substances  expand  on  being  melted,  while  others 
contract.  When  a  substance  expands  on  being  melted,  and 
it  is  subjected  to  increase  of  i)ressure  above  normal  during 
the  fusion  process,  the  effect  is  to  raise  its  melting  point. 
On  the  other  hand,  a  substance  which  contracts  on  melting, 
when  subjected  to  increase  of  pressure,  has  its  fusing  point 
decreased.  By  reversing  the  pressures,  opposite  results  are 
obtained. 

The  range  of  fusibility  or  the  melting  points  of  the 
various  metals  differs  greatly.  Mercury  melts  at — .39  deg.  C, 
and,  consequently,  is  liquid  at  ordinary  temperatures.  Bis- 
muth, tin,  lead,  zinc  and  antimony  melt  below  a  red  heat; 
aluminum  requires  a  red  heat ;  gold,  silver  and  copper  a  bright 
red  heat;  iron  and  nickel,  an  intense  white  heat,  while  plat- 
inum and  i:ialladium  are  still  more  refractory,  fusing  only  in 
the  electric  arc  or  the  oxyhydrogen  flame. 

Some  metals,  when  heated  beyond  their  melting  points, 
readily  vaporize,  zinc,  antimony  and  mercury  being  the  most 
common  examples  of  this  class.  As  a  matter  of  fact,  all  of 
the  metals  can  be  volatilized  if  subjected  to  a  sufficiently  high 
temperature. 

Most  of  the  metals  pass  from  the  solid  to  the  liquid  state 
under  the  influence  of  heat  and  under  increased  temperature 
volatilize.  Osmium,  however,  is  an  exception  to  this  rule, 
as  it  passes  from  the  solid  to  the  volatile  condition  without 
assuming  the  liquid  state. 

The  following  table,  by  Pouillet,  will  give  an  idea  of 
temperature  as  displaved  bv  color: 

°C.  °F. 

Incipient  red  corresponds  to 525  977 

Dull  red  corresponds  to 700         1292 

Incipient  cherry  red  corresponds  to 800         1472 

Cherry  red  corresponds  to 900         1652 

Clear  cherry  red  corresponds  to 1000         1832 

Deep  orange  corresponds  to 1100         2012 

Clear  orange  corresponds  to 1200        2192 

White  corresponds  to 1300        2372 

Bright  white  corresponds  to 1400        2552 

Dazzling  white  corresponds  to 1500        2732 

Most  metals  expand  when  heated,  and  contract  on  cooling. 
Within  certain  limits  the  expansion  is  proportional  to  the 
degree  of  heat  to  which  they  are  subjected.    There  are,  how- 


AN    OUTLINE    OF    METALLURGY  983 

ever,  certain  exceptions  to  tliis  rule.  Aiitimonj'  expands  at 
the  moment  of  becoming  solid,  and  bismuth  occupies  more 
space  in  the  solid  than  in  the  liquid  state.  This  property  ren- 
ders these  metals  particularly  useful  in  alloys  of  type  and 
fusible  metals,  where  sharp,  well-defined  castings  are  de- 
sirable. 

MALLEABILITY 

Mallealnlity  is  that  property  of  metals  by  which  they 
may  be  beaten  out  or  otherwise  extended  into  thin  sheets 
without  a  break  in  the  continuity  of  their  surfaces.  This  prop- 
erty varies  in  different  metals,  some  possessing  it  to  a  marked 
degree,  while  in  others  it  is  almost  entirely  absent. 

Gold  is  the  most  malleable  of  all  of  the  metals.  It  can 
be  beaten  out  into  extremely  thin  attenuated  sheets,  1/300000 
of  an  inch  tliick.  In  other  words,  it  would  require  300,000 
sheets  laid  one  upon  the  other  to  measure  an  inch  in  thick- 
ness. Gold,  therefore,  is  taken  as  the  standard  or  unit  of 
measurement  of  the  degree  of  malleability  of  metals,  and  is 
rated  "first  rank." 

This  property  is  seriously  impaired  l)y  the  presence  of 
impurities,  and  also  by  heat,  although  the  latter  tends  to  in- 
crease the  malleability  in  zinc.  This  metal,  when  cast,  is 
crystalline  and  brittle,  but  when  heated  to  about  150°C.,  it  is 
capaltle  of  being  rolled  into  thin  sheets,  and  these  retain  their 
malleability  to  a  considerable  degree  when  cold. 

Metals  of  a  crystalline  structure  are  almost  totally  de- 
void of  this  property,  while  those  of  a  soft  and  tenacious 
character  are  the  most  malleable. 

DUCTILITY 

Ductility  is  that  property  possessed  by  metals  by  means 
of  which  they  may  be  drawn  out  into  wire  or  rods,  by  lateral 
compression,  without  breaking. 

Gold  liossesses  this  in  the  highest  degree,  since  it  can  be 
drawn  out  into  the  most  delicate  wire ;  a  piece  one  mile  in 
length  having  been  drawn  from  less  than  one  gram 
weight. 

The  softness  and  tenacity  of  a  metal  control  the  degree 
of  ductility. 

Ductility  is  affected  by  heat,  which  increases  this  property 
in  some  metals  and  decreases  it  in  others. 

Lead  is  the  least  ductile  because  of  the  slight  tenacity  by 
which  the  molecules  are  held  together.     Bismuth  and  anti- 


984  AN    OUTLINE    OF    METALLURGY 

iriony  are  examples  of  metals  in  which  this  property  is  almost 
wholl}'  absent  because  of  their  crystalline  structure. 

Steel  is  extremely  ductile,  and  is  now  being  drawn  into 
wire  1/1000  of  an  inch  in  diameter  for  commercial  purposes. 

Ductility  is  modified  by  mechanical  working,  the  latter 
affecting  metals  to  such  an  extent  at  times  as  to  render  them 
unworkable  until  this  ])roperty  is  again  restored  by  an- 
jiealing. 

ANNEALING 

This  process  consists  in  heating  metals  and  cooling,  slowly 
in  some  cases,  and  rapidly  in  others. 

Annealing  changes  metals  from  the  hardened  condition 
produced  by  hammering,  rolling,  wire-drawing,  burnishing 
and  polishing,  to  a  soft,  pliable  condition. 

It  is  sui^posed  that  the  molecules  in  a  metal,  changed 
by  the  i^rocesses  mentioned,  are  under  a  greater  or  less  degree 
of  tension  which,  while  not  of  sufificient  force  to  do  so,  tends 
to  return  them  to  their  former  relation.  Under  the  influence 
of  heat,  and,  as  before  stated,  in  the  case  of  some  metals,  fol- 
lowed by  sudden  chilling,  as  when  plunged  into  cold  water 
while  hot,  the  tension  referred  to  is  destroyed  and  the  mole- 
cules are  brought  to  a  normal  relation  to  each  other  under 
the  changed  conditions. 

The  degree  of  hardness  developed  in  metals  h}^  mechan- 
ical woi'king  is  dependent  upon  the  character  and  amount  of 
force  applied  within  and  up  to  certain  limits.  In  other  words, 
a  moderate  amount  of  manipulation  will  jiroduce  a  moderate 
degree  of  hardness,  while  an  excessive  amount  of  working  will 
produce  the  extreme  degree  of  hardness  capable  of  being  pro- 
duced in  a  particular  metal. 

If  a  metal  be  worked  to  its  extreme  limit  of  hardness, 
and  is  then  annealed,  a  greater  or  less  amoimt  of  warpage  is 
noticeable.  This  is  apparent  in  swaging  metal  plates.  The 
base,  when  swaged,  may  lie  in  absolute  contact  with  the  die, 
yet,  when  annealed,  the  adaptation  will  be  found  to  have 
changed.  A  slight  amount  of  swaging  will  again  restore  the 
adaptation,  and,  if  annealed  again,  very  little,  if  any,  change 
Avill  be  noticeable. 

This  fact  renders  it  imperative  that  matrices  of  platinum 
or  gold  foil,  when  adapted  to  cavities  for  inlay  work,  should 
be  annealed  thoroughly,  and  a  final  adaptation  secured  before 
introducing  the  porcelain  for  baking.  By  observing  this  sug- 
gestion, misfits  traceable  to  this  cause  are  obviated. 


AN    OUTLINE    OF    METALLURGY  985 

Intentional  or  accidental  alloying  of  the  metals  also 
modifies  their  degrees  of  ductility,  sometimes  increasing,  and 
again  diminishing,  this  property.  The  slightest  trace  of  lead, 
zinc,  bismuth  or  antimony  in  gold  impairs  its  ductility  to  a 
marked  degree,  hence  the  necessity  in  dental  laboratory  pro- 
cedures of  keeping  gold  perfectly  free  from  these  baser  metals. 

TENACITY 

Tenacity  is  that  property  of  metals  which  enables  them 
to  resist  stress  or  dead  weight  when  applied  to  rods  or  wires 
in  the  direction  of  their  length. 

This  property,  as  well  as  those  of  malleability  and  duc- 
tility, is  greatly  affected  and  readily  influenced  by  the  pres- 
ence of  other  metals  or  impurities,  and  bj^  heat,  which  in 
some  cases  increase  and  in  others  decrease  these  various 
properties 

The  tenacity  of  iron,  for  instance,  is  greatly  increased  by 
the  addition  of  a  small  per  cent  of  carbon,  while  the  presence 
of  silicon  diminishes  it. 

In  addition  to  the  ordinary  or  comparative  tests  of  te- 
nacity of  a  metal,  several  other  kinds  should  be  considered, 
and  these  are  classified  according  to  the  externally  acting 
force. 

Ordinary  tenacity,  as  before  stated,  relates  to  resistance 
to  traction  or  direct  pull ;  relative  tenacity,  resistance  to  frac- 
ture; reactive  tenacity,  resistance  to  crushing;  shearing  te- 
nacity, resistance  to  lateral  displacement;  torsional  tenacity, 
resistance  to  twisting. 

When  metal  bars  are  subjected  to  a  certain  amount  of 
tension,  permanent  elongation  occurs.  If  the  tension  is  nor 
sufficient  to  produce  this  result,  the  bar  will  return  to  its  orig- 
inal length.    This  line  of  division  is  called  the  elastic  limit. 

In  machine  construction,  when  wires  or  rods  are  used,  it 
is  essential  that  such  parts  be  composed  of  metals  of  suitable 
kind,  and  be  of  sufficient  size,  to  withstand  stress  without 
passing  beyond  the  elastic  limit. 

TENSILE  STRENGTH 

The  tenacity  or  tensile  strength  of  metals  and  alloys  is 
tested  by  placing  a  bar  of  the  metal  of  one  inch  sectional  area 
in  a  suitable  testing  machine  and  applying  stress  sufficient  to 
fracture  it.     The  following  table  will  convev  an  idea  of  the 


986  AN    OUTLINE    OP    METALLURGY 

wide   ratine  of  (lirrci-cncc  in   tciiacity  of  vai'ious  inctals  and 

iilloys.     (From  ( "a  i-n  chic's  liaiifllxiok.) 

Average, 
Pounds. 

Brass 18,000 

Brass,  wire   49,000 

Bronze  or  "unnieial ."JG.OOO 

Copper,  cast 19,000 

Copper,  bolts ;!6,000 

Copper,  wire  16,500 

Iron,  cast  16,500 

Iron,  wrouglit 53,000 

Iron,  wire 70,000  to  100,000 

Lead,  sheet 3,300 

Steel   50,000  to     80,000 

Tin,  cast 4,600 

Zinc  7,000  to     8,000 

ELASTICITY 

This  property  refei-s  to  tlie  amount  of  force  wliieh  can 
be  resisted  by  metals  under  stress  without  permanent  de- 
formation or  "set"  being  i^roduced. 

The  "modulus  of  elasticity"  is  the  force  that  would  be  re- 
quired to  double  the  length  of  a  bar  if  its  elasticity  remained 
perfect.  The  "modulus"  is  an  index  of  the  stretching  capacity 
of  a  metal. 

FLOW 

Metals  which  in  a  solid  state  can  be  shaped  into  any 
required  form  by  pressure  are  said  to  possess  the  property  of 
flowing. 

Stamijings,  lead  ])ipe,  rods,  coins,  medals,  etc.,  are  ex- 
amples of  what  can  be  accomplished  through  this  property. 
The  flowing  property  depends  upon  a  combination  of  other 
qualities,  such  as  malleability,  ductility  and  toughness,  to- 
gether with  a  siitificient  amount  of  tenacity  to  permit  the  mole- 
cules of  metals  to  roll  over  each  other  without  adhesion  being 
destroyed. 

CONDUCTIVITY    OF   HEAT 

Conductivity  of  heat  refers  to  the  property  of  different 
substances  for  transmitting  heat.  The  degree  of  rapidity  of 
heat  transmission  varies  greatly  in  different  substances, 
metals  being  the  best  conductors.    This  property  also  varies 


AN    OUTLINE    OF    METALLURGY  987 

in  the  different  metals,  silver  being  the  best,  and  it  is,  there- 
fore, taken  as  the  standard  of  measurement,  and  is  rated  100. 

CONDUCTIVITY  OF  ELECTRICITY 

Conductivity  of  electricity  refers  to  the  capacity  of  metals 
for  receiving-  and  transmitting  a  current  of  electricity.  Silver 
in  this  case  also  is  the  best  conductor,  and  is  taken  as  the 
standard  of  comparison,  being  rated  100.  As  a  general  thing, 
the  best  conductors  of  heat  are  also  the  best  conductors  of 
electricity.    There  are,  however,  exceptions  to  this. 

Those  metals  ranking  low  in  the  scale  of  conductivity 
of  electricity  oiTer  resistance  to  the  passage  of  a  current.  This 
resistance  is  very  apparent  in  platinum,  iron  and  nickel,  and 
as  resistance  to  the  passage  of  a  current  is  marked  by  a  rise 
in  temperature,  these  metals,  as  well  as  the  alloy  known  as 
German  silver,  are  used  for  rheostat  and  electric  furnace 
construction. 

The  electric  furnace,  commonly  used  in  poreclain  work, 
consists  of  a  metal  case  lined  with  fireclay,  so  shaped  as  to  give 
a  muffle  form  to  the  interior,  in  which  the  piece  to  be  baked 
is  placed.  In  the  inner  walls  of  the  fireclay  is  imbedded  fine 
platinum  wire,  and  as  the  current  passes  through  this,  it  be- 
comes heated,  and  the  temperature  in  the  interior  of  the  fur- 
nace is  gradually  raised  to  the  iioint  of  fusion  of  the  porcelain, 
usually  about  1200°  C. 

The  following  table  gives  the  comparative  conductivity 
of  heat  and  electricity  of  fourteen  metals,  and,  as  before 
stated,  silver  heads  the  list  in  both  tallies: 

Heat.  Electricitv. 

Silver    100        Silver    ." 100 

Copper 85        Copper   97.8 

Gold 53.2     Gold    76.7 

Aluminum    31.3     Aluminum    65.5 

Zinc 28.1     Zinc  29.6 

Cadmium    20.1     Cadmium   24.4 

Tin    15.5     Iron 14.6 

Mercurv  13.5     Platinum    14.5 

Iron     ." 11.9     Tin    14.4 

Nickel   Nickel   12.9 

Lead    8.5     Lead    8.4 

Platinum    '. 8.4     Antimony 3.6 

Antimony    4.0     Mercury  1.8 

Bismuth ' 1.8     Bismuth   1.4 

The  conductivity  of  a  substance,  as  a  rule,  diminishes 
with  a  rise  in  temperature. 


988  AN    OUTLINE    OF    METALLURGY 

EXCEPTION   TO  THE   GENERAL   RULE   OF  CONDUCTIVITY   OF 
ELECTRICITY 

One  important  exception  to  this  might  be  mentioned  here. 
The  oxides  of  some  of  the  metals,  especially  when  combined, 
exliibit  the  opposite  quality,  viz.,  being  non-conductors  when 
cold  and  conductors  when  heated.  This  principle  is  made  use 
of  in  the  construction  of  pyrometers  or  instruments  for  mea- 
suring heat  units  and  applied  to  porcelain  furnaces. 

Two  methods  are  employed.  In  one  ease  a  thermopile, 
an  apparatus  consisting  of  two  or  more  plates  of  dissimilar 
metals,  which  upon  being  heated  generate  a  mild  current  of 
electricity,  are  built  in  the  back  of  the  furnace.  As  the  fur- 
nace gradually  rises  in  temperature,  the  current  in  the  thermo- 
pile increases,  which  is  indicated  by  a  mila-voltmeter  modified 
to  correctly  register  the  fusing  point  of  the  various  por- 
celains. 

In  the  other  case,  a  Nernst  glower,  a  small  rod  composed 
of  the  oxides  of  zirconium  and  yttrium,  which  when  cold  is  a 
non-conductor,  but  which  when  heated  readily  transmits  a 
current,  is  placed  in  the  muffle  and  connected  with  an  inde- 
pendent dry  cell  current. 

As  the  furnace  temperature  rises  the  dry  cell  current 
finds  its  way  through  the  glower  and  is  registered  by  an  ap- 
paratus similar  to  the  one  before  described. 

Profs.  Dewar  and  Jenkins,  in  determining  the  conduc- 
tivity of  metals  and  alloys  at  very  low  temperatures,  found 
that  the  resistances  of  pure  metals  decrease  in  such  ratio  as 
to  convej'  the  idea  that,  if  absolute  zero  could  be  obtained, 
all  resistance  would  vanish.  The  resistance  of  alloys,  how- 
ever, does  not  diminsh  in  the  same  ratio.  For  example,  at — 
200°  C.  the  alloys — platinoid,  German  silver,  platinum  silver 
and  phosphor  bronze — show  nearlv  the  same  resistance  as  at 
0°  C. 

An  illustration  of  the  wide  range  of  conductivity  of  the 
metals  can  be  presented  by  making  a  chain  composed  of  al- 
ternative links  of  platinum  and  silver  wire  of  the  same  size 
and  passing  a  current  of  electricity  through  it.  The  platinum 
links  will  become  heated,  while  the  silver  links  will  remain 
normal  except  at  their  junction  with  the  platinum,  where  the 
heat  from  the  latter  is  transmitted  by  contact. 

SPECIFIC  HEAT 

It  has  been  found  that  different  metals  are  capable  of 
absorbing  different  amounts  of  heat  when  subjected  to  the 
same  degree  of  temperature. 


AN    OUTLINE    OF    METALLURGY  989 

The  amount  of  heat  necessary  to  raise  one  kilogram  of 
water  through  one  degree  of  temperature,  from  4°  to  5°  C, 
is  taken  as  the  unit  or  standard  of  specific  heat,  and  this  is 
called  the  thermal  unit. 

The  quantitj'  of  heat  necessary  to  raise  a  kilogram  of  mer- 
cury through  one  degree  C.  is  only  0.033  of  the  heat  unit,  and 
this  fraction  expresses  the  specific  heat  of  mercury  relatively 
to  water.  It,  therefore,  follows  that  the  same  quantity  of  heat 
required  to  raise  one  kilogram  of  water  through  one  degree 
of  temperature  would  produce  an  equal  increase  in  temper- 
ature in  about  30  kilograms  of  mercury. 

The  greater  the  specific  heat  of  a  substance,  the  greater 
the  heat  necessary  to  raise  the  temperature  through  any  given 
degree,  and  conversely,  the  less  the  specific  heat,  the  smaller 
quantity  of  heat  required. 

TABLE   OF   SPECIFIC   HEAT 

Mercury   0.03332     Silver    0.0570 

Gold    ." .0.03244     Cadmium   0.0567 

Iron 0.1138       Tin    0.0562 

Nickel   0.1086       Antimouv 0.0508 

Cobalt 0.1070       Lead   0.0314 

Zinc    0.0956       Palladium    0.0308 

Copper 0.0952       Platinum    0.0311 

Palladium 0.0593  : 

EXPANSION 

It  is  a  well-known  law  of  physics  that  substances  ex- 
pand when  heated. 

This  movement  is  particuarly  marked  in  metals,  since 
they  are  good  conductors  of  heat. 

THE  CO-EFFICIENT   OF  EXPANSION  OF  SUBSTANCES 

The  co-efficient  of  expansion  of  any  substance  is  the 
amount  which  the  unit  of  length  (surface  or  volume)  expands 
in  passing  from  0°  to  1°  C. 

The  co-efficient  of  expansion  is  constant  in  metals  crystal- 
lizing in  the  regular  systen).  In  the  others,  the  expansion 
varies  according  to  crystallization,  this  movement  occurring 
in  the  direction  of  the  various  axes.  Such  metals  are  usually 
tested  by  compressing  their  powders. 

In  the  industrial  field  a  thorough  knowledge  of  the  ex- 
l)ansion  of  different  material  is  essential  so  that  provision 


990  AN    OUTLINE    OF    MRTALLURGY 

may  bo  madt"  Toi-  compensating'  for  it  in  the  construction  of 
buildings,  bridges,  and  large  pieces  of  machinery. 

In  assembling  bridges  in  the  dental  laboratory  it  is  es- 
sential that  an  investing  material  be  used  whose  co-efficient 
of  expansion  is  about  equal  to  that  of  gold. 

If  one  is  employed  whose  co-efficient  of  expansion  is  much 
greater,  the  assembled  pieces  will  l)e  moved  apart  as  the  in- 
vestment expands  under  heat,  and  while  in  that  changed  re- 
lation become  fixed  by  the  solder,  the  result  being  that  the 
bridge  is  lengthened. 

The  following  table  gives  the  linear  expansion  occurring 
in  metals  when  raised  from  a  temperature  of  0°  to  100°  C, 
The  fraction  represents  the  ratio  of  linear  expansion  per 
length  of  rod : 

Cadmium    OO.SOfi?  or  1/326 

Lead 002932  "  1/342 

Zinc    002915  "  1/313 

Aluminum 002307  "  1/432 

Tin  002232  "  1/448 

Silver    001930  ' '  1/518 

Copper 001()72  "  1/598 

Bismuth    001620  "  1/617 

Gold  001451  "  1/689 

Nickel    001270  "  1/787 

Iron    001070  "  1/934 

Antimonv   001050  "  1/952 

Platinum 000900  "  1/1123 

COLOR 

Most  metals  are  gray  or  wiiite  in  color,  these  colors 
merging  into  ])luish  tinges  in  some  cases.  Gold  is  a  rich 
yellow  color  in  masses,  but  transmits  a  greenish  tinge  in  thin 
attenuated  sheets.  Copper  is  of  a  decidedly  red  color.  The 
color  of  most  metals  is  changed  by  alloying  with  other  metals. 

Gold  alloyed  with  silver  is  changed  to  a  greenish  tinge, 
and  when  alloyed  with  copper  a  decidedly  red  color  is  im- 
parted to  it.  By  combining  silver  and  copi^er  in  proper  pro- 
portions, gold  may  be  reduced  in  fineness  without  material 
change  in  color. 

WELDING 

This  i^rocess  consists  in  uniting  two  ]iieces  of  metal  to- 
gether by  pressure  so  as  to  form  one  compact  piece.  The 
requisites  of  a  metal  necessary  to  successful  welding  are  that 


AN    OUTLINE    OF    METALLURGY  991 

it  must  be  clean,  soft,  and  that  it  should  possess  cousiderable 
malleability  and  toughness. 

In  the  case  of  iron,  some  of  these  properties  are  devel- 
oped only  at  a  higli  temperature,  in  which  condition  it  is  in 
a  pasty  state.  The  surfaces  to  be  united  are  cleaned  and  cov- 
ered with  borax  to  remove  any  oxide  that  may  be  present 
and  prevent  further  oxidation,  or  sand  can  be  used  also,  which 
by  combining  with  the  iron  forms  a  fusible  silicate,  and  which, 
under  the  lilows  of  the  hammer,  is  forced  out  from  the  contact 
surfaces. 

When  subjected  to  hammering  or  pressure,  the  mole- 
cules of  metal  are  capable  of  interpenetrating  or  diffusing  into 
and  among  each  other  so  as  to  form  a  continuous  piece. 

Steel  must  be  welded  at  a  considerably  lower  temperature 
than  iron  because  of  its  lower  fusing  point.  The  carbon  also 
is  liable  to  burn  out  when  overheated,  and  its  quality  thus  be- 
come impaired.  Because  of  the  difference  in  the  melting 
points,  and  for  the  reason  just  stated,  it  is  difficult  to  weld 
iron  and  steel  together. 

Gold  is  an  example  of  a  metal  which  can  be  welded  cold. 
In  the  form  of  foil,  pure  gold  is  rolled  into  pellets  or  folded 
into  small  pieces  and  packed  into  tooth  cavities  by  mallet 
force  or  hand  pressure.  Under  favorable  conditions  it  can 
be  worked  into  a  mass  seemingly  as  solid  as  though  it  had  been 
cast. 

In  electric  welding,  the  pieces  to  be  united  are  placed  in 
a  suitable  device  for  holding  them  in  proper  contact  and  re- 
lation to  each  other,  and  a  powerful  current  of  low  tension 
is  passed  from  one  piece  to  the  other.  The  high  resistance  at 
the  junction,  caused  by  imperfect  contact,  develops  an  intense 
heat  at  this  point,  and  when  heated  sufficiently  the  surfaces 
are  jammed  together  and  union  occurs. 

The  metals  which  weld  most  readily  are  gold,  silver,  tin, 
lead,  iron  and  nickel. 

As  a  matter  of  fact,  a  number  of  the  metals,  when  pow- 
dered and  subjected  to  intense  pressure,  can  be  welded  cold. 

The  following  table,  by  Professor  Spring,  shows  the 
amount  of  compression  required  to  unite  those  listed  into  a 
solid  mass : 

Tons  per 
sq.  inch. 

Lead  13 

Tin    19 

Zinc    38 


992  AN    OUTLINPJ    OF    METALLURGY 

Aiitiiiiony 38 

Alumiiniiii    38 

Bi.simith  38 

Copper  33 

Lead  flows  at 33 

Tin  flows  at 47 

WELDING  COPPER  TO  IRON 

A  remarkable  yet  simple  method  of  tveldivg  eoi^per  to 
iron  is  being  employed  for  many  purposes  in  the  industrial 
fields.  The  copper  and  iron  objects  it  is  desired  to  unite  are 
bound  in  contact,  placed  in  a  crucible,  and  finely  ground  retort 
carbon,  moistened  slightly  with  sugar  water  to  make  it  ad- 
hesive, is  packed  closely  around  them.  The  crucible  is  then 
heated  in  a  furnace  for  half  an  hour  at  a  temperature  about 
midway  between  the  melting  point  of  copper  and  iron,  when 
perfect  fusion  of  the  two  metals  will  occur,  the  welded  joint 
being  tougher  than  either  of  the  two  metals. 

A  peculiar  fact  concerning  this  process  is  that  the  sur- 
faces of  the  metals  to  be  united  need  not  be  prepared,  cleansed 
or  fluxed  in  any  manner,  the  graphite  and  sugar  taking  the 
place  of  the  ordinary  fluxes,  clearing  away  any  oxide  that 
may  be  present,  and  preventing  the  atmospheric  oxygen  from 
getting  to  the  joint.  The  molecular  cohesion  is  as  strong  and 
perfect  between  copper  and  iron  as  between  the  molecules  of 
the  individual  metals;  such  a  weld  is  not  to  be  compared  to 
the  ordinary  brazed  joint,  which  is  merely  an  imperfect  super- 
ficial surface  union. 

The  process  is  utilized  in  welding  steel  teeth  to  cast  iron 
wheels,  in  joining  pieces  of  wrought  iron  where  ordinary 
welding  operations  are  not  practicable,  in  the  construction 
of  large  gun  projectiles,  in  ship  construction,  in  the  electrical 
and  many  other  fields  where  an  absolute  union  between  pieces 
of  similar  as  well  as  dissimilar  metals  is  desirable.  Professor 
Simpson,  of  London,  is  given  credit  for  this  remarkable 
method  of  welding  copper  to  dissimilar  metals. 

ALUMINOTHERMY 

From  1760,  when  Moreau,  a  French  chemist,  named  the 
white  substance  he  obtained  by  calcining  alum,  "alumina," 
because  he  believed  it  to  be  the  oxide  of  a  metal,  until  Wohler 
isolated  it  in  1827,  rejjeated  but  futile  efforts  were  made  by 
many  to  discover  some  means  of  reduction  of  aluminum  from 
its  ores. 


AN    OUTLINE    OF    METALLURGY  993 

The  strong  atSnity  of  alumiuiim  for  certain  non-metallic 
elements,  particularly  oxygen,  is  very  marked.  It  is  only 
through  the  action  of  a  powerful  electric  current  together 
with  suitable  fluxes  that  the  oxide  of  aluminum  is  decomposed. 
When  freed  from  oxygeu,  however,  aluminum  under  ordinary 
conditions  is  not  readily  oxidized,  but  under  favorable  con- 
ditions the  two  elements  most  energetically  unite,  with  the 
evolution  of  intense  heat. 

This  places  aluminum  amoug  the  most  powerful  of  tlie 
reducing  agents,  since  many  metallic  oxides  which  cannot  be 
broken  up  with  carbon  are  readily  reduced  by  it.  Professor 
Goldschmidt,  of  Essen,  Germany,  in  1904,  discovered  this  fact 
and  applied  it  to  industrial  purposes.  So  effective  has  it 
proven  that  "alumino-thermics,"  as  the  process  is  called, 
occupies  a  unique  and  iireviously  unfilled  place  in  high  tem- 
perature chemical,  metallurgical,  and  industrial  fields. 

The  process  is  comparatively  simple  and  easy  of  applica- 
tion. Finely  granular,  metallic  aluminum  together  with  the 
oxide  of  iron  and  some  substance  to  act  as  a  flux,  as  fluor  spar, 
are  placed  in  a  suitable  receptacle.  Some  magnesium  filings 
mixed  with  barium  or  sodium  peroxide — a  mixture  highly 
combustible — are  thrown  on  top  to  "kindle  the  fire,"  or  start 
chemical  action. 

Almost  instantly  there  is  a  flash,  the  development  of  a 
temperature  of  more  than  3000  C,  and  in  the  bottom  of  the 
crucible  lies  a  little  button  of  iron  with  a  film  of  slag,  the  oxide 
of  aluminum,  covering  its  surface. 

A  mixture  of  granular  alumini;ra  and  oxide  of  iron  is 
sold  for  industrial  purposes  under  the  name  of  "thermit." 
This  mixture  when  placed  in  a  very  simple  hopper-like  appa- 
ratus from  which  it  is  fed  to  the  point  desired,  constitutes  a 
most  powerful,  portable  blacksmith  shop.  It  is  used  for  unit- 
ing the  ends  of  street  car  rails,  welding  them  together  to 
form  a  "continuous  rail."  Large  castings  of  iron  or  steel 
when  broken  can  l^e  perfectly  welded  by  this  means,  and,  as 
before  intimated,  the  oxides  of  many  of  the  metals  can  be 
easily  and  quickly  reduced  without  the  annoying  combinations 
of  metal  with  carbon  that  so  frequently  follow  ordinary  fuel 
reduction  processes. 

TEMPERATURES,  COMMON  AND  EXTRAORDINARY 

Although  most  of  the  metals  can  be  welded  cold,  under 
heavy  pressure,  it  is  found  more  convenient  as  well  as  econ- 
omical to  render  the  surface  to  be  united  jDlastic  by  heat,  so 


994  AN    OUTLINE    OK    MBTALLUIUiY 

that  the  molecidos  may  more  readily  iiitcriioiiotrato  and 
molecular  xmion  be  established. 

The  degree  of  heat  necessary  to  apply  in  successful  weld- 
ing operations  coincides  closely  with  the  fusing  points  of  the 
metals  to  be  united,  and  in  soldering  operations  with  the 
fusing  point  of  the  solder  employed. 

The  following  list  indicates  some  of  the  temperatures 
ordinarily  employed  in  soldering  and  welding  operations,  as 
well  as  some  developed  for  special  purposes.  Comparative 
heat  of  the  sun  and  hottest  stars  as  indicated  by  the  spectro- 
scope is  also  given. 

180  to  200  C  soft  soldering  operations. 

1000  to  1200  C  hard  soldering,  as  silver  and  the  varioiis 
alloys  of  gold. 

1800  C  is  about  the  highest  temperature  attainable  in  a 
fuel  furnace  on  account  of  the  fire  clay  lining  fusing  at  this 
point. 

2000  C  represents  about  the  temperature  of  the  oxy- 
hydrogen  flame. 

3000  to  3300  C.  Thermit. 

3400  C  oxv-acetvlene  blow-pipe. 

3500  to  4000  C.  "electric  arc. 

5000  C.  cordite,  confined  and  exploded  exerts  a  pressure 
of  50  tons  per  square  inch. 

6000  C.  estimated  temperature  of  the  sun. 

30000  C.  estimated  temperature  of  some  of  the  hottest 
stars   (Lockyer). 

The  last  of  these  records  can,  of  course,  be  only  approx- 
imate, since  time,  space,  refraction  of  light,  and  other  possible 
sources  of  error,  detract  from  the  accurac.y  of  the  spectro- 
scopic scale,  by  means  of  which  temperature  readings  of 
celestial  spheres  are  determined. 

Even  Lockyer 's  temperature  estimates,  astonishing 
though  they  seem,  pale  into  insignificance  when  compared 
with  those  of  Arrhenius,  who  suggests  a  possible  temperature 
of  7,000,000  C.  in  some  of  the  larger  stellar  bodies,  which, 
of  course,  consist  of  elements  in  a  highly  rarefied  gaseous 
state,  and  in  an  intensely  heated  and  active  condition. 

SOLDERING 

Soldering  consists  in  uniting  the  surfaces  of  metals  to- 
gether by  heat  without  pressure.  This  is  usually  accomplished 
by  the  interposition  of  another  metal  or  alloy,  called  a  solder, 


AN    OUTLINE    OF    METALLURGY  .  995 

that  fuses  at  a  lower  temperature  than  the  metals  to  be 
united. 

Soft  soldering  is  accomplished  l)y  using  a  solder  that  fuses 
below  a  red  heat,  and  liard  sohlcriiif/  l)y  means  of  one  that 
fuses  above  a  red  heat. 

Autogenous  soldering  is  a  process  of  uniting  metals  by 
direct  fusion  of  their  contact  surfaces,  and  is  used  principally 
in  plumbing  operations.  In  crown  and  bridge  work  this 
method  is  sometimes  employed  for  uniting  the  two  ends  of  a 
gold  band  together  without  the  interjiosition  of  solder,  and 
is  commonly  termed  sweating. 

In  all  three  methods  of  soldering  it  is  essential  that  a 
flux  be  used.  This  prevents  oxidation  of  the  solder  and  sur- 
faces to  be  united,  and  also  dissolves  any  oxide  that  may  be 
present.  In  hard  soldering  and  sweating  operations,  borax 
or  a  solution  of  boracic  acid  is  used  most  frequently.  For 
soft  solder,  chloride  of  zinc,  to  which  a  little  sal  ammoniac 
is  sometimes  added,  is  most  frequently  used. 

Eosin  is  also  used  for  this  purpose,  and  in  plumbing  op- 
erations where  lead  joints  are  to  be  united,  stearin,  or  tallow, 
is  often  employed. 

CONDITION   ESSENTIAL   TO    SUCCESSFUL    SOLDERING 

The  conditions  necessary  to  successfid  soldering  are  as 
follows : 

1.  Close  contact  of  the  surfaces  to  be  united. 

2.  Exposure  of  clean,  bright  surfaces  over  which  the 
solder  is  to  flow. 

3.  Use  and  proper  distribution  of  a  suitable  flux. 

4.  A  solder  which  will  fuse  at  a  slightly  lower  tempera- 
ture than  the  metals  on  which  it  is  to  be  used,  and  which 
will  flow  freely.  It  should  also  conform,  as  closely  as  possible, 
in  color  and  fineness  to  the  metals  to  be  united.  This  is  a 
necessary  consideration  in  gold  dental  substitutes. 

5.  There  should  be  a  gradual  and  uniform  application 
and  distribution  of  heat,  and  in  dental  operations  involving 
the  use  of  i)orcelain  facings,  the  flame  should  be  directed 
around  the  base  and  sides  of  the  investment  to  drive  off  the 
moisture,  heat  the  porcelain  and  allow  it  to  expand  before 
the  platinum  pins  are  heated,  otherwise  fracture  of  the  por- 
celain is  likely  to  occur. 

6.  The  reducing  flame  should  be  used  to  prevent  oxi- 
dation of  the  solder  and  the  sufaces  to  l>e  united. 


AN    OUTLINE    OF    METALLURGY 


THE   STRUCTURE   OF   FLAME 

To  solder  successfully,  it  is  necessary  to  understand  the 
structure  of  flame.  A  common  candle  flame  will  serve  as  an 
illustration.  A  flame  of  this  character  consists  of  four  parts: 
(1)  a  dark  central  zone  or  supply  of  unburned  gas  surround- 
ing the  wick;   (!')   the  Inininous  zone  or  area  of  incomplete 


OUT   OF    CANDLE  FLAME 


I  SEMI-HiMIXOrS   FLAME 

II  LUMINOUS    FLAME 

III  UNBURNED  GAS  ZONE 

IV  CARBON    MONOXID    PIxAME 


combustion  immediately  outside  the  inner  zone;  (3)  the  outer 
or  non-luminous  zone,  or  area  of  complete  combusion;  (4)  a 
deep  blue  flame  at  the  base  which  extends  only  a  slight  dis- 
tance upward,  consisting  of  cai'bon  monoxide  gas.  The  cen- 
tral zone  of  unburned  gas  is  generated  by  the  heat  of  the 
flame  acting  on  and  decomposing  the  fat,  and  is  highly  charged 
with  carbon.  In  the  luminous  flame  the  particles  of  carbon 
in  the  inner  zone  float  outward  and  become  heated  and  incan- 
descent, imperfect  combusion  occurring,  since  the  supply  of 
oxygen  is  insufficient  to  form  CO^. 

In  the  outer  zone  the  supply  of  oxygen  from  the  surround- 
ing air  is  sufficient  to  produce  complete  combustion. 

The  small,  deep  blue  part  at  the  base  of  the  flame  con- 
sists of  carbon  monoxide  gas. 


AN    OUTLINE    OF    METALLURGY  997 

THE    BUNSEN    FLAME 

In  the  Bunsen  flame  the  gas  is  admitted  into  the  base 
of  the  burner,  and  passes  up  through  a  tube  to  the  point  of 
ignition.  Near  the  bottom  of  the  tube  are  openings  for  admit- 
ting air.  As  the  gas  passes  upward,  the  air  is  drawn  in  also, 
and  mixes  with  the  gas;  and  when  ignited  the  flame  burns 
without  himinosity,  but  with  intense  heat,  because  the  admitted 
air  furnishes  the  necessary  amount  of  oxygen  for  complete 
combustion. 

THE  BLOWPIPE  FLAME 

The  blowpipe  usually  consists  of  two  tubes — a  large 
outer  one  for  conducting  the  gas,  and  a  small  inner  one  for 
admitting  the  air — and  so  shaped  as  to  be  convenient  to 
handle.     (See  page  998.) 


"Oxiduin^  Flame. 
--Reducin|  Flame 

"Mi.-xed  Gas  and  Air 


E 


■    -Inlet  for  Air. 


BUNSEN   FLAME 


When  in  operation  the  air  is  forced  in  the  center  of  the 
flame  through  the  inner  tube  by  compression,  and  the  requisite 
amount  of  oxygen  for  complete  combustion  thus  supplied. 

The  blowpipe  flame  consists  of  three  zones,  an  inner  one 
of  mixed  unburned  gas  and  air;  a  middle  zone  of  bluish  tinge, 


998  AN    OUTLINE    OF    METALLURGY 

and  an  outer  zone,  sligiitly  yellowish  in  color.  Just  beyond 
the  tip  of  the  inner  blue  flame  is  a  point  termed  the  reduc- 
ing flame.  If  this  flame  be  directed  upon  the  oxidized  surface 
of  a  metal,  for  example,  a  copper  coin,  the  surface  is  immedi- 
ately brightened,  and  tlie  oxide  removed.  This  is  due  to  the 
presence  of  particles  of  carbon  in  excess  in  this  part  of  the 
flame  uniting  with  the  oxygen  in  combination  with  the  copper, 
and  under  the  influence  of  heat  COo  is  formed,  and  passes  off 
as  a  gas,  leaving  the  metal  clean  and  untarnished. 

When  the  flame  is  removed,  however,  the  oxygen  from  the 
air  immediately  re-combines  with  the  copper  again,  unless 
some  means,  such  as  a  flux,  like  borax,  is  used  to  prevent  it. 

Near  the  extremity  of  the  outer  cone  is  a  point  known 
as  the  oxidizing  flame,   so-called  because,  when  applied  to 

..J^/pe  for  air. 
Space  for -4  as . 


Air  blast. 


'/ieduciriif  flame . 
Oxydiz  in4  f/'^''ne  ■ 


BLOWTIPE  FLAME 


metallic  surfaces,  regardless  of  how  bright  and  clean,  they 
immediately  become  oxidized  by  the  action  of  the  external 
air. 

In  all  soldering  operations,  therefore,  care  sliotild  be  taken 
to  cover  the  solder  and  the  surfaces  over  which  it  is  to  flow 
ivith  flux,  and  apply  the  reducing  flame. 

When  solder  is  applied  in  considerable  bulk,  as  in  back- 
ing crowns  and  dummies,  in  bridge  work,  the  flame  of  the 
blowpipe  should  be  continued  some  little  time  upon  the  fused 
solder,  to  jiermit  the  flux  in  the  deei)er  parts  to  find  its  way 
to  the  surface.  If  this  precaution  is  not  observed,  the  re- 
tention of  the  flux  in  the  solder  causes  pits  to  form  through- 
out the  mass,  and  in  grinding  down  and  finishing  the  piece 
these  are  frequently  exposed.  When  this  condition  occurs, 
the  case  requires  resoldering,  or  the  exposed  pits  must  be 
filled  by  plugging  with  material  of  essentially  the  same  char- 
acter as  that  of  which  the  piece  is  constructed. 


AN    OUTLINE    OF    METALLURGY  999 

MICRO    STRUCTURE    OF    METALS 

The  study  of  the  structure  of  metals  under  the  micro- 
scope is  a  field  apart  from  that  of  general  metallurgy,  and  may 
more  properly  be  included  in  the  science  of  metallography. 

It  is  impossible  to  obtain  sections  of  metals  transparent 
enough  for  examination  in  the  ordinary  manner  under  the 
microscope,  therefore  they  must  be  studied  by  reflected  light. 

The  surfaces  of  specimens  to  be  examined  are  first 
ground,  and  then  highly  polished. 

This  is  accomplished  by  the  use  of  stones  and  emery 
paper  of  gradually  increasing  fineness,  and  aftenvards  fin- 
ishing witli  fine  polishing  powder. 

Tlie  polished  surface  is  then  etched  with  very  dilute 
nitric  acid.  A  mixture  of  equal  parts  sulphuric  acid  and  bi- 
chromate of  potassium,  with  ten  times  its  bulk  of  water,  is 
frequently  used  for  this  purpose. 

The  etching  process  brings  out  the  structure  of  the  metal 
or  alloy  being  examined,  so  that  nnder  the  microscope  it  is 
readily  determined  whether  the  structure  is  crystalline,  gran- 
ular, or  amorphous. 

In  the  examination  of  some  steels  by  this  method  it  has 
been  observed  that  they  are  not  homogeneous  throughout,  but 
composed  of  imperfectly  crystallized  grains  called  ferrite, 
crystals  of  iron  and  carbon  called  cemenite,  and  a  combina- 
tion of  ferrite  and  cementite,  called  pearlite.  This  method 
of  examining  metals  and  alloys  has  proven  of  great  practical 
value  in  the  industrial  world,  for  by  it  the  means  of  producing 
the  best  qualities  of  crude  and  finished  material  have  been 
determined,  and  data  established  by  means  of  which  stock 
material  already  manufactured  may  be  selected  for  a  given 
])urpose. 

ALLOYS 

Most  of  the  metals  can  be  united  with  one  another  in 
various  proportions  by  the  aid  of  heat.  The  product  of  such 
a  combination  is  termed  an  alloy. 

Alloys  cannot  be  regarded  as  chemical  combinations,  al- 
though it  is  probable  in  some  instances  that  chemical  com- 
binations may  occur. 

MATTHIESSEN'S   THEORIES  AS   TO   THE   NATURE   OF  ALLOYS 

Mattliiessen  expressed  the  belief  that  an  alloy  of  two 
metals  may  be : 

First,  a  solution  of  one  metal  in  another. 


1000  AN    OUTLINE    OP    METALLURGY 

Second,  a  chemical  combination. 

Third,  a  mechanical  mixture. 

Fo^irth,  a  solution  or  mixture  of  two,  or  all  of  those  men- 
tioned, or  a  perfectly  homogeneous  diffusion  of  one  body  in 
another. 

AFFINITY  OF  METALS  FOR  EACH   OTHER 

The  affinity  of  metals  for  each  other  is  variable,  and  con- 
sequently they  will  not  alloy  uniformly.  A  good  example  of 
this  is  seen  by  melting  lead  and  zinc  together.  When  melted 
and  agitated  they  may  be  diffused  through  each  other,  but  if 
allowed  to  cool  slowly,  they  separate,  the  zinc,  being  lighter, 
rising  to  the  top,  while  the  lead  will  settle  to  the  bottom  of  the 
crucible. 

LIQUATION 

This  tendency  of  metals  to  separate  on  cooling  is  known 
as  liquation.  In  some  cases  it  can  be  overcome,  and  in  others 
partially  so,  by  breaking  up  the  ingot  and  remelting  it. 

OBJECT   IN    ALLOYING    METALS 

The  prime  object  in  alloying  metals  is  to  fit  them  for 
some  special  application  for  which  in  their  pure  state  they 
are  unfitted. 

Some  of  the  results  of  alloying  may  be  tabulated  as  fol- 
lows : 

1.  To  increase  strength,  elasticity  and  tenacity. 

2.  To  harden. 

3.  To  reduce  the  melting  point. 

4.  To  modify  the  color  or  structure. 

5.  To  facilitate  the  production  of  sound  and  workable 
castings. 

6.  To  resist  corrosion  or  oxidation. 

Examples :  Grold  is  alloyed  with  copper  and  silver  to 
harden  it ;  its  fusing  point  reduced  and  its  color  modified 
according  to  the  proportions  of  the  metals  used. 

Silver  is  rendered  harder  and  its  color  modified  by  the 
addition  of  copper. 

Copper  is  hardened  by  the  addition  of  zinc,  its  touglmess 
reduced,  and  its  reddish  color  changed  to  yellow,  as  is  appa- 
rent in  the  many-colored  brasses  produced.  Its  strength, 
tenacity,  and  elasticity  are  enhanced  by  the  addition  of  nickel. 

By  the  addition  of  tin  to  copper  an  alloy  known  as  bell 


AN    OUTLINE    OF    METALLURGY  1001 

metal  is  produced,  in  wbicli  is  developed  a  quality  of  sonor- 
ousness not  present  in  either  of  the  uncombined  metals. 

As  a  general  rule,  the  alloying  of  one  metal  with  another 
reduces  the  melting  point  of  the  most  difficultly  fusible,  and 
sometimes  reduces  the  fusing  point  of  the  alloy  below  that 
of  the  least  fusible. 

In  making  alloys,  if  the  fusing  points  of  the  metals  being 
combined  are  widely  separated,  it  is  best  to  melt  the  most 
refractory  first,  and  then  add  the  lower  fusing  constituents. 
This  will  prevent  to  a  great  extent,  at  least,  the  tendency  of 
the  latter  to  volatilize.  The  union  of  the  low  with  the  high 
fusing  metal  should  be  effected  at  as  low  a  temperature  as 
possible. 

EUTECTICS 

When  two  or  more  metals  are  fused,  and  combined  by 
heat,  on  cooling  down,  or  freezing,  certain  portions  of  the 
molten  alloy  frequently  exhibit  a  tendency  to  crystallize  be- 
fore the  entire  mass  solidifies.  Such  behavior  indicates  that 
the  union  by  fusion  of  the  component  metals  has  resulted  in 
not  one,  but  a  series  of  alloys,  differing  in  fusibility  and  usu- 
ally in  physical  properties. 

The  most  liquid  portion  of  the  alloy,  or  that  which  solidi- 
fies last,  is  called  a  entectic  alloy,  from  en,  well,  and  teko  fuse, 
meaning  well  fused.     (G-r.) 

The  formation  of  eutectics  may  be  partially  obviated  by 
stirring  the  molten  alloy  until  it  begins  to  congeal. 

When  metals  are  alloyed  in  certain  i^roportions  for  some 
definite  purpose,  as  in  the  compounding  of  solders  and  dental 
amalgam  alloys,  the  formation  of  eutectics  is  a  disadvantage 
because  the  component  metals  will  not  be  uniformly  diffused 
throughout  the  mass. 

AMALGAMS 

An  amalgam  is  an  alloy  of  two  or  more  metals,  one  of 
which  is  mercury. 

A  dental  amalgam  alloy  usually  consists  of  tin  and  sil- 
ver, to  which  is  sometimes  added  a  small  percentage  of  other 
metals,  such  as  platinum,  gold,  zinc,  copper,  etc.,  for  the  sup- 
posed improvement  of  color,  edge  strength,  hardness  and 
resistance  to  stress. 

As  a  matter  of  fact,  any  amalgam  alloy  will  in  time  dis- 
color in  the  mouth,  while  as  to  resistance  to  stress,  edge 
strength,  etc.,  it  has  been  demonstrated  that  an  alloy  of  silver 
and  tin  in  the  proportion  of  72.5  to  27.5,  when  properly  tern- 


1002  AN    OUTLINE    OF    METALLUIUIY 

pered  and  amalgamated,  i'ullils  the  requirementH  as  well  as 
most  of  the  alloys  containing  additional  metals. 

Dental  amalgam  alloys  are  finely  comminuted,  being 
either  in  the  form  of  filings  or  of  shavings,  in  order  to  fa- 
cilitate their  amalgamation  with  mercury. 

Copper  amalgam  consists  of  pure  copper  and  mercury 
usually  brought  into  combination  with  the  galvanic  current. 
It  softens  when  heated  and  hardens  again  on  cooling.  It  is 
used  very  often  in  the  tilling  of  temporary  teeth.  On  account 
of  its  tendency  to  discolor,  oftentimes  becoming  lilack,  it  is 
not  extensively  used  for  permanent  operations. 

SPECIFIC  GRAVITY  OF  ALLOYS 

The  specific  gravity  of  an  alloy,  as  a  rule,  differs  from 
the  mean  of  the  specific  gravities  of  its  constituents.  In  case 
of  contraction  occurring,  the  density  of  the  mass  has  in- 
creased, and  when  expansion  occurs,  the  reverse  condition 
prevails.  It  is  thought  probable  that,  when  the  density  of  an 
alloy  is  greater  than  the  mean  of  the  specific  gravities  of  the 
metals  involved,  chemical  combination  has  occurred. 

The  following  table,  by  Thenard,  illustrates  the  varia- 
tions of  density  in  a  number  of  alloys: 

Alloys     of     greater     specific     Alloys  of  lower  specific  grav- 
gravity    than    the    mean  ity  than  the  mean  of  their 

of  their  constituents.  constituents. 

Gold  and  zinc.  Palladium  and  Ijismuth. 

Gold  and  tin.  Gold  and  silver. 

Gold  and  bismuth.  Gold  and  iron. 

Gold  and  antimony.  Gold  and  lead. 

Gold  and  cobalt.  Gold  and  copper. 

Silver  and  zinc.  Gold  and  iridium. 

Silver  and  lead.  Gold  and  nickel. 

Silver  and  tin.  Silver  and  copper. 

Silver  and  bismuth.  Copper  and  lead. 

Silver  and  antimony.  Iron  and  Insmuth. 

Copper  and  zinc.  Iron  and  antimony. 

Copper  and  tin.  Iron  and  lead. 

Copper  and  palladium.  Tin  and  lead. 

Copper  and  bismuth.  Tin  and  palladium. 

Copper  and  antimony.  Tin  and  antimony. 

Lead  and  bismuth.  Nickel  and  arsenic. 

Lead  and  antimony.  Zinc  and  antimony. 
Platinum  and  molybdenum. 


AN    OUTLINE    OF    METALLURGY 


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1004  AN    OUTLINE    OF    METALLURGY 

GOLD 

Gold  has  been  known  and  nsed  from  the  remotest  an- 
tiquity, and  its  value  as  a  medium  of  exchange  recognized  by 
civilized  and  uncivilized  peoples  in  all   ages. 

Alchemy  was  defined  as  the  art  of  transmuting  the  base 
metals  into  gold  and  silver,  and  the  ancient  alchemists  ex- 
perimented with  this  end  in  view.  Their  labors,  however, 
while  not  accomplishing  the  discovery  of  this  much  desired 
process,  did  i-esult  in  the  discovery  of  many  curious  scientific 
truths  on  which  the  foundation  of  modern  chemistry  stands, 
and  thus  gold  has  played  a  very  important  part  in  the  ad- 
vancement of  science  and  civilization. 

There  is,  perhaps,  no  other  metal  whose  intrinsic  value 
has  remained  so  permanent  as  has  that  of  gold.  Its  compara- 
tive scarceness,  its  beautiful,  rich,  yellow  color,  the  ease  with 
which  it  can  be  worked  into  different  forms,  together  with 
the  fact  that  it  does  not  readily  tarnish  or  oxidize  under  ordi- 
nary conditions,  may  account  for  the  high  regard  in  which 
gold  is  held.  As  before  stated,  it  has  been  used  from  time 
immemorial  as  a  medium  of  exchange,  and  in  most  coun- 
tries to-day  is  the  basis  or  standard  of  the  monetary  systems. 

OCCURRENCE  AND  DISTRIBUTION 

Although  comparatively  scarce,  gold  is  found  qiiite  wide- 
ly distributed  over  the  earth.  It  occurs  native  or  in  metallic 
condition,  and  also  combined  with  silver,  lead,  tellurium,  or 
with  sulphides.  It  is  obtained  from  two  very  different 
sources;  first,  from  placer  or  alluvial  deposits  of  rivers  and 
streams,  both  ancient  and  modern,  and,  second,  from  veins 
in  rocks. 

PLACER  DEPOSITS 

The  placer  deposits  are  the  result  of  the  weathering  arid 
disintegration  of  the  rocks  carrying  the  vein  gold,  and  as 
these  fall  to  pieces  they  are  washed  down  stream  with  the 
sand,  gravel  and  soil  and  settle  in  the  beds  of  rivers.  In  time 
the  channels  of  the  streams  change,  and  the  beds  of  gravel 
or  placer,  bearing  the  gold,  ai'e  left  high  and  dry  sometimes 
miles  from  any  water.  The  vast  placer  deposits  on  the  west- 
ern slopes  of  the  Sierra  Nevada  mountains  are  supposed  to  be 
the  beds  of  ancient  rivers  long  since  obliterated. 

Placer  gold  is  usually  in  the  form  of  small  pellets,  flake^ 
or  rounded  grains,  the  larger  pieces,  those  weighing  i/o  ounce 
or  more,  being  called  nuggets.    The  largest  mass  of  gold  ever 


AN    OUTLINE    OF    METALLURGY  1005 

found  in  one  piece  was  taken  from  the  placer  deposits  of  Vic- 
toria, Australia,  and  weighed  183  poimds,  its  value  being  over 
$40,000.  Another  one,  the  "Blanch  Barkley"  nugget,  also 
found  in  Australia,  weighed  146  pounds.  A  nugget  was  found 
in  Prussia  in  1842  which  weighed  96  pounds,  and  in  Califor- 
nia a  number  of  pieces  have  been  found  which  weighed  20 
pounds  or  more.  These,  however,  are  rare  instances  of  gold 
occurring  in  large  masses,  the  usual  form  being,  as  before 


PANNING    PLACim   COLD 


stated,  in  small  flakes  and  grains,  and  frequently  as  fine  dust, 
the  particles  being  so  small  as  to  be  indistinguishable  without 
the  aid  of  a  lens. 

PLACER  MINING 

Gold  is  obtained  from  placer  deposits  in  several  ways,  the 
most  simple  of  which  is  by  means  of  the  "pan."  This  con- 
sists of  a  shallow  vessel,  usually  of  sheet  iron,  about  14  or  16 
inches  in  diameter  and  two  or  three  inches  deep,  in  which  the 


AN    OUTLINE    OF    METALLURGY 


soil  bearing  the  gold  is  placed.  This  is  then  held  in  water 
and  the  pan  given  a  rotary  and  side-to-side  motion,  which 
washes  out  the  soil  and  sand  and  leaves  the  gold  in  the  bot- 
tom of  the  pan. 


^^  ^  --^vV    ,J-^-  ^.^   -X 


WASHING   I'LAVEIt   i;()I,ll    IN 


The  cradle  is  a  similar  device,  constructed  on  a  some- 
what larger  scale,  for  washing  larger  quantities  of  soil. 

The  sluice  is  a  convenient  means  of  washing  still  larger 
quantities  of  soil  where  running  water  is  convenient.  It  con- 
sists of  a  long  flat-bottomed  trough  set  on  a  slight  incline  so 
that  the  water  mav  readilv  run  through  it  from  end  to  end. 


WASHING   PlyACER  GOLD    IN  A  SI.L'IC'E 


Across  the  bottom,  sti'ips  are  placed  parallel  with  the 
water  current,  and  others  are  placed  at  right  angles  to  these, 
thus  forming  a  series  of  small  comi)artments  which  con- 
tain mercury.  Since  mercury  has  a  strong  affinity  for  gold, 
the  smallest  particles  are  saved  in  this  manner.     The  soil 


AN    OUTLINE    OF    METALLURGY  1007 

is  thrown  into  the  upper  end  of  the  shiice  and  the  current 
washes  it  down  over  the  ridges,  the  lighter  particles  being 
thus  carried  off,  leaving  the  gold  amalgam  in  the  bottom. 

At  regular  intervals  the  mercury  charged  with  the  gold 
is  removed,  placed  in  retorts  and  subjected  to  heat.  This  dis- 
tills off  the  mercury  and  leaves  the  gold.  The  mercury  is  re- 
covered by  conducting  its  vapor  into  suitable  condensers, 
when  it  is  again  ready  for  use. 

These  sluices  vary  from  a  few  feet  to  several  hundred  in 
length,  those  used  in  hydraiilic  mining  often  being  a  mile  long. 

In  the  small  sluices  the  soil  is  thrown  in  with  shovels, 
while  in  hydraulic  mining  it  is  loosened  by  a  large  forcible 
stream  of  water  directed  against  the  bank  or  hill  of  gravel  by 
means  of  a  hose  with  nozzle.  The  water  used  for  tearing 
down  the  soil  is  directed  into  the  sluices  and  is  utilized  for 
washing  the  gravel. 

VEIN  GOLD 

When  gold  is  found  in  veins  in  rocks,  the  rock  or  min- 
eral with  which  it  is  associated  is  first  mined,  then  crushed  to 
reduce  it  all  practically  to  a  powder.  This  is  accomplished  by 
first  crushing  the  rock  into  small  pieces,  and  then  stamping 
tlic  l)i-oken  pieces  of  special  machinery  called  a  stamp  mill. 

EXTRACTION  OF  GOLD  FROM  ORES 

More  or  less  variation  exists  in  the  construction  and 
operation  of  stamp  mills,  depending  principally  on  the  char- 
acter of  the  ore  to  be  reduced.  Stamp  mills  are  usually  built 
on  a  side  hill  or  inclination  having  a  fall  of  at  least  30  feet  in 
the  length  of  the  mill.  For  economical  reasons  they  should  be 
situated  convenient  to  both  fuel  and  water. 

The  inclination  of  the  ground  enables  the  various  pieces 
of  machinery  to  be  placed  so  tliat  gravity  carries  the  crushed 
ore  from  one  to  the  other  without  difficulty.  In  the  highest 
part  of  the  mill  is  placed  the  platform,  which  receives  the  ore, 
and  from  which  it  is  shoveled  into  the  crusher.  This  breaks 
the  mineral  into  pieces  ?i  inches  or  less  in  diameter,  in  which 
condition  it  is  carried  down  to  the  stamp  mill. 

The  stamp  mill  consists  of  large,  flat-bottomed  iron  mor- 
tars, into  which  are  fitted  heavy  iron  pestles,  each  weigliing 
from  500  to  1,000- pounds.  These  are  lifted  by  cam  devices, 
keyed  on  a  revolving  horizontal  shaft,  and  fall  by  their  own 
weight.  Stamps  are  usually  ranged  in  line,  in  groups  of  five 
stamps  each,  operating  in  a  connnon  mortar  box.     A  stream 


1008  AN    OUTLINE    OF    METALLURGY 

of  water  carries  tin?  pulverized  material  against  amalgamated 
copper  plates,  placed  in  the  sides  of  the  mortar,  the  mercury 
ou  which  retaius  llic  gold,  wliilc  tlie  earthy  couslitucuts  are 
washed  away. 

At  intervals,  before  the  mercury  has  become  saturated 
with  the  gold,  the  plates  are  removed  and  scraped,  and  the 
amalgam  thus  collected  subjected  to  powerful  pressure  in 
leather  bags.  This  squeezes  out  the  excess  of  mercury 
through  the  pores  of  the  leather.  The  thick  amalgam  remain- 
ing is  then  placed  in  retorts,  subject  to  heat,  and  the  mer- 
cury distilled  off. 

The  gold  remains  in  the  retort  in  a  spongy  state,  and  is 
usually  quite  free  from  other  metals,  with  the  exception  of 
silver.  It  is  then  melted  with  suitable  fluxes,  cast  into  bars 
and  shipped  as  bullion. 

CHLORINATION   PROCESS 

Gold  ores  can  be  reduced  and  the  gold  freed  by  means 
of  chlorine  gas.    The  process  is  as  follows : 

The  ore  is  first  crushed,  then  roasted  to  expel  sulphur, 
arsenic,  antimonj^  or  other  volatile  substances  that  may  be 
present.  The  roasted  ore,  slightly  dampened,  is  then  placed 
in  wooden  vats  having  false  bottoms. 

When  the  vats  are  charged,  close-fitting  covers  are  placed 
over  them  and  chlorine  gas  is  introduced  under  the  false  bot- 
tom. This  in  time  rises  through  the  false  bottom  and  into  the 
moistened  ore,  converting  the  gold  into  a  soluble  chloride, 
which  is  afterward  removed  by  washing.  From  this  solution 
the  gold  can  be  precipitated  by  the  sulphate  of  iron. 

CYANIDE  PROCESS 

This  iDrocess  is  much  in  favor  in  many  parts  of 
the  world  because  of  its  cheapness  and  from  the  fact  that 
low-grade  ores  which  cannot  be  worked  economically  by  other 
processes  can  be  reduced  profitably  by  this  method. 

The  advantage  of  the  cyanide  over  the  chlorination  pro- 
cess lies  in  the  fact  that  in  the  method  under  consideration 
it  is  unnecessary  to  roast  the  ore. 

The  process  is  as  follows :  The  ore  is  first  crushed,  and 
in  this  condition  is  placed  in  vats  with  false  bottoms  sim- 
ilar to  those  used  in  the  chlorination  process,  but  deeper. 
Water  containing  a  small  percentage  of  c}'anide  of  potassium 
is  then  added  to  the  contents  and  allowed  to  slowly  percolate 
through  the  mass.    This  process  is  known  as  lixiviation.    The 


AN    OUTLINE    OF    METALLURGY 


gold  is  dissolved  by  the  cyanide  and  carried  out  in  solution, 
when  it  is  afterward  precipitated  by  zinc  shavings. 

PHYSICAL  PROPERTIES 

The  fusing  point  of  pure  gold  is  106-1  deg.  C,  its  specific 
gravity  19.4,  malleability  and  ductility  first  rank,  tenacity 
seventh  rank,  conductivity  of  heat  53.3,  electricity  76.7,  and 
specific  heat  .0324. 

PREPARATION    OF   PURE    GOLD 

In  the  dental  laboratory  gold  scraps  and  filings  accumu- 
late, and  these  can  be  refined,  the  base  metals  eliminated  and 
the  pure  gold  reduced  to  the  desired  carat  by  alloying  with 
pure  metals  in  proper  proportions. 

Filings  should  be  spread  on  a  paper  and  a  liorsesboe  mag- 
net passed  back  and  forth  through  them  to  remove  any  par- 
ticles of  iron  that  may  be  present.  They  should  then  be 
treated  with  acids,  to  remove  such  of  the  baser  metals  as  are 
not  actually  alloyed  with  the  gold. 

The  gold  is  now  placed  in  a  flat-bottomed  flask  that  may 
be  subjected  to  heat  without  breaking  and  covered  with  aqua 
regia.  This  is  composed  of  two  parts  of  concentrated  hydro- 
chloric to  one  part  of  nitric  acid.  Heat  is  then  applied  and 
additions  made  to  the  acid  from  time  to  time  until  the  gold  is 
all  in  solution. 

The  solution  is  then  weakened  with  water  and  filtered.  If 
any  silver  is  present,  it  will  be  retained  on  the  filter  paper. 
The  solution  should  be  further  dihited  until  only  very  slightly 
acid.  A  clear  solution  of  ferrous  sulphate  is  now  slowly  add- 
ed and  time  allowed  the  gold  in  solution  to  precipitate.  This 
usually  requii'es  several  hours.  The  clear  liquid  is  then 
drawn  off  and  the  brown  precipitate  of  metallic  gold  is  heat- 
ed several  times  with  dilute  hydrochloric  acid  to  remove  iron. 
The  precipitate  is  then  thoroughly  washed  to  remove  every 
trace  of  acid,  dried  out,  the  filter  paper  carrying  the  gold 
folded  and  placed  on  charcoal  block  or  in  furnace,  borax  and 
saltpeter  added  and  the  metal  fused. 

TREATMENT  OF  SCRAP  PLATE 

When  the  clippings  from  plate  of  the  same  carat  are 
allowed  to  accumulate  and  kept  separate,  these  may  be  simply 
remelted,  cast  into  the  ingot  mold  and  rolled  out  into  plate 
of  the  required  thickness  without  the  necessity  of  refining. 


mUl  AN    OITTLINI';    OF    MKTALLUKGY 

ALLOYING  GOLD 

For  most  dental  purposes,  with  the  exception  of  foil  for 
filling  and  plate  for  backing  porcelain  facings,  gold  is  reduced 
in  fineness.  That  in  most  common  nse  for  crowns  and  bridges 
is  22  C.  and  21.6  C.  (coin  gold) ;  20  and  18  C.  gold  is  used  for 
dentures. 

The  term  carat,  used  in  this  connection,  indicates  the 
nunilier  of  parts  of  pure  gold  there  is  in  an  alio}'.  Pure  gold 
is  called  24  carat,  and  may  be  regarded  as  24-24ths  pure; 
22  carat  is  22-24ths  pure,  or  22  parts  pure  gold  and  2-24  alloy; 
20  carat  is  20-24ths  pure  and  4-24  alloy,  etc. 

REDUCTION  OF  GOLD 

The  dentist  can  make  his  own  gold  plate  and  solder  of 
any  desired  carat,  if  ordinary  skill  is  exercised. 

Gold  plate  of  a  known  carat  can  be  increased  or  decreased 
in  fineness  by  the.  addition  of  pure  gold,  or  of  gold  plate  of  a 
higher  or  lower  carat.  This  process,  whether  raising  or  low- 
ering, is  called  rcchtcf'wn. 

BOSER'S  RULE 

A  general  rule  that  answers  for  l)oth  methods  is  that 
known  as  Boser's  rule.  "The  difference  betiveen  the  carat  of 
gold  used  to  reduce  with  and  the  required  carat,  is  to  the  dif- 
ference betiveen  the  required  carat  and  the  carat  of  gold  to 
be  reduced,  as  the  iveight  of  the  gold  to  he  reduced  is  to  the 
iveight  of  reduction  metal  required.  The  iveight  of  the  entire 
mass,  when  alloyed,  may  be  found  by  adding  the  iveight  of 
gold  reduced  to  the  weight  of  reduction  metal  required." 

U.  S.  gold  coin  is  90  per  cent  pure  gold  and  10  jjer  cent 
alloy  (silver  and  copper),  or  21.6  carat  fine.  This  is  fre- 
quently employed  in  crown  and  bridge  work.  It  is  a  little 
darker  in  color  than  22  carat  gold  because  of  the  percentage 
of  copper  contained,  and  is  more  difficult  to  work,  since  it  is 
harder  and  stiffer;  22  carat  gold  is,  perhaps,  most  generally 
used  in  crown  and  bridge  work,  and  20  carat  and  18  carat  in 
denture  construction. 

Pure  gold  is  frequently  used  for  backing  teeth  because 
of  its  softness  and  ease  of  adaptation  to  the  porcelain. 

An  alloy  of  75  parts  pure  gold  and  25  parts  pure  silver 
(18  carat)  is  sometimes  used  for  backing  teeth  when  it  is 
necessary  to  impart  a  greenish  tinge  to  the  porcelain.  Tliis 
alloy  is  known  as  green  gold. 


AN    OUTLINE    OF    METALLURGY 


GOLD  SOLDERS 


Most  solders  contain  a  trace  of  zinc  or  cadmium  to  re- 
duce the  fusing  point  of  the  gold  so  that  solder  of  a  given 
carat  may  be  fused  upon  plate  of  tlie  same  carat  without 
danger  of  melting  the  latter. 

Dr.  Dorrance  gives  the  following  alloy  as  a  practical  one 
for  making  good  colored  gold  solders : 

Pure  silver   1  part 

Pure  zinc 2  parts 

Pure  copper   3  parts 

These  are  melted  together  to  form  an  alloy,  the  coppei 
and  silver  being  melted  first,  after  which  the  zinc  is  added 
quickly  in  small  pieces  and  the  mass  stirred  to  insure  thor- 
ough mixing  of  the  metals,  then  poured  into  water  to  granu- 
late it. 

If  20  carat  solder  is  desired,  it  can  be  made  by  taking  4 
parts  of  this  alloy  and  20  parts  pure  gold;  18  carat  gold 
solder  may  be  made  by  taking  6  parts  of  the  alloy  and  18  parts 
pure  gold,  etc. 

The  proportion  of  the  zinc  in  most  solders  is  1  to  21  parts 
of  the  entire  alloyed  mass. 

Dr.  W.  H.  Trueman  recommends  the  following  solders  as 
being  of  good  color,  easy  flowing,  and  as  tough  as  gold  plate. 
An  excess  of  zinc  is  added  to  compensate  for  some  slight  loss 
from  volatilization : 

22  Carat  Solder.  18  Carat  Solder. 

Pure  gold  22         Gold  18 

Copper   1        Copper 2 

Zinc    114     Silver 3 

Zinc    11/2 

TABLE    OF   MIXED    CARATATION 

Tlie  following  table  gives  the  proportions  of  the  various 
metals  used  in  jewelers'  gold  plate: 

Carats.  Copper. 

23  1/2 

22  1 

20  2 

IS  3 

IG  .' 5 

15  r 6 

14  7 

12  SV2 

10  10 

8  10% 


Silver. 

Gold. 

V2 

23 

1 

22 

2 

20 

3 

18 

3 

16 

3 

15 

3 

14 

SVa 

12 

4 

10 

5% 

8 

lOllJ  AN    OUTLINE    OK    METALLUKGY 

Gold  i)late  may  be  made  l)y  using  all  copper,  or  all  silver, 
as  the  alloying  agent,  Init  its  color  is  materially  changed  in 
either  case,  becoming  darker  when  alloyed  with  the  former, 
and  lighter  or  of  a  green  tinge  when  alloyed  with  the  latter. 

As  before  stated,  pure  gold  may  be  reduced  in  tineness 
without  material  change  of  color  l)y  the  use  of  silver  and  cop- 
per in  pro]ior  proportions. 

CLASP   GOLD 

Platinum  is  added  to  gold  to  impart  elasticity  to  it,  and 
when  gold  is  so  alloyed  it  is  called  clasp  'metal.  The  follow- 
ing formula  is  one  recommended  by  Harris : 

20  carat  clasp  gold : 

Pure  gold    20  dwt. 

Coijper   2  dwt. 

Silver    1  dwt. 

Platinum 1  dwt. 

Clasp  gold  is  usually  made  of  26,  24  and  22  gauge,  the 
thickness  of  plate  required  for  a  given  case  depending  on  the 
length  of  teeth  to  be  clasped,  long  teeth  requiring  thin,  and 
short  teeth  thick,  plate.     (See  Clasp  Metals,  ])age  1033.) 

PLATINUM  SOLDER 

Formerly  jolatinum  base  plates,  dentures  and  the  metal 
parts  of  porcelain  crowns  and  bridges  were  soldered  with  pure 
gold,  but  this  method  was  not  satisfactory,  because  the  gold 
diffused  itself  into  the  platinum  and  formed  a  brittle,  crys- 
talline alloy,  incapable  of  resisting  much  stress.  For  this 
reason  the  use  of  pure  gold  as  a  solder  for  platinum  has  been 
abandoned  and  an  alloy  of  gold  and  platinum  substituted  by 
which  the  difficulty  mentioned  is  obviated : 

No.  1. 

Pure  gold    75  parts 

Pure  platinum   25  parts 

No.  2. 

Pure  gold 80  parts 

Pure  platinum   20  parts 

No.  3. 

Pure  gold    85  parts 

Pure  platinum   15  parts 


AN    OUTLINE    OF    METALLURGY  1013 

SOME  RECENT  WORK  CONCERNING  GOLD  ALLOYS 

The  following  section,  from  page  1013  to  1063,  is  the  result 
of  a  series  of  recent  researches  in  gold  alloys  and  kindred 
subjects.,  by  Dr.  L.  J.  Weinstein  of  New  York,  the  copyright 
of  which  he  holds. 

This  section  was  written  specially  for  and  will  appear  in 
Dr.  F.  A.  Peeso's  work  on  "Bemovable  Crown  and  Bridge 
Work,"  now  in  press. 

The  author  of  this  valuable  contribution  has  kindly 
granted  the  writer  the  privilege  of  its  presentation  in  this 
Ijook. 

AUTHOR'S  PREFACE 

"In  the  preparation  of  this  contribution,  it  has  been  the 
aim  of  the  author  to  present  a  brief  and  practical  rather  than 
an  academic  discussion  of  the  subject. 

"In  addition  to  a  consideration  of  the  gold  alloys,  it  was 
found  advisable  to  include  a  section  on  the  closely  allied  and 
important  sul)jects  of  refractory  materials  and  fluxes  used  in 
connection  with  gold,  during  soldering  or  casting  operations. 

"The  series  of  investigations,  upon  which  this  contribu- 
tion is  based,  was  started  during  the  year  1908,  when  the 
author  experienced  considerable  difficulty  in  attempting  the 
execution  of  removable  bridge  work  along  the  lines  laid  down 
by  Dr.  Peeso. 

"In  attempting  to  use  the  coin  gold  and  modifications  of 
same  in  the  form  of  solders,  he  was  seriously  handicapped  by 
the  comparatively  low  melting  point  of  the  coin  gold  and  the 
inadequacy  of  the  other  gold  alloys  usually  obtainable,  which, 
to  the  man  of  exceptional  skill,  is  not  so  apparent  as  to  one 
of  average,  or  even  less  than  average,  skill. 

"In  view  of  the  well-known  fact  that  platinum  is  a  metal 
that  could  be  alloyed  with  gold  to  increase  the  melting  point 
of  the  latter,  a  number  of  experiments  were  made  to  produce 
a  formula  for  a  gold  alloy  sufficiently  high  in  melting  point 
so  that  it  could  be  used  as  a  substitute  for  coin  gold  and 
thereby  eliminate  the  process  of  "sweating,"  which,  in  the 
hands  of  the  author  and  many  other  novices,  was  a  more  or 
less  hazardous  procedure,  and  instead,  soldering  the  resultant 
high  fusing  gold  with  other  gold  of  a  melting  point  equal  to 
that  of  24  or  22k.,  and  thus  obtaining  a  strong  union  that 
would  withstand  the  subsequent,  and  often  numerous,  solder- 
ing operations  required  for  the  completion  of  the  case. 


1014  AN    OUTLINK    OF    METALLURGY 

"The  alloys  finally  (Icvclopcd  wore  found  so  satisfactory 
that  it  is  not  too  mucli  to  say  that  even  in  the  hands  of  the 
most  skilled  operator  these  alloys  will  prove  of  considerable 
value,  if  for  no  other  reason  than  the  very  great  difference  in 
the  melting-  point  between  the  highest  and  lowest  fusing  alloys 
in  the  series  and  the  consequent  increased  facility  and  safety 
during  the  necessary  subsequent  soldering  operations. 

"In  the  author's  efforts  to  obtain  information  from  which 
to  formulate  alloys  he  was  greatly  handicapped,  inasmuch 
as  there  were  no  dental  publications  bearing  to  any  extent  on 
the  subject.  After  a  thorough  study  of  the  then  recently  re- 
vised books  on  dental  metallurgy,  a  number  of  experiments 
were  made,  the  results  of  which  did  not  appear  to  correspond 
with  the  data  in  the  text  books.  A  number  of  works  on  general 
metallurgy  were  consulted  and  found  to  differ  materially  with 
the  dental  text  books  in  a  great  many  instances,  particularly 
on  data  concerning  the  properties  of  the  binar.y  alloys  of  gold 
and  silver,  gold  and  platinum,  etc.  In  order  to  establish  a 
definite  foundation  upon  which  to  base  further  researches,  the 
author  proceeded  to  make  a  series  of  binary  alloys  and  from 
the  resultant  data  was  enabled  to  proceed  with  the  develop- 
ment of  more  complex  alloys. 

"The  resultant  formute  given  herein  have  been  in  prac- 
tical use  for  a  period  ranging  from  two  to  five  years,  and  while 
the  author  does  not  claim  that  his  is  by  any  means  the  last 
word  on  the  subject,  he  trusts  that  the  results  of  his  research 
will  prove  of  some  immediate  benefit  to  both  advanced  students 
and  practitioners. ■ . ' ' 

INTRODUCTION 

The  elements  following  gold  have  been  divided  into  four 
groups.  This  division  is  an  arbitrary  one,  and  made  solely 
for  the  purpose  of  facilitating  future  references.  (See  table 
1,  page  1015.) 


BINARY  ALLOYS 

It  is  a  well-known  fact  that  pure  gold  has  but  a  limited  use 
in  the  construction  of  various  dental  appliances  and  that  it 
is  necessary  to  alloy  it  with  various  other  metals  in  order  to 
increase  its  durability,  hardness,  tenacity  and  to  vary  the  melt- 
ing point  above  or  below  that  of  pure  gold,  as  may  be  re- 
quired.   The  metals  in  common  use  for  this  purpose  have  been 


AN    OUTLINE    OF    METALLURGY 


copper,  silver  and  platinum,  the  latter  to  a  Hunted  extent; 
also  zinc,  cadmium,  etc.,  for  solders,  which,  of  course,  require 
a  considerably  lower  melting  point  than  the  gold  upon  which 
thev  are  to  lie  used. 


NECESSITY   OF   A   KNOWLEDGE   OF   BINARY   ALLOYS 

A  thorough  knowledge  of  the  properties  of  the  simple 
binary  alloys  is  of  paramount  importance,  because  these  prop- 
erties almost  invariably  give  an  indication  of  what  may  be 
expected  from  more  complex  alloys. 

It  is  generally  accejjted  by  metallurgists  that  l)inary  alloys 
of  gold  and  silver,  copper,  platinum  or  palladiiuii  form  solid 

TABLE  NO.  1. 
THE  MELTING  POINTS*  AND  DENSITIES  OF  METALS. 


Name  of  Metal 

Symbol 

M.P.'F 

M.P.'C 

Density 

GOLD 

Au 

1945 

1063 

19.3 

GROUP 

I 

Silver 

Copper 

Platinum 

Palladium 

Ag 
Cu 
Pt 
Pd 

1761 
1981 
3190 
2820 

960 
1083 
1755 
1550 

10.5 
8.9 
21.5 
11.4 

Iridium 

Ir 

Os 
Rh 

4170 
4900 
3525 

2300 
2700 
1940 

22.5 
22.5 
12  1 

GROUP 
11 

Osmium 

Rhodium 

Zn 
Cd 

Sn 
Al 

787 
610 
460 
1218 

420 
321 
232 
658 

8  6 
7.3 
2.7 

GROUP 

III 

Tin 

Aluminum 

GROUP 

Nickel 

Cobalt 

Manganese 

Chromium 

Tantalum 

Ni 
Co 
Mn 
Cr 
Ta 
W 
Mo 

v 

Ti 

2646 
2714 
2237 
2750 
5160 
5430 
450n 
31.50 
3450 

1452 
1490 
1225 
1510 
2,S50 
3000 
2500 
1730 
1900 

8.9 
8.7 
7.4 
6.9 

14  5 

15  7 
8,6 
6.1 
4.5 

IV 

Tungsten 

Molvbdenum 

Vanadium 

"From  Circular  No.  35,  U.  S.  Bureau  of  Standards. 

solutions.  That  is,  solutions  of  one  metal  in  another,  if  in 
proportions  within  certain  limits.  Such  binary  alloys  as  will 
be  discussed,  form  solid  liomogeneous  solutions  except  when 
otherwise  noted. 

It  is  therefore  unnecessary  to  enter  into  an  academic  dis- 
cussion of  the  possible  molecular  affinity  existing  among  vari- 
ous elements  or  of  eutectics  formed  between  the  metals  in 
the  binary  alloys  that  will  be  considered,  because  such  com- 
pounds or  mixtures  do  not  occur  in  such  alloys  as  may  be  con- 
sidered fit  for  use  in  the  mouth.  For  example,  alloys  of  gold 
and  copper  in  the  proportion  of  82  per  cent  gold  to  18  per  cent 
copper  (by  weight)  form  a  eutectic,  which  is  tlie  lowest  fus- 


1016  AN    OUTLINK    OF    METALHTRGY 

ing  of  the  gold  copjaer  series,  and  wlicu  more  than  18  per  cent 
copper  is  present  the  copper  is  not  in  uniform  solution  and 
segregates.  As  the  alloys  containing  over  15  per  cent  copper 
are  extremely  brittle  and  lack  uniformity,  no  binary  alloys 
containing  more  than  10  to  12  per  cent  copper  will  be  consid- 
ered. In  other  words,  alloys  of  gold  and  coppei",  where  cop- 
per does  not  exceed  12  or  13  per  cent,  do  not  form  any  com- 
pounds with  special  characteristics. 

To  simplify  the  references  to  ternary,  quaternary  or 
more  complex  combinations  of  metals,  alloys  of  only  two 
metals  will  be  termed,  as  is  customary,  "binary,"  but  the 
alloys  composed  of  three  or  more  metals  will  be  termed  "com- 
plex" alloys. 

SECTION  I. 

GOLD  AND  SILVER 

Silver  is  commonly  utilized  as  an  alloying  element  with 
gold.  It  is  used,  to  a  considerable  extent,  as  part  of  the  alloy 
in  dental  golds,  and,  as  will  be  shown  later,  principally  as  a 
cheapening  agent. 

EFFECT   OF   SILVER   UPON   GOLD 

There  seems  to  prevail  generally  an  erroneous  concep- 
tion regarding  the  properties  of  silver-gold  alloys.  It  has 
been  stated*  that  silver  is  used  to  harden  and  to  lower 
the  melting  j^oint  of  gold.  This  deduction  is  distinctly  con- 
trary to  the  results  obtained  by  the  author.  After  making  a 
number  of  binary  alloys,  it  was  proven  that  even  the  maximum 
percentage  that  may  be  used  in  dental  work,  say  25  per  cent 
of  silver  to  75  per  cent  gold,  does  not  confer  any  perceptible 
hardness  upon  the  gold,  neither  does  it  lower  the  melting 
point  to  such  an  extent  that  the  difference  could  be  measured 
with  a  pyrometer. 

Practically  the  only  effect  silver  (even  if  present  to  the 
extent  of  25  per  cent)  has  upon  gold  is  to  discolor  the  gold, 
making  it  greenish,  and  lower  the  specific  gravity,  thus  in- 
creasing the  volume.  It  will  thus  be  seen  that  silver  confers 
no  special  benefit  upon  gold,  except  cheapening  it  and  acting 
as  a  color  modifying  agent.  On  the  other  hand,  it  may  prove 
detrimental,  as  a  considerable  proportion  of  silver  may  inter- 
fere with  the  action  of  other  alloying  elements  when  attempt- 


*Essig's  Metallurgy   (Koenig's  revision),  p.  163. 
♦Hodgen's  IVTetallurgy   (Milberry's  revision),  p. 


278. 


AN    OUTLINE    OF    METALLURGY  1017 

ing  to  produce  a  complex  gold  alloy,  and  also  on  account  of  the 
strong  affinity  that  oxygen  and  other  gases  possess  for  silver. 
It  will  thus  be  readily  seen  that  small  percentages  may  some- 
times be  used  to  advantage  as  a  color  modifying  agent,  but 
a  large  percentage  of  silver  is  distinctly  contraindieated. 

Silver,  in  such  proportions  as  may  be  needed  for  dental 
golds,  alloys  uniformly  and  without  difficulty  and  may  be  de- 
pended upon  to  remain  in  uniform  distribution. 

The  author  has  found  that  gold  alloys,  with  a  high  j^er- 
centage  of  silver,  when  remelted  and  cast,  show  in  the  casting 
a  considerable  variation  of  the  silver  content  which  indicates 
that  a  partial  separation  takes  ]ilace.     This  lii^s  not  been  in- 

Melting  Points  Or  Alloys 
Of  Gold  And  Silver. 


PERCENTAOE  WEIGHT    Or    SILVER 

5%   Ag.    M.P  1945"^.      1063°C. 

10%    •• 

15%  ■•       ■■  1943°  r.    loez'-c. 

30%    •■           ■•  1942^.      1061°  C, 


vestigated  further  for  the  reason  that  castings  of  gold  with 
a  high  percentage  of  silver  have  no  practical  application. 
As  stated  before,  small  percentages  of  silver  have  practically 
no  effect  upon  the  gold  and  this  fact  has  been  taken  advan- 
tage of  for  a  considerable  period  of  time  by  at  least  one  manu- 
facturer who  alloys  pure  gold  with  from  one  to  two  per  cent 
of  silver  and  sells  it  as  24k.  This  alloy  appears  so  similar  to 
pure  gold  that  the  ordinary  eye  is  deceived  and  the  unprinci- 
pled manufacturer  is  the  gainer. 

Fig.  1  illustrates  the  melting  point  curve  of  gold-silver 
alloys. 

Practically  the  same  determination  appears  in  very  re- 
cent works  on  metallurgy.* 

♦Penchel's  Metallurgy. 


1018  AN    OUTLINE    OF    METALLURGY 

Hilvor-platimim  alloys  have  been  used  to  a  considerable 
extent  for  crown  posts,  dowels,  backings,  etc.  As  a  rule, 
alloys  of  this  character  (20  to  30  per  cent)  are  extremely  un- 
satisfactory, both  during  their  manipulation  and  in  ultiiuate 
service,  and  their  use  should  be  avoided.  They  are  somewhat 
improved  with  higher  percentages  of  platinum,  but  the  alloys 
are  extremely  non-uniform  and  still  quite  solui)le  in  acids  and 
apt  to  discolor  and  corrode.  The  cost  with  more  platinum 
is  considerably  higher,  and  even  then  the  alloys  are  not  equal 
to  a  fair  grade  of  alloyed  gold,  either  in  usefulness  or 
economy. 

GOLD  AND  COPPER 

Copper  is  one  of  the  most  commonly  used  and  most  use- 
ful alloying  elements.  It  confers  hardness  and  elasticity 
upon  gold,  but  is  detrimental  when  used  in  large  proportions 
on  account  of  its  great  tendency  to  lower  the  melting  point  of 
the  alloy  and  the  strong  oxidation  and  brittleness  of  the  alloys 
when  the  copper  is  in  high  proportion.  It  is,  however,  a  most 
useful,  and,  in  fact,  an  indispensable  alloying  element  if  em- 
ployed judiciously.  Alloys  of  gold  and  copper,  such  as  U.  S. 
coin  gold  (An.  90  Gu.  10),  have  been  used  with  most  satis- 
factory results,  both  from  the  standpoint  of  durability  and 
resistance,  against  action  of  the  oral  fluids,  and  an  alloy  of 
this  character  is  ideal  for  crown  work,  except  for  the  disad- 
vantage of  its  low  melting  point,  which  is  caused  by  the  cop- 
per content,  and  its  range  of  usefulness  is  therefore  limited 
even  in  the  hands  of  the  skilled  operator.  This  inadequacy, 
as  will  be  shown  later,  can  be  corrected  by  substituting  pla- 
tinum, etc.,  for  some  of  the  copper,  tlms  raising  the  melting 
point  and  reducing  oxidation  without  changing  the  valuable 
properties  the  coin  gold  possesses,  namely,  strength  and  dur- 
ability. 

Fig.  2  illustrates  the  melting  point  curve  of  gold-copper 
alloys. 

As  will  be  seen  from  the  chart,  the  melting  point  of  pure 
gold  drops  rapidly  upon  the  addition  of  copper;  5  per  cent 
copper  lowers  the  melting  point  about  100  degs.  F.,  10  per 
cent  copper  lowers  the  melting  point  of  gold  about  200  degs. 
F.,  15  per  cent  copper  lowers  the  melting  point  about  250  degs. 
F.,  and  18  per  cent  causes  a  drop  in  melting  point  of  about 
300  degs.  F.  As  will  be  seen  from  the  illustration,  the  lowest 
melting  point  between  gold  and  copper  is  when  18  per 
cent  cu.  is  present.    The  addition  of  more  than  18  per  cent  cu. 


AN    OUTLINE    OF    METALLURGY  1019 

causes  a  rise  in  melting  point  until  the  melting  point  of  cop- 
per, 1980  degs.  F.,  is  reached. 

As  mentioned  previously,  it  is  advisable  to  limit  the  total 
copper  content  to  10  or  12  per  cent.  Consequently,  if  the 
melting  i^oiiit  of  an  alloy  of  gold  and  copper  of  requisite 
strength  and  hardness  is  too  low,  it  is  necessary  to  use 
platinum  or  palladium  to  bring  it  to  the  point  desired. 

The  valuable  properties  of  copper  as  a  hardening  agent 
have  ajiparently  been  underestimated  by  writers,  but  taken 


Melting  Points  Of  Alloys 
Of  Gold  And  Copper. 

/ 

\ 

/ 

/ 

\ 

/ 
/ 

/ 

\ 

/ 

\ 

\ 

^ 

/' 

leso 

V 



PERCCNTACt    WEI6MT    OF    COPPER 


5%   Cu. 

10%   •■ 

15%     " 

18%    ■• 


1840^. 
1735°F. 
1690°F, 
166  IT, 


1004"'C. 
946°C 
9E1°C. 
905''C. 


advantage  of  by  manufacturers,  as  will  be  noted  in  the  com- 
position of  commercial  clasp  metals. 


GOLD  AND  PLATINUM 

Platinum  is  being  used  to  some  extent  as  an  alloying  ele- 
ment with  gold  principally  for  clasp  metal,  etc.  It  has  been 
stated  that  platinum  confers  great  elasticity  and  hardness 
upon  gold,  which  appears  correct,  only  to  a  limited  extent. 
The  author's  experiments  have  indicated  that  platinum  has 
comparatively  little  effect  as  a  hardening  agent  upon  gold.  It 
does,  however,  raise  the  melting  point  considerably,  as  will 
be  shown  later. 


AN    OUTLINE    OF    METALLURGY 


Platinum  is  much  inferior  to  copper  as  a  hardening  agent. 
This  is  readily  proven  upon  an  examination  of  a  binary  alloy 
of  gold  and  copper  containing  10  per  cent  cojaper  and  a  binary 
alloy  of  gold  and  platinum  containing  25  per  cent  platinum 
(so  called  platinum  solder).  A  comparison  of  two  pieces  of 
equal  dimensions  will  show  that  the  gold-copper  alloy,  with  10 
per  cent  copper,  is  fpiite  as  hard  and  elastic  as  the  gold  alloy 

Melting  Points  Of  Alloys 
Of  Gold  And  Platinum 


/ 

^7- 

/ 
/ 
/ 

/ 

/' 

/ 

/ 

/ 

/ 

/ 

r 

/ 

/ 

0 

0 

0           3 

0             4 

0            5 

0           6 

0             7 

0            8 

0              S 

0            100 

percentage:  weight  of  platinum 


5%  Pt. 
10%  " 
15%  ■• 
20%    •■ 


BOIS-F, 
2085°F, 
2165°F, 
2260"^. 


1102°C. 
1141°C. 
1165°C 
1228°C 


with  25  per  cent  platinum,  and  more  uniform.  It  is  there- 
fore evident  that  platinum  is  not  the  most  suitable  hardening 
agent  and  its  range  of  usefulness  as  an  alloying  element  is 
therefore  limited. 

Platinum,  however,  is  an  excellent  adjunct  to  copper,  as 
it  tends  to  raise  the  melting  point,  which  is  lowered  sensibly 
by  any  considerable  ijercentage  of  copper. 

Fig.  3  illustrates  the  melting  point  curve  of  gold- 
platinum  alloys. 


AN    OUTLINE    OF    METALLURGY  1021 

Large  percentages  of  platinum  cannot  be  alloyed  uni- 
formly with  gold,  and  in  order  to  insure  a  uniform  alloy  it  is 
not  advisable  to  use  more  than  5-10  per  cent  in  a  binary  alloy 
and  10-15  per  cent  in  a  complex  alloy.  In  the  latter  the  other 
alloying  elements  help  to  hold  the  platinum  in  uniform  dis- 
trihution.  If  it  is  desired  to  raise  the  melting  point  of  an 
au.-cu.  alloy  higher  than  5-10  per  cent  platinum  makes  pos- 
sible, it  is  advisable  to  use  palladium,  which  combines  per- 
fectly in  both  the  binary  and  complex  alloys  that  will  be  con- 
sidered. 

GOLD  AND   PALLADIUM 

Palladium  is  as  yet  a  comparatively  rare  metal.  It  has 
been  used  to  some  extent  in  the  industries  and  arts,  but  prac- 
tically to  no  extent  in  dental  golds.  Palladium  is  a  metal 
very  similar  to  platinum  except  for  its  specitic  gravity,  11.4, 
which  is  considerably  lower  than  platinum  and  its  melting 
point,  which  is  also  considerably  lower  than  that  of  platinum. 


TABLE   2 
MELTING    POINTS    OF    BINARY    ALLOYS 


GOLD, 

1945°  F,  1063°  C 

GOLD, 

1945°  F,  1063°  C 

SILVER,    1761°  F,     960"  C 

PLATI 
Gold 

NTUM,    3190°  F,  1755°  C 

Gold 

95%— Silver     5% 

95%— Platinum     5% 

1945°  F 

2015°  F 

1063°  C 

1102°  C 

Gold 

907c— Silver  10% 

Gold 

90%,— Platinum  10% 

1945°  F 

'  2085°  P 

1063°  C 

1141°  C 

Gold 

85%— Silver  15% 

Gold 

85%— Platinum  15% 

1943°  F 

2165°  P 

1062°  C 

1165°  C 

Gold 

70%— Silver  30% 

Gold 

80c;— Platinum  20% 

1942°  F 

2260°  P 

1061°  C 

1228°  C 

GOLD, 

1945°  F,  1063°  C 

GOLD, 

1945°  P,  1063°  C 

COPPER,   1980°  F,  1083°  C 

PALLA 
Gold 

DIUM,  2820°  P,  1550°  C 

Gold 

95% — Copper     5% 

95%— Palladium     5% 

1840°  F 

2060°  P 

1004°  C 

1127°  C 

Gold 

90%,— Copper  10% 

Gold 

90%— Palladium  10% 

1735°  F 

2145°  F 

946°  C 

1174°  C 

Gold 

85%— Copper  15% 

Gold 

85':;— Palladium  15% 

1690°  P 

2250°  P 

921°  C' 

1232°  C 

Gold 

82%— Copper  18% 

Gold 

80',— Palladium  20% 

1661°  F 

2340°  P 

905°  C 

1282°  C 

1022  AN    OUTLINE    OF    METALLURGY 

It  has  been  stated  that  palladium  makes  gohl  brittle. 
This  is  contrary  to  the  author's  findings.  More  than  twenty- 
five  different  alloys  were  made  containing  from  1  to  30  per 
cent  palladium.  All  of  them  api)eared  perfectly  uniform  and 
remarkably  malleable,  ductile  and  tenacious. 

Palladium  also  forms  excellent  uniform  alloys  with  co])- 
per,  silver,  etc.,  and  it  is  a  very  valuable  adjunct  to  i)latinuni 


2500 
2450 

Melting  Points  Or  Allots 
Of  Gold  And  Palladium. 

, 

--'' 

■' 

*' 
•^ 

2350 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

0            1 

3             2 

0          i 

0             4 

0            5 

0            6 

0             7 

9            S 

0            3 

P          100 

plrcentage;    weight  or  palladium 


5%   Pd.    MP 
10%    •■ 
15%    •• 

20%    •• 


2060°F. 
2145-F. 
2250°F. 
2340-?. 


U27»C. 
1174»C. 

1282''C 


in  complex  gold  alloys.  Its  use,  however,  is  limited  on  ac- 
count of  the  fact  that  it  exerts  a  strong  decolorizing  action 
upon  gold,  3-5  per  cent  turning  gold  sensibly  lighter  and  15 
to  20  per  cent  almost  white  (platinum  color). 

Fig.  4  illustrates  the  melting  point  curve  of  gold-pal- 
ladium alloys. 

Another  remarkable  and  most  valuable  property  that  pal- 
ladium possesses  is  the  fact  that,  although  the  melting  point, 


AN    OUTLINE    OF    METALLURGY  1023 

2820  degs.  F.  (1550  degs.  C),  is  considerably  lower  tliau  that 
of  platinum,  a  given  percentage  of  palladium  (by  weight) 
will  increase  the  melting  point  of  gold  more  than  an  equal 
amount  of  platinum,  and  in  view  of  the  fact  that  platinum  in 
considerable  percentages  does  not  alloy  uniformly  with  gold, 
it  is  well  to  use  palladium,  as  it  alloys  uniformly  with  gold  in 
all  proportions.  Therefore,  in  alloys  where  color  is  no  object, 
palladium  may  lie  incor]iorato(]  to  very  great  advantage. 

GOLD  AND  METALS  IN  GROUP  II 
IRIDIUM 

Iridic  platinum  is  usually  employed  in  place  of  pure 
platinum  on  account  of  its  greater  hardness  and  dui-ability. 
When  experimenting  with  the  series  of  binary  alloys  previ- 
ously discussed,  it  naturally  occurred  to  the  author  that  gold 
alloyed  with  iridic  platinum  instead  of  pure  platinum  would 
prove  superior  to  gold  alloyed  with  pure  platinum.  A  number 
of  alloys  were  attempted  and  the  results  obtained  were  found 
invariably  inferior  to  alloys  of  gold  and  pure  platinum.  The 
unsatisfactory  results  should  have  been  anticipated  because 
it  is  well  known  that  iridium  will  not  alloy  with  gold  uniform- 
ly, but  segregates  on  account  of  its  extremely  high  melting 
point  and  high  specifie  gravity.  It  is  quite  certain  that  in 
attempting  to  make  the  alloy,  the  following  occurred :  When 
the  iridio-platinum  was  brought  into  the  gold,  the  heat  used 
was  sufficient  to  melt  the  ])latinum  and  set  free  the  particles 
of  iridium  which  did  not  go  into  solution  with  the  gold  plat- 
inum mixture,  but  susyjended  and  then  segregated  in  the  same 
way  as  if  free  iridium  were  added  to  gold  without  the  pres- 
ence of  the  platinum. 

The  experimental  alloys  were  made  of  pure  gold  and  15 
per  cent  iridio-platinum  and  compared  with  alloys  made  of 
pure  gold  and  15  per  cent  platinum.  On  rolling  both  to  equal 
gauge,  polishing  and  etching,  the  gold-platinum  alloy  was 
found  quite  uniform,  whereas  some  sections  of  the  gold  iridio- 
platinum  alloy  (?)  were  harder  and  higher  fusing,  while 
other  sections  were  softer  and  lower  fusing  than  the  gold- 
platinum  alloy.  In  addition,  all  the  gold-platinum-iridiura 
mixtures  appeared,  streaky  and  non-uniform,  even  to  the  naked 
eye,  while  the-g'old-platinmn  alloys  appeared  almost  perfect, 
even  under  the  microscope. 

Numerous  other  ex]ieriments  were  made  along  these  lines, 
and  in  spite  of  the  fact  that  some  have  advocated  the  use  of 


1024  AN    OUTLINE    OF    METALLURGY 

iridio-platiniim  instead  of  pure  platinum  in  alloys,  it  is  the 
autlior's  conclusion  that  pure  platinum  is  far  superior  to 
iridio-))latinuin  as  an  alloying  element  with  gold. 

OSMIUM 

No  attempts  have  yet  been  made  to  form  alloys  with 
osmium,  as  it  is  even  higher  fusing  than  iridium  and  therefore 
poor  results  may  be  anticipated.  The  author  expects,  how- 
ever, to  experiment  with  osmium  shortly  to  determine  if  there 
is  any  possible  benefit  to  be  derived  from  it,  because  alloys  of 
Os.  per  cent  are  claimed  to  be  superior  to  alloys  of  Ir.  per 
cent.* 

RHODIUM 

Rhodium  is  a  metal  of  the  platinum  group  that  will  prove 
of  considerable  benefit  if  sufficient  of  it  can  be  obtained  at  a 
moderate  cost.  It  is  quite  similar  to  palladium.  It  also  has  a 
low  specific  gravity,  12.1,  and  is  considerably  higher  fusing 
than  platinum  (according  to  U.  S.  Bureau  of  Standards). 

The  author  has  not  experimented  with  it  in  the  pure  state, 
but  procured  a  quantity  of  it  in  the  form  of  platinum  con- 
taining 10  per  cent  rhodium.  This  platinum-rhodium  alloy 
was  used  for  a  considerable  time  instead  of  pure  platinum. 
The  alloys  were  quite  satisfactory,  but  the  advantages  over 
pure  platinum  as  an  alloying  agent  are  so  slight  and  the  cost 
so  high  that  it  appeared  advisable  to  discontinue  its  use  at 
the  time. 

GOLD   AND   METALS   IN    GROUP  III 

A  discussion  of  gold  and  metals  in  Group  III  will  be  found 
in  the  section  on  Gold  Solders,  page  10o6. 

GOLD  AND  METALS  IN  GROUP  IV 

Some  time  after  the  introduction  of  recent  casting  proc- 
esses, it  became  apparent  that  in  order  to  utilize  such  proc- 
esses to  advantage,  alloys  other  than  ordinarily  obtainable 
would  have  to  be  made  in  order  to  insure  satisfactory  results. 
The  ordinary  plate  golds  obtainable  when  cast  in  small  bulk 
were  too  soft  and  frail,  and  the  sections  had  to  be  cast  larger 
and  heavier  than  normal  and  were  therefore  objectionable. 

A  number  of  experiments  were  made  in  attempting  to  cast 
the  various  clasp  metals  and  the  results  obtained  were  very 
unsatisfactory.    At  this  time  began  to  appear  literature  re- 

*F.    Zimmerman,    Alloy    of    Platinum    and    Osmium,    U.    S.    Patent    No. 
1055119. 


AN    OUTLINE    OF    METALLURGY  1025 

garding-  industrial  alloys,  both  ferrous  and  non-ferrous,  with 
the  so-called  rare,  or  little  known,  metals,  such  as  nickel, 
cobalt  manganese,  tungsten,  vanadium,  etc.,  enumerated  in  the 
table  of  elements  under  group  4. 

Some  remarkable  results  were  obtained  in  various  indus- 
trial steels,  brasses  and  bronzes  and  it  was  not  unreasonable 
to  expect  that  some  of  these  rare  metals  could  be  utilized  to 
advantage  in  the  formation  of  gold  alloys  for  casting  pur- 
poses. 

In  view  of  the  fact  that  there  was  no  precedent  to  follow 
and  no  literature  on  the  relation  of  these  metals  to  gold  ob- 
tainable, it  can  readily  be  understood  that  the  author's  at- 
tempts to  alloy  these  rare  metals  with  gold  were  more  or  less 
empirical  and  the  results  obtained  wei'e  no  better  than  should 
have  been  anticipated.  Meeting  with  such  poor  success,  the 
author  proceeded  with  the  series  of  researches  into  both  the 
binary  and  complex  alloys  of  gold  with  the  elements  in  groups 
one,  two  and  three,  and  the  resultant  formulte  developed  are 
given  in  the  following  pages. 

Since  then  a  number  of  experiments  have  been  made  by 
other  investigators  in  attempting  to  utilize  some  of  the  rare 
metals,  such  as  nickel,  tungsten,  molybdenum,  titanium,  etc., 
as  substitutes  for  iridio-platinum.  The  resiilts  so  far  have 
not  proven  successful. 

This  non-success  will  not  appear  strange  to  those  familiar 
with  both  the  chemical  and  physical  characteristics  of  the  ele- 
ments mentioned.  Unless  some  radical  method  of  handling 
these  metals  is  evolved  iridio-platinum  will  continue  to  retain 
the  position  it  occupies.  See  "elastic"  gold  under  clasp 
metals.) 

The  author  has  not  hy  any  means  given  up  hope  of  the 
possible  utilization  of  some  of  the  "rare"  elements  in  connec- 
tion with  alloys  for  casting.  He  is  now  engaged  in  a  series 
of  experiments  which  have  already  shown  promising  results 
and  he  hopes  to  have  data  of  importance  available  for  pub- 
lication in  the  near  future. 

SECTION  II 
A  NEW  SERIES  OF  ALLOYS 

From  the  ]ireceding  data  on  the  properties  of  the  binary 
alloys  of  gold  wilIi  the  metals  in  group  one,  certain  conclu- 
sions may  be  drawn  and  data  obtained  and  it  then  becomes 
a  comparatively  simple  matter  to  form  complex  alloys  for 
our  requirements.     Before  proceeding  to  formulate  a  com- 


1026  AN    OUTLINE    OF    METALLURGY 

plex  alloy,  it  will  be  well  to  consider  again  the  hardness  con- 
ferred upon  gold  by  the  metals  in  group  one. 

As  will  be  seen  from  Fig.  5,  pure  silver  has  practically  no 
effect  on  gold  as  far  as  increasing  the  hardness.  Palladium 
has  some  hardening  properties  and  it  is  well  to  bear  that  in 
mind  when  formulating  an  alloy.    Platinum  has  considerably 

100%  Au 

90%  Au-|0%A^. 

90%Au-|0%Pd. 

90%Au.-IO%Pt 


Comparative  Haedne$s  Or  Binary  Alloys 
Of  Gold  With  10%  Ag..  Pd,  Pt..  and  Cu. 

FIGURE  5 

more  hardening  jiower  than  palladium  and  is  a  factor,  but  cop- 
per is  the  most  valuable  agent  of  them  all  and  in  proceeding 
to  formulate  the  complex  alloys  we  must  consider  the  copper 
as  the  principal  hardening  agent  and  the  others  as  adjuncts. 

GOLD    FOR   CROWN.   BRIDGE    AND    PLATE   WORK 

Bearing  in  mind  the  hardening  power  and  the  effect  on 
melting  point  produced  by  the  alloying  elements,  let  us  con- 
sider such  a  formula  as  the  following: 

Fonmila  of  Gold  Plate  No.  1 

Per  Cent 

Gold 88.0 

Platinmn 7.5 

Palladium 2.5 

Silver 2.0 

Total 100.0 

Melting  point,  2075  degs.  F.,  1135  degs.  C. 

This  alloy  is  equivalent  in  hardness  to  ordinary  22k.  gold, 
containing  91.6  per  cent  gold,  3.5  to  -t  per  cent  copper  and  4.5 
to  5  per  cent  silver — 100  per  cent.  Now,  as  the  co]iper  is  the 
acti\'e  hardening  agent  in  the  22k.  gold,  and  as  we  know  from 
the  preceding  data  that  jilatinum  and  palladium  exert  some- 
what less  than  half  of  the  hardening  influence  of  copper,  it 
will  be  seen  that  the  total  of  10  parts  platinum  and  palladium 


AN    OUTLINE    OF    METALLURGY  1027 

are  about  equal  in  liardeuing  loower  to  the  3.5  to  4  parts  of 
copper  usually  present  in  l22k.  gold,  and  thus  we  get  an 
alloy  equivalent  in  hardness  to  the  ordinary  22k.  plate. 

The  silver  content,  2  parts,  is  no  factor  whatever,  except 
as  a  color  modifying  agent,  because  it  is  an  object  to  adhere 
to  a  certain  standard  of  color  throughout  the  whole  series  of 
alloys.  As  there  is  no  copper  present  in  this  alloy,  it  is  abso- 
lutely non-oxidizable,  but  the  great  advantage  that  an  alloy  of 
this  character  possesses  over  ordinary  22k.  plate  is  the  fact 
that  its  melting  point  is  much  above  that  of  ordinary  22k.  gold, 
approximately  225  degs.  F  to  250  degs.  F.  higher,  and  instead 
of  sweating  a  band  and  floor  it  may  be  very  easily  soldered 
with  pure  gold  or  22k.  plate  and  resoldered  with  the  same  or 
lower  grade  plate  gold  innumcralile  times  without  any  dan- 
ger of  burning  or  blistering. 

Any,  or  all,  of  the  alloys  in  the  series  following  plate  No. 
2  may  be  safely  used  as  solders  on  plate  No.  1,  thus  permit- 
ting many  soldering  operations  tcifhoiif  dauger  of  hurning  the 
gold,  as  may  occur  in  sweating,  or  the  danger  of  the  solder 
(if  poor  quality)  burning  into  and  alloying  with  the  gold,  as 
often  occurs  when  using  the  so-called  "easy  flowing"  solders. 
It  is  evident,  therefore,  that  this  alloy  offers  a  great  many 
advantages  over  the  ordinary  22k.  plate  gold. 

GOLD  PLATE  NO.  2 

As  has  been  impressed  by  Dr.  Peeso.  it  is  absolutely 
essential  to  use  for  removable  bridge  work  a  hard,  durable 
gold  such  as  U.  S.  coin  gold.  It  may  be  well  at  this  time  to 
state  that  U.  S.  coin  gold  contains  90  per  cent  pure  gold  and 
30  per  cent  copper,  whereas  the  so-called  coin  gold  obtainable 
from  most  supph"  houses  contains,  as  a  rule,  some  silver, 
which  softens  it  and  makes  it  icork  more  easily,  and  it  there- 
fore does  not  possess  the  strength  and  durability  required. 

The  following  formula  replaces  coin  gold  most  satisfac- 
torily : 

Formiihi  of  Gold  Plate  No.  2 

Per  Cent 

Gold 84.5 

Platinum 8.5 

Palladium 2.0 

Silver  .- 0.5 

Copper  4.5 

Total    100.0 

Melting  point,  1975  degs.  F.,  1080  degs.  C. 


1028  AN    OUTLINE    OF    METALLURGY 

In  this  formula,  in  order  to  obtain  the  equivalent  hard- 
ness of  coin  gold,  it  is  necessary  to  use  copper.  We  can  again 
readily  see  just  how  the  hardening  properties  of  the  alloying 
elements  are  utilized.  We  have  4.5  per  cent  copper  and  the 
platinum  and  palladium  replace  the  rest  of  the  copper,  thus 
giving  us  an  alloy  equal  to  U.  S.  coin  gold.  This  oxidizes, 
of  course,  to  a  slight  extent,  but  the  oxidation  is  not  objec- 
tionable, and  this  alloy  can  be  used  to  replace  coin  gold  prac- 
tically for  every  purpose  and  may  be  soldered  with  other  al- 
loys in  the  series  which  have  the  same  color.  When  soldered 
with  casting  gold,  B  or  C,  the  attachment  of  the  floor  to  a 
band  cannot  open  up  during  the  final  soldering  unless  de- 
liberately abused,  because  the  soldered  junctions  are  actually 
higher  in  melting  point  than  ordinary  gold  plate. 

The  fusing  point  of  this  alloy  is  approximately  225  degs. 
F.  higher  than  coin  gold,  and  it  possesses  all  the  advantages 
over  coin  that  the  No.  1  formula  has  over  22k.  gold. 

These  alloys,  Nos.  1  and  2,  can  be  utilized  to  great  ad- 
vantage in  the  construction  of  swaged  plates,  both  full  and 
partial,  especially  where  it  is  desired  to  make  the  plates  of 
two  or  three  thin  layers,  on  account  of  the  high  melting  point 
of  the  alloys  which  permits  of  thorough  soldering  of  the 
laminfE  without  danger  of  burning.  When  used  in  conjunc- 
tion with  the  other  alloys  in  the  series,  these  golds  enable  the 
operator  to  produce  dentures  far  superior  to  those  made  from 
the  golds  ordinarily  employed  on  account  of  increased 
strength,  minimized  bulk  and  perfect  color  harmony  through- 
out the  whole  structure. 

It  should  be  borne  in  mind  that  high  fusing  golds,  such  as 
these,  cannot  be  "sweated"  advantageously.  This  is  a  char- 
acteristic of  all  gold  alloys  high  in  platinum  metals,  on  account 
of  the  total  absence  of  or  minimum  oxidation.  The  "sweat- 
ing" of  an  alloy  such  as  coin  gold  is  facilitated  by  the  fact  that 
the  high  oxidation  of  the  copper  content  helps  to  prevent  tlie 
flow  of  areas  not  fluxed. 

ALLOYS  FOR  PROSTHETIC  CASTING 

As  has  been  previously  stated,  in  order  to  cast  sections 
of  bridge  work,  saddles,  partial  plates,  etc.,  it  is  essential  to 
have  alloys  that  are  rigid  in  the  cast  form  to  obviate  the 
necessity  for  increased  bulk.  Again,  the  value  of  the  harden- 
ing properties  of  the  allojdng  elements  becomes  apparent,  as 
in  the  following : 


AN    OUTLINE    OF    METALLURGY  1029 

FoDiiitIa  of  Castiiiq  Gold  "B" 

Per  Cent 

Gold 80.0 

Platinum   9.5 

Palladium 2.5 

Silver 1.0 

Copper    7.0 

Total   100.0 

Melting  point,  1900  degs.  F.,  1035  degs.  C. 

We  have  here  7  per  cent  copper  and  a  total  of  12  per  cent 
of  the  platinum  metals  which  makes  an  alloy  considerably 
harder  than  coin  gold.  When  cast,  this  alloy  is  about  mid- 
way in  hardness  between  rolled  coin  gold  and  clas^D  metal. 
The  melting  point  of  this  alloy  is  about  50  degs.  F.  below  pure 
gold.  It  is  intended  for  use  with  the  nitrous  oxide  blow-pipe 
and  should  be  melted  with  same,  if  a  considerable  quantity  of 
gold  is  to  be  cast.  Sufficient  quantities  for  small  castings  can 
be  melted  with  the  ordinary  blow-pipe.  The  copper  content 
being  comparatively  low  permits  of  the  use  of  the  nitrous- 
oxide  blow-pipe  without  any  material  change  or  deterioration 
of  the  alloy,  if  a  suitable  reducing  flux  is  used  in  connection 
with  it. 

This  alloy  corresponds  in  color  with  plates  Nos.  1  and  2 
and  may  be  used  to  cast  cusps  or  cusps  and  contours  directly 
to  bands  of  either  plate  No.  1  or  plate  No.  2.  It  makes  a 
particularly  suitable  gold  for  cast  occlusal  surfaces  on  account 
of  its  hardness  and  durability. 

The  next  formula  is  a  modification  of  "B"  and  brings  out 
an  interesting  point  in  connection  with  the  effect  of  copper 
and  the  platinum  metals  on  the  decrease  and  increase  of  melt- 
ing points. 

Fonintla  of  Castiiu/  Gold  "C" 

Per  Cent 

Gold 80.5 

Platinum 6.5 

Palladium 2.0 

Silver   2.0 

Copper  9.0 

Total    100.0 

Melting  point,  1800  degs.  F.,  980  degs.  C. 

We  note  in  this  fornmla  an  increase  of  two  parts  of  co]i- 
per  and  a  decrease  of  a  total  of  3.5  parts  platinum  and  pal- 


1030  AN    OTITLINE    OF    METALUTnOY 

liulium,  tlie  conscKjucnce  being  that  tlic  melting-  point  is 
<li()])ped  ))y  tlie  increase  of  copp(;r  and  by  tlie  decrease  of  the 
j^latinnni  inetals.  The  melting  i)oint  is  droi)ped  about  100 
degs.  F.  and  brought  down  to  a))])roxiniately  that  of  22k.  gold. 
This  lowering  of  the  melting  point  permits  this  alloy  to  be 
melted  readily  for  large  or  small  eastings  with  an  efficient 
illuminating  gas  and  air  blow-pipe.  It  is  identical  in  strength; 
hardness,  color,  etc.,  with  casting  gold  "B"  except  the  fusing 
point  and  resistance  to  the  nitrous-oxide  blow-pipe  flame.  If 
the  latter  is  used,  precaution  must  be  taken  to  use  a  reducing 
flux  and  not  superheat  the  metal.  This  applies  to  coin  gold, 
too,  if  same  is  cast.  Excessive  heat,  if  applied  with  the  ni- 
trous-oxide blow-pipe,  and  lack  of  a  suitable  reducing  flux  will 
permit  the  oxidation  of  considerable  copper  and  the  dissem- 
ination of  oxide  throughout  the  casting. 

GOLD  FOR  INLAY  CASTING 

Since  the  introduction  of  the  casting  process,  pure  gold 
has  been  generally  advocated  for  cast  fillings,  etc.,  on  account 
of  its  supposed  minimum  shrinkage,  softness  and  malleabil- 
ity and  consequent  ease  with  which  the  margins  could  be  bur- 
nished to  eliminate  the  cement  line  of  an  inlay. 

A  good  many  operators  have  failed  to  cast  pure  gold  sat- 
isfactorily and  claim  that  they  can  cast  inlays  with  scrap  gold 
and  produce  better  and  sharper  margins.  To  those  who  have 
not  experienced  this  difficulty  it  may  appear  very  strange,  but, 
nevertheless,  it  is  a  fact  that  alloyed  gold,  when  properly 
alloyed,  and  under  fair  casting  conditions,  invariabl.y  casts 
with  sharp,,  true  margins,  whereas  pure  gold  has  very  often 
failed  to  accomplish  the  purpose,  both  at  the  hands  of  the 
aiithor  and  many  others. 

It  may  be  well  to  consider  that  the  casting  of  scrap  gold 
of  indefinite  composition  is  rather  a  hazardous  and  usually 
unsatisfactory  ^^I'ocedure,  and  a  great  many  operators  recog- 
nizing that  fact  are  using  22k.  gold,  coin  gold,  etc.,  with  bet- 
ter results  than  they  have  been  able  to  obtain  with  pure  gold. 

It  is  a  well-known  fact  that  pure  platinum,  pure  palla- 
dium and  pure  silver  absorb  hydrogen,  oxygen  and  other  gases 
while  in  the  molten  state  and  retain  some  of  the  gases  upon 
solidification.  It  is  not  generally  known,  but  nevertheless 
true,  that  pure  gold  absorbs  nitrogen,  hydrogen  and  oxygen, 
and  retains  a  considerable  percentage  of  one  or  more  of  the 
absorbed  gases  upon  solidification.*     This  tendency  on  the 

*T.  K.  Rose   (in  Metallurgy  of  Golci),  quoting  Roberts-Austen. 


AN    OUTLINE    OF    METALLURGY  1031 

part  of  the  metals  meutioued  to  absorb  gases  is  minimized 
and  sometimes  entirely  eliminated  by  alloying  and  a  small 
percentage  of  copper,  palladinm  or  platinnm  will  materially 
alter  the  behavior  of  pure  gold  upon  solidification.  Castings 
made  with  a  slightly  alloyed  pure  gold  will  be  found  to  pos- 
sess sharp  margins  and  practically  equal  to  pure  gold  in 
color,  ductility  and  facility  of  burnishing,  but  comparativel>' 
free  from  cavities  or  blow-holes,  such  as  are  often  found  in 
the  unalloyed  gold  castings. 

A  number  of  eases  under  observation  have  shown  that  fill- 
ings of  slightly  alloyed  gold  do  not,  after  a  period  of  wear, 
present  the  same  pitted  surface  so  characteristic  of  east  pure 
gold  fillings  under  the  same  conditions. 

The  rounding  of  the  margins  in  cast  pure  gold  fillings  is 
usually  accompanied  by  a  separation  of  the  residue  button 
from  the  casting,  which  takes  place  just  prior  to  the  comple- 
tion of  solidification.  This  occurs  particularly  when  a  com- 
paratively large  sprue  is  used  and  more  especially  when  a 
large  residue  button  is  used  at  the  same  time.  An  explanation 
of  this  occurrence  may  reasonably  be  attributed  to  the  follow- 
ing: If  the  sprue  is  quite  large  and  the  gold  residue  button 
large,  the  residue  remains  fluid  for  a  considerable  period  of 
time  after  the  casting  pressure  has  been  applied  and  there 
appears  to  be  a  tendency  for  the  large  button  to  draw  to  it  the 
gold  of  the  casting  through  the  medium  of  the  large  gate  (the 
sprue).  A  large  button  of  gold  very  often  draws  only  part 
of  the  sprue  to  it,  thus  separating  the  connection  between  the 
residue  button  and  the  casting  and  arresting  the  exercise  of 
the  casting  pressure  which  would  otherwise  be  transmitted 
from  the  button  to  the  sprue  and  then  to  the  casting  proper. 
For  those  who  wish  to  use  pure  gold  for  casting  it  is  suggested 
that  the  quantity  of  gold  used  in  the  casting  operation  should 
not  exceed  more  than  three  pennyweights  above  the  amount 
actually  required  for  the  casting  proper,  and  also  that  the 
sprue  be  no  larger  than  16  gauge  B.  and  S.  This  will  serve  to 
lessen  the  area  of  connection  between  the  casting  and  residue 
button  so  that  this  area  (the  sprue)  may  solidify  more  rapidly 
and  in  conjunction  with  the  smaller  button,  which  naturally 
freezes  more  rapidly,  tend  to  prevent  the  separation  previ- 
ously discussed. 

Another  ]ioint'  that  is  well  to  consider  is  the  fact  that 
alloying  of  gold  reduces  the  surface  tension  and  cohesion  of 
the  molecules  while  in  a  molten  state  and  increases  the  fluid- 
ity,  thus  facilitating  the   flow   of  the   metal,   requiring  less 


1032  AN    OUTLINE    OF    METALLURGY 

pressure  to  force  the  gold  into  the  mold,  and  consequently 
lessening  the  danger  of  distorting  the  mold.  (See  investment 
compounds  for  casting.) 

Fonmihi  of  ('asliiig  (jold  "A" 

Per  Cent 

Gold 97.0 

Platinum 1.5 

Palladium 0.3 

Silver 0.3 

Copper  0.9 

Total   ..100.0 

Melting  point.  1945  (legs.  F.,  1063  degs.  C. 

This  alloy  makes  an  efficient  substitute  for  pure  gold,  as 
the  comparatively  small  amount  of  alloy  does  not  harden  the 
gold  sufficiently  to  prevent  burnishing,  nor  does  it  affect  the 
color  perceptibh'.  Copper  is  the  most  suitable  agent  for  in- 
creasing the  fluidity  and  the  small  percentage  used  does  not 
materially  harden  the  gold.  The  drop  in  melting  point  is 
compensated  for  by  the  platinum,  and  the  small  percentage  of 
silver  counteracts  the  coloring  effect  of  the  copper  on  the 
gold,  the  consequent  alloy  possessing  practically  the  same 
melting  point  as  pure  gold  and  producing,  almost  invariably, 
sound  castings  without  the  special  precautions  which  must  be 
taken  when  pure  gold  is  used. 

This  alloy  will  be  found  suitable  for  use  in  teeth  close  to 
others,  with  fillings  or  inlays  made  of  pure  gold,  in  order  to 
maintain  color  harmony. 

As  all  the  alloys  in  the  series,  excepting  the  casting  gold 
A  and  the  elastic  alloy  described  later,  are  practically  of  a 
uniform  color  and  somewhat  lighter  (grayish  red)  and  less 
conspicuous  than  pure  gold  or  coin  gold,  it  has  been  found 
advisable  to  also  formulate  an  alloy  for  casting  inlays  to 
harmonize  in  color  with  the  rest  of  the  series. 

Foiiniihi  for  Casting  Gold  " D" 

Per  Cent 

Gold 95.0 

Palladium 3.3 

Silver   .  . '. 0.4 

Copper  1.3 

Total   100.0 

Melting  point,  1945  degs.  F.,  1063  degs.  C. 


AN    OUTLINE    OF    METALLURGY  1033 

In  this  alloy,  the  palladium  decolorizes  the  pure  gold  and 
raises  the  melting  point.  The  copper  brings  it  back  to  the 
pure  gold  standard  and  by  the  addition  of  the  small  percent- 
age of  silver  to  counteract  the  reddening  effect  of  the  copper 
a  color  elTect  is  obtained  in  perfect  harmony  with  the  rest  of 
the  series. 

This  gold  is  quite  soft  and  malleable  and  may  be  bur- 
nished with  ]3ractically  the  same  facility  as  pure  gold.  This 
question  of  burnishing  margins  of  inlays  is  rather  a  more  or 
less  indefinite  procedure.  It  is  the  author's  opinion  that  very 
little  effective  burnishing  (spinning)  can  be  done  on  inlay 
margins  and  that  only  after  the  margins  are  stoned  down  to 
an  extremely  thin  edge.  Experience  has  shown  that  it  is 
advisable  to  use  hard  and  duralile  alloys  for  inlays,  especially 
those  intended  to  aid  in  supporting  liridge  work  and  then  only 
when  supplemented  with  posts  or  dowels. 

This  alloy  D  can  be  combined  with  B  or  C  to  obtain 
harder  alloys,  with  no  difficulty  and  no  change  in  color,  thus 
enabling  the  operator  to  obtain  practically  any  degree  of 
hardness  for  special  requirements  in  inlay  casting. 


SECTION  III 
CLASP  METALS 

The  alloys  known  as  clasp  metal,  or  platinized  gold,  as 
ordinarily  obtainable,  have  been  used,  with  poor  results,  for 
casting  sections  of  bridge  woi'k,  etc.,  and  are  being  used  to  a 
large  extent  and  with  but  mediocre  results  as  a  substitute  for 
iridio-platinum  for  crown  posts,  dowels,  etc.  The  ordinary 
clasp  metal  is  also  used  to  a  considerable  extent  for  posts  or 
dowels  in  the  construction  of  cast  base  crowns,  with  usually 
poor  results  on  account  of  its  brittleness,  especially  after  it 
has  been  cast  again.  There  appear  to  be  about  four  distinct 
types  of  clasp  metal  obtainable  at  the  supply  houses. 

The  following  formula  are  nearly  exact  and  types  one  and 
two  readily  indicate  the  particular  role  that  copper  plays  as 
a  hardening  agent. 

Typo  one  represents  a  class  of  clasp  metals  of  which  there 
are  several  on  the  market.  They  contain  a  trace  of  platinum, 
so  that  they  may  legally  be  called  platinized  gold,  and  a  very 
high  percentage  of  copper.  The  copper  content  confers  a 
high  degree  of  hardness  and  elasticity  upon  the  alloy,  lint 
during  subsequent   heating    (soldering  and   annealing)    and 


AN    OUTLINE    OF    METALLURGY 


working,  the  alloy  softens  considerably  and  loses  a  good  deal 
of  the  original  elasticity  and  sometimes  becomes  very  brittle, 
especially  when  overheated.*  As  the  melting  point  is  quite 
low,  soldering  with  even  a  eominvratively  low  fusing  solder 


COMPOSITION  OF  CLASP  METALS. 


CONSTITUENT 
METALS. 

TYPE 

1* 

TYPE 

2* 

TYPE 
I!* 

TYPE 

4" 

■ELASTIC" 
GOLD 

GOLD  

(i3 
14 
21 

65 
15 
13 

fi3 
17 
7 
13 

05 
f) 

18 
4 

64 
1.5 
7.(1 

11 

16.5 

SILVER 

COPPER 

PLATINUM 

PALLADIUM 

COMPARATIVE 
MELTING  POINT 

1600°F 
870''C 

1725°F 
n40°C 

1S60°F 
1015°C 

I9G()°F 
1070<'C 

2100°F 
1150°C 

is  apt  to  endanger  the  integrity  of  the  alloy  more  often  than 
not. 

Type  two  represents  a  class  of  clasp  metals  which  con- 
tain a  larger  percentage  of  platinum  and  less  copper.  This 
alloy,  while  not  qnite  as  elastic  before  annealing,  retains  its 
elasticity  after  annealing  or  soldering,  better  than  type  one, 
and  makes  a  quite  satisfactory  material  for  clasps  for  vul- 
canite work,  etc.,  if  not  excessively  heated  and  otherwise 
abused. 

Neither  of  the  two  alloys  is  suitable  for  work  requir- 
ing repeated  soldering  operations.  Posts  or  dowels  made  of 
these  alloys  and  cast  against  usually  show  a  partial  fusion, 
and  although  this  fusion  is  not  always  evident,  the  posts  if 
cast  against  break  away  (at  the  junction)  ultimately.  These 
alloys  are  absolutely  unfit  for  the  making  of  split  pins. 

Type  three  offers  a  much  better  material.  It  contains 
still  less  copper  and  more  platinum,  but  has  not  sufficient 
strength  and  elasticity.  For  want  of  a  better  material  it  has 
been  used  for  the  construction  of  split  pins  for  a  number  of 
years.  In  addition,  the  fusing  point,  although  higher  than 
that  of  types  one  and  two,  is  too  low,  and  when  attempting 

*Gold-silver-copper  alloys  containing  over  15  per  cent  copper  are  quite 
brittle,  very  non-uniform,  and  variable  in  behavior  upon  annealing. 


AN    OUTLINE    OF    METALLURGY  1035 

to  solder  the  solid  portion  of  a  split  pin  with  coin  gold,  the 
metal  is  apt  to  fvase  partly,  becoming  granular  and  brittle,  and 
the  finished  pin  is  apt  to  give  out  in  use.  The  t>iJe  three  clasp 
metal  has  been  cast  against  with  fair  results,  but  the  danger 
of  burning  it  is  imminent. 

In  the  three  types  of  clasp  metals,  under  discussion,  is 
demonstrated  the  value  of  copper  and  its  superiority  over 
platinum  as  a  hardening  agent  and  the  value  of  platinum  in 
raising  the  melting  point  lowered  by  the  copper. 

A  number  of  experiments  were  made  to  improve  the  type 
three  clasp  metal  and  it  can  readily  be  seen  from  formula  of 
type  four  how  comparatively  simple  it  was  to  do  so,  having 
established  the  i^roperties  of  the  binary  alloys  as  a  founda- 
tion. By  raising  the  platinum  to  18  points,  the  melting  point 
and  the  elasticity  were  increased  somewhat.  Even  at  this 
stage  the  advance  in  melting  point  appeared  insufficient,  and, 
as  it  was  deemed  advisable  to  avoid  more  platinum  on  account 
of  the  danger  of  its  not  alloying  uniformly,  palladium,  which 
alloys  readily,  was  added  and  the  melting  point  increased  to 
a  total  of  app.  100  degs.  F.  above  type  three.  No  more  pal- 
ladium was  used  on  account  of  its  decolorizing  action.  With 
the  comparatively  small  content  (4  per  cent),  the  color  of 
the  alloy  is  still  quite  goldlike. 

This  alloy  has  been  used  with  uniformly  good  results. 
It  may  be  soldered  safely  with  coin  gold  (for  split  pins)  and 
may  be  cast  against  safely  if  a  comparatively  heavy  gauge 
of  wire  (above  16  g.  B.  &  S.)  is  used. 

In  view  of  the  fact  that  for  split  pins,  dowels  for  cast  base 
crowns,  etc.,  color  is  no  object,  it  was  deemed  advisable 
to  raise  the  melting  point  even  above  that  of  type  four  and 
the  elastic  gold  was  formulated,  using  a  considerable  percent- 
age of  palladium.  The  palladium,  of  course,  decolorized  the 
alloy  completely,  but  raised  the  melting  point  very  consider- 
ably, and,  in  conjunction  with  tlie  copper  and  the  considerable 
percentage  of  platinum,  produced  an  elasticity  even  beyond 
that  of  type  four  and  a  melting  point  very  considerably 
higher. 

This  alloy  can  be  soldered  with  perfect  safety  with  pure 
gold  or  anything  below  that  in  melting  point.  It  may  be 
cast  against  with  perfect  safety  (except  very  thin  wire)  and 
retains  its  strength  and  elasticity  after  any  reasonable  num- 
ber of  soldering  operations  that  it  may  necessarily  be  sub- 
jected to.  It  may  he  soldered  veri/  readily  and  nnth  better 
union  that  iridio  platinum.    It  is  much  more  rigid  than  ordi- 


1036 


AN    OUTLINE    OF    METALLURGY 


iKiiji  ii'idiii  jildlhinni  (iihI  possesses  elasticity  that  is  prac- 
tically absent  in  all  of  the  iiidio  platinum  alloys,  and  it  may 
therefore  replace  tlic  hilhr  and  ordinary  clasp  metal  for  a 
great  many  purposes. 

In  the  making  of  split  posts  of  the  elastic  gold  it  is  advis- 
al)le  to  solder  the  area  that  is  intended  should  remain  solid 
with  coin  gold,  as  it  offers  a  strong  color  contrast  to  the  com- 
paratively white  elastic  gold. 

The  line  of  demarkation  between  the  solid  and  the  split 
13ortions  of  the  post  will  be  then  readily  distinguished.  As 
the  coin  gold  is  of  sufficiently  high  melting  point  it  will  not 
reflow  during  later  soldering  operations. 

The  comparative  hardness  and  the  elasticity  of  the  four 
types  of  clasp  metals  and  the  "elastic"  gold  is  approximately 
as  illustrated  in  the  following: 


COMPARATIVE  ELASTICITY  AFTER 
ROLLING    AND    ANNEALING    ONCE 

Type 
One 
10 

Type 

Two 

9 

Type 

Three 

8 

Type 
Four 

9  + 

"Elastic" 
Gold 

10  + 

Fig.  7 

COMPARATIVE    LOSS    OF    ELASTICITY    AFTER 
SOLDERING   AND   ANNEALING   THREE   TIMES 

Type 
One 
2-3 

Type 
Two 
1-2 

Type 
Three 

1  + 

Type 
Pour 

1 

"Elastic" 
Gold 
.5-1 

Types  one  and  two  become  very  brittle  if  overheated  dur- 
ing soldering.  Type  three  is  subject  to  same  to  a  lesser  de- 
gree, and  type  four  only  rarely.  The  "Elastic"  gold  appears 
practically  immune  to  temperatures  below  the  melting  point 
of  pure  gold. 

Clasp  metal  should  always  be  annealed  before  use,  as 
manufacturers  often  neglect  to  do  so  after  the  rolling  or 
drawing  operations. 

SECTION  IV 

GOLD  SOLDERS 

In  order  to  obtain  the  desirable  uniformity  of  color  in  a 
denture  without  subsequent  gold  "washing,"  it  was  neces- 
sary to  formulate  solders  to  correspond  in  color  with  the 


AN    OUTLINE    OP    METALLURGY  1037 

other  alloys.  Ineideutally,  it  is  well  to  consider  the  imposition 
that  has  been  practiced  upon  the  profession  by  some  of  the 
unscrupulous  manufacturers   of  gold   solders. 

For  many  years  a  great  many  in  the  profession  have 
been  under  the  im23ression  that  gold  solders  stamped  18k. 
were  actually  18k.  (75  per  cent  gold)  in  fineness.  This  was 
not  so,  and  a  number  of  the  manufacturers  were  producing, 
and  are  still  producing,  solders  marked  18k.,  etc.,  anywhere 
from  two  to  six  karats  below  the  mark.  In  addition,  the  sol- 
ders mentioned  are  not  only  deficient  in  gold  content,  but  con- 
tain man.v  deleterious  alloying  elements,  such  as  high  per- 
centages of  cadmium,  iron,  etc.,  in  order  to  complete  the  re- 
quired total  content  of  metals  in  the  solders. 

On  the  other  hand,  the  reputable  manufacturers  have  con- 
sistently stated  that  their  solders  were  approximately  two 
karats  below  the  mark  and  intended  for  use  on  that  karat  of 
plate.  The  reputable  manufacturers  have  recently  started  to 
stamp  the  actual  fineness  on  their  solders  and  the  others  have 
followed  suit;  but  some  manufacturers  still  persist  in  the 
practice  of  misrepresentation  by  not  actually  furnishing  the 
gold  content  indicated  by  the  fineness  stamp  on  the  product. 

ALLOYS  OF  GOLD  WITH   METALS  IN  GROUP  3 

Besides  zinc,  the  other  three  metals  in  Group  3,  namely, 
cadmium,  tin  and  aluminum,  are  being  used  to  a  very  large 
extent  as  alloying  elements  in  making  gold  solders.  Cadmium, 
if  used  in  large  percentages,  debases  the  alloy  very  consid- 
erably and  renders  it  practically  unfit  for  use  in  the  mouth. 

Tin  is  also  used  to  a  considerable  extent,  as  it  lowers  the 
melting  point  of  gold  very  considerably,  but  it  renders  the 
gold  quite  brittle  and  aids  materially  in  the  tendency  of  the  sol- 
der to  burn  into  the  work,  which  property  is  characteristic  of 
all  the  so  called  easy  flowing  solders.  The  term  "easy  flowing" 
is  undoubtedly  a  misnomer.  Bather,  these  solders  melt 
"easy,"  but  do  not  flow  easy.  They  ball  up  and  stick  and  if 
the  heat  is  forced  to  induce  flow,  they  burn  into  the  work  with 
consequences  too  well  laiown  to  require  fui'ther  discussion. 

The  volume  of  aluminum  as  a  constituent  of  gold  solders 
is  yet  to  be  proven.  It  is  a  constituent  of  most  of  the  patent 
commercial  alloys  used  by  jewelers  in  compounding  their 
solders. 

Solders  made  according  to  the  following  formula?  will 
be  found  satisfactory  in  color,  strength  and  fusing  point,  al- 
though higher  in  fusing  point  than  the  so-called  easy  flowing 


1038  AN    OUTLINE    OF    METALLURGY 

solders  for  which  there  seems  to  be  a  "popnUir"  demand. 
They  will  be  foimd  to  flow  readily  if  the  work  on  which  they 
are  to  be  used  is  brought  up  to  the  proper  temperature. 

FORMULA    FOR    GOLD    SOLDERS 
SOLDER  NO.   84 

TGoW    84.09^  1 

M.    P.    1650°   F,   900°    C-^  SHver   ITv   f    "^       KsiTut  fine. 

Izinc    3.0%  J 

SOLDER  NO.   76 

rGoId    76.0%  1 

M.    P.    1550°    F,    840     C    g°/^'g^'"   '^8'5%  (     ^**        ^^''^^  ""^' 

Izinc    4.07pJ 

SOLDER  NO.   68 
roold    68.07f,-| 

M.   P.    1450°   F.   785°    C"^  ^"P^®'"   It'lt?  [    ^^V-   Karat  fine. 

Sliver  12.5%  ( 

I  Zinc    5.0%  J 

The  first  and  second,  84  and  76,  will  be  found  sufficiently 
low  in  melting  point  for  all  ordinary  operations,  and  where 
Dr.  Peeso  recommends  the  use  of  his  No.  21  and  No.  19  solder. 
The  number  68  solder,  although  higher  in  actual  gold  content 
than  the  best  so-called  18k.  solder  obtainable,  is  still  too  low 
a  grade  to  be  used  in  general  work,  especially  in  fixed  bridge 
work,  but  may  be  used  in  connection  with  removable  bridge 
work  or  plate  work,  because  in  that  work  or  repair  work  there 
is  I'equired  at  times  a  lower  fusing  solder. 


SECTION  V 
COMPOUNDING  OF  GOLD  ALLOYS 

Although  the  new  series  of  alloys,  made  with  practically 
no  deviation  from  the  formula?  which  are  given  herein,  may 
be  purchased  from  the  supply  houses,  the  author  considers  it 
well  to  give  a  number  of  directions  to  those  who  may  desire 
to  compound  the  various  alloys. 

It  is  not  practical  to  make  a  small  quantity,  especially  if 
for  plate  gold  or  solder,  which  is  to  be  poured  into  an  ingot 
mold  and  rolled.  The  higher  the  melting  point  of  the  alloy, 
the  more  necessary  it  is  to  have  a  comparatively  large  quan- 
tity and  it  is  well  not  to  attempt  less  than  five  ounces  for  plate 
gold  and  three  ounces  for  solder.  The  elastic  alloy  should  be 
made  in  even  larger  quantity,  as  it  freezes  very  rapidly. 

It  is  practically  impossible  to  alloy  platinum  or  palladium 
with  gold  in  the  small  blast  furnace  which  the  practitioner  is 


AN    OUTLINE    OF    METALLURGY  1039 

likely  to  have  in  his  laboratory.  For  all  alloys  with  platinum 
metals  (made  on  the  small  scale  previouslj^  mentioned)  it  is 
well  to  alloy  the  gold  and  the  platinum  metals  (rolled  very 
thin)  first  on  a  charcoal  block,  using  the  nitrous  oxide  and 
illuminating  gas  blow-pipe,  or  preferably  the  oxygen  and 
illuminating  gas  blow-pipe.  A  number  of  the  alloyed  nuggets 
can  then  be  placed  in  a  crucible  on  top  of  the  required  silver 
and  copper  content,  covered  with  a  suitable  I'educing  flux  and 
melted,  poured  into  an  ingot  mold  and  rolled  or  drawn. 

When  copper  is  to  be  used,  it  is  essential  that  same  be 
chemically  pure  and  especial  precaution  must  be  exercised  to 
prevent  oxidation  as  far  as  possible,  which  latter  can  be  ac- 
complished by  the  use  of  a  strong  reducing  flux.  (See  under 
fluxes.) 

A  slight  excess  of  copper  should  always  be  added  to  allow 
for  some  loss  which  invariably  occurs. 

If  the  alloy  that  it  is  intended  to  make  is  to  be  used  for 
casting  purposes,  the  procedure  is  the  same  as  previously  de- 
scribed, excepting  that  the  metal,  when  properly  molten,  can 
be  poured  into  a  pail  of  water  and  thus  granulated.  This  pro- 
cedure saves  the  labor  of  rolling  the  ingot  and  the  granulated 
form  of  gold  is  as  convenient  to  use  for  casting  as  any  other. 

In  all  cases,  just  before  pouring  the  contents,  the  crucible 
should  be  well  shaken  to  insure  a  thorough  admixture  of  the 
metals. 

Some  writers  advocate  the  preparation  of  alloys  for  cast- 
ing in  the  following  manner:  Melt  the  gold,  feed  the  platinum 
(very  thin)  into  the  molten  gold  and  then  add  copper,  etc.  It 
is  impossible  to  make  a  uniform  alloy  in  this  manner,  espe- 
cially if  copper  is  used,  because  a  considerable  amount  of  the 
copper  is  oxidized  on  account  of  direct  contact  with  the  blow- 
pipe flame  and  in  the  author's  hands  the  directions  previously 
given  have  been  found  to  work  out  admirably. 

In  compounding  solders  where  zinc  and  copper  are  the 
constituents  it  has  been  advocated  that  brass  which  contains 
copper  and  zinc  be  used  in  order  to  prevent  the  loss  of  zinc 
through  oxidation  and  volatilization.  This  is  a  very  danger- 
ous practice  and  the  results  are  very  unsatisfactory,  because 
it  is  impossible  to  obtain  a  commercial  brass  that  does  not 
contain  a  considerable  percentage  of  lead,  tin,  and  traces  of 
antimony,  etc.,  ^t^hich  are  all  very  harmful  substances  and 
invariably  teiid  to  make  the  solders  brittle.  It  is  therefore 
necessary  to  first  make  an  alloy  of  chemically  pure  zinc  and 
chemically  pure  copper  in  a  proportion  of,  say,  one  part  zinc 


1040  AN    OUTLINE    OV    METALLURGY 

and  two  pai'ts  copper.  Tliis  alloy,  when  properly  melted, 
is  granulated  by  ijouring  into  water  and  then,  if  carefully 
gathered,  dried  and  weighed,  the  loss  of  zinc  can  be  deter- 
mined. The  necessary  additional  copper  to  make  the  required 
alloy  is  then  calculated  and  added  when  compounding  the 
solder. 

It  is  well,  of  course,  to  make  a  considerable  cpiantity  of 
the  copper  zinc  alloy,  as  the  cost  is  slight  and  the  prepared 
alloy  is  then  available  when  wanted.  It  has  been  stated  that 
zinc  volatilates  very  readily  from  solders.  This  is  quite  con- 
trary to  the  author's  findings.  The  small  percentage  of  zinc 
as  given  in  the  formulas  herein  is  quite  stable  after  remelting 
several  times.  The  authors  who  claim  this  strong  volatiliza- 
tion of  zinc  may  have  been  dealing  with  a  solder  of  unknown 
constitution  in  which  they  suspected  zinc,  but  which  probably 
contained  a  high  percentage  of  cadmium,  which  volatilates 
quite  readily. 

SECTION  VI 

REFRACTORY    MATERIALS 

INVESTMENT   COMPOUNDS    FOR   SOLDERING 

The  normal  contraction  of  gold  from  the  molten  to  solid 
state  is  approximately  2  per  cent.  The  contraction  of  gold 
solder  is  practically  the  same,  although  some  of  the  constitu- 
ents have  a  higher  contraction  than  gold,  but  when  combined 
in  an  alloy  the  movement  is  practically  the  same. 

While  possibly  there  may  be  a  slight  difference  between 
the  contraction  of  solder  and  gold,  a  considerable  contraction 
occurs  nevertheless  and  is  the  cause  of  a  great  deal  of  trouble. 

A  number  of  soldering  investment  compounds  on  the 
market  are  claimed  by  the  manufacturers  to  possess  neither 
expansion  nor  contraction  and  therefore  perfect.  Granting, 
for  the  sake  of  the  argument,  that  such  is  the  case,  we  still 
have  the  contraction  of  solder  to  contend  with  and  how  are  we 
to  produce  a  soldered  bridge  or  denture  that  will  tit  and  go 
into  place  accurately  when  a  number  of  the  units  in  the  work 
have  been  drawn  together  by  the  contraction  of  the  solder? 

Unfortunately,  we  have  not  merely  the  contraction  of  the 
solder  to  contend  with,  but  we  have  a  much  more  prolific  cause 
of  disaster.  For  example,  we  have  a  number  of  completed  sec- 
tions, such  as  castings,  to  join  together  where  but  a  very 
small  quantity  of  solder  is  to  be  used,  and  yet  after  soldering 
we  find  that  the  finished  piece  is  contracted  and  distorted  and 


AN    OUTLINE    OF    METALLURGY  1041 

will  not  go  into  position.  The  fact  of  the  matter  is,  that  prac- 
tically all  the  commercial  compounds  shrink  upon  heating 
when  brought  up  to  the  proper  temperature  for  soldering. 

In  some  commercial  investment  compounds,  the  shrinkage 
is  extremely  high,  fully  six  or  seven  per  cent,*  so  it  is  evident 
that  the  principal  cause  of  the  troiible  lies  not  so  much  in  the 
actual  contraction  of  the  solder  as  it  does  in  the  great  contrac- 
tion of  the  average  investment,  even  before  the  case  is  quite 
hot  enough  to  apply  the  solder. 


Fig.  8  shows  an  ordinary  simple  bridge  assembled  and 
read}^  for  investment.     The  porcelain  facings  are  spaced  as 


FIGURE  0 


per  instructions  from  time  immemorial.     Fig.  9  shows  the 
case  invested  and  the  distinct  spacing  of  the  backings. 


The  case  is  then  heated,  and  if  an  examination  of  the 
investment  is  made  with  a  magnifying  glass,  just  before  plac- 
ing it  on  the  soldering  block,  it  will  be  noticed  that  the  units 
have  been  drai''n  together,  as  in  Fig.  10,  and  when  the  case  is 

*See  papers  of  J.  G.  Lane  in  Dental  Cosmos  and  Dental  Digest,  1910-14. 
Also  M.  A.  Ward  in  Dental  Cosmos.  These  contributions  are  very  inter- 
esting and  tlie  most  valuable  that  have  appeared  pertaining  to  the  subject. 


1042  AN    OTITI.INK    OF    METAIJATRGY 

soldered  and  cooled,  tlie  facings  are  very  apt  to  be  checked  on 
account  of  having  been  brought  together  into  very  strong 
contact. 

When  attempting  to  place  back  on  the  cast,  difficulty  is 
encountered,  but  as  the  plaster  yields,  the  bridge  is  forced 


down  and  then  becomes  evident  tlie  loss  of  the  contact  points, 
as  illustrated  in  Fig.  11. 

This  discrepancy  will  not  be  considered  by  some  oper- 
ators as  a  serious  factor.  In  fact,  those  who  solder  directly 
on  the  cast  destroy  the  evidence  for  the  time  being.  If  it  is  a 
fixed  bridge,  it  is  forced  home  some  way  or  other  and  let  go 
at  that,  but,  on  the  other  hand,  if  a  removable  bridge,  even  as 
small  in  dimension  as  the  one  illustrated,  it  is  practically 
impossible  to  place  it  in  position  and  the  matter  is  a  most 
serious  one,  as  a  good  many  operators  have  found. 

Some  writers  advocate  completing  the  dummies  and  then 
placing  them  in  perfect  contact  to  prevent  the  shrinkage  of 
the  solder  used  to  unite  the  sections.  This  is  practically  im- 
possible, because  the  metallic  units  are  infinitely  stronger  than 


the  investment  and  expanding  under  heat  will  invariably  split 
the  investment  (see  Fig.  12),  and  thus  often  cause  a  serious 
distortion  in  the  soldered  piece. 

There  seems  to  have  been,  as  a  search  of  the  literature 
has  shown,  absolutely  no  consideration  given  to  the  movement 
of  the  refractory  mass  that  holds  the  parts  in  situ  during  the 
preliminary  heating  and  final  soldering  operations. 


AN    OUTLINE    OF    METALLURGY  1043 

The  author's  aim  in  experimenting  has  been  not  merely 
to  produce  an  investment  compound  that  would  not  shrink, 
but  one  that  would  actually  expand,  move  in  unison  with  the 
solid  invested  metal,  and  spread  the  units  sufficiently  so  that 
when  a  reasonable  amount  of  solder  is  flowed  to  connect  the 
units,  the  contraction  of  the  total  piece  loould  he  neutralized 
by  the  expansion  of  the  investment. 

Before  attempting  to  formulate  an  investment  compound 
possessing  such  properties,  it  is  necessary  to  consider  the 
chemical  and  physical  properties  of  refractory  materials  which 
may  be  employed  in  the  compounding  of  investment  materials. 

In  one  of  the  well-known  books  on  crown  and  bridge 
work.*  the  following  appears. 

"Many  substances  may  be  used  in  combination  with  plaster  of 
Paris,  which  is  necessarily  the  basis  because  imparting  the  property 
of  crystallization,  and  which  must  be  incorporated  to  the  extent  of 
at  least  50%. 

"The  remaining  proportion  may  be  then  composed  of  such  ma- 
terials as  will,  by  virtue  of  their  characteristics  and  physical  prop- 
erties, meet  such  requirements.     The  following  are  serviceable: 
Powdered   Silex,  Pulverized   Pipe  Clay, 

Pine    Asbestos,  Powdered  Fire  Brick, 

Beach  Sand,  Magnesium  Oxide, 

Marble  Dust,  Pumice   Stone. 

"A  combination  of  any  of  these  ingredients  in  varying  propor- 
tions with  the  proper  quantity  of  plaster  will  usually  possess  the 
necessary  qualities,  etc.,  etc." 

Before  even  considering  a  compound  of  expanding  prop- 
erties, it  is  well  to  thoroughly  understand  the  properties  of 
plaster  of  paris  and  the  other  materials  enumerated  in  the 
list  of  suitable  refractories  in  order  to  see  if  it  is  possible  to 
even  produce  an  investment  compound  that  will  at  least  not 
shrink  under  heat. 

PLASTER  OF  PARIS 

Plaster  of  paris,  Ca  SO4  (calcium  sulphate),  is  made  by 
burning  gypsum  rock.  In  the  process  of  burning,  most  of  the 
water  is  driven  off.  The  phenomena  of  recombining  with 
water  and  crystallizing  is  well  known  and  need  not  be  discussed 
here.  It  is  universally  employed  as  the  binder  for  all  in- 
vestment compounds  used  both  for  soldering  and  casting.  It 
shrinks  very  strongly  upon  heating,  but  for  want  of  a  better 
material  must  be  employed. 

The  more  plaster  used  in  an  investment  compound,  the 
harder  the  resultant  mass  will  be  and  the  more  shrinkage  will 
take  place.  As  will  be  shown  subsequently,  any  such  propor- 
tion as  the  50  per  cent  mentioned  by  the  author  quoted  is  abso- 

•Goslee's  Principles  and  Practice  of  Crown  and  Bridge  Work,  pp.  36-37. 


1044  AN    OUTLINE    OF    METALLURGY 

lutely  out  of  question,  because  it  has  been  found,  so  far,  im- 
possible to  compensate  for  this  contraction  of  the  binder  by 
the  addition  of  any  other  material,  even  if  possessing  the 
property  of  expansion. 

POWDERED    SILEX 

Silex  is  the  commercial  term  applied  to  silicon  dioxide 
(Si  Oo),  which  is  the  main  constituent  of  rocks,  stones,  clays 
and  many  other  minerals.  A  great  deal  of  it  is  also  found 
in  a  free  state  and  in  the  form  of  quartz,  rock  crystal,  flint, 
opal,  chalcedony,  etc.  The  so-called  silex  is  often  practically 
pure  Si  O2.  However,  different  varieties  of  silicon  dioxide 
exist,  and  although  all  of  a  similar  chemical  composition  they 
possess  varying  physical  properties. 

Silica  obtained  from  quartz  or  rock  crystal  consists  of 
sharp  crystalline  particles  and  possesses  a  high  specific  grav- 
ity, 2.6  to  2.8.  It  expands  considerably  upon  heating,  but 
loses  this  property  gradually  upon  reheating  frequently  or 
fusing  completely.*  The  melting  point  of  pure  silica  is  ap- 
proximately 3,200  degs.  F. 

Another  variety  of  silica  that  exists  quite  as  frequently  as 
the  crystalline  is  an  amorphous  form  which  possesses  a  lower 
specific  gravity,  2.2  to  2.4.  It  has  very  little  expansion  upon 
heating  and  some  varieties  of  the  same  type  do  not  expand  at 
all.**  ' 

Still  a  third  variety  exists  in  a  tabular  form  and  is  ex- 
tremely light  and  porous.  It  is  known  as  diatomaceous  earth 
or  kieselguhr.  Its  specific  gravity  is  1.6  to  1.8.  It  is  mined 
in  very  great  quantities  and  used  very  extensively  as  a  heat 
insulating  agent,  but  contracts  very  strongly  and  therefore  is 
totally  unfit  for  use  as  part  of  a  dental  refractory  compound. 

As  stated  before,  these  various  forms  of  silica  can  be  ob- 
tained in  almost  a  pure  state  and  are  alike  chemically,  but 
the  term  "powdered  silex"  means  nothing  unless  a  particu- 
lar type  is  specified,  and  the  individual  who  is  not  conversant 
with  tlie  matter  is  as  likely  as  not  to  purchase  and  use  a 
grade  of  least  expansion.     The  crystalline  variety,  of  high 

*Utensils  made  of  fused  silica  are  replacing  platinum  ware  to  a  great 
extent  in  chemical  work.  As  the  coefficient  expansion  is  very  small 
(.00000054  per  °  C)  it  is  possible  to  subject  crucibles,  casseroles,  etc.,  to 
rapid  changes  of  temperature  without  danger  of  breakage.  Apparatus  suit- 
able for  dental  purposes  is  manufactured  by  the  Thermal  Syndicate,  Ltd., 
of  New  York. 

**Both  surface  and  volume  expansion  of  silica  must  be  considered  in 
selecting  the  grades  of  silica  to  be  used. 


AN    OUTLINE    OF    METALLURGY  1045 

specific  grarifij,  expands  coiisiderabltj  under  heat,  and  in  this 
fact  lies  tJie  solution  of  the  whole  problem. 

A  mixture  of  50  per  cent  plaster  of  paris  and  50  per  cent 
silica,  even  if  the  latter  is  of  the  variety  possessing  the  highest 
expanding  properties,  contracts  very  considerably  when 
bronglit  np  to  the  temperatnre  required  for  soldering  or  cast- 
ing oi^erations. 

In  order  to  be  brief,  the  author  will  state  that  all  the 
otlier  items  in  the  list  of  suitable  materials  have  a  positive 
shrinkage,  with  the  exception  of  beach  sand.  The  objection 
to  the  latter  is  the  fact  that  it  is  often  quite  impure  and  the 
iron  and  alkalies  that  form  the  major  portion  of  the  impuri- 
ties usually  act  as  a  flux  and  thus  lower  the  melting  point. 

It  is  well  to  state  that  magnesium  oxide  and  marble  dust, 
which  latter  is,  of  course,  calcium  carbonate,  are  subject  to  a 
particularly  strong  contraction  under  heat. 

Fig.  13  illustrates  the  comparative  shrinkage  of  one  of  the 
best  commercial  compounds  olitainable.    A  considerable  space 


will  be  noted  between  the  mass  of  investment  and  the  rim  of 
the  metallic  ring  in  which  it  was  placed  after  mixing,  permit- 
ted to  set  and  heated  to  soldering  temperature. 

Fig.  14  (in  cross-section)  shows  even  more  clearly  the  con- 
traction, after  heating,  when  a  straight  edge  is  placed  across 
the  top  of  the  flask. 

To  summarise  the  whole  proposition,  the  author  will  state 
that  in  order-to  produce  an  investment  compound  that  merely 
does  not  shrink,  but  actually  expands  siifficiently  to  follow  the 
movement  of  a  red  hot  ring,  that  it  is  necessary  to  use  a  grade 
of  silica  as  pure  as  possible  and  of   the   highest   expansion, 


AN    OUTLINE    OF    METALLURGY 


ii'liich  mediis  of  course  a  fjrade  silica  from  the  quarts  group 
and.  a  grade  of  plaster  of  paris  of  the  least  contraction*  As 
previously  mentioned,  any  such  proportion  as  50  per  cent 
plaster  cannot  he  used,  because  the  expansion  of  the  best  sil- 
ica, great  as  it  is,  is  not  sufficient  to  compensate  for  even  the 
slirinkage  of  the  plaster,  hence  a  loiver  percentage  of  plaster 
and  a  higher  percentage  of  silica  must  be  used. 

Formula  for  Inresf)nent   Compound    {Soldering) 

Per  Cent 
Plaster  of  paris  (Excelsior  Brand  No.  ?>) .  .Parts     33 

Silica  (fine)  (F.  F.  F.) Parts     45 

Silica  (coarser)  (M.  C.)   Parts     22 

Total    100 

A  componnd  made  according  to  this  formula  will  be  found 
to  expand  upon  heating  to  soldering  temperature  sufficiently 
to  fill  a  red  hot  ring,  as  in  Figs.  15  and  in. 


FIGUEE  IC 


This  property  of  expansion  is  sufficient  to  counteract  the 
contraction  of  a  normal  bulk  of  solder.  Furthermore,  this 
expansion  is  sufficient  to  follotv  the  movement  of  invested 
metallic  sections  that  have  been  previously  completed.  This 
compound  sets  promptly  and  is  sufficiently  strong  to  hold  the 
invested  parts  in  situ  firmly.  It  will  withstand  the  action  of 
boiling  water  (when  washing  out  the  wax)  without  disintegra- 
tion. 

*It  is,  no  doubt,  well  known  that  fine  plaster  contracts  more  than  coarse 
plaster  when  subjected  to  heat.  Most  of  the  coarse  building  plasters  are 
rather  non-uniform  and  do  not  possess  the  binding  power  of  the  finer  plasters. 
The  grade  selected  is  quite  uniform  and  not  too  coarse  to  prevent  efficient 
binding  of  the  mass. 


AN    OUTLINE    OF    METALLURGY  1047 

Dr.  Peeso  has  long  ago  demonstrated  the  great  impor- 
tance of  not  soldering  Avork  directly  on  the  cast.  The  work 
should  be  so  assembled  that  the  waxed  up  structure  could  be 
lifted  off  the  east,  which  is  made  of  plaster  of  paris  or  a  more 
durable  material  such  as  "Artificial  Stone"  (made  from  the 
author's  formula)  and  then  transferred  to  the  investment 
compound.  After  soldering,  the  work  could  be  placed  back 
on  the  cast,  which  is  intact,  and  required  corrections  could  be 
made  by  grinding  or  trimming  where  necessary  before  the 
structure  is  even  tried  in  the  mouth. 

Of  course,  the  author  has  made  numerous  and  exhaustive 
experiments  to  determine  the  properties  and  behavior  of  vari- 
ous refractory  materials  and  it  is  important  that  the  grades 
of  silica  and  plaster  specified  be  used. 

As  the  reader  can  deduct  from  the  preceding,  the  terms 
silica  and  plaster  of  paris  mean  very  little,  because  while  the 
different  grades  of  silica  are  practically  alike  chemically,  they 
differ  very  materially  physically.  To  the  author's  knowledge, 
it  is  possible  to  purchase  at  least  three  or  four  himdred  dif- 
ferent brands  of  plaster  and  over  a  thousand  distinct  grades 
of  silica  with  varying  percentages  of  impurities  and  varying 
sizes  of  particles.*  There  is  no  intention  to  claim  that  this 
is  the  last  word  on  the  subject.  No  doubt,  other  experiment- 
ers will  succeed  in  producing  as  good  or  even  a  better  com- 
pound with  other  grades  of  material. 

INVESTMENT    COMPOUNDS    FOR   CASTING 

The  elements  of  error  caused  by  the  physical  behavior  of 
the  metallic  alloys  and  the  refractory  materials  utilized  in 
the  casting  process  are  cjuite  analogous  to  the  conditions  that 
exist  in  the  soldering  process.  Gold,  no  matter  how  alloyed, 
as  far  as  present  knowledge  of  the  subject  indicates,  does  con- 
tract in  the  transition  from  the  fluid  or  plastic  state  to  the 
solid  or  frozen  state,  and  an  inlay  investment  compound  that 
possesses  the  property  of  expansion  will  at  least  in  a  measure 
compensate  for  the  contraction  of  gold. 

It  is  not  the  author's  aim  here  to  exhaustivelj'  discuss 
casting  problems  in  general.    He  simply  wishes  to  suggest  a 

*The  materials  used  in  the  formulae  given  were  obtained  from  W.  B. 
Daniels,  252  Front  street.  New  York  City,  who  is  a  dealer  in  minerals  and 
chemicals.  He  will  supply  the  ingredients  for  both  the  soldering  and  casting 
compounds  in  quantities  suitable  for  the  requirements  of  the  practitioner. 
Of  course  it  must  be  remembered  that  such  comparatively  cheap  materials 
are,  as  a  rule,  sold  by  the  ton  or  carload.  Hence,  Mr.  Daniel's  willingness 
to  furnish  these  materials  in  small  (luantities  at  a  moderate  price  deserves 
commendation. 


1048  AN    OtTTLINE    OF    METALLURGY 

fonuula  for  what  lie  considers  a  better  investment  compound 
than  is  inireliaseable  and  to  point  out  some  of  the  physical  phe- 
nomena of  existing  conditions.  Before  discussing  the  formula, 
it  is  well  to  first  consider  some  of  the  conditions  that  have 
to  be  dealt  with.  We  have  not  only  the  contraction  of  gold 
to  contend  with,  but  we  also  have  the  contraction  of  the  wax, 
and  that  is  a  most  serious  factor  indeed.  The  contraction  of 
wax  is  usually  productive  of  a  greater  degree  of  error  than 
the  actual  contraction  of  gold. 

This  subject  has  been  covered  most  thoroughly  by  Dr.  C. 
S.  Van  Horn  of  Bloomsburg,  Pa.,  in  his  articles  in  the  Den- 
tal CosmoS;*  and  his  conclusions  are  yet  to  be  controverted. 

The  conditions  which  he  successfully  corrects  are  the  fol- 
lowing: After  the  removal  of  a  wax  pattern  from  the  mouth 
at  body  temperature,  it  contracts  considerably  upon  reaching 
room  temperature  and  still  more  when  invested  with  cold 
water.  His  method  consists  of  investing  the  pattern  at  ap- 
proximately 110  degs.  F.,  which  increase  in  temperature  not 
merely  compensates  for  the  contraction  of  the  wax,  but  also 
expands  the  wax  to  almost  completely  counteract  the  shrink- 
age of  the  gold. 

In  addition,  he  uses  an  expanding  investment  (made 
from  the  author's  formula)  and  the  total  expansion  of  the 
wax,  coujiled  with  the  expansion  of  the  investment,  enables 
Dr.  Van  Horn  to  produce  the  most  accurate  fitting  inlays  the 
author  has  ever  seen. 

A  study  of  Dr.  Van  Horn's  technique  will  amply  repay 
anyone  who  is  desirous  of  obtaining  better  results. 

Dr.  James  G.  Lane  of  Philadelphia  was  among  the  first 
to  point  out  the  value  of  silica  as  an  ingredient  of  inlay  in- 
vestment compounds,  on  account  of  its  expansion  and  conse- 
quent ability  to  counteract  the  contraction  of  plaster  of  paris 
(the  binder).  The  formula  that  he  used  (plaster  25  per  cent 
and  silica  75  per  cent)  expands  considerably.  Dr.  Lane  was 
also  among  the  first  to  point  out  the  fact  that  a  hot  mold  was 
stronger  than  one  that  was  heated  and  allowed  to  cool. 

In  the  utilization  of  the  casting  process,  there  are  a  great 
many  important  factors  to  be  considered,  among  them  the  fus- 
ing point  of  the  investment  compound  ivhich  constitutes  the 
mold;  the  relation  of  this  degree  of  fusibility  to  the  tempera- 
ture of  the  mold  at  the  time  the  molten  metal  enters  it;  the 
temperature  of  the  molten  metal  at  the  time  it  enters  the  mold 
and  the  pressure  used,  to  force  the  molten  metal  into  the  mold. 

*1911,    pp.    664,    472,    1109;    1912,    pp.   890,   973;    1914,  p.   940. 


AN    OUTLINE    OF    METALLURGY  1049 

The  fusing  point  of  an  inA'estment  compound,  made  of 
plaster  of  paris  and  pure  silica,  is  under  3000  degs.  F.  Some 
of  the  commercial  investment  compounds,  which  are  made 
with  impure  silica  containing  a  considerable  percentage  of 
iron  and  feldspar,  which  latter  contains  alkalines,  such  as 
sodium  and  potassium,  are  often  considerably  lower  fusing, 
consequently  when  superheated  gold  is  cast  into  such  a  com- 
paratively fusible  investment  a  partial  vmion  is  bound  to  take 
place,  with  the  consequence  that  the  gold  partly  unites  with 
the  investment  and  the  resultant  casting  is  quite  rough  and 
inaccurate. 

The  strong  jjossibility  of  such  a  condition  as  described 
leads  the  author  to  state  his  opinion  on  that  apparently  never 
ending  controversy  regarding  the  casting  of  gold  in  a  liot  or 
cold  flask.  This  point  has  been  argued  time  and  time  again, 
some  operators  claiming  that  they  obtain  better  results  by 
casting  into  a  hot  fiask  and  others  maintaining  the  reverse. 
In  order  to  discuss  the  subject  intelligently,  we  must  also  bear 
in  mind  the  degree  of  heat  that  is  utilized  for  melting  the 
metal  to  prepare  for  its  entrance  into  the  mold. 

Let  ns  first  consider  the  following: 

HOT    OR    COLD    MOLD— USING    ILLUMINATING    GAS    AND 
COMPRESSED    AIR   BLOW-PIPE 

We  will  discuss  this  phase  first,  because  the  great  major- 
ity of  castings  are  accomplished  by  using  the  ordinary  gas  and 
air  blow-pipe.  The  maximum  temperature  that  it  is  possible 
to  produce  with  artificial  gas  and  compressed  air  is  approx- 
imately 2450  degs.  F.  The  temperature  of  the  investment  in 
the  casting  ring  when  red  hot  is  about  1300  degs.  F.  If  this 
"red  hot"  flask  is  placed  on  the  casting  apparatus  and  a  quan- 
tity of  gold,  say,  5  dwts.,  placed  in  the  ci'ucible,  it  will  take 
about  two  and  a  half  minutes'  exposure  to  an  efficient  blow- 
pipe flame  to  bring  the  gold  to  the  proper  state  of  fluidity  to 
enter  the  mold.  In  the  meantime,  the  "red  hot"  mold  (on  the 
casting  apparatus)  has  cooled  considerably  and  the  actual 
temperature  of  the  cavity  in  the  mold  at  the  time  the  gold 
enters  it  can  be  safely  calculated  not  to  exceed  900  degs.  F. 
Therefore,  casting  into  a  "red  hot"  flask  with  an  ordinary 
gas  and  air  blow-pipe  is  done  with  the  mold  not  red  hot,  but 
at  a  temperature  approximately  900  degs.  F. 

In  casting  into  a  so-called  "cold"  flask,  using  the  same 
blow- pipe  and  quantity  of  metal,  it  will  be  found  that  it  takes 
longer,  say  four  minutes,  to  bring  the  metal  into  a  state  of 


lono  AN    OUTLINE    OF    METALLURGY 

fluidity,  and  altlion,i;li  llic  flask  is  at  room  temperature  when 
the  process  of  melting  the  gokl  is  started,  the  subjection  of  the 
mold  to  the  flame  of  tiie  efficient  blow-pipe  for  a  period  of 
approximately  four  minutes  raises  the  temperature  of  the 
mold  to  an  extent  of  nearly  700  degs.  F.  Therefore,  when  it 
is  attempted  to  make  a  casting  with  the  ordinary  gas  and  air 
blow-pipe  in  a  so-called  "cold"  flask,  the  temperature  of  the 
mold  at  the  time  the  gold  enters  it  is  approximately  700  degs. 
F. 

Upon  considering  both  conditions  and  comparing  the  tem- 
peratures of  the  molds,  namely,  900  degs.  and  700  degs.,  it 
will  be  readily  seen  that  there  is  comparatively  little  difference 
between  the  tivo  at  the  actual  time  that  the  casting  is  done, 
and  consequently  both  the  "hot  mold"  and  "cold  mold"  advo- 
cates are  right,  strange  as  that  may  appear,  providing,  of 
course,  that  the  ordinary  gas  and  air  blow-]iipe  is  em- 
ployed. 

The  author's  experiments  along  this  line  have  shown  con- 
clusively that  it  is  hardly  possible  to  superheat  the  gold  with 
an  ordinary  gas  and  air  blow-pipe  or  bring  the  gold  to  such  a 
temperature  that  it  will  unite  with  the  investment  at  any  stage 
of  the  procedure,  and  it  is  the  author's  firm  opinion  that  in 
the  hands  of  the  careless  or  inexperienced  operator,  the  ordi- 
nary gas  and  air  hloiv-pipe  is  a  positive  insurance  against 
superheatifig  the  gold,  and  therefore  insures  a  casting  satis- 
factory, at  least  as  far  as  errors  consequent  to  the  superheat- 
ing of  gold  are  concerned. 

HOT   OR   COLD   MOLD— USING   ILLUMINATING   GAS    AND 
NITROUS  OXIDE  OR  OXYGEN  BLOW-PIPE 

Here  we  have  a  totally  different  and  quite  often  a  dan- 
gerous condition  to  contend  with.  While  the  ordinary  gas 
and  air  blow-pipe  is  capable  of  producing  temperatures  only 
somewhat  beyond  2400  degs.  F.,  it  is  possible  to  obtain,  with- 
out difficulty,  3400  to  3500  degs.  F.  from  nitrous  oxide  and 
illuminating  gas  and  over  4000  degs.  F.  from  pure  oxygen 
and  illuminating  gas.  It  may  be  well  at  this  time  to  call  at- 
tention to  the  fact  that  the  often  used  term  "Oxyhydrogeu" 
is  incorrect  when  used  in  connection  with  illuminating  gas 
because  of  the  fact  that  in  order  to  produce  an  oxyhydrogen 
flame  it  is  necessary  to  have  both  oxygen  gas  and  hydrogen 
gas,  whereas  ordinary  illuminating  gas  contains  less  than 
half  of  its  volume  of  hydrogen  and  the  balance  is  principally 
methane   (carbon,  etc.). 


AN    OUTLINE    OF    METALLURGY  1051 

II  is  rather  dillicnlt  to  avoid  superheating  gold  when  ap- 
pl\  iug  such  extreme  temperatures  and  extreme  caution  must 
he  exercised  hy  the  operator. 

As  a  rule,  the  cold  flask  is  indicated  when  using  extreme 
temperatures  for  melting  the  gold,  because  the  gold  melts 
very  rapidly  (15  to  20  seconds),  and  comparatively  little  heat 
is  transmitted  to  the  mold.  The  mold  is  then  comparatively 
cool,  and  even  if  somewhat  sujoerheated  gold  is  cast  it  is  not 
so  apt  to  unite  with  the  investment  as  when  both  the  gold 
and  the  mold  are  superheated. 

The  author  has  very  often  made  failures  of  castings  on 
account  of  superheating  the  gold  and  he  wishes  to  impress 
strongly  the  fact  that  extreme  caution  must  he  exercised  in 
this  connection. 

The  nitrous  oxide  or  oxygen  and  gas  blow-pipe  offers  ad- 
vantages over  the  ordinary  gas  and  air  blow-pipe  as  a  means 
of  producing  heat  rapidly,  but  the  maximum  temperature 
attainable  with  the  ordinary  gas  and  air  blow-pipe  acts  as  a 
sort  of  an  insurance  against  superheating  and,  in  fact,  if 
efficiently  used,  produces  satisfactory  casting  results  in  all 
ordinary  operations. 

One  of  the  most  prolific  causes,  in  fact,  probably  the  great- 
est cause  that  is  productive  of  faulty  castings,  is  the  excessive 
pressure  used  in  forcing  metal  into  the  mold.  The  principal 
reason  for  this  is  due  to  the  fact  that  in  the  majority  of  cast- 
ing apparatus,  there  is  no  provision  for  obtaining  a  definitely 
measured  and  indicated  amount  of  force.  It  takes  just  so 
much  and  no  more  pressure  to  force  gold  into  a  given  mold 
and  hold  it  there  until  solidification  begins.  Excessive  pres- 
sure will  not,  lander  ordinary  conditions,  prevent  the  normal 
contraction  of  gold,  because  the  mold  into  which  the  gold  is 
cast  yields  and  hence  vnll  distort  in  the  same  proportion  as 
excessive  pressure  is  applied.  It  may  be  true  that  a  pressure 
of  2,000  pounds  per  square  inch  may  totally  prevent  contrac- 
tion, hut  ivhere  is  the  mold,  that  will  stand  that  pressure? 

It  is  unfortunate  that  more  operators  do  not  realize  the 
true  value  of  an  efficient  casting  apparatus,  such  as  the  Tag- 
gart,  and  the  false  economy  resulting  from  the  use  of  an  in- 
trinsically faulty  ©r  makeshift  device. 

By  using  a  grade  of  silica  of  maximum  expansion  and  a 
grade  of  plaster  of  minimum  contraction,  it  is  possible  to  pro- 
duce an  investment  compound  as  follows: 


1052  AN    OUTLINE    OF    METALLURGY 

Formula  for  Investment  {Casting) 

J^laster  (Excelsior  Brand  No.  3) Parts     2!) 

Silica  (Fine)   (F.  F.  W.) Parts     71 

Total 100 

The  plaster  is  the  same  as  is  used  in  the  soldering  invest- 
ment. The  silica  is  similar  to  the  tine  grade  ntilized  in  the 
soldering  investment  fornmJa,  bnt  it  is  purified  and  combines 
with  water  readily  withont  releasing  dirt,  scum,  etc.,*  and 
consequent  bnlibles.  An  investment  made  from  this  formula 
will  be  found  to  expand  slightly  more  than  Dr.  Lane's  formula, 
although  the  plaster  of  paris  content  is  higher  and,  for  the 
same  reason,  somewhat  stronger  and  more  resistant  to  ex- 
cessive pressure. 

COMPOUNDING    OF    INVESTMENT    MATERIALS 

It  is  a  well-known  fact  that  very  few  commercial  invest- 
ment comiiounds  are  uniform  in  composition.  In  other  words, 
although  manufacturers  claim  that  their  formulae  are  adhered 
to,  there  appear  variations  in  batches  purchased  at  different 
times.  This  is  due  to  the  fact  that  insufficient  attention  is 
paid  to  testing  the  different  batches  of  raw  material  and  also 
to  the  faulty  compounding  due  to  the  large  quantities  mixed 
at  a  time.  One  commercial  preparation  has  been  found,  on 
the  contrary,  quite  uniform,  for  the  simple  reason  that  the 
manufacturer  pays  especial  attention  to  the  testing  of  the  raw 
materials  and  compounds  the  mixture  in  comparatively  small 
quantities  (200  to  300  lbs.  to  the  mix). 

In  mixing  the  plaster  of  paris  and  silica,  it  is  not  neces- 
sary to  do  anj'  sifting,  because  the  specified  materials  may 
be  obtained  evenly  and  definitely  graded.  All  that  is  required 
is  a  thorough  mixture  without  excessive  trituration. 

A  very  efficient  small  mixing  apparatus  may  be  obtained 
from  J.  H.  Day  Co.,  Cincinnati,  Ohio.  It  is  known  as  the 
"Hunter"  (experimental  size)  and  will  handle  from  seven 
to  eight  pounds  of  material.  The  ingredients  are  weighed 
out,  placed  in  the  container  and  the  apparatus  revolved  slowly 
for  25  to  30  minutes.  This  produces  a  uniform  and  intimate 
mixture  without  crushing  or  grinding  the  plaster.  This  point 
is  very  important,  and  if  smaller  quantities  are  mixed  in  a 
mortar,  it  is  important  to  use  very  light  pressure  in  order  not 

*Bubbles  and  froth  produced  upon  attempting  to  combine  investment 
compound  and  water  are  often  caused  by  dirt  or  sucli  impurities  as  mica, 
etc.,  contained  in  the  silica. 


AN    OUTLINE    OF    METALLURGY  1053 

to  crush  the  plaster  particles.    The  mixed  material,  of  course, 
should  be  properly  stored  and  protected  against  moisture. 

INVESTMENTS,  DIRECTIONS  FOR  USE 

The  soldering  investment  should  be  mixed  quite  thick. 
The  thicker,  the  better,  up  to  a  certain  limit,  of  course.  If 
mixed  too  dry,  the  i:)laster  of  paris  content  does  not  obtain 
sufficient  moisture  to  crystallize  properly  and  act  efficiently. 
A  good  consistency  is  41  to  42  grammes  powder  to  each  15 
c.c.  water  or  26  dwts.  (Troy)  to  one-half  fluid  oz.  water. 

The  inlay  investment  should  be  mixed  in  a  proportion  of 
32  grammes  powder  to  15  c.c.  water,  or  20  dwts.  (1  Troy  oz.) 
powder  to  i-^  fluid  oz.  water.  This  quantity  is  sufficient  to 
fill  an  ordinary  inlay  fiask. 

These  proportions  produce  a  mixture  tliat  allows  ample 
time  for  manipulation,  provided  considerable  time  is  not  spent 
in  adding  a  little  more  water,  a  little  more  powder,  etc.  Tlie 
setting  time  of  the  plaster  naturally  controls  the  setting  time 
of  the  whole  mixture,  and  as  the  action  of  retarding  agents 
added  to  control  the  set  of  plaster  is  sometimes  indefinite  and 
often  harmfid,  it  is  advisable  not  to  attempt  to  interfere  ivith 
the  normal  setting  time  of  the  plaster. 

The  compound,  if  mixed  without  any  unnecessary  delay, 
sets  sufficiently  slow  for  all  ordinar.y  operations.  It  is  the 
author's  i^ractice  to  have  on  hand  a  number  of  cork-stoppered 
bottles  containing  the  dry  compound  (weighed)  and  a  num- 
ber of  rubber-stoppered  vials  containing  water  (measured). 
The  accurately  measured  powder  and  water  are  thrown  sim- 
ultaneously into  the  mixing  bowl  and  having  no  bubbles  or 
froth  (as  with  graphite  compounds*)  to  contend  with,  the 
mix  can  be  made  ready  for  use  in  from  30  to  40  seconds,  thus 
allowing  ample  time  for  coating  the  pattern  and  imbedding  in 
flask.  This  method  is  superior  to  using  the  automatic  weigh- 
ing apparatus  furnished  by  some  of  the  compound  manufac- 
turers, as  they  are  often  either  inaccurate  or  not  sufficiently 
"flexible." 

It  is  not  advisable  to  attempt  to  invest  more  than  one 
pattern  at  a  time.     When  a  larger  mix  is  to  be  made  for  a 

*Most  of  the  compounds  that  contain  flake  graphite  are  very  difficult 
to  mix  on  account  of  the  air  content  in  the  flaltes  and  their  tendency  to 
"float."  Such  a  compound  requires  a  considerable  period  of  time  to  mix, 
and  therefore  a  retarded  plaster  is  usually  employed.  Nodules,  or  "ghosts," 
on  castings  occur-  frequently  because  the  material  is  not  "dormant"  until 
"set."  A  manufacturer  of  such  a  compound  claims  that  it  is  the  plaster 
and  not  the  graphite  that  causes  the  bubbles.  This  statement  appears 
quite  contrary  to  the  facts.  Kerr's  "Graphite"  Investment  is  made  with 
previously  treated  graphite  and  it  is  the  best  commercial  preparation  that 
the  author  knows  of. 


1054  AN    OUTLINE    OF    METALLTTROY 

liii'gor  flask,  throe  to  five  per  cent  more  powder  than  a  given 
quantity  of  water  demands  is  not  only  permissible,  but 
advisable. 

Another  advantage  in  using  measured  and  stored  water 
lies  in  the  fact  that  it  is,  when  used,  at  room  temperature  and 
not  at  hydrant  temperature,  and  the  room  temperature  water 
does  not  induce  a  further  coufrdcHtni  of  the  wax  pattern  dur- 
ing the  process  of  investing. 

HEATING   OF   INVESTMENTS 

The  soldering  investment  may  be  heated  quite  ]n-omptly 
upon  setting.  Boiling  water  does  not  atTeet  it  materially  and 
the  wax  may  be  washed  out  thoroughly,  the  case  fluxed  and 
immediately  placed  on  the  heat,  moderate  at  first  and  then 
brought  up  quite  rapidly  to  a  good  red  heat  prior  to  the  actual 
soldering  operation. 

It  is  the  inefficient  and  insufficient  lieatinc/  of  the  invested 
work  that  is  partly  to  blame  for  the  "popular"  demand  for 
"easy  floiving"  solders.  Properly  heated  investments  facili- 
tate the  floiv  of  normal  or  even  high  fusing  solder. 

A  small  quantity  of  potassium  sulphate  or  sodium  chlo- 
ride may  be  used  to  hasten  the  setting  of  the  investment,  but 
that  is  rarely,  if  ever,  necessary,  because  it  sets  quite  promptly 
if  mixed  to  the  proper  consistency. 

The  inlay  investment  should  be  permitted  to  set  for  at 
least  thirty  mimites  to  insure  a  fair  crystallization  (so-called 
"initial  set")  of  the  plaster.  The  flask  should  then  be  placed 
over  a  low  heat  and  kept  there  until  the  moisture  disappears 
and  the  wax  begins  to  dit¥use  and  carbonize.  The  heat  is  in- 
creased somewhat  during  the  latter  part  of  this  operation 
and  still  further  increased  until  the  mold  is  brought  up  to 
either  a  dull  red  heat  (for  cold  mold)  or  a  bright  red  lieat 
(for  hot  mold). 

The  initial  stages  of  heating  must  be  a  temperature  that 
will  not  permit  the  wax  to  run  out  of  the  mold,  as  it  is  im- 
portant that  the  wax  be  absorbed  in  the  mold.  Forced  heat- 
ing and  a  generation  of  steam  during  the  initial  stages  of  the 
drying  process  will  force  the  wax  out  of  the  mold  and  pro- 
duce a  rough  interior  which  in  turn  will  show  its  etfects  upon 
the  casting,  the  resultant  casting  being  rough,  incorrect,  and 
usually  unfit  for  use.  It  is,  of  course,  essential  to  confine  and 
concentrate  the  (higher)  heat  in  order  to  bring  the  mold  to 
the  proper  temperature  within  a  reasonable  period  of  time. 

Prolonged  heating  of  the  investment  is  even  more  dan- 


AN    OUTLINE    OF    METALLURCtV  1055 

gerous  than  iinderheating,  as  plaster  of  paris,  which  is  the 
binder,  shrinks  in  proportion  to  the  time  that  it  is  exposed  to 
heat.  The  total  heating  operation  for  an  ordinary  mold  (in- 
lay, etc.)  should  not  exceed  fifty  minutes,  or  an  hour  at  most. 
It  may  be  divided  into  three  periods,  say  twenty-five  to  thirty 
minutes  for  low  drying  heat,  then  increased  somewhat  for  ten 
to  fifteen  minutes,  and  finally  subjected  to  the  highest  heat  for 
not  more  than  from  ten  to  fifteen  minutes. 

It  is  permissible  not  to  heat  a  case  imtil  two  or  three 
hours  after  the  investment  has  been  mixed,  but  if  it  is  per- 
mitted to  stand  for  a  day  or  two  and  loses  all  moisture,  if  then 
heated  and  cast,  the  resultant  casting  is  apt  to  be  very  poor. 
It  is  hard  to  determine  the  actual  principle  involved,  and  it 
is  not  important  to  do  so,  but  the  fact  does  exist.  In  addition, 
under  such  conditions,  the  investment  is  very  apt  to  crack  or 
split  upon  heating.  The  author  usually  heats  and  casts  into 
"green"  molds,  but  has  found  that  a  dry  mold,  if  moistened 
prior  to  heating,  appears  to  behave  almost  as  well  as  a 
"green"  mold.  If  the  mold  is  only  a  few  hours  old  it  is  moist- 
ened slightly,  but  if  it  is  more  than  a  day  old  it  is  placed  in 
water  until  saturated  to  the  extent  of  a  "green"  mold. 

Both  the  soldering  and  casting  investment  compounds 
are  practically  immune  to  "checking"  or  "cracking"  even 
under  the  most  severe  heating  conditions.* 


SECTION  VII 

FLUXES 
FLUXES   FOR   SOLDERING   AND   CASTING 

For  sweating,  soldering  or  melting  metals  in  the  construc- 
tion of  bands,  crowns,  bridges  or  castings,  the  selection  and 
use  of  the  proper  flux  or  fluxes  is  a  matter  of  the  utmost  im- 
portance, especially  if  the  metals  or  alloys  used  are  oxidizable 
or  volatile  when  subjected  to  heat. 

Ordinary  borax,  or  calcined  borax,  has  been  the  principal 
flux  used  for  this  purpose.  It  has  been  almost  rmiversally 
used  by  jewelers  and  the  dentist  has  followed  suit.    There  is, 

*This  fault  is  inherent  in  most  investment  compounds,  the  causes  are 
numerous  and  principally  due  to  the  producers  ignoring  the  physical  laws 
governing  the  selection  and  compounding  of  materials  for  the  purpose. 
One  of  the  principal  errors  in  this  connection  is  the  attempt  to  form  a 
"concrete-like"  mass  without  realizing  that  there  is  a  very  great  difference 
in  the  behavior  of  dental  investment  compounds  and  concrete  used  in  build- 
ing   operations. 


105G  AN    OUTLINR    OF    METALLURGY 

liowever,  a  consideral)le  difference  between  the  dass  of  work 
that  the  jeweler  and  tlie  dentist  perform. 

In  dental  soldering,  we  use  higher  grade  solders  and  a 
considerably  higher  heat,  during  the  various  operations.  As 
ordinary  borax  melts  at  a  comparatively  low  temperature,  it 
does  not  act  as  efficiency  during  the  higher  temperature  stages 
as  the  requirements  demand.  The  tendency  of  borax  when 
considerable  heat  is  applied  is  to  liquefy  strongly  and  run 
down  to  the  deep  portions,  leaving  the  otlier  portions,  that 
it  is  desired  to  solder,  insufficiently  protected.  Dr.  Peeso 
recognized  this  long  ago  by  using  a  combination  of  borax  and 
boric  acid,  which  combination  melts  at  a  higher  temperature 
than  borax  alone,  does  not  liquefy  so  readily,  stays  on  the 
surface  and  protects  the  work  longer  and  is  more  efficient  in 
every  way. 

An  efficient  flux  that  has  served  verj^  satisfactorily  in  the 
author's  hands  for  a  considerable  period  of  time  is  the  fol- 
lowing: 

Formula  for  Soldering  Flux 

C.  P.  Borax  Glass  (fused) Parts     55 

C.  P.  Boric  Acid  (not  fused)   Parts     35 

C.  P.  Silica Parts     10 

Total    100 

The  ingredients  are  placed  in  a  clean  clay  or  sand  cruci- 
ble and  brought  to  a  fair  red  heat.  They  combine  quite  read- 
ily and  when  quite  fluid  the  mistiire  is  poured  into  cold  water. 
As  this  glass  is  quite  soluble,  it  must  be  removed  from  the 
water  as  soon  as  possible,  dried  and  pulverized  to  pass  an 
80-mesh  sieve.  It  may  be  pulverized  without  difficulty,  as  the 
particles  are  very  frail  and  brittle. 

This  flux  may  be  used  either  in  the  powdered  form  or 
compounded  with  "vaseline,"  to  form  a  i^aste,  or  dissolved  in 
Iroiling  water  and  the  saturated  solution  used.  In  the  liquid 
form,  it  will  be  found  suitable  for  all  general  operations  where 
the  work  can  be  heated  so  as  to  drive  off  the  moisture  and 
thus  leave  a  coating  of  the  flux,  as  in  bands,  crowns,  etc.  When 
the  work  is  in  an  investment,  the  grease  flux  will  be  found  most 
useful,  as  it  may  be  applied  just  after  the  case  is  waslied  out 
and  still  warm.  The  carrier  (vaseline)  flows  down  into  the 
deep  portions  and  crevices,  carrying  the  particles  of  flux 
along.  The  powdered  dry  flux  can  be  used  on  invested  work 
under  the  blow-pipe  when  more  flux  is  required.     Strips  of 


AN    OUTLINE    OP    METALLURGY  1057 

solder  can,  of  courso,  be  coated  with  either  tlie  liquid  or  the 
grease  flux  and  heated  ))rior  to  use. 

This  soldei'hui  /hu  ni  a  ponvleii'd  form  inU  also  he  used 
as  the  base  for  both  flic  reducing  and  ().ridr::iii()  flii.res  to  be 
discussed. 

It  is  important  that  the  forms  of  borax  and  boric  acid 
specified  be  adhered  to  because  of  the  variable  amount  of 
water  that  these  materials  contain  when  purchased. 

The  formula  of  borax  glass  is  Na2B40;,  whereas  ordinary 
borax,  either  powdered  or  crystals,  contains  a  considerable 
jiroportion  of  water  which  is  evident  from  the  formula 
Na.BiOj  +  10H,( ).  Therefore  the  borax  glass  is  preferable  to 
the  ordinary  borax  containing  water  because  it  occupies  much 
less  space  and  is  therefore  more  convenient  to  handle  in  small 
crucibes.  However,  if  ordinary  borax  is  used  the  water  con- 
tent must  be  calculated  and  provided  for  in  weighing  out  the 
ingredients.  The  lioric  acid  used  does  contain  water,  as  will 
i)e  seen  from  the  formula  lIsBO;,,  because  it  is  more  stable  than 
the  fused  boric  acid  BJ)^  and  more  readily  obtainable.  The 
silica  should  be  pure  and  in  the  form  of  a  fine  powder  so  that 
it  may  combine  readily.* 

REDUCING   FLUX 

In  connection  with  the  casting  process,  it  is  necessary  to 
treat  buttons  of  gold,  both  during  casting  and  before  recasting, 
with  a  flux  that  will  take  care  of  the  accpiired  impurities.  Very 
often  there  have  apjieared  statements  to  the  effect  that  a  mix- 
ture of  potassium  nitrate  and  borax  be  used  to  cleanse  but- 
tons before  recasting.  This  statement  has  been,  in  a  good 
many  cases  to  the  author's  knowledge,  misunderstood.  Potas- 
sium nitrate  is  an  excellent  oxidizing  agent  and  does  remove 
base  metals,  but  its  use  in  treatment  of  casting  buttons  is  con- 
tra-indicated, because  generally  when  casting  gold  alloys  con- 
taining copper,  etc.,  it  is  desired  to  retain  the  base  metal,  the 
copper,  ill  a  reduced  metallic  form  and  not  in  an  oxidized  form. 
Consequently,  if  a  fiiix  is  to  be  used  it  must  be  of  a  distinctly 
reduciiifi  nature. 

Reducing  fluxes  are  used  extensively  in  assaying  and 
smelting  operations  and  their  properties  are  well  known.  In 
the  case  of  casting,  it  is  rather  difficult  to  utilize  all  the  benefit 
that  mav  be  derived  from  a  reducing  flux  on  account  of  the 


♦The  grade  (P.  P.  W.)  used  in  inlay  casting  investment  is  quite  suitable. 


1058  AN    Ol'TLINK    OF    METALLURGY 

difficulty  of  applying  same  to  the  molten  metal  which  is  ex- 
posed to  the  blo\v-i)ipe  Hame  which  drives  off  the  flux  almost 
as  fast  as  it  is  api)lied.  Therefore,  to  obtain  any  considerable 
benefit  from  a  reducing  flux,  it  is  necessary  to  not  merely 
apply  same  while  the  gohl  is  fluid  under  the  blow-pipe,  but 
also  to  sprinkle  an  additional  amount  in  the  manner  described 
in  the  following:  After  placing  flask  on  casting  apparatus, 
place  button  or  nuggets  of  gold  into  crucible,  melt  without  flux 
until  the  mass  of  gold  assumes  a  spheroidal  form  and  coni- 
l)letely  covers  the  s])rue  hole.  Then  api)ly  some  flux  by  sprin- 
kling, continue  melting  until  the  gold  is  in  a  projicr  state  of 
fluidity  for  casting,  then  remove  flame,  add  some  more  flux 
and  instantly  apply  the  casting  pressure. 

Formula  for  Rcdiic'nig  Flux 

Soldering  Flux   (  Base)    Parts  40 

Borax  Glass  Parts  30 

Argol Parts  25 

Animal  (."harcoal  Parts  5 

Total 100 

Argol  is  the  commeicial  term  for  crude  postassium  bi- 
tartrate,  KHC4H4O0  (cream  of  tartar),  and  has  a  higher  re- 
ducing power  than  pure  cream  of  tartar.  If  the  latter  is  used 
it  should  be  increased  to  about  25  parts  and  the  soldering  flux 
and  borax  glass  content  reduced  in  proportion. 

A  flux  of  this  character  will  practically  prevent  the  bring- 
ing into  the  casting  of  oxidized  material  and  can  be  used  to 
advantage  in  remelting  and  cleansing  buttons  of  gold  for 
recasting. 

The  author's  procedure  for  this  operation  is  as  follows: 
After  a  casting  is  made,  the  residue  button  is  placed  into 
hydrofluoric  acid  for  15  or  20  minutes,  removed  and  melted 
with  the  blow-pipe  in  a  charcoal  block,  using  the  reducing  flux, 
which,  in  addition  to  reducing  the  oxidized  copper  in  the  but- 
ton, combines  with  the  silica,  traces  of  which  may  still  adhere 
to  the  button.  After  the  button  is  melted  and  the  flux  used 
has  segregated  into  a  globule,  the  hlow-pipe  is  removed  and 
a  small  quantity  of  ammonium  chloride  is  sprinkled  on  the 
button.  As  soon  as  the  button  has  solidified,  and  while  still 
red.  it  is  plunged  in  dilute  hydrochloric  or  sulphuric  acid. 
Most  of  the  glass  formed  by  the  flux  will  splinter  off.    If  any 


AN    OUTLINE    OF    METALLURGY  1059 

considerablo  quantity  adlicrcs,  it  may  he  rt'iiioNcd  l)y  boiling 
in  the  same  acid. 

OXIDIZING  FLUX 

Potassium  nitrate  is  a  most  excellent  oxidizing  agent  and 
removes  base  metals,  the  only  objection  being  the  strong  fumes 
which  are  given  off  during  the  melting  ])rocess.  Although  tlie 
operator  should  rarely  attempt  to  do  refining,  it  is  well  to 
have  a  suitable  oxidizing  flux  that  will  not  give  off  the  objec- 
tionable fumes  characteristic  of  potassium  nitrate. 

Formula  for  Oxidizing  Flux 

Soldering  Flux  (base)   Parts     55 

Potassium  Chlorate   Parts     20 

Sodium  Perborate Parts     25 

Total 100 

This  flux  will  be  found  useful  for  revivifying  buttons  of 
gold  which  are  contaminated.  It  is  sufficiently  powerful  to 
volatilize  such  impurities  as  tin,  cadmium,  liismuth.  etc.  It 
will  combine  with  adherent  investment  comi>ound  and  not  at- 
tack copper  very  strongly,  so  that  a  button  of  gold  that  has 
been  used  several  times  and  is  quite  sluggish  and  dirty  can  be 
usually  brought  into  good  shape  without  diflicult\'. 

A  button  treated  with  this  flux  should  be  cleansed  in  acid, 
as  previouslj'  described,  and  then  remelted  trith  the  reducing 
fltix  prior  to  use  for  casting. 

In  cases  of  refining,  where  a  stronger  action  is  recjuired, 
the  potassium  chlorate  and  sodium  perborate  can  be  increased 
to  obtain  the  same  efficiency  that  a  high  percentage  of  potas- 
sium nitrate  would  give  without  the  objectionable  fumes  char- 
acteristic of  the  latter. 

It  is  expected  that  pre^sared  flux  made  according  to  the 
formulas  given  will  be  very  shortly  available  from  the  sup- 
ply houses.  Until  such  time,  a  modification  of  the  soldering 
flux  formula,  which  also  acts  as  a  base  for  tiie  reducing*  and 
oxidizing  fluxes,  is  given  herewith  for  the  benefit  of  those 
who  have  not  the  facilities  for  fusing  and  pulverizing  the 
material.     These  ingredients  make  a  flux  which  appears  to 

*There  are  a  number  ot  better  reducing  agents  than  those  suggested 
by  the  author  used  industrially.  They  are  not  mentioned  because  of  either 
difficulty  of  application  under  casting  conditions,  or  on  account  of  not  being 
obtainable  in  small  quantities.  A  study  of  the  methods  used  in  deoxidizing 
copper,  brass  and  bronze  is  suggested  to  those  particularly  interested. 


]060  AN    OIITLINK    OF    METALLnuCY 

woik  imich   iiioic  satisfactorily  lliaii  (udiniiix    hdiax  or  any 
(it  llic  sccri't   lircjiarations  ])iir('liasal)lc. 

FoiiiiiiIk    fur   Suldcriii//    Flux    (Snhsl il iilc) 

C.  P.  Borax  Glass Parts     50 

C.  P.  Boric  Acid Parts     43 

C  P.  Siidiuin  Silicate  (i\vy  pmvd.) Parts       7 

Total  , 100 

Tliis  is  mixed  tliorouglil)'  in  a  niorlar  and  mnst  be  fine 
eiiougli  to  pass  an  80-mesli  siexc 

The  author  trusts  that  his  icmarks  ni)on  the  importance 
of  producing  castings  with  all  the  metal  in  a  reduced  form  and 
not  in  a  partially  oxidized  form  will  be  given  some  considera- 
tion by  the  reader,  as  this  probhnii,  on  an  immeasurably  larger 
scale,  has  been  and  is  one  of  the  most  important  ones  in  the 
api)lication  of  industrial  alloys,  and  is  being  coped  with  suc- 
cessfully. 

TABLE  4 
MELTING  POINTS  OF  THE  NEW  SERIES  OF 
ALLOYS   AND   STANDARD   DENTAL   GOLDS 

"F  Alloy  °C 

2100  *"Elastic"  Gold  1150 

2075  *Plate  No.  1  1135 

1975  *Plate  No.  2  1080 

1960  Type  4  Clasp  1070 

1945  Pure  Gold  1063 

1945  *Casting  Gold  "A"  1063 

1945  *Casting  Gold  "D"  1063 
1945     "Green"  Gold  [App.  Au.  80',; — Ag.  20c;  ]     1061 

1900  *Casting  Gold  "B"  1035 

1900  Light  22K  Plate  1035 

1860  Medium  22K  Plate  1015 

1860  Type  3  Clasp  1015 

1825  Dark  22K  Plate  995 

1800  *Casting  Gold  "C"  980 

1760  Light  20K  Plate  960 

1735  Coin  Gold   (21.6K)  946 

1725  Type  2  Clasp  940 

1650  *Gold  Solder  No.  84  900 

1625  Gold  Solder  for  22K  885 

1600  Type  1  Clasp  870 

1550  *Gold  Solder  No.  76  840 

1525  Gold  Solder  for  20K  820 

1450  *Gold  Solder  No.  68  785 

1425  Gold  Solder  for  18K  770 

The  ten  alloys  marked  *  constitute  the  new  series.  They 
are  all  uniform  in  color  with  the  exception  of  "Elastic"  Gold, 
which  is  similar  to  ]ilatinum  in  color,  and  Casting  Gold  "A," 
which  is  similar  to  pure  gold  in  color. 


AN    OUTLINE    OF    METALLURGY  1061 

SOME  OF  THE  APPLICATIONS  OF  THE  NEW  SERIES  OF 

ALLOYS  IN  THE  PEESO  SYSTEM  OF  REMOVABLE 

BRIDGEWORK 

As  will  he  seen  from  the  preceding  table,  tbe  series  of 
alloys  offers  a  wide  range  of  variation  in  melting  point  over 
the  ordinary  alloys,  tlms  facilitating  the  performance  of  suc- 
cessive soldering  operations. 

CONSTRUCTION    OF    BANDS,   FLOORS   AND    INNER    CAPS 

As  has  been  ju'evionsly  stated,  coin  gold  is  the  most  suit- 
able alloy  for  the  construction  of  bands,  floors,  etc.  It  is 
therefore  necessary  to  use  its  equivalent  in  the  new  series  of 
alloys.  The  band  should  therefore  be  made  of  the  No.  2  plates 
(M.  P.  1975  degs.  F.,  1080  degs  C),  and  united*  by  soldering 
with  the  next  lowest  fusing  alloy,  namely,  Casting  Gold  "B" 
(M.  P.  1900  degs.  F.,  1035' degs"c.). 

The  band  is  also  prepared  of  No.  2  plate  and  attached 
with  Casting  Gold  "B"  (the  pliers  grasping  the  band  at  pre- 
viously joined  portion). 

The  method  will  make,  for  all  intents  and  purposes,  a 
seamless  cap.  The  melting  point  of  the  soldered  junctions 
will  be  still  considerably  above  that  of  coin  gold.  The  tube 
may  be  then  attached  with  the  No.  84  solder. 

Outer  caps  for  telescope  crowns  are  made  in  exactly  the 
same  manner.  As  the  hardness  and  tenacity  of  the  No.  2  plate 
is  the  same  as  that  of  coin  gold,  the  same  gauges  of  plate  are 
to  be  used  as  with  coin  gold.  The  casting  gold,  if  used  as 
solder,  should  be  of  practically  the  same  thickness  as  ordinary 
gold  solder,  app.  27  or  28  gauge  B.  &  S.,  or  preferably  thinner 
(30  to  32  g.). 

OUTER  HALF  BANDS  AND  TELESCOPE  CROWNS 

After  completing  the  inner  cap,  the  outer  half  band  and 
floor  are  made  of  suitable  gauge  No.  2  plate  and  the  split  pin 
is  attached  and  the  half  band  united  to  the  floor  with  the  No. 
84  solder. 

For  telescope  crowns,  the  outer  band  is  made  of  the  No. 
2  plate  and  the  joint  soldered  with  Casting  Gold  "B."  The 
wings  are  made  of  No.  2  plate  and  soldered  to  the  band  with 
Casting  Gold  '.'C."  The  cusp  is  swaged  of  No.  1  plate  (higher 
fusing  than  pure  gold),  filled  with  Casting  Gold  "C"  in  the 
same  manner  as  a  pure  gold  cusp  is  filled  with  coin  gold  and 
"See  Dr.  Peeso's  method  of  band  preparation  for  sweating. 


1062  AN    OUTLINK    OF    MKTALLUIUIV 

attac'lied  to  the  previously  ('(iinplctcd  outer  liaml  and  wiugs 
with  No.  84  solder. 

If  tlie  cusp  is  to  be  cast,  C'asting  Gold  "B"  or  "('"  should 
be  selected  according'  to  the  blow-pipe  used  and  attached  to 
the  contoured  band  with  No.  84  solder. 

As  all  of  the  alloys  of  the  series  used  in  this  operation 
are  of  the  same  color  and  the  No.  84  solder  is  actually  liOk.  tine, 
there  will  be  no  line  of  deniarkatiou  evident  in  the  finished 
work. 

INLAY  ABUTMENTS 

The  shell  for  the  inner  inlay  may  be  cast  with  Casting 
Gold  "D"  and  adapted  to  the  cavity  by  burnishing.  The 
tube  is  then  soldered  and  completed  with  No.  84  solder.  The 
outer  inlay  matrix  can  then  be  made,  using  the  comparatively 
soft  but  high  fusing  plate  gold  No.  1  and  Casting  Gold  "C," 
instead  of  pure  gold  and  coin  gold. 

CONSTRUCTION  OF  SADDLES 

The  saddles,  if  swaged  of  platinum,  may  be  reinforced 
with  Casting  Gold  "B"  or  "C,"  instead  of  coin  gold,  or  the 
saddles  may  be  swaged  of  No.  1  plate  (softer  than  No.  2)  and 
reinforced  with  Casting  Gold  "C."  If  the  saddles  are  to  be 
cast;  Casting  Gold  "B"  or  "C"  should  be  selected  according 
to  the  blow-pipe  used. 

CONSTRUCTION   OF  DUMMIES 

In  constructing  the  dummies  (if  all  porcelain),  the  bases 
and  dowels  may"  be  cast  with  either  "B"  or  "C"  and  attached 
to  the  saddles  with  the  84  or  76  solder. 

They  may  also  be  made  by  burnishing  .34  g.  pure  gold 
backings  to  the  prepared  porcelain  crowns,  fitting  and  sol- 
dering dowels  made  of  "Elastic"  gold  or  type  four  clasp 
metal  to  the  backings  (or  boxes)  and  attaching  the  com- 
pleted backings  to  the  saddles  with  84  and  76  solder. 

REMARKS 

The  author  cannot  close  without  calling  attention  to  the 
fact  that  a  broad  conception  of  the  scientific  principles  in- 
volved in  the  chemical  and  ]ihysical  behavior  of  the  various 
materials  utilized  in  connection  with  the  construction  of 
prosthetic  restorations  is  a  most  potent  factor  toward  the 
attainment  of  the  ideal. 

He  has  been  aided  materiallv  in  arriving  at  the  conclu- 


AN    OUTLINE    OF    METALLURGY  1063 

sions  presented  herein  by  the  kindness  of  Mr.  H.  C.  Ney, 
president  of  the  J.  M.  Ney  Co.,  who  unstiutingly  placed  at 
the  author's  command  all  the  facilities  of  their  metallurgical 
research  laboratory  in  Hartford.  ("Dental  Metallurgy," 
Weinsteiu.) 

IRON 

Iron,  like  gold,  has  hecn  known  and  used  since  the  earliest 
times.  It  is  almost  uni\ersally  distributed  over  the  earth  in 
some  form  or  other.  The  oxide  of  iron  in  the  form  of  red 
and  yellow  ochre  is  the  principal  coloring  pigment  in  clay, 
sand  and  rocks.  The  ores  of  iron  are  also  found  in  abnost 
every  country  on  the  face  of  the  globe.  These  are  in  the  form 
of  oxides,  carbonates  and  sulphides,  and  their  name  and 
chemical  composition,  according  to  Bloxam.  are  given  in  the 
table  below : 

Common  Xaiiie.  CJteiiiicdl  Nmiic.  Coiiiposiiio)/. 

Magnetic  iron  ore.  Protosesquioxide  of  iron.  Fcs  O4. 
Bed  haematite.       Sesqnioxide  of  iron.  Fe,  0:,. 

Specular  iron.         Sesqnioxide  of  iron.  Fe^  O.,. 

Brown  haematite.  Ilydrated  sesqnioxide  of 

"iron.  2  Fe,  ( ),  3IL  O. 

Si)athic  iron  ore.     Carbonate  of  iron.  Fe  0  CO^. 

Clay  iron  stone.       Carbonate    of  iron  with 
clay. 

{Carbonate    of   iron   with 
clay     and     bituminous 
matter. 
Iron  i)yrites.  Bisulphide  of  iron.  Fe  Sa. 

Iron  very  rarely  occurs  native,  owing  to  its  strong  atlinity 
for  oxygen  and  other  non-metallic  elements.  It  is  found  na- 
tive in  meteorites  and  in  minute  particles  in  basaltic  rocks, 
but  not  in  quantity  sufficient  to  be  of  recognized  value. 

Magnetic  iron  ore  is  the  protosesquioxide  of  iron,  and  is 
commonly  called  lodestone  when  strongly  magnetic,  and  pos- 
sesses the  property  of  attracting  small  ]iarticles  of  iron 
similar  to  a  horseshoe  magnet.  It  furnishes  a  most  excellent 
quality  of  iron,  examples  of  which  are  the  Wootz  steel  and 
the  Swedish  iron.  . 

Red  haema'iie,  so  called  from  its  dark,  blood-red  color, 
is  a  sesquioxide  of  iron.  It  is  a  remarkably  abundant  ore, 
being  found  all  over  the  world,  and  contains  about  70  per 
cent  iron,  30  per  cent  oxygen. 


1064  AN    orTLINIO    OP"    MKTALLtTRrrY 

The  scsqnioxidc  sometiuios  occurs  us  a  steel-gray  iiiin- 
eral,  and  it  is  then  called  specular  iron  ore. 

Brown  haematite  is  also  a  very  common  ore  of  iron,  and 
is  the  hydrated  sesqxiioxide  of  iron,  containing  ahout  15  per 
cent  water.  It  is  sedimentary  in  character  and  is  often  mixed 
with' wood,  clay  and  sand.  The  lahe  ores  of  Europe  and  this 
country  are  of  this  variety. 

Spathic  iron  ore  is  the  carbonate  of  iron  and  occurs  crys- 
tallized in  veins  and  beds,  and  also  in  glol)ular  masses.  When 
first  mined  it  is  yellow,  but  soon  turns  brown  on  exposure 
to  air.  Most  of  the  iron  used  by  the  Krup]i  iron  works  of 
Essen  is  derived  from  this  ore. 

Clay  ironstone  is  the  carbonate  of  iron  with  clay,  and 
contains  about  34  per  cent  of  iron.  It  often  occurs  with  or 
accompanies  coal  formations,  of  which  it  is  the  characteristic 
ore. 

Black  band.  When  clay  ironstone  contains  more  than 
10  per  cent  coaly  matter  it  resembles  shale,  slate  or  cannel 
coal,  and  is  a  valuable  ore  for  the  reason  that  the  coal  it  con- 
tains is  sufficient  to  burn  or  roast  it. 

Iron  pyrites  is  the  bisulphide  of  iron  and  is  of  a  bright 
yellow,  crystalline  structure,  with  a  distinct  metallic  luster. 
It  is  largely  used  in  the  manufacture  of  sulphuric  acid,  but  is 
not,  to  any  extent,  of  value  as  an  ore  of  iron. 

REDUCTION  OF  IRON  ORES 

Most  iron  ores  containing  carlion  dioxide  or  sulphur  are 
roasted  to  drive  off  these  elements  or  combinations  and  to 
reduce  the  ore  to  an  oxide.  The  ore  is  then  mixed  with  cer- 
tain proportions  of  calcium  carbonate  (limestone),  which 
acts  as  a  flux,  and  with  coal,  charcoal  or  coke,  and  thrown  into 
a  blast  furnace.  Under  the  influence  of  heat  and  the  blasts 
of  air  which  are  directed  into  the  bottom  of  the  furnace  the 
fuel  is  converted  into  CO,.  As  this  ascends  in  the  furnace 
it  x^asses  over  the  red-hot  fuel  in  the  liigher  portions  and  is 
converted  into  CO. 

The  carbon  monoxide  thus  formed  reduces  the  ore  to  the 
metallic  state  by  combining  with  the  oxygen  with  which  the 
iron  is  united  and  becomes  CO2  gas,  which  is  thrown  out  of 
the  furnace,  leaving  the  iron  free  and  uncombined.  This 
sinks  through  the  slag  (the  calcium  carbonate  which  has 
united  with  the  earthly  impurities  of  the  ore)  to  the  bottom 
of  the  furnace,  where  it  is  retained  in  a  fluid  condition  until 
sufficient  quantity  has  accumulated,  when    the    furnace    is 


AN    OUTLINE    OF    METALLURGY  1065 

tapped.  The  slag  from  time  to  time  is  removed  through  open- 
ings placed  higher  iu  the  furnace  than  that  from  which  the 
iron  is  drawn. 

The  metal  is  drawn  off  from  the  furnace  and  conducted 
into  a  ditch  or  trough  formed  in  the  sand,  and  from  this  into 
lateral  oj^enings  in  the  form  of  half  cylinders,  called  pigs.  In 
this  condition  it  is  crude  cast  iron,  and  can  l)e  used  in  this 
form  for  many  purposes  or  be  refined  by  sulisequeut  opera- 
tions and  reduced  to  the  imrer  condition  of  steel  or  wrought 
iron. 

For  general  purposes  iron  is  used  in  three  distinct  forms, 
as  cast  iron,  steel  and  ivroiight  iron,  all  consisting  of  iron 
with  more  or  less  carbon. 

Cast  iron  contains  the  largest  percentage  of  carbon,  the 
quantity  varying  from  11/2  to  7  per  cent.  Steel  contains  from 
1  to  11/2  per  cent  of  carbon,  and  wrought  iron  contains  the 
smallest  percentage  of  the  three  varieties,  having  less  than 
1/4  of  1  per  cent. 

PRODUCTION  OF  WROUGHT  IRON 

Wrougltt  iron  is  produced  from  cast  iron  by  extracting 
most  of  the  carbon  present.  This  is  accomplished  by  remelt- 
ing  pig  iron  and  directing  a  lilast  of  air  upon  the  heated  sur- 
face of  the  molten  metal  to  remove  some  carbon  and  other 
impurities  that  may  be  present,  after  which  it  is  cast  into 
molds,  and  is  now  known  as  plate  metal. 

The  second  step  is  designed  to  more  fully  free  the  metal 
from  its  carbon,  and  this  is  done  by  the  process  called  pud- 
dling. The  ingots  of  plate  metal  are  introduced  into  a  rever- 
beratory  furnace,  and  again  melted.  At  a  certain  stage  oxide 
of  iron  is  added  to  the  molten  metal  and  the  mass  mixed,  or 
puddled,  as  it  is  called,  with  long  iron  bars,  until  the  oxide  of 
iron  is  diffused  through  the  molten  metal. 

Under  continued  heat  the  oxygen  in  the  last  mass  added 
unites  with  the  carbon  in  the  i^late  metal  and  forms  COo, 
which  escapes  as  a  gas.  After  a  time  the  mass  assumes  a 
i:)asty  condition,  when  it  is  divided  into  balls  of  about  90 
pounds  each,  removed  from  the  furnace  and  subjected  to  in- 
tense pressure  by  rolls  and  converted  into  bars  or  blooms. 

Two  or  three '  of  these  blooms  are  again  heated  and 
welded  together,  and  the  rolling  process  repeated  once,  twice 
and  sometimes  three  times,  depending  on  the  quality  of  the 
iron  desired.  In  this  changed  condition  it  is  tough  and  fibrous 
and  elastic,  its  malleability,  ductility  and  tenacity  has  in- 


AN    OUTLINK    OF    MRTALLITRCY 


creased,  and  it   is  now  caiiaMc  of  hciiii;-  wcIiIimI,  a   proiicrty 
which  cast  ircm  docs  nol  possess. 


PRODUCTION    OF   STEEL 

Steel  is  maih'  in  two  ways,  first  by  direct  process  from 
cast  iron,  wliicli  is  known  as  the  Bessemer  pn/cess.  and  I'l-oni 
wrouglit  iron  by  tlie  cevinitation  process. 

THE   BESSEMER  PROCESS 

Tlie  Bessei)icr  /^roce.s.s  consists  in  melting  cast  iron  in 
large  crucibles  called  converters,  capable  of  liolding  several 
tons,  and  when  in  a  molten  condition,  directing  a  blast  of  cold 
air  upon  its  surface.  The  oxygen  in  the  air  unites  with  the 
carbon  in  the  molten  metal  and  frees  the  iron  from  car- 
bon in  this  manner  to  a  greater  or  less  extent,  depending  on 
the  length  of  time  the  process  is  continued.  The  best  results 
are  attained  by  purifying  the  iron  to  as  great  a  degree  as 
possible,  and  afterward  adding  a  given  quantity  of  cast  iron 
containing  a  known  iiercentage  of  carbon. 

THE   CEMENTATION   PROCESS 

Tlu:  cemeiildfioii.  pri)cess  consists  in  placing  bars  of 
wrought  iron  in  fire  brick  muffles,  together  with  alternate  lay- 
ers of  charcoal,  and  sealing  the  charge  in  so  as  to  exclude  the 
air.  Heat  is  then  applied  to  the  exterior  of  the  muffle  and 
maintained  for  7  or  8  days. 

Upon  examination  it  will  be  found  that  the  fil)rous  struc- 
ture of  the  iron  has  become  granular  and  that  its  hardness, 
elasticity  and  sonorousness  has  increased. 

It  is  more  brittle  and  less  malleable  and  ductile  than  be- 
fore. Its  surface  is  covered  with  blisters,  and  in  this  condi- 
tion is  known  as  blister  steel.  By  arranging  it  in  bundles, 
subjecting  it  to  heat  and  the  l)lows  of  a  trip  hammer,  it  is 
rendered  dense  and  comi)act. 

This  reduces  it  to  a  condition  known  as  shear  steel.  This 
process  is  sometimes  repeated,  and  it  is  then  known  as  double 
shear  steel.  When  blister  steel  is  remelted  and  cast  into  in- 
gots it  is  known  as  cast  steel. 

HARDENING    AND    TEMPERING    STEEL 

Steel  possesses  the  property  of  being  rendered  so  hard 
that  no  tools  of  ordinary  form  or  composition  will  affect  its 
surface.    This  is  accomplished  by  heating  it  to  a  full  (cherry) 


AN    OUTLINE    OF    METALLURGY  1067 

red,  and  suddenly  chilling  it  by  plunging  in  water  or  some 
medium  that  will  rapidly  conduct  away"  the  heat.  This  is 
called  full  hardening.  For  many  purposes  steel  in  this  condi- 
tion is  too  hard  for  use,  and  its  hardness  must  be  reduced  or 
tempered  to  meet  the  required  purposes. 

When  instruments  are  shaped  to  proper  form  they  are 
first  full  hardened.  The  surfaces  are  then  polished  so  that  the 
colors  which  appear  on  subsequent  heating,  and  which  indi- 
cate the  varying  degree  of  hardness,  may  be  accurately  ob- 
served. 

The  polished  steel  is  now  i)assed  back  and  forth  ihrougli 
a  Bunsen  flame  or  heated  in  any  other  manner,  if  more  con- 
venient, until  the  jiroper  color  appears,  when  the  instrument 
.sliould  be  suddenly  cooled  to  prevent  further  reduction  of  its 
hardness.  Sometimes  an  alloy  of  tin  and  lead,  which  melts  at 
a  known  temperature,  is  used  for  drawing  the  temper  to  the 
required  point. 

Bessemer  steel  usually  contains  such  a  small  percentage 
of  carbon  that  it  is  not  possible  to  render  it  full  hard,  and, 
consequently,  it  cannot  be  tempered. 

All  dental  instruments,  especially  edge  tools,  should  be 
made  from  the  finest  tool  steel. 

The  following  table  indicates  the  various  colors  as  they 
appear  on  steel  when  drawing  the  temper,  the  yellows  appear- 
ing first.  It  also  indicates  the  alloy  that  may  be  used  for 
securing  any  given  temper: 

TEMPERING  STEEL.  ALLOYS  FOR  TEMPERING 

Color.  Temper.  Lead.  Tin.  Melting 

points. 

Very  faint  yellow  to  Lancets,     razors,     surgical     in.struments, 

pale  straw  color. .        enamel  chisels 7  85      4  215°— 232°  C 

Full  yellow Excavators,  very  small  cold  chisels 10           4  243°  C 

Brown Pluggers,  scissors,  pen  kniyes 14           4  254°  C 

Brown   with    purple  Aires,    plain   irons,    saw^s,   cold   chisels — 

spots large.    19           4  265°  C 

Purple Table  kniyes,  large  shears 30           4  276°  C 

Bright  blue Swords,  watch  springs 48           4  287°  C 

Full  blue Fine  saw.s.  augers       50           4  293°  C 

Dark  blue Hand  and  pit  saws.                 Boiling  oil.  315°  C 

PLATINUM 

Platinum  was  discovered  in  17;]5  in  the  province  of 
Choco,  Columbia,  South  America,  in  the  sands  of  the  river 
Pinto.  The  credit  of  this  discovery  belongs  to  Antonio  de 
Ulloa,  a  Spanish  naval  officer  and  explorer.  Six  years  later 
an  Englishman,  a  Mr.  Wood,  who  was  traveling  in  Jamaica,, 
secured  some  specimens  of  this  metal  and  presented  them 
to  Watson,  a  noted  chemist  at  that  time,  who  recognized  in 
them  the  presence  of  an  unknown  metal,     Some  years  later 


Temp 

era- 

ture 

!15°— 232°C 

243° 

C. 

254° 

(• 

265" 

0 

276° 

T 

287" 

■V. 

293" 

v. 

315" 

c 

1068  AN    OUTLINK    OF    METALLUFtGY 

ScluifTci-,  wlio  was  iwaiiiiiiiiiu-  tlu'  new  iiiclal.  (Icclait'd  it  to  be 
"wliite  gold."  Ill  Spain  it  was  called  "piatina  del  Piuto," 
whifli,  translated,  moans  "little  silver  of  the  Pinto,"  and  from 
wliicli  tlie  present  name,  phitiiniiii,  was  derived. 

In  ISO.')  Wollaston  discovered  two  other  metals  associated 
witii  platimnn,  viz.,  palladium  and  rhodium. 

About  the  same  time  Tennant  discovered  iiidiiun  and 
osmium. 

In  1828  Berzelins  analyzed  pohixi^ne,  the  Siberian  plat- 
inum mineral,  and  found  it  contained  platinum,  iron,  pal- 
ladium, iridium,  rhodium,  osmium  and  coi)])er.  With  the  ex- 
ception of  iron  and  copper,  these  metals  lariiely  constitute 
what  is  known  as  the  platinum  group. 

DISTRIBUTION 

Platinum  is  found  in  many  parts  of  the  world.  South 
America,  Australia,  Canada,  United  States  and  Mexico — all 
yielding  moderate  amounts. 

Eecently  some  discoveries  of  vein  platinum  in  Wyoming 
have  been  made  which  promise  to  be  very  productive. 

The  largest  bulk  of  the  world's  supply  comes  from  Rus- 
sia, whose  i)latinum  placers  and  mines  have  1)ecome  world 
renowned. 

The  total  production  in  that  country  from  1824  to  the 
present  time  amounts  in  round  numbers  to  250,000  pounds. 

Platinum  was  used  as  money  in  Russia  from  1828  to  1845. 
During  this  period  the  volume  of  coinage  amounted  to  4.250,- 
000  roubles,  or  about  $3,000,000. 

The  production  of  platiniim  during  the  i)eriod  of  its  coin- 
age was  greatly  stimulated,  which,  however,  almost  entirely 
ceased  when  it  was  demonetized. 

The  great  demand  for  platinum  in  recent  years  for  elec- 
trical, chemical  and  general  scientific  purposes  has  been  so 
marked  that  the  metal  is  being  as  eagerly  sought  for  as  is  gold 
in  all  of  the  principal  productive  fields  of  the  world.  On 
account  of  the  great  demand  and  limited  supply,  it  ranks  in 
value  very  much  above  gold. 

OCCURRENCE 

Platinum  usually  occurs  in  nature  in  placer  deposits,  sim- 
ilar to  gold,  frequently  accompanying  the  latter  in  the  allu- 
vial deposits  of  rivers. 

The  mother  lode,  from  which  the  placer  de])osits  are  de- 
rived, consists  usually  of  serpentine  or  magnesium  iron 
silicate,  which  is  closely  related  to  chrysolite. 


AN    OUTLINE    OF    MKTALLUHr,Y  1069 

PliK'cr  pijitiiiuiii  usually  dccurs  in  roiindcd  n'raiiis,  tinkers 
or  pellets,  nccasidiially  nuggets  of  iiicdiuin  size  are  t'ound, 
and  ill  two  (ir  tliicc  iiistaiiees  large  (uics  weighing  from  15  to 
21  poniids  lia\c  liccn  discox'ered.  Tlic  largest  one  ineiilioned 
is  preserveil  in  the  Demidoff  innseinn. 

PHYSICAL   PROPERTIES 

Pure  platinum  is  a  very  soft  metal,  tin  white  in  color. 
It  is  not  readily  acted  on  by  acids,  witli  the  exception  of  nitro- 
niuriatic,  in  which  it  is  readily  dis.solved.  It  does  not  oxidize 
even  at  very  high  temperatures,  and  for  this  reason  lills  a 
]>lace  in  the  arts  and  sciences  for  which  the  oxidizahle  metals 
are  unsuited. 

MALLEABILITY 

Platinum  is  \<'ry  malleable,  and  can  be  beaten  out  into 
extremely  thin  foil,  in  which  form  it  is  used  for  many  pur- 
poses.   It  ranks  sixth  in  this  quality  among  the  other  metals. 

DUCTILITY 

'Phis  metal  can  be  drawn  into  exti'emely  fine  wire.  Dr. 
Arendt  states  that  a  cylinder  of  platinum  5  inches  long  and  1 
inch  in  diameter  can  be  drawn  into  a  wire  sufficiently  long  to 
encircle  the  globe.  The  fine  wire  used  in  microscopic  ej^e- 
])ieces  is  made  by  coating  platinum  wire  with  silver  and  draw- 
ing this  composite  wire  to  the  finest  possible  state,  then  dis- 
solving off  the  silver  with  nitric  acid. 

TENACITY 

In  point  of  tenacity  platinum  occupies  third  rank.  This 
pi()])erty  is  so  marked  in  ])latinum  as  to  render  it  es])ecially 
valuable  for  dowels  in  crowns  and  for  the  truss  work  in  porce- 
lain bridges.  The  addition  of  from  10  to  15  per  cent  of 
iridium  greatly  increases  its  tenacity,  as  well  as  its  liardness, 
elasticity,  infusibility,  and  resistance  to  chemical  action. 

SPECIFIC  GRAVITY 

The  specific  gravity  of  ])latinum  is  21.4,  two  others  hav- 
ing greater  density — osmium  22.47  and  indium  22.40.  These 
three  are  the  heaviest  of  the  metals. 

CONDUCTIVITY  OF  HEAT 

Platinum  is  low  in  heat  conductivity.  Compared  with 
silver  at  100,  it  ranks  8.4.    Its  co-efficient  of  expansion  is  low, 


1070  AN    OUTLINE    OF    METALLURGY 

being  only  .OOOi).  For  this  reason  it  is  especially  valuable  for 
the  ])ins  of  i)or('elain  teeth,  sinee  the  expansion  of  botli  the 
metal  and  jioreelain  is  nearly  the  same,  and  consequently 
there  is  less  liability  of  fracturing  the  porcelain  in  baking. 

CONDUCTIVITY    OF   ELECTRICITY 

Compared  with  siivci',  which  ranks  100  in  conductivity 
of  electricity,  i)latinuni  ranks  14.5,  or,  in  other  words,  this 
metal  offers  about  seven  times  more  resistance  to  the  passage 
of  a  current  than  does  silvei'. 

FUSING   POINT 

Platinum  fuses  at  1779  deg.  C,  the  oxyhydrogen  blowpii)e 
or  the  electric  arc  being  required  to  effect  it. 

Dr.  L.  Fj.  Custer  of  Dayton,  Ohio,  has  devised  a  simple 
yet  effective  method  of  fusing  platinum  scrap,  the  outline  of 
which  is  here  given  : 

The  first  method  consists  in  fastening  the  ])ositive  end 
of  a  wire  capable  of  carrying  a  110-volt  current  into  a  carbon 
block.  ^Vn  ordinary  battery  plate  will  answer  the  purpose. 
To  the  negative  pole  is  attached  an  electric  light  carbon  of 
ordinary  size.  A  resistance  coil,  lamp  or  electric  furnace 
should  be  included  in  the  circuit  capable  of  furnishing  from 
8  to  12  ohms  resistence  to  prevent  the  fuses  from  blowing  out. 

It  is  necessary  to  make  the  positive  and  negative  connec- 
tions as  described,  as  when  so  arranged  the  fusing  can  be  ac- 
complished more  rapidly  and  with  less  noise  than  when  re- 
versed. 

With  12  ohms  resistance  from  6  to  8  pwts.  can  be  fused  at 
once,  while  with  8  ohms  an  ounce  can  be  melted  at  one  time. 
By  keeping  the  edge  of  a  bulk  heated  and  adding  a  fresh 
supply,  the  mass  can  be  elongated  indefinitely.  As  much  as  10 
ounces  have  been  melted  in  this  manner  in  the  form  of  a  rod, 
and  the  rod  afterward  drawn  into  a  fine  wire. 

Platinum  fused  in  this  manner  is  harder  than  new  plat- 
inum, the  cause  assigned  being  due  to  a  small  per  cent  of 
carbon  uniting  with  the  platinum. 

To  obviate  this  hardness  a  second  method  was  devised, 
which  is  as  follows  : 

A  piece  of  heavy  platinum  wire  is  attached  to  the  posi- 
tive terminal,  and  this  is  laid  on  a  block  of  lime  so  shaped  as 
to  serve  as  a  receptacle  for  the  scrap.  The  other  terminal 
consists  of  a  brass  rod  five-eighths  of  an  incli  in  diameter  and 
8  inches  long,  covered  most  of  its  length  with  wood  to  insulate 


AN    OUTLINE    OF    METALLURGY 


it.  In  Ihe  exposed  eml  a  slit  is  made,  in  whicli  a  nn.nget  of 
])latinnni  of  at  least  one-half  oz.  weight  is  fastened.  Too  small 
a  piece  would  fuse  in  the  are.  The  scraps  are  laid  on  the 
platinum  wire  forming  the  positive  terminal,  which  is  placed 
in  the  depression  in  the  lime  hlock.  The  arc  is  established  by 
interposing  a  stick  of  carbon  between  the  negative  pencil  and 
the  scrap,  and,  when  established,  quickly  removing  it.  Tliis 
step  is  necessary  to  prevent  the  scrap  fusing  to  the  nugget 
on  the  negative  end. 

The  eyes  sliould  be  protected  by  wearing  glasses  of  the 
darkest  variety,  as  the  arc  light  is  intensely  brilliant.     This 

_-Wboti  HcLTi^le. 

,,BrdssRodL. 

Pla^iMum  Point. 
'Platinum  Wire 


-pole.. 


metliod  of  fusing  iilatinum  is  recommended  as  practical  for 
dental  laboratory  procedures. 

In  a  fused  condition  platinum  absorbs  oxygen,  and  when 
cooling  "spits"  as  the  gas  is  given  off,  none  of  it  being  re- 
tained or  occluded  when  cold. 

When  a  jet  of  hydrogen  is  directed  on  spongy  i)latinum, 
the  latter  begins  to  glow,  and  the  gas  ignites. 

Platinum  black  is  formed  by  adding  platinum  chloride 
solution  to  a  boiling  mixture  of  3  parts  of  glycerine  and  2 
parts  of  caustic  soda.  The  platinum  is  thrown  down  as  a 
black  powder.  In  this  form  it  absorbs  about  800  times  its 
volume  of  oxygen  from  the  air. 

USES 

Platinum  is  used  for  many  purposes  in  dentistry,  espe- 
cially in  combination  with  porcelain.    It  is  used  as  base  plates 


1072  AN    OlITLINIO    ()!•'    MKTAI.LtTRGY 

I'di'  (■(i)i(iiiii(ius  i;iiiii  ilciitui-cs,  the  iiiclal  piii'ts  and  trusses  in 
continuous  i;uni  dcnlui'cs,  llic  metal  pai'ts  and  trusses  in 
jJorcH'hiin  crown  and  hridii'e  work,  as  a  matrix  nuiterial  in 
inlay  work,  for  pins  in  poicelain  teeth  and  I'or  electric  fur- 
nace constriu'tioii.  It  is  also  used  in  combination  with  gold 
in  the  form  of  foil,  foi'  tillins'  teeth,  heini;,-  harder  and  more 
neutral  in  color  than  ]aire  gold.  It  requires  more  care  in 
condensation  than  pure  gold,  however,  to  develop  its  welding 
property  in  the  highest  degree. 

In  the  chemical,  electrical  and  sci entitle  fields,  it  has  a 
wide  range  of  usefulness,  being  utilized  in  many  instances  for 
purposes  for  which  no  otliei-  metal  is  ada])ted. 

ALLOYS 

Its  ]3rincipal  alloys  for  dental  ])ur])oses  are  its  combiiui- 
tions  with  iridium,  for  hardening  and  increasing  its  tenacity, 
and  gold  in  the  composition  of  solders  for  platinum,  and  for 
clasp  metal. 

It  is  also  comhined  with  silver,  the  resulting  alloy  being 
harder  than  either  of  component  metals  and  less  oxidizable 
than  silver.  This  alloy  is  known  as  dental  alloy,  and  is  used 
to  a  considerable  extent  in  Europe  as  a  base  for  artificial 
dentures. 

DENTAL  ALLOY 

Silver   70  or  80 

Platinum    30  or  20 

Gold  solder  can  be  used  in  conjunction  with  this  alloy. 

PLATINUM   SOLDER   AND   CLASP   METAL 

These  formulas  are  given  in  connection  with  the  alloys  of 
gold. 

IRIDIUM 

Iridium  is  one  of  the  metals  of  the  platinum  group,  and 
resembles  the  latter  in  some  respects,  but  is  much  harder. 
When  combined  with  ])latinum,  the  resulting  alloy  has  greater 
tenacity  and  hardness  than  platinum,  and,  therefore,  for  this 
quality  alone  it  is  valuable  for  dental  uses. 

The  specific  gravity  of  iridium  is  :2:].40,  atomic  weight 
192.65,  and  fusing  jtoint  2200  deg. 

On  account  of  its  hardness,  it  is  used  alone  and  in  com- 
bination with  osmium  for  watch  and  compass  bearing,  the 
knife  edges  of  delicate  balances,  and  for  the  nibs  of  gold  pens. 
It  ranks  in  value  somewhat  higher  than  platinum. 


AN    OUTLINE    OF    METALLURGY  1073 

SILVER 

Silver  is  fuiiiul  in  iiiany  parts  of  tlie  world,  but  the  West- 
ern Continent  has  the  richest  and  most  extensive  deposits 
known. 

It  is  im]iossihle  to  l)riefly  enumerate  the  many  practical 
uses  found  for  this  metal. 

It  is  brilliant  white  in  color,  very  soft,  malleable  and 
ductile,  and  moderately  tenacious.  Its  speciiic  gravity  is 
10.53,  specitic  heat  .056,  and  it  fuses  at  960  deg.  C.  It  is  the 
best  known  conductor  of  heat  and  electricity,  and  is  taken  as 
the  standard  of  measurement  of  all  of  the  metals  in  these 
properties,  being  rated  at  100. 

ORES   OF  SILVER 

Silver  sometimes  occurs  luiiire,  but  is  more  often  asso- 
ciated with  other  metals  and  with  non-metallic  substances. 
One  of  the  in-incii)al  ores  of  silver  is  the  sulphide  Ag.  S, 
called  argeiitite.  This  is  grayish  black  in  color,  and  is  read- 
ily fusible.  It  contains  about  87  of  silver.  Pyrargyrite  Ag,, 
Sb  S3.  Silver  copper  glance  (Ag  Cu)2S.  Stephanite  Ags  Sb 
S4,  with  lead  as  argentiferous  galena  and  in  several  other 
combinations. 

REDUCTION 

The  reduction  of  silver  is  accomplished  by  three  princi- 
pal methods. 

First.     Amalgamation. 
Second.     By  the  wet  method. 
Third.     By'  the  lead  method. 

AMALGAMATION 

In  the  first  process,  the  silver,  after  being  reduced  to  a 
chloride,  is  amalgamated  with  mercury,  from  which  it  is  re- 
covered by  distilling  the  latter  off.  There  are  three  different 
methods  of  recovery  of  silver  by  amalgamation,  each  of  whicli 
is  more  or  less  complicated,  and  in  this  treatise  it  is  not  ad- 
visable to  enter  into  the  details  of  them. 

WET  METHOD 

There  are  several  wet  i)rocesses,  all  of  which  depend 
upon  the  solubility  of  the  sulphide  and  chloride  of  silver  in 
water,  or  some  other  solvent,  from  which  the  silver  is  thrown 
down  by  a  precipitant,  usually  copper. 


AN    OUTLINIO    OK    MRTALLUUfiY 


THE  LEAD  METHOD 


By  this  iiu'tliod  the  .silver  is  eouceiitratcd  in  a  (|uaiitity 
of  k'ad,  from  whicli  it  is  recovered  by  cupellatioii. 

Cupellation  consists  in  heating  an  alloy  of  silver  and  lead 
in  a  porous  cupel,  or  shallow  crucible,  made  from  i)re))ared 
bone  ash.  Under  the  influence  of  heat,  the  lead  is  oxidized 
and  absorbed  by  the  ])or()us  cupel,  while  the  silver  remains 
in  the  crucible. 

USES  IN   DENTISTRY 

Silver  occupies  a  ])rominen(  ])lace  in  the  dental  office  and 
laboratory.  It  is  the  principal  metal  used  in  the  compounding 
of  dental  amalgam  alloys.  It  is  iised  as  an  alloying  agent  with 
copper  and  gold  in  the  various  gold  plates  and  solders  used  in 
the  laboratory. 

Were  it  not  for  the  fact  that  sulphur  has  such  a  strong 
affinity  for  silver,  as  to  readily  discolor  it,  the  latter  would 
have  a  much  greater  range  of  usefulness.  For  the  reason 
mentioned,  although  it  possesses  most  of  the  necessary  re- 
quirements, silver  is  not  suitable  as  a  base  for  artificial  den- 
tures, nor  for  crowns  and  bridges.  Before  the  introduction 
of  vulcanite,  however,  it  was  used  extensively  as  a  base  i>late 
because  of  its  cheapness  as  compared  with  gold  or  continuous 
gum  dentures. 

It  is  not  possible  to  attach  teeth  to  silver  base  plates  with 
vulcanite,  because  the  suli)hur  in  the  rubl>er  acts  on  the  silver, 
forming  silver  sulphide.  It  disintegrates  the  rubber  to  such 
an  extent  that  all  attachment  of  vulcanite  to  base  plate  is  de- 
stroyed or  never  effected. 

Silver  is  not  readily  acted  upon  by  oxygen,  but  when 
fused  it  mechanically  absorbs  about  22  times  its  volume  of  this 
gas.  The  "spitting"  so  noticeable  when  fused  silver  solidi- 
fies, is  due  to  the  forcing  out  or  escape  of  the  oxygen,  nearly 
all  of  which  is  expelled. 

This  peculiar  affinity  between  oxygen  and  silver  in  a 
fused  state  renders  the  jn-oduction  of  sharp  castings  of  this 
metal  a  difficult  matter. 

ALLOYS  OF  SILVER 

U.  S.  coin  silver  is  composed  of  90  parts  silver  and  10 
copper.  The  latter  is  added  to  harden  the  silver,  which,  un- 
alloyed, is  almost  as  soft  as  pure  gold. 

In  Great  Britain  and  Europe  the  profession  is  using  an 
alloy  composed  of  silver  and  jilatinum  for  dental  purposes. 


AN    OUTLINE    OF    METALLURGY  1075 

It  does  uot  discolor  quite  so  readily  as  silver  alone,  but  is 
not  by  any  means  free  from  the  action  of  snlplmr.  It  is  more 
rigid  than  coin  silver,  and  in  some  months  can  be  worn  for  a 
long  time  without  discoloring. 

In  compounding  this  alloy,  the  rule  commonly  followed 
of  melting  tlie  highest  fusing  ingredient  first  is  reversed.  The 
platinum  is  rolled  into  a  very  thin  ribbon,  the  silver  melted, 
and  the  platinum  gradually  fed  into  it.  The  two  metals  will 
unite  at  a  temperature  far  below  the  fusing  point  of  platinum. 

Silver  solders  are  composed  of  silver  and  copper,  with 
some  other  ingredient,  usually  zinc,  to  reduce  the  fusing 
point.  The  following  are  standard  formulas  for  some  of  the 
solder  used  in  the  dental  laboratory  and  by  jewelers : 

Low  fusing.  High  fusing. 

Silver    6     Silver     (J 

Copper    3     Copper    2 

Zinc    2     Zinc    1 

A  method  followed  by  jewelers  is  to  take  a  silver  coin, 
add  one-half  its  weight  of  spring  brass  wire,  and  fuse  under 
a  flux.    Solder  prepared  in  this  manner  usually  flows  readily. 
Purple  of  Cassius,   a   jngment  used  to   impart   a   pink- 
color  to  porcelain  enamel,  is  formulated  as  follows : 

Silver 432  grs. 

Gold 48  grs. 

Tin 36  grs. 

The  gold,  silver  and  tin  are  melted  together  in  the  order 
named,  and  granulated  by  pouring  into  cold  water,  repeating 
the  process  several  times  to  insure  through  mixture  of  the 
metals. 

The  granulated  alloy  is  then  treated  with  nitric  acid  to 
remove  the  silver,  the  residue  is  a  brown  powder  of  unknown 
composition,  but  containing  gold  and  tin,  which  is  called 
Purple  of  Cassius,  and  which,  as  before  stated,  will  produce 
varying  shades  of  pink  in  porcelain,  according  to  the  amount 
used.  It  may  also  be  prepared  by  adding  a  solution  of  stan 
nous  and  stannic  chlorides  to  auric  chloride. 

THE  CHEMISTRY  OF  PHOTOGRAPHY 

Some  of  the  salts  of  silver,  as  the  bromide  and  the  iodide, 
are  exceedingly  sensitive  to  the  influence  of  light,  and  when 
('X])osed  to  it  are  readily  reduced  to  black  metallic  silver  on 
being  subjected  to  the  action  of  various  reducing  agents. 


1076  AN    OUTLINE    OF    METALLURGY 

Pliotographio  plates  or  liluis  ai'e  eoal('(l  with  a  layci-  of 
gelatin  eiuulsiou,  coutaiuiiig  one  or  both  ol'  tlie  salts  men- 
tioned. The  emulsion  is  applied  to  one  side  of  the  i)lates 
oidy,  in  the  dark,  or  with  ruhy  light,  allowed  to  dry,  after 
which  they  are  wrapped  in  light-proof  paper,  packed  and 
sealed  in  boxes  or  packages,  in  wliich  condition  they  nnist  be 
kept  until  ready  for  use. 

When  a  plate  so  prepared  is  i)laced  in  the  plate-holder 
of  the  camera  and  light  is  transmitted  to  it  through  the  lens, 
the  various  areas  of  the  plate  are  atTected  in  different  de- 
grees by  the  light  which  falls  i;pon  them,  according  to  the 
depth  or  intensity  of  the  shadows  and  lights  of  the  view  re- 
flected and  the  time  of  exposure.  Where  no  light  falls,  the 
silver  salt  is  unaffected.  Medium  shadows  produce  moderate 
decomposition,  while  bright  light  atfects  the  silver  salt  most 
intensely.  When  an  exposed  plate  is  examined  under  ruliy 
light,  no  visible  altei'aticm  in  the  film  can  be  seen  until  ))rought 
to  view  by  develophtg. 

To  develop  the  latent  inuige  and  make  it  visible,  the  plate 
is  immersed  in  a  licjuid  developer.  The  silver  salt  upon 
which  the  strongest  light  was  directed  is  first  and  most  read- 
ily decomposed  by  the  develo^jer,  being  resolved  into  metallic 
silver.  The  portions  not  so  strongly  affected  by  the  light 
are  acted  uiaon  more  slowly,  and  on  developing  sliow  corre- 
spondingly lighter  shadows.  When  the  image  shows  up  dis- 
tinctly and  clearly,  the  development  must  be  stopjied  imme- 
diate!}'; otherwise  the  plate  will  liecome  fogged  from  the 
action  of  the  developer  on  the  less  affected  portions  of  the 
silver,  which  will  in  time  be  reduced. 

The  development  is  arrested  and  the  plate  cleared  up 
l)y  immersing  it  in  a  solution  of  ln'])osulphite  of  soda,  which 
dissolves  out  the  unreduced  silver  bromide,  but  does  not  act 
readily  on  the  metallic  silver.  The  heavy  shades  and  shad- 
ows are  formed  by  the  reduced  or  metallic  silver,  which  is 
held  in  suspension  in  the  film  of  gelatin  and  thus  accounts 
for  the  varying  degrees  of  intensity  of  the  negatire. 

The  hypo,  as  it  is  called,  must  be  removed  by  thorough 
washing  before  the  negative  is  exposed  to  the  light,  other- 
wise the  silver  salt  which  is  dissolved  by  it,  but  not  yet  re- 
moved, will  thicken  the  shadows  and  the  transparency  of  the 
jilate  be  affected. 

Many  kinds  of  developers  are  in  use,  each  having  some 
peculiar  quality  which  renders  it  specially  adapted  for  some 
particular  purpose.     The  following  expresses  in  a  general 


AN    OUTLINE    OF    METALLURGY  1077 

way  the  chemical  action  which  occurs  in  the  use  of  any  of 
the  standard  developers : 

SAgCl  +  3FeS04  =  3Ag-  +  FeCh  +  Fe,(lSU,). 

The  negative  is  a  reverse  of  the  object  photographed,  the 
light  shades  being  dark  and  the  dark  tints  light.  To  obtain 
a  positive  or  true  likeness,  a  similar  process  is  carried  out, 
the  silver  salts  again  being  the  sensitized  factor  in  the  paper 
on  which  the  picture  is  to  be  ])riuted.  In  printing,  tlie  dark 
areas  of  the  negative  produce  light  tints  on  the  i)aper,  and 
tlie  light,  dark,  according  to  the  facility  with  which  the  liglit 
passes  through  negative  and  decomposes  the  silver  in  th.e 
sensitized  paper. 

Ag.I.,  the  iodide  Ag.Br.  bromide,  and  Ag.  CI.,  tlie  chlo- 
ride, are  used  in  photography. 

COPPER 

Copper  was  one  of  the  first  metals  known  to  the  ancients, 
probably  because  it  is  found  so  widely  distributed  over  the 
earth.  From  it  weapons,  ornaments,  and  useful  implements 
of  all  kinds  were  made.  The  ancients  employed  a  method  of 
tempering  edge  tools  made  from  this  metal,  which  is  now  con- 
sidered a  lost  art. 

Copper  is  distinguished  from  all  other  metals  by  its  red 
color.  It  is  very  soft,  mallealile,  ductile  and  tenacious.  It 
fuses  at  lOS-l^C,  or  a  little  below  pure  gold.  Copper  is  an 
excellent  conductor  of  electricity,  ranking  97,  silver  being 
100.  Its  specific  gravity  is  8.95,  sjiecific  heat  .09.3  and  atomic 
weight  63.6. 

Copper  is  not  readily  oxidized  in  dry  air  at  ordinary  tem- 
lierature,  but  is  easily  affected  under  tlie  influence  of  heat. 
In  moist  air  a  green  carbonate  is  quickly  formed,  and  whea 
acted  u])on  l)y  acid  fumes,  it  oxidizes  rai)idly. 

ORES 

Copper  frequently  occurs  native  in  large  masses,  par- 
ticularly in  the  Lake  Superior  region.  The  most  common 
ores  of  copper  are  tabulated  below : 

Cu  O2 — cuprite,  or  red  oxide. 

Cu  0 — Melaconite,  or  black  oxide. 

Cu  Fe  S..  Chalcopvrite — copper  p\Tites. 

Cu  CO.  Cu  H,  d.,— Green  malachite. 

(2  Cu  CO3  Cu  H,  02)— Blue  malachite. 

Cu;  S — Chalcocite — Copper  glance. 


AN    OUTLINIO    OF    METALLURGY 


REDUCTION 


Tlie  ores  of  copper  are  reduced  ))>•  two  principal  metli- 
ods,  known  as  the  dry  and  the  wet  method.  In  tlie  dry  metliod 
the  ore  is  snljjected  to  treatment  in  the  reverheratory  furnace, 
which  drives  oif  impurities  and  leaves  it  free  as  a  sulphide.  It 
is  then  strongly  heated  with  sand,  which  reduces  it  to  an  ox- 
ide. Tlie  oxide  is  then  mixed  with  some  form  of  carbon  and 
sul)jected  to  a  very  high  temperature.  The  oxygen,  in  com- 
bination with  the  copi)er,  unites  with  the  carbon  to  form  CO.. 
which  escapes,  leaving  the  metal  free. 

When  the  wet  method  is  employed,  the  ore  is  mixed  with 
rock  salt  and  calcined,  which  converts  the  copper  into  a  sol- 
uble cupric  chloride.  The  calcined  ore  is  then  lixiviated  with 
water,  and  from  the  resulting  solution  the  copper  is  thrown 
down  in    a  metallic  state  by  the  addition  of  scrap  iron. 

USES 

Copper  is  used  for  many  purposes,  and  in  great  quan- 
tities, unalloyed,  especially  in  the  electrical  field.  On  land, 
and  under  the  sea,  hundreds  of  thousands  of  miles  of  copper 
wire  are  laid,  and  by  means  of  the  telephone  and  telegraph, 
communication  with  most  parts  of  the  civilized  world  is  pos- 
sible in  a  few  minutes  or  hours'  time  at  most. 

In  every  dynamo  and  motor,  copper  wire  is  used,  and  in 
numberless  instances  a  single  machine  contains  many  miles 
of  wire. 

It  is  used  in  the  manufacturing  and  chemical  industries, 
and  occupies  a  field  no  other  metal  can  fill. 

ALLOYS 

Cojiper  forms  the  basis  of  two  prominent  classes  of  al- 
loys— l)rasses  and  bronzes — and  occupies  a  minor  but  imjior- 
tant  place  in  the  composition  of  many  other  useful  and  val- 
uable alloys,  particularly  in  the  compounding  of  gold  plate 
and  solder. 

BRASS 

Under  this  head  may  be  included  most  of  the  alloys  of 
copper  and  zinc.  Brasses,  with  a  wide  range  of  strength 
and  color,  can  be  produced  by  alloying  copjter  and  zinc  to- 
gether in  varying  proportions. 

Name  and  Color.  Copper.    Zinc. 

Pinchbeck  (reddish  vellow) 88.8         11.2 

Sheet  brass  (yellow) 84  16 


AN    OUTLINK    OF    METALLURGY  1079 

Nfiinc  and  ( 'olor.  ('(ii>pcr.  Ziiie. 

Similor    (yellow)    80  '20 

Brass  wire  (bright  yellow)   70  30 

White  brass  (very  light ) o4  (>() 

Common  brass  (full  yellow) (54  '.Uj 

Machine  brasses,  bearing  metal,  iiumj)  valves,  steam 
whistles,  cog  wheels,  etc.,  usually  contain  some  tin,  in  addi 
tion  to  copper  and  zinc. 

BRONZES 

Bronzes  are  metallic  alloys,  composed  principally  of 
copper  and  tin.  They  cast  with  great  clearness  of  outline,  and 
are  therefore  extensively  used  in  making  statues,  medals, 
busts,  and  were  also  formerly  much  used  in  making  cannon 
and  field  ordnance. 

P  h  o  s  - 
Copper.       Tin.     ]ihorous.    Zinc. 

U.  S.  ordnance  bronze 90  10 

Phosphor  bronze   ()0.;14  8.90         .7(i 

Statuary  bronze 84.42  4.30  11.28 

Speculum  metal  66.66         33.34 

Bell   metal    72-85         28-15 

Aluminum  bronze  consists  of:  Coi)per,  90;  and  alumi- 
num, 10  ])arts.  This  alloy  very  much  resembles  gold  in  color, 
is  not  readily  tarnished,  has  pronounced  elastic  property,  can 
be  turned  and  engraved,  and  fuses  at  about  860°  C. 

ALUMINUM 

Although  aluminum  is  the  most  abundant  metal  in  the 
earth's  crust,  it  never  occurs  native.  It  forms  the  basis  of 
the  feldspar  rocks,  which  when  disintegrated  by  the  action 
of  the  elements,  lose  their  potassium  and  sodium.  The  residiie 
is  silicate  of  alumiimm,  or  common  clay,  which  is  found  almost 
everywhere.  Clay  containing  impurities  and  coloring  mat- 
ter as  iron  oxides  is  known  as  sienna,  umber,  ochre.  Fuller's 
earth,  etc.,  according  to  composition. 

It  also  enters  into  the  composition  of  slate  rocks,  mica, 
jumiice  stone,  and  is  found  in  many  other  forms  too  numerous 
to  mention. 

It  occurs  in  crystalline  form  as  an  oxide,  and  among  the 
many  interesting  and  curious  results  of  this  combination,  may 
be  mentioned  the  ruby,  garnet,  sapphire,  emerald,  topaz  and 
amethvst.     Corundum  and  emery,  substances  in  crystalline 


1080  AN    OUTLINIO    OF    METALLTTROY 

I'oriii  and  cxtrciiic  liardiicss,  used  for  ni'iiiditiu'  and  pulishiiig 
j)Ui'))()S('s,  ai'c  also  iriflndcd  in  this  class  of  oxides. 

REDUCTION 

Must,  oi'  the  aliiuiinuni  at  the  [tresent  time  is  produced  at 
the  gigantic  electrical  works  at  Niagara  Falls,  N.  Y.,  and  is 
o])tained  by  the  electrolytic  process. 

The  i)rinciple  of  reduction  depends  u])on  the  i)o\ver,  the 
fused  double  fluoride  of  aluminum  and  i)otassiuni  or  sodiinii 
has  of  reducing  the  ores  of  aluminum.  The  apparatus  con- 
sists of  a  large  iron  box,  lined  with  carbon,  in  which  there  is 
a  receptacle  for  the  ore  about  -i^'-^  feet  long  by  L'Vo  feet  wide 
and  G  inches  in  depth. 

The  carbon  lining  acts  as  the  cathode.  Tliere  are  usually 
40  anodes,  consisting  of  carbon  cylinders  3x10  inches,  sup- 
ported above  the  pot  in  which  the  ore  is  placed,  their  lower 
ends  resting  in  the  bath  of  fused  fluorides.  The  heat  is  de- 
veloped by  the  resistance  of  the  fluoride  to  the  passage  of 
the  current  from  the  anode  to  the  cathode.  The  ore  to  be 
reduced  is  ]jlaced  in  the  bath  of  fluoride,  and  renewed  from 
time  to  time  as  that  in  the  pot  becomes  reduced. 

The  resistance,  and  consequently  the  heat,  increases  as 
the  ore  is  reduced,  which,  by  means  of  an  incandescent  lamp 
attached  to  the  furnace,  becomes  apparent  to  the  furnace  at- 
tendant by  the  brightening  of  the  lamp,  when  he  immediately 
reiilenishes  the  charge. 

The  ore  introduced  in  the  furnace  is  an  oxide,  and  the  re- 
action under  heat  is  due  to  the  oxygen  in  combination  with  the 
metal  uniting  with  the  carbon  of  the  anodes  forming  COo, 
which  escapes,  leaving  the  metal  free.  The  process  is  con- 
tinuous, being  carried  on  day  and  night.  The  metal  is  drawn 
off  every  twenty-four  hours,  100  pounds  per  furnace  being 
the  usual  amount  reduced  in  that  length  of  time.  As  there 
are  more  than  100  of  these  furnaces  in  operation  in  a  plant, 
the  yield  per  day  is  about  10,000  pounds.  A  current  of  20 
volts  and  1700  amperes  is  required  to  effect  the  reduction. 

PHYSICAL   PROPERTIES 

Aluminum  is  a  white  metal,  with  a  slightly  bluish  tint, 
reseml)ling  zinc  in  color.  It  is  soft  and  workable,  capable  of 
taking  a  high  polish,  and  does  not  discolor  appreciably  on 
exposure  to  air,  moisture  or  siilplnir.  It  is  not  readily  acted 
upon  bj'  nitric  or  sulphuric,  but  can  readily  be  dissolved  in 
hvdrochloric  acid  or  solutions  of  caustic  potash  or  soda. 


AN    OUTLINE    OF    METALLURGY  1081 

Alumimun  is  very  malleable,  ductile  and  (juite  tenacious, 
ranking  eighth  in  respect  to  the  latter  property.  It  is  a  mod- 
erately good  conductor  of  heat  and  electricity,  ranking  about 
half  way  between  silver  and  platinum. 

Its  si:)ecific  gravity  is  2.6,  the  lightest  of  all  of  the  metals 
except  magnesium.  Its  atomic  weight  is  27.1,  specific  heat  — , 
and  its  melting  point  700°  C. 

Aluminum  is  soft,  and  in  working  it,  files  soon  clog.  It  is 
best  to  use  single  rather  than  cross-cut  files,  and  when  clogged 
they  may  l)e  cleaned  by  dijjping  in  a  solution  of  caustic  soda 
and  wasiiing  in  hot  water.  In  annealing,  aluminum  should  not 
be  heated  above  200°  C.  The  proper  heat  is  attained  when  n 
soft  wood  stick  will  leave  a  brown  streak  when  di'awn  across 
the  heated  surface. 

SOLDERING 

It  is  very  difficult  to  solder  successfully,  although  this 
operation  can  be  accomplished  under  proper  conditions.  The 
difficulty  is  supposed  to  be  due  to  a  film  of  oxygen  adhering 
to  the  surface,  which  by  means  of  the  known  fluxes  can  only 
with  difficulty  be  removed. 

Many  formulas  for  fluxes  and  solders  have  been  ])vo- 
posed,  some  of  which  are  successful  when  applied  with  skill. 
The  following  solder  and  flux  is  recommended  as  being  suc- 
cessfully used  in  the  manufacture  of  aluminum  jewelry: 

Zinc 80     or     85     or     90 

Al 20     or     15     or     10 

The  soldering  iron  is  dipped  in  a  mixture  of  copaiba 
balsam  3  parts;  Venetian  turpentine,  1  ]iart;  lemon  juice,  a 
few  drops. 

Another  method  recommended  by  Page  and  Anderson 
consists  in  spreading  ])owdered  silver  chloride  along  the  joint 
to  be  united,  and  applying  common  solder  with  a  l)lowpipe. 

USES 

Aluminum  can  be  applied  in  many  ways  in  dentistry.  It 
makes  an  excellent  base  for  dentures,  16  or  18  gauge  plate 
l)eing  recommended,  and  the  teeth  attached  with  vulcanite. 
Although  not  as  lasting  as  some  other  bases,  on  account  of 
the  action  upon  it  of  the  fluids  of  the  mouth,  its  lightness, 
cleanliness  and  good  conductivity  commend  its  use. 

Basei)lates  are  frequently  cast  over  models  of  investment 
nuiterial,  which  to  a  limited  extent  are  satisfactory,  but  as 
the  density  of  such  casting  is  fr(M|uciitly  imi)erfect,  the  action 


1082  AN    OUTLINl':    OF    MIOTALLURGY 

of  tlio  fluids  ol'  the  inoutli   is  iinirc   rapid  tliaii  updii   swa^c*! 
base-plate.s. 

On  account  of  its  extreme  liglitness,  aluminum  is  em- 
ployed to  a  considerable  extent  in  tlie  manufacture  of  physical 
apparatus  of  all  varieties.  It  is  especially  valuable  for  light 
balance  weights,  instrument  handles,  etc.  In  powder  form 
it  is  used  as  a  paint,  wliich  is  not  readily  acted  upon  by  the 
air  or  moisture. 

ALLOYS 

As  mentioned  elsewhere,  aluminum  with  copiHT  makes 
an  excellent  bronze,  which  is  used  for  many  ))urposes.  It 
also  unites  with  zinc  to  form  alloys  used  as  solders  for  the 
metal  itself. 

Silver  and  aluminum  unite  readily,  and  produce  alloys 
of  commercial  importance. 

The  silicate  of  aluminum,  or  kaolin,  the  double  silicate, 
feldspar  and  the  oxide  of  silicon,  form  the  basis  of  porcelain 
teeth,  and  the  porcelain  bodies  used  in  continuous  gum,  crown, 
bridge  and  inlay  work. 

It  is  not  generally  known  that  aluminum  can  be  used  as 
a  whetting  agent,  like  the  ordinary  oil  stone.  A  keen,  smooth 
edge,  not  possible  to  secure  with  fine  oil  or  water  stones,  can 
be  developed  on  fine  edge  instruments,  and  especially  razors, 
by  using  a  true  ])lane  slal>  of  ahnuinum  and  oil. 

Combined  with  magnesium,  a  very  important  alloy  known 
as  magnalium  is  formed.  It  is  used  in  the  making  of  fine 
instruments,  such  as  mathematical  instruments,  balances,  etc. 

ZINC 

The  ancients  were  familiar  with  the  ores  of  zinc,  since 
they  were  able  to  compound  brass,  liut  the  separation  of  the 
metal  itself  from  its  ores  is  of  comparatively  recent  date. 

ORES 

The  carbonate,  sulphide,  silicate  and  oxide  are  the  prin 
ci]ia]  ores  of  this  metal,  the  formulas  of  which  are  as  follows : 
Zn  CO;; — calamine  or  carbonate. 
Zn  S — zinc  blend  or  suli^hide. 
Zn  0  Si  O2 — willemite  or  silicate. 
Zn  0 — red  zinc  ore  or  oxide. 

REDUCTION 

Those  ores,  other  than  the  oxide,  are  reduced  by  roast 
ing  to  an  oxide.    In  this  form  the  ore  is  mixed  with  coke  or 


AN    OUTLINE    OF    METALLURGY  1083 

cliarcoal,  and  lieated  in  a  retort.  Tlie  carhon  imitcs  witli  tlu' 
oxygen  of  the  ore  to  form  COj  and  the  zinc  volatilizes  and  is 
condensed  in  receivers. 

Usually  some  slight  amount  of  oxide  passes  over  with  the 
zinc,  which  can  be  removed  by  remelting. 

PROPERTIES 

Zinc  is  bluish  white  in  color.  It  tarnishes  readily  in 
moist  air  or  when  heated,  an  oxide  being  formed  on  the  sur- 
face. When  exposed  to  the  vapor  of,  or  fiuids  containing, 
carbonic  acid,  a  film  of  zinc  carbonate  is  formed.  It  is  sol- 
ulile  in  most  of  the  acids,  and  is  readily  acted  upon  l)y  alkaline 
solutions. 

Its  fusing  point  is  433°  C.  Specific  gravity,  7;  atomic 
weight,  64.9,  and  specific  heat,  .0956.  It  ranks  low  in  malle- 
ability, ductility,  and  tenacity,  on  account  of  its  crystalline 
character,  which  renders  it  brittle  at  ordinary  temperatures. 
When  heated  to  a  temperature  between  100°  and  150°  C.  it 
can  be  rolled  and  drawn  into  wire,  becoming  both  malleable 
and  ductile,  and  retaining  these  properties  in  a  degree  when 
cold. 

Considerable  contraction  occurs  in  jiassing  from  the  fused 
to  the  solid  state. 

USES 

For  many  years  zinc  was  about  the  only  metal  in  use 
for  constructing  dies  for  swaging  baseplates,  but  Babbitt's 
metal  has  largely  taken  its  place.  The  advantages  claimed 
for  it  were  its  hardness  and  ability  to  stand  the  stress  of 
swaging  without  the  face  of  the  die  becoming  mutilated,  and 
that  its  contraction  in  cooling  compensated  for  the  expansion 
in  the  plaster  model.  It  does  not  seem  possible,  however,  that 
uniform  contraction  without  warpage  can  readily  occur,  and 
therefore,  it  is  best  to  compensate  for  the  expansion  of  the 
plaster  model  by  scraping  properly  and  use  a  die  metal  that 
will  not  perceptibly  contract,  such  as  Babbitt's  metal. 

When  zinc  is  used  for  dies,  lead  can  be  used  for  coun- 
terdies,  as  there  is  enough  variation  in  their  respective  melt- 
ing points  to  obviate  the  melting  of  the  zinc  by  the  lead  when 
the  latter  is  i)oured  upon  the  die. 

A  coating  of  whiting  and  alcohol  painted  over  the  ex- 
posed surface'  of  the  die  will  further  tend  to  prevent  the 
fusion  of  the  zinc  and  union  of  the  two  metals  in  counterdie 
construction. 


1084  AN    OtlTLINh:    OF    MRTALLITUnY 

Tlic  oxide  of  zinc  oilers  into  the  coiiiposit ion  of  oxy- 
pli()si)licite  and  oxycliloi-ido  dental  cements.  In  fact,  the  pow- 
der of  these  cements  is  nothing  more  than  the  retined  oxide 
of  zinc,  citiiei-  pui-e,  oi-  containiiii;'  some  piiiincnt  to  slightly 
color  it. 

The  li(iuid  constituent  of  the  oxyphosi)hate  consists  of 
glacial  phosi)horic  acid  in  distilled  water,  reduced  to  a  syrup- 
like consistency  by  e\'aporation. 

The  oxychloride  licjuid  is  made  1)\-  adding  one-half  ounce 
of  crystalline  chloride  of  zinc  to  two  drains  of  distilled  water, 
allowing  it  to  stand  for  two  or  three  days,  then  drawing  off 
the  clear  liquid.  Both  liquids  should  be  kept  in  tightly  stoji 
pered  bottles  to  prevent  deterioration. 

Zinc  has  a  wide  range  of  aj^plication  in  the  chemical, 
scientific  and  industrial  fields.  In  recent  years  there  has 
been  an  increasing  demand  for  it  as  a  precipitant  of  gold  in 
the  cyaniding  process  of  recovery.  Its  vise  in  the  electrical 
field  for  cheap  and  efficient  battery  work  is  fully  as  great 
as  ever,  while  in  foundry  work  there  seems  to  be  a  greater 
demand  for  zinc  than  ever  in  the  compounding  of  brasses, 
some  of  the  formulas  for  which  are  given  in  connection  with 
copper.  Zinc  is  used  for  coating  iron  to  prevent  oxidation 
(galvanized  iron),  in  the  development  of  hydrogen  gas,  and 
for  very  many  other  useful  purposes. 

CADMIUM 

Cadmium  is  usually  found  associated  with  zinc  as  a  sul- 
phide, and  is  recovered  in  the  refining  of  zinc.  As  it  is  more 
volatile  than  the  latter,  the  vapor  first  given  off  is  directed 
into  a  separate  chamber  and  condensed,  the  product  being 
cadmium  with  some  zinc  and  oxides. 

Redistillation  further  refines  it. 

Cadmium  resembles  tin  in  color,  and  is  capable  of  taking 
a  high  polish.  It  is  subject  to  slow  oxidation  on  exposure  to 
air.  It  is  malleable,  ductile  and  slightly  tenacious.  It  fuses 
at  320°  C,  has  a  specific  gravity  of  8.6,  and  specific  heat  of 
.05(37.     Its  principle  ore  is  greenockite. 

ALLOYS 

Cadmium  enters  into  the  composition  of  a  numl^er  of 
alloys,  among  which  might  be  specifically  mentioned  one  fre- 


AN    OUTLINE    OF    METALLURGY  1085 

(liK'iitly  used  in  cast  l)ase  lower  dentures,  iustead  of  Watt 
metal,  the  foiinuhi  ol'  which  is  as  t'oUows: 

Tin,  16. 

Cadmium,  1. 

Cadmium  also  is  one  of  the  component  metals  of  "Wood's 
Alloy." 

LEAD 

Lead  might  he  called  an  ahundaut  metal,  yet  the  constant 
and  increasing  demand  for  it  for  old  as  well  as  new  purposes 
is  so  great  that  its  value  is  constantly  heing  enhanced. 

It  occurs  in  nature  in  several  forms,  the  principal  ones  of 
which  are  here  mentioned: 

(Pb  S) — Galena  or  sulphide. 

(Pb  COa) — White  lead  or  carbonate.     (Cerussite.) 

(Pb  Or  64) — Crocoesite  or  chromate. 

(M  Oi  Pb)— Wulfenite. 

(Pb  So.)— Sulphate. 

Lead  ore  carrying  silver  is  designated  as  argentiferous 
galena. 

REDUCTION 

The  ores  are  first  roasted  to  reduce  them  to  oxides  and 
sulphates.  Upon  raising  the  temperature  of  the  furnace  these 
two  compounds  react  on  themselves,  as  indicated,  lead  and 
SO,  resulting: 

2Pb  O+Pb  S=S0,+3  Pb  and 

Pb  SO.+Pb  S=2SO.+2  Pb. 

PROPERTIES 

Lead  is  a  bluish  gray  metal,  so  soft  that  it  can  be  readily 
cut  or  scratched,  quickly  tarnishes  in  the  air,  forming  a 
suboxide,  but  is  not  readily  acted  on  by  water,  hence  its  ex- 
tensive use  in  plumbing  operations. 

Its  fusing  i)oint  is  326°  C.  Specific  gravity,  11.4  Atomic 
weight,  206.47,  and  speciiic  heat,  .0314.  It  is  quite  malleable 
and  ductile,  Imt  is  deficient  in  tenacity. 

USES 

The  prinrijial  use  of  this  metal  in  the  laboratory  is  for 
counterdies,  being  used  unalloyed  with  zinc,  and  in  the  propor- 
tion of  1  of  tin  to  7  of  lead  with  Babbitt's  metal  dies. 


1086  AN    Or'J'LINIO    Ol'    MIOTALU'KCY 

ALLOYS 

Coinnioii  tinners'  solder  eonsists  of  lead  and  tin  in  vary- 
ing i)roi)ortions,  those  having  the  most  tin  being  considered 
the  best. 

(xrade  Tin        Lead 

Fine    2  1 

Common    1  1 

Coarse    1  - 

Another  series  of  valual)le  alloys  in  whieh  lead  plays  an 
important  part  is  gi\('ii  in  the  section  on  bismntli. 

The  alloj's  given  in  the  section  on  tempering  steel  also 
form  an  important  series  in  which  lead  is  the  principal  metal 
employed. 

TIN 

Tin  occurs  usually  as  a  native  oxide,  Sn  O.  in  crystals  of 
quadratic  form,  usually  colored  by  manganic  or  ferric  oxide. 

REDUCTION 

The  ore  is  first  washed  and  stami^ed,  then  roasted  to 
drive  off  any  arsenic  or  sulphur  tliat  may  be  present,  at  a  tem- 
perature that  will  not  fuse  the  ore.  It  is  then  mixed  with 
fine  anthracite  coal  and  smelted  for  five  or  six  hours,  when, 
after  thorough  stirring  the  melted  metal  is  drawn  off.  The 
reaction  during  the  process  is  as  follows : 

Sn  0,+2  C=Sn+2C0. 

PROPERTIES 

Tin  is  a  white,  soft,  lustrous  metal,  quite  malleable,  some- 
what ductile,  but  with  very  little  tenacity.  It  fuses  at  232°C., 
and  is  not  perceptibly  volatilized  at  ordinary  temperatures. 
It  does  not  oxidize  readily,  and  for  this  reason  is  largely 
used  as  a  coating  or  protection  for  iron  plates.  In  this  form 
it  is  known  as  the  sheet  tin  of  commerce. 

When  a  bar  of  tin  is  cut,  it  apiiears  to  be  devoid  of  crys 
talline  structure,  but  if  tlie  surface  is  etched  with  dilute  acids, 
its  crystalline  cliaracter  becomes  apparent.  When  a  bar  of 
tin  is  bent,  it  emits  a  peculiar  crealcing  sound,  known  as  the 
tin  cry,  and  whicli  is  undoubtedly  due  to  the  sliding  or  rear- 
rangement of  the  crystalline  facets. 

The  specific  gravity  of  tin  is  7.3,  and  its  spcific  heat 
0.0562. 


AN    OUTLINK    OF    METALLURGY 


USES 


Tiu  is  used  in  the  dental  office  and  laboratory  in  the 
form  of  foil  for  filling  teeth  and  for  covering  jjlaster  models 
in  vulcanite  work,  to  give  a  finished  surface  to  rubber.  After 
being  vulcanized,  the  foil  is  removed.  It  is  questionable 
whether  this  is  a  good  plan  to  follow,  since  the  model  is  en- 
larged by  the  addition  of  the  foil,  which  must  impair  the 
close  adaptation  of  the  denture  to  the  tissues. 

Tin  is  also  one  of  the  principal  ingredients  in  the  compo- 
sition of  dental  amalgam  alloys,  from  'I'l  to  35  per  cent  l)eim': 
used  with  77  to  fi5  ]iev  cent  of  silver. 

HASKELL'S  BABBITT  METAL 

It  is  also  used  in  the  composition  of  fusible  alloys  and 
counterdie  metal,  and  forms  in  conjunction  with  copper  and 
antimony  a  hard  and  practically  non-contractile  die  material, 
known  as  Babbitt's  metal. 

The  formula  for  Haskell's  P>abl)itt  metal  is  Cu  1,  anti- 
mony 2,  tin  8  parts. 

The  coiniterdie  metal  used  in  conjunction  with  Ba))bitt's 
metal  is:  Lead  7,  tin  1  part.  Tlie  tin  is  added  to  reduce  the 
melting  i)oint  of  the  lead.  Babbitt's  metal  melts  at  260°C., 
while  the  fusing  point  of  lead  is  .S25°C.  If  lead  is  poured  upon 
a  Babbitt  metal  die,  the  heat  is  sufficient  to  fuse  the  latter, 
and  union  of  tlie  two  will  very  likely  occur. 

This  undesirable  result  is  obviated  by  the  addition  of  tin 
to  lead  in  the  proportions  before  mentioned,  which  gives  an 
alloy  with  a  fusing  point  of  about  225°C. 


MERCURY 

Mercury  sometimes  occurs  in  nature  free,  though  it  is 
commonly  found  as  the  red  sulphide  Hg.  S.,  called  cinnabar. 
It  is  fi'equently  found  forming  an  amalgam  with  silver,  and 
also  in  the  form  of  a  protochloride  or  native  calomel. 

DISTRIBUTION 

Mercury  is  found  in  Spain,  Corsica,  Mexico,  California, 
Peru  and  China. 

At  the  present  time  California  itroduces  a  greater  bulk 
tlian  any  other  country  in  the  world.  The  ore  is  very  rich 
in  mercury,  yielding  as  higli  as  70  per  cent,  while  the  oi'e  from 


1088  AN    OUTLINE    OF    METALLURGY 

tilt'   Spuiiisli    iiiiiics,   the  next    largest   ]»i'()(lnccrs,   yields   only 
38  per  eeiit. 

COMBINATIONS 

Mei'L'ury  forms  two  oxides,  inercurons  oxidis  ll^-O, 
and  mercuric  oxide,  trig  ().  It  ;dso  forms  two  chlorides  of 
prominence,  HgCL — corrosive  .^iihUnidfc — a  powerful  disin- 
fectant, and  Hg,  CL,  called  calnnicl. 

Vermilion — or  mercuric  sulphide,  JJg.  S. — a  brilliant  red 
color,  is  used  extensively  as  a  ])igment  in  paints  and  for  the 
coloring  agent  in  the  manufacture  of  red  and  i)ink  rubber  and 
celluloid. 

As  is  well  known,  mercury  is  extensively  employed  for 
thermometers,  barometers,  etc.,  and  for  many  other  useful 
purposes  in  the  arts  and  sciences. 

ALLOYS  OF  MERCURY 

Mercury  uniti's  with  many  of  the  metals  to  form  amal- 
gams. It  is  used  very  extensively  with  (h-ntal  alloys  for  the 
filling  of  teetli. 

PROPERTIES 

Mercury  is  silver  white  in  color,  tarnishes  slightly  in 
air,  but  is  not  acted  upon  by  water.  It  is  tasteless  and  odor- 
less. It  is  liquid  at  ordinary  temperature,  boils  at  357. 3°C., 
and  can  be  soliditied  by  subjecting  it  to  a  temperature  of 
— 39.5°  C.  It  contracts  noticeably  in  passing  from  tlie  liquid 
to  the  solid  state,  and  assumes  a  crystalline  form.  When 
solid  it  can  be  flattened  out  under  hammer  blows,  thus  prov- 
ing that  it  is  malleable.  In  this  condition  it  can  also  be 
welded,  and  can  be  cut  into  shavings  with  a  knife. 

The  specific  gravity  of  mercury  is  13.6,  specific  heat  .032, 
and  its  atomic  weight  200.6. 

EEDrCTION 

Mercury  is  obtained  from  the  native  sulphide  in  two 
ways.  The  first  method  consists  in  crushing  the  cinnabar  ore 
and  mixing  with  lime.  The  mixture  is  then  placed  in  cast- 
iron  retorts,  which  are  connected  with  earthenware  receivers 
l)artially  filled  with  water.  Upon  the  application  of  heat  the 
sulphur  coml)ines  with  the  calcium  and  forms  calcium  sulph- 
ide, while  tlie  mercury  is  distilled  over  and  condensed  in  the 
receivers. 

4HgS  +  4Ga()  =  3CaO  +  CaSO,  +  4Hg.  The  second 
method  of  recovery  consists  in  exposing  the  ore  directly  to  the 


AN    OUTLINE    OF    METALLURGY  1089 

oxidizing-   flame,   aiul   conductiiiii,'   the   nuTeurial   vapor   witli 
suitaMe  aiiparatns  into  condensers. 

NICKEL 

Nickel  is  a  silvery  wliite  metal,  witli  a  brilliant  luster, 
which  does  not  tarnish  readily  in  air.  It  is  as  tenaeioi;s  as 
iron,  is  ductile,  hard,  and  somewhat  malleable.  It  is  slightly 
magnetic,  resembling  iron  somewhat  in  this  respect.  Its  spe- 
cific gravity  is  9,  increased  by  hammering  to  9.93.  Specific 
heat  0.1086."  Atomic  weight  58.68,  and  fuses  at  about  1500°  C. 
Nickel  is  used  extensively  with  copper  to  form  german  silver 
— an  alloy  which,  on  account  of  its  color,  hardness,  tenacity, 
and  many  other  good  qualities,  is  used  in  large  quautities  for 
innumerable  purposes. 

A  coiumon  formula  for  german  silver  is :  Co])per  55, 
zinc  '2b,  nickel  16  parts  each. 

The  hardness  and  strength  of  steel  is  increased  by  the 
addition  of  a  small  \^er  cent  of  nickel.  This  allow  is  known  as 
armor  |i]ate,  and  is  used  in  the  const  ruction  of  warships. 

USES 

This  metal  is  made  use  of  to  a  great  extent  for  plating 
purposes,  since  it  does  not  readily  tarnish,  is  not  easily  ox- 
idized, and  can  be  quickly  and  firmly  dejiosited  upon  iron, 
steel,  brass,  german  silver,  and  copi»er,  by  electro-deposition. 

BISMUTH 

Bismuth  is  a  crystalline  metal  of  a  gray-white  color, 
with  a  decidedly  reddish  tinge.  On  account  of  its  highly  crys- 
talline character  it  can  be  easily  jmlverized.  It  is  almost 
totally  lacking  in  the  qualities  of  malleability,  ductility,  and 
tenacity.  Its  specific  gravity  is  9.75,  and  specific  heat  0.0308. 
Fuses  at  270".    Atomic  weight  208. 

Bismuth  is  the  most  diamagnetic  eh'Uient  known,  a  sphere 
of  it  when  suspended  close  to,  is  repelled  by  a  magnet. 

Bismuth  is  very  useful  in  the  composition  of  fusible  al- 
loys, reducing  the  fusing  points  of  the  more  difficultly  fusible 
ingredients,  and  imiDarting  clearness  and  sharpness  of  outline 
to  castings  made  from  such  alloys. 

In  conjunction  with  tin  and  h^ad,  it  forms  a  number  of 
alloys  which  are  in  constant  use  in  the  dental  hdtoratory.  The 
following  is  a  partial  list  of  such  alloys: 


Name 

HiSMllltll 

Tin 

I>ea(i 

Hodgen's 

metal 

S 

3 

5 

Mellotte's 

S 

5 

."! 

Essig's 

3 

r. 

:', 

Darcet's 

4 

1 

:! 

Rose's 

2 

1 

1 

Newton's 

8 

r, 

Onion's 

5 

2 

:i 

Wood's 

4 

1 

2 

Lipowitz's 

15 

4 

,s 

Darcet's 

2 

1 

1 

1090  AN    OtTTLINfO    OK    MRTALLUKOY 

FUSIBLE  ALLOYS 

Melting 

11      Merciir\-      A  ril  iniMii\'       Point 

2      105°  C. 

100°  C. 

96°  C. 

96°  C. 

95°  C. 

94°  C. 

92°  C. 

65°  C. 

63°  C. 

10  45°  C. 

In  eoiii])onn(lin,n-  alloys  (if  this  cliai'actcr  they  sliduld  lie 
melted  under  chai'coal  to  prevent  oxidation,  and  stirred  with 
a  stick  of  soft  wood  just  before  pouring,  to  prevent  the  load 
from  separating. 

When  cadmium  or  mercury  are  incoriioratcd,  the  other 
metals  should  ))e  melted  tirst,  and  these  added  just  before 
]iouring',  to  prevent  volatilization. 


ANTIMONY 

Antimony  usually  occurs  as  a  sulphide,  and  with  other 
metals,  as  silver,  iron  and  cop]ier.  It  is  reduced  liy  heating 
the  sulphide  with  scra]i  iron,  ii-on  sulphide  being  formed  and 
the  antimony  set  free. 

PROPERTIES 

It  is  extremely  low  in  malleability,  ductility  and  tenacity, 
being  crystalline  in  structure  and  very  brittle.  The  atomic 
weight  of  antimony  is  120.2,  fusing  point  632^(_'.,  specific  grav- 
ity 6.71,  specific  lieat  .0508. 

Its  principal  uses  in  dentistry  are  as  a  component  of 
Haskell's  Babbitt  metal  and  for  certain  low-fusing  alloys.  It 
is  also  used  extensively  in  the  manufacture  of  ty]>e  for  print- 
ing, as  alloys  containing  antimony  expand  in  cooling,  thus  in- 
suring sharp  castings. 

Primarily  common  Balibitt  metal  is  an  anti-friction  al- 
loy, and  that  intended  for  such  purpose  contains  a  larger 
percentage  of  copper  and  antimony,  while  it  is  softer  and  more 
easilv  defaced  than  that  prepared  after  the  formula  of  Dr. 
Haskell.     (See  page  1087.) 

Britannia  metal  is  an  alloy  used  for  making  spoons,  tea- 
pots, trays,  etc.,  and  is  composed  of  several  metals  and  in 
different  proportions. 


AN    OUTLINE    OF    METALLURGY 


Tlie  followiug-  is  oiio  of  the  formulas  nnicli  used :  Copper 
1.85,  tin  81.90,  antimony  16.25.  Zinc,  lead  and  bismuth  are 
also  used  in  some  of  the  formulas  of  this  alloj". 


TUNGSTEN 

Tungsten  occurs  combined  with  ferrous  oxide  in  the 
mineral  called  wolfram,  or  wolframite,  FeWOi.  also  with 
calcium  in  the  mineral  called  scheelite,  CaAVOj.  These  are 
called  the  tungstates  of  iron  and  calcium,  respectively. 

Its  principal  use  imtil  recently  was  as  a  mordant  in  dye- 
ing and  a  fireproofing  material  for  cotton  goods.  It  has  also 
been  iised  as  a  hardening  component  for  steel,  usually  in  the 
l^roportion  of  from  5  jjer  cent  to  9  per  cent. 

PHYSICAL  PROPERTIES 

The  fusing  point  of  tungsten  is  sliglitly  over  3000  C. 
Atomic  wt.,  184.  Specific  gravity,  19.2.  Acids  have  but 
slight  effect  upon  the  metal  at  ordinary  temperatures.  It 
is  very  difficult  to  convert  the  powder,  in  which  form  it  is 
usually  sold  commercialI>',  into  a  solid,  on  account  of  its  ex- 
tremely high  fusing  point.  By  heavy  compression  into 
definite  form,  and  the  application  of  an  electric  current  of 
high  amperage,  coiipled  with  careful  swaging,  the  rod  or  bar 
of  compressed  powder  is  gradually  rendered  compact  and 
the  granules  sufficiently  coherent  to  enable  it  to  be  drawn 
out  into  wires  of  various  sizes,  even  as  fine  as  the  1/1000  of 
an  inch. 

At  high  temperatures  it  is  readily  oxidized,  unless  pro- 
tected from  the  air.  This  deleterious  property,  however,  does 
not  inhibit  its  use  for  electric  lamp  filaments,  since  it  is 
placed  within  a  ^•acuum  globe  or  one  filled  with  nitrogen. 
In  either  case  the  oxygen  is  excluded,  and  consequently  oxida- 
tion does  not  occur. 

USES 

Dr.  Weston  A.  Price  of  the  Scientific  Research  Commis- 
sion of  the  N.  D.  A.  presented  a  paper  on  metals  and  alloys 
at  the  meeting  in  Rochester,  N.  Y.,  in  July.  1915,  in  which  some 
of  the  valuable  points  of  this  metal  were  disclosed.  In  that  he 
showed  that  the  hi-gh  fusing  point  of  tungsten,  its  low  range 
of  expansion.  Its  great  rigidity  and  hardness  rendered  it 
extremely  vahiable  in  prosthetic  operations. 

A  bar  of  this  material,  threaded,  coated  with  ])alladium 


1092  AN     Uiri'LINIO    UK    MP^TALLIJIUIY 

or  S'old  to  prcxciil  oxidnlioii.  iiiid  imcstcd  in  ii  matrix  for 
a  complex  iiil;i\',  the  wire  cNlciHliiii;'  iiicsin-dislall)  llirou^h  1  lie 
easting,  i)ra('tically  inliiliits  the  cnnl  ractidii  of  liic  ?;(ild  on 
itself,  wliicli,  witlidiil  sucli  coiitnil,  al\va>s  dccurs  in  coDliii!;'. 
its  rigiditx',  couiilcd  witii  great  tensile  strength.  rend<'i's  it 
specially  \alual»le  I'or  dowels  in  crowns  and  inla>s. 

The  principal  disadvantages  are  its  oxidation  at  solder- 
ing and  casting  temiierntni'es  and  the  difficnlty  in  t'nsing 
any  of  the  metals  to  it  in  the  oiien  air  becanse  of  such  oxida- 
tion. 

The  solntion  offered  was  to  coat  the  wire  with  an  alloy 
of  Pd-An  or  PdAg.,  after  which  gold  may  be  cast  or  soldered 
to  it  readily. 

To  illustrate  its  hardness,  mention  was  made  of  the  fact 
that  a  phonogra))hic  needle  of  tungsten  will  outwear  two 
hundred  of  the  standard  hard-steel  points  in  common  use. 
The  iDossibilities  of  this  metal  for  use  in  cutting  instruments 
was  suggested,  when  the  methods  of  working  it  are  better 
developed. 

THE  MEASUREMENT  OF  PLATE  AND  WIRE 

In  all  scientilic  and  meclianical  fields,  the  accurate  deter- 
mination of  weights,  dimensions  and  strength  of  materials, 
when  such  measurements  are  called  for,  is  a  recognized  ne- 
cessity; the  same  holds  true  in  prosthetic  procedures,  for 
without  a  reasonably  accurate  knowledge  of  the  strength  of 
the  various  materials  entering  into  the  structure  of  re]iIaco- 
ments,  the  prosthetist's  efforts  will  often  jn'ove  inefficient. 

Gold,  platinum,  and  various  other  metals,  are  reduced 
from  ingot  form  to  plate  by  means  of  a  device  called  a  rolling 
mill.  This  may  be  done  in  the  dental  laboratory  with  pi'oper 
equipment. 

More  often,  however,  the  prosthetist  obtains  the  ])recions 
metals  in  plate  form,  direct  from  the  supply  liouses. 

In  either  case,  it  is  essential  that  the  laboratory  be 
ecjuipped  with  suitable  measuring  devices  for  testing  the  dif- 
ferent gauges  of  material  used. 

Tlie  measurement  of  the  thickness  of  gold  and  platinum 
plate  and  the  gauging  of  the  diameter  of  wire  in  an  intelli- 
gent manner — that  is,  so  that  a  just  estimate  may  be  formed 
of  the  relative  thickness  and  strength  of  the  materials  being 
used — aids  materially  in  the  planning  and  construction  of 
successful  prosthetic  substitutes  of  all  classes. 


AN    OUTLINE    OF    METALLURGY  1093 

AVitli  tliis  end  in  view,  the  pvosthetist  ^^honkl  lieconie 
familiar  witli,  and  can  to  advantage  apply  in  practice,  the 
methods  and  instruments  nsed  by  scientists  and  artisans  in 
otlier  lines  of  work. 

Various  measnrini;-  devices  are  in  use  for  determining 
the  tliickness  of  plate  and  the  diameter  of  wire,  as  well  as 


A    COMMON    TYPE    OF    ROI.LINI!    MILL 


for  sundry  other  measurement  readings.  These  instruments 
are  known  under  the  common  name  of  c/dKC/es,  calipers,  etc., 
the  forms  of  which  vary,  depending  upon  the  jmrposes  for 
which  thev  are  desioned. 


THE  UNIT  OF  MEASUREMENT  OF  GAUGES 

The  unit  cf  measurement  of  gauges  used  in  England 
and  the  United  States  is  generally  the  fractional  jjart  of  an 
inch  and  of  tiic  millimeter. 


1094  AN    OUTLINK    OF    METALLURGY 

LACK  OF  UNIFORMITY  OF  THE  VARIOUS  GAUGE  SYSTEMS 

With  exceptions  to  be  noted,  most  of  the  various  gauge 
systems  do  not  show  a  uniformly  decreasing  ratio  from  thick 
to  thin  measurements,  Imt  llic  stejis  between  tlie  various 
gauge  numbers  appear  tti  ha\e  been  ai-bitrarily  established, 
without  following  any  fixed  standard. 

THE  BIRMINGHAM  GAUGE 
Tliis  is  true  of  the  li'u  iii'uKjhatii,  also  known  as  the  Eiuj- 
lisli  Standard,  and  again  as  Stub'a  Soft  Iron  Wire  Gauge, 
so  called  to  distinguish  it  from  Stub's  Steel  Wire  Gauge. 
The  discrepancies  noted  are  plainly  apparent  in  this  gauge, 
as  will  be  seen  by  examining  the  first  few  largest  numbers. 

DISCREPANCIES  OF  THE  BIRMINGHAM  GAUGE 

No.  0000  =  .454  of  an  incli.        No.        0  =  .340 
No.    000  =  .425  No.        1  =  .300 

Difference  .029  Difference  .040 

No.    000  =  .425  No.        1  =  .300 

No.      00  =  .380  No.        2  =  .284 

Difference  .045  Difference  .016 

No.      00  =  .380  No.        2  =  .284 

No.        0  =  .340  No.        3  =  .259 

Difference  .040  Difference  .025 

To  summarize,  the  difference  between  the  first  seven 
numbers  of  the  Birmingham  gauge  is  as  follows:  .029 — 
.045— .040— .040— .016— .025. 

The  Birmingham  gauge  was  for  years  used  extensively, 
but  not  exclusively,  in  this  country,  in  machine-shop  i)ractice 
and  various  other  fields.  Some  wire  and  plate  manufacturers 
used  one  gauge,  some  another.  More  or  less  confusion  and 
misunderstanding  naturally  resulted,  since  no  one  gauge  sys- 
tem was  accepted  as  standard  and  each  varied  slightly  from 
the  others. 

THE  BROWN  AND  SHARP  GAUGE 

To  correct  the  discrepancies  noted,  the  Brown  &  Shar]^ 
Manufacturing  Company  of  Providence,  R.  I.,  designed  a 
gauge  having  approximately  the   same   range   of  measure- 


AN    OUTLINE    OF    METALLTTRGY  1095 

iiieut  as  the  Birmiiiiiiiani,  hut  the  various  gauge  numbers, 
from  the  largest  downward,  decrease  in  a  definite  ratio. 

This  gauge  has  proven  so  satisfactory  that  it  has  been 
generally  adopted  in  this  country,  and  is  now  known  as  the 
America)!  Standard  Gauge.  It  should  not,  however,  be  con- 
founded with  the  United  States  Standard  Gauge,  which  was 
designed  for,  and  approved  by,  Congress  in  1893,  and  is  used 
in  determining  duties  and  taxes  levied  by  the  United  States 
Government  on  sheet  and  plate  iron  and  steel. 

The  principle  on  which  the  Brown  &  81iar]i  gauge  is 
constructed  is  as  follows:  Two  straight  bars  of  steel  are 
fitted  together  at  one  of  their  ends,  and  permanently  fixed 
in  such  manner  as  to  form  a  divergent  space  between  the 
two,  about  one-half  inch  across  at  the  outer  end  of  the  gauge. 
The  gauge  numbers  are  marked  on  the  inner  edges  of  the 
arms,  next  the  divergent  space.  The  general  form  of  tliis 
gauge  is  similar  to  the  jeweler  gauge.     (See  page  1096.) 

No.  0000,  or  .-46  of  an  inch,  is  the  largest  dimension  of 
the  gauge,  and  from  this  all  of  the  other  gauge  dimensions 
are,  either  directly  or  indirectly,  derived. 

The  next  lowest  dimension  —  No.  000  —  is  obtained  by 
nuiltiplying  its  predecessor,  .-1-6,  by  0.890522,  which  is  equiva- 
lent to  deducting  10.9478  per  cent.  Placii  succeeding  lower 
number  is  obtained  in  a  similar  manner,  by  nuiltiplying  the 
last  determined  gauge  length,  or  thickness,  cstablislKMl,  l)y  the 
decimal  above  given. 

It  will  thus  be  seen  that  any  gauge  number  under  0000 
is  approximately  10  jjer  cent  less  than  the  preceding  higher, 
or  greater  than  the  succeeding  lower  number.  The  steps 
between  the  various  gauges  represent  gradual  and  uniform 
decrements  as  the  gauge  numbers,  although  rising  numeri- 
cally, become  thinner.  The  last  gauge  of  the  scale  is  No.  40, 
or  .003144  of  an  inch  thick,  although  still  thinner  numbers 
can  be  correctly  formulated  l)y  the  plan  given. 


FORMS  OF  GAUGES 

THE  JEWELER'S  GAUGE 

The  jeweler's  gauge  is  liased  u])oii  the  same  general 
princijile  as  the  Original  Brown  &  Sharp  gauge,  viz.,  two 
rigidly  fixed,  cliverging  arms.  These  are  graduated  on  the 
inner  margins  so  as  to  read  in  nniltiples  of  one-thousandths 
of  an  inch. 


lOiifi  AN    OUTLINE    OK    M  lOTALLURGV 

.Mlliouyli  tlic  I'oriii  dl'  _!;an,i;('  Just  (Icscrilicd  is  siiilalilc 
and  very  t'oiiwiiiciit  t'oi  inciisurinn  wire  and  small  rods,  it  is 
not  well  adapted  for  gaiis^-iiiii,-  plate,  hecause  tiie  edge  of  the 
latter  is  very  fi'e(|ueiitly  inari-eij  in  shearinu.  so  that  a  niar- 
ginal  readiiin',  in  such  cases,  will  seldom   he  aeeurate.     Some 


A    JEWELER'S    GAUliE     liKAl>I> 
TO  THE  1/1000  OF  AX    IXIII 


form  of  appliance  capable  of  passing  beyond  the  margin  of 
the  plate,  and  calipering  nndistnrbed  surfaces,  is,  therefore, 
neeessarv  for  securing  accui'ate  in(^asurements. 


THE  PLATE  AND  WIRE  GAUGE 

One  of  the  most  connnon  forms  of  plate  and  wire  gauge 
in  use  consists  of  a  steel  disc  about  two  and  one-half  inches 
in  diameter  and  one-eighth  of  an  inch  thick.  In  the  perii)hery 
of  this  disc  are  accuratelv  cut   and   nninbei'ed   slots,  which 


AN    OUTLINE    OF    METALLURGY  1097 

represeut  tlie  tliickiicss  ut'  tlif  various  .naiigc  muiiher.s  of  the 
system  used.  To  measure  a  piece  of  i)late  or  wire,  the  various 
slots  of  the  gauge  are  applied  to  the  piece  until  a  ueat  fit 
is  obtained,  or,  in  case  the  piece  being  measured  is  not  of 
exact  gauge  thickness,  the  two  proximating  gauges  are  found, 
one  of  which  is  larger  and  the  other  smaller  than  the  wire 
or  plate  being  calipered.     This  form   of  gauge,   as  before 


AN    ORDINARY    FDRJ!    1JI--    i:\I  lii:    Full    I'l.ATI- 


stated,  is  satisfactory  for  measuring  standard  thickness  of 
plate  and  wire,  but  is  not  ada]ited  to  accurate  and  imiversal 
readings,  when  the  materials  are  not  standardized. 

THE  MICROMETER  CALIPER 

An  instrument  of  this  type  consists  of  a  U-shaped  steel 
frame,  the  arms  of  which  are  parallel.  One  arm  is  threaded 
and  contains  the  adjustable  screw,  by  means  of  which  read- 
ings are  made.  The  other  arm  holds  an  adjustable  stop, 
which  is  never  moved  except  for  adjustment  purposes,  when 
the  instrument  is  worn  or  sprung.  The  face  of  the  stop  and 
the  end  of  the  screw,  presented  toward  it,  form  exactly 
jiarallel  planes.  Tiie  object  to  lie  gauged  is  ])]aced,  one  side 
against  the  face  of  the  stop,  while  the  screw  in  the  other  arm 
is  brought  in  contact  with  the  opposite  side.  The  reading  is 
made  on  the, screw  spindle  and  on  the  hub,  or  nut,  through 
which  it  passes.  In  the  foHowing  description,  the  micrometer 
graduated  to  read  to  the  1/1000  of  an  inch,  will  be  used  as 
an  example  of  tliis  general  type.     Some  of  the  more  recent 


AN    OUTLINE    OF    METALLURGY 


forms   li;i\c  i\   \cniicr  attarliinciit,   liy   iiicaiis  of  which   read- 
ing's can  be  made  as  line  as  tlie  l/iUUUU  of  an  incli. 

The  screw  spindle  has  a  lioUow  head  in  tlie  furni  of  a 
deep  sleeve,  whidi  telescopes  over  the  cylindrical  extension 
of  the  nut  of  Ihc  frame.  As  the  screw  is  turned  toward  or 
away  from  tlie  stoj)  in  the  o])posite  arm,  the  sleeve  rotates 
and  travels  with  it.  The  inner  end  of  the  sleeve  is  beveled 
and  graduated  into  25  ecjnal  parts,  and  nmnbered  0,  5,  10, 
15,  20,  while  25  is  reached  on  the  complete  revolution  to  0. 
When  the  screw  is  closed  and  in  close  contact  with  the  stop, 
the  0  of  the  sleeve  stands  opposite  the  0  on  the  nut.  The 
screw  pitch  is  40 — that  is,  there  are  40  threads  to  the  inch 
on  the  spindle.  By  multiplying  the  divisions  on  the  sleeve 
by  the  number  of  threads  to  the  incli  on  the  sjiindle,  it  will 


A  MICROMETER  GACUE  BEADING  TO  TIIE    1 /I.OUd   OF    AX    I 


be  seen  that  1,000  divisions  must  pass  the  longitudinal  line 
on  the  hub  in  moving  the  screw  outward  one  inch.  Each 
division,  therefore,  registers  the  1/1000  of  an  inch  move- 
ment of  the  screw  toward  or  away  from  the  stop  in  the  op])o- 
site  arm.  To  facilitate  rapid  readings  of  pieces  of  consider- 
able thickness,  the  hub  is  also  graduated.  The  space  between 
the  gradations  on  the  hub,  or  nut,  is  equal  to  the  distance 
between  contiguous  threads.  As  the  screw  is  turned  once 
around,  in  opening,  an  unexposed  gradation  api^ears  on  the 
hull  under  the  edge  of  the  sleeve,  showing  tliat  the  screw 
has  been  moved  25/1000  of  an  inch.  Every  fourth  gradation 
on  the  hub  is  accordingly  numbered,  the  beginning  or  closed 
position  of  screw  being  0,  the  fourth  division  1,  or  100/1000; 
the  second  2,  or  200/1000,  etc. 

In  using  this  gauge  three  sources  of  error  must  be  kept 
in  mind,  viz.,  imperfect  paralleling  of  the  piece  being  meas- 


AN    OUTLINE    OP    METALLURGY  1099 

ured,  with  the  i'at'e  of  the  st'Vew;  excessive  i)ressure  will 
spring  the  frame  and  give  imperfect  results;  slight  variation 
in  the  pitch  of  the  screw,  clue  to  wear. 

No  dust  or  dirt  should  adhere  to  the  screw,  stop  or  piece 
being  gauged.  A  spring  ratchet  is  frequently  applied  to  the 
extreme  outer  end  of  the  screw  to  insure  against  excessive 
force  being  applied  in  making  measurements. 


VARIOUS  SYSTEMS  OF  WIRE  AND  PLATE  GAUGES  AND 

THEIR  EQUIVALENTS  IN  THOUSANDTHS 

OF  AN  INCH 

For  convenience  in  finding  any  required  gauge,  the  wii-e 
and  plate  gauge  numbers  are  given  on  the  right  and  left 
sides  of  the  table. 


Difference 

No.  ot 
Wire 
Oauge. 

Brown  & 

Sharp 
American 
Standard. 

between 
Consecu- 
tive 
Numbers 

in 
Decimals. 

Birming- 
ham or 
Stub's 
Wire. 

Wash- 
burn & 
MoenCo, 
Wire. 

Imperial 

Wire 
Gauge. 

Stub's 
.Steel, 
Wire. 

U.  fg.  Stand  „ 
ard  for    ^ 
Plate.    c 

&M. 
Wire 
auge. 

No.ol 
Wire 
Gauge. 

000000 

.464 
.432 
.400 

.46875 
.4375 
.40625 

0095 
010 
Oil 

000000 

00000 



00000 

0000 

^46  

^454 

.3938 

0000 

000 

.40964 

!65036 

.3625 

.372 

.375 

012 

000 

00 

.3648 

.04484 

^38 

..3310 

.348 

.34375 

0133 

00 

0 

.32486 

.03994 

.34 

.3065 

.324 

.3125 

0144 

0 

1 

.2893 

,03556 

,2830 

,300 

■■:227 

.28125 

0156 

1 

2 

.25763 

.03167 

^284 

,2625 

.276 

.219 

.265625 

0166 

2 

3 

.22942 

.02821 

.259 

.2437 

.252 

.212 

.25 

0178 

3 

4 

.20431 

.02511 

.238 

.2253 

.232 

.207 

.234375 

0188 

4 

5 

.  18194 

.02237 

.22 

.2070 

,212 

.204 

.21875 

0202 

5 

6 

. 16202 

,01992 

,203 

.1920 

,192 

.201 

.203125 

0215 

6 

7 

.14428 

.01774 

,18 

.1770 

.176 

.199 

.1875 

023 

7 

8 

.12849 

.01579 

,165 

.1620 

.160 

.197 

.171875 

0243 

8 

9 

.11443 

.01406 

,148 

.1483 

.144 

.194 

. 15625 

0256 

9 

10 

.10189 

.01254 

,134 

.1350 

,128 

.191 

.140625 

027 

10 

11 

.090742 

.01105 

12 

.1205 

,116 

.188 

.125 

0284 

11 

12 

.080808 

.00993 

m 

.1055 

,104 

.185 

. 109375 

0295 

12 

13 

071961 

.00885 

095 

.0915 

,092 

.182 

.09375 

0311 

13 

14 

.064084 

.00788 

,083 

.0800 

,080 

.180 

.078125 

0325 

14 

15 

.05768 

.00702 

072 

.0720 

,072 

.178 

.0703125 

0343 

15 

16 

.05082 

.00625 

065 

.0625 

,064 

.175 

.0625 

0359 

16 

17 

.045257 

.00556 

,058 

0540 

,056 

.172 

.05625 

0378 

17 

18 

.040303 

,00495 

,049 

.0475 

,048 

.165 

.05 

0395 

18 

19 

.03589 

.00441 

,0(2 

.0410 

,040 

.164 

.04375 

0414 

19 

20 

.031961 

.00393 

,0.35 

.0348 

,036 

.161 

.0375 

043 

20 

21 

.028462 

.00350 

,032 

.03175 

,032 

.157 

,034375 

0461 

21 

22 

.025347 

.00311' 

,028 

.  0286 

,028 

.155 

,03125 

0481 

22 

23 

,022571 

.00278 

025 

.0258 

.024 

.153 

,028125 

0506 

23 

24 

.0201 

.00247 

,022 

.0230 

.022 

.151 

,025 

0547 

24 

25 

.0179 

.00220 

02 

.0204 

.020 

.148 

,021875 

0585 

25 

26 

.01594 

,00196 

,018 

,0181 

.018 

.146 

,01875 

0626 

26 

27 

.014195 

,00174 

,016 

,0173 

.0164 

.143 

,0171875 

0663 

27 

28 

.012641 

,00155 

014 

,0162 

,0149 

.139 

,015625 

0719 

28 

29 

.011257 

,00138 

,013 

,0150 

,0136 

.134 

0140625 

076 

29 

30 

.010025 

.00123 

,012 

,0140 

,0124 

.127 

or25 

080 

30 

31 

.008928 

.00110 

,01 

,0132 

,0116 

.120 

,0109375 

31 

32 

.00795 

.00098 

,009 

,0128 

,0108 

.115 

,01015625 

32 

33 

.00708 

.00087, 

,008 

,0118 

,0100 

,112 

,009375 

33 

34 

.006304 

.00078 

,  007 

,0104 

,0092 

,110 

,00959375 

34 

35 

.005614 

,-00069 

005 

,0095 

,0084 

.108 

,0078125 

35 

36 

.005 

,00061 

004 

,0090 

,0076 

.106 

,00703125 

36 

37 

.004453 

,00055 

,0068 

.103 

,006640625   , 

37 

38 

.003965 

,00049 

,0060 

.101 

.00625 

38 

39 

.003531 

,00043 

,0052 

,099 

39 

40 

003144 

,00039 

,0048 

,097 

40 

1100  AN    OIITMNE    OF    METALLURGY 

TABLES  OF  SOME  OF  THE  VARIOUS  GAUGE  SYSTEMS 
IN  USE 

The  tabic  ol'  gauges  wliicli  is  liei'c  apiK'ndcd  will  enable 
any  one  to  determine  aceurately,  by  means  of  a  micrometer 
gauge,  the  relative  tliiekiiess  of  plate  and  wire,  regardless 
of  what  system  of  gauging  lias  been  used  b\'  llie  manufacturer 
in  its  prodnction. 

Attention  is  s])eci;dly  cjdied  to  tlie  table  of  piano-wire 
gauges,  as  it  is  at  variance  with  the  other  systems  tabulated. 
The  diameters,  or  thicknesses,  of  the  gauges  in  this  system 
increase  as  the  numbers  rise  numerically.  Since  piano  wire 
is  used  extensively  in  orthodontic  operations,  those  engaged 
in  this  specialty  will  find  the  table  of  assistance  in  judging 
the  relative  thickness  of  the  various  sizes  of  wire  employed. 

Practically  all  supply  houses  use  the  American  Stand- 
ard, also  called  tlu'  Brown  &  Sharp  gauge,  for  gauging  the 
precious  metals.  For  this  reason,  therefore,  distinction 
should  be  made  between  the  American  Standard  gauge,  which 
is  almost  universally  employed  for  the  purpose  mentioned, 
and  the  United  States  Standard  gauge,  the  principal  use  of 
which,  as  before  stated,  is  in  the  measurement  of  iron  and 
steel  plate,  and  is  seldom  used  in  prosthetic  operations. 


(Ml  APT!-:  II     XXXIII 
A  BRIEF  HISTORY  OF  PROSTHETIC  DENTISTRY 

All  t'xact  and  detailed  history  of  the  treatment  of  dental 
lesions,  spanning  the  period  from  very  ancient  to  modern 
times,  liowever  interesting  and  instructive  it  might  prove, 
has  not  been  and  never  can  be  written,  because  of  lack  of 
accurate  and  consecutive  data. 

Many  of  the  I'ecords  of  earlier  times  on  this  subject 
are  incomi^lete,  or  sadly  lacking  in  detail ;  some  have  been 
lost;  and  still  others  now  in  existence  are  only  copies  of 
manuscripts  having  a  much  earlier  origin. 

Some  of  the  original  old  records  now  remaining,  rest  in 
government  archives  of  Old  World  countries,  or  in  the  li- 
braries of  their  universities. 

To  the  uninitiated  student  of  dental  lore,  many  of  these 
historic  treasures,  written  in  a  foreign,  dead,  or  almost  imde- 
cipherable  and  forgotten  language,  have  been  until  recently 
as  completely  out  of  his  reach  as  though  they  never  existed. 

The  efforts  of  a  number  of  men,  fitted  by  training  and 
experience,  and  conveniently  located  near  to  these  manu- 
script depositories  as  well,  have  been  directed  to  clearing 
up  and  collating  such  ancient  and  median-al  historical  data 
of  medicine  and  dentistry  as  are  available.  Notable  among 
these  the  names  of  Prof.  George  Ebers,  a  celebrated  German 
Egyptologist,  and  Dr.  Mncenzo  Guerini,  of  Naples,  Italy, 
stand  out  most  prominent. 

THE  EBERS  PAPYRUS 

In  1873  Professor  Ehers  obtained  from  "an  inhabitant 
of  Luxor,  Up]ier  Egypt,"  a  manuscript  written  in  hieratic 
characters  on  pa])yrus  paper,  which  u})on  deciphering 
proved  to  be  the  most  complete,  as  well  as  probably  the  most 
ancient  of  the  early  records  relating  to  tlie  treatment  of 
disease,  both  general  and  dental. 

Two  translations  of  this  manuscript  have  been  made,  one 
by  Professor  Ebers  in  1875,  and  the  other  by  Dr.  Heinrich 
Joachim  in  ]8n().  'Quoting  from  Guerini,  the  sco])e  and  an- 
tiquity of  tliis  manuscript  is  made  apparent: 

"Lepsius,  and  with  him  the  greater  part  of  Egyptol- 
ogists ai*e  of  the  opinion  that  the  Ebers  papyrus  is  not  an 

1101 


11(12  A    liKII'^F    IlISTOliY    OP    I'ROSTlllOTU;    DKNTISTRY 

original  wdik  at  all,  l)iit  simply  a  copy  of  medical  writings 
of  still  earlier  date,  belungiiig  to  diffci'eiit  epochs,  and  which 
were  collected  and  reunited  lo  form  a  kind  of  manual  on 
medicine. 

ANTIQUITY  OF  THE  PAPYRUS 

"From  some  indications  existing  in  the  papyrus  itself, 
Ebers  has  been  able  to  argue,  with  quasi  certainty,  that  the 
papyrus  was  written  toward  the  year  1550  B.  C.  But  some 
parts  of  it  have  their  origin  in  a  far  more  remote  epoch; 
they  go  back,  that  is,  to  thirty-seven  centuries  or  more  be- 
fore the  Christian  era.  In  fact,  at  page  ciii  of  the  lObers 
papyrus  one  reads : 

"  'Beginning  of  the  book  about  the  treatment  of  the 
uxeda  in  all  the  members  of  a  person,  such  as  was  found  in 
a  writing  under  the  feet  of  the  god  Anubis,  in  the  city  of 
Letopolis;  it  was  brought  to  His  Majesty  Usaphais,  King 
of  Upper  and  Lower  Egypt.'  Now  as  Joachim  remarks, 
the  Usaphais  herein  named  was  the  fifth  king  of  tlie  first 
Egyptian  dynasty,  and  he  reigned  toward  3,700  years  before 
the  Christian  era.  Hence,  it  may  be  argued  that  some,  at 
least,  of  the  writings  from  which  the  Ebers  papyrus  was 
taken  were  composed  in  the  very  remote  epoch  to  which  we 
have  just  alluded,  or  perhaps  still  farther,  for  it  is  impossi- 
ble to  know  whether  the  book,  deposited  by  unknown  hands 
at  the  foot  of  the  statue  of  the  god  Anubis,  had  been  written 
biit  a  short  time  previous  or  at  a  much  earlier  epoch." — 
Guerin. 

This  suggests  a  possible  age  of  5,600  years  for  some  of 
the  prescriptions  offered  for  the  relief  of  pain.  The  \ixeda 
mentioned  literally  means  a  painful  swelling,  and  might 
ajjply  to  inflammatory  conditions,  accompanied  by  swelling, 
in  any  part  of  the  body,  alveolar  abscess  included.  In  fact, 
specific  mention  is  made  in  several  places,  of  remedies  for 
the  cure  of  "growth  of  the  uxeda  in  the  teeth  (alveolar  ab- 
cess?)  and  also  "bennut  blisters  in  the  teeth,"  the  latter 
supposed  to  mean  small  fistulous  ojienings  to  abscesses  of 
dental  origin. 

No  reference  of  any  sort  in  regard  to  prosthetic  oper- 
ations is  found  in  the  papjyrus.  It  does  not  follow,  however, 
that  prosthesis  was  not  attempted  in  very  ancient  times. 
In  fact,  positive  evidence  exists  to  prove  that  replacement 
of  one  or  more  teeth  was  a  recognized,  although  ]ierhaps 
not  common  method  of  practice,  almost  or  quite  3000  years 
ago.     Mention   of  this   will  be  made  later. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1103 

GUERINI'S  HISTORY  OF  DENTISTRY 

Within  recent  years,  tlie  most  tiiorongh,  exliaustive, 
and  painstaking  inquiry  in  ancient  and  mediaival  liistory  of 
dentistry  ever  undertaken  by  one  individual,  lias  been  car- 
ried out  by  Dr.  Vincenzo  Guerini,  of  Naples,  Italy.  It  repre- 
sents an  effort  on  the  part  of  this  distinguished  gentleman, 
quoting  his  words,  to  "contribute  to  the  diffusion  of  exact 
historical  knowledge  as  to  the  origin  and  gradual  develop- 
ment  of  dentistry." 

The  results  of  his  labours,  which  represent  a  vast 
amount  of  researcli  work  and  much  financial  outlay  as  well, 
he  has  generously  jn-esented  to  the  profession  in  America, 
through  the  National  Dental  Association,  as  a  token  of  his 
appreciation  of  American  progress  in  dental  science  and  de- 
velopment. 

That  the  results  of  Dr.  Guerini 's  efforts  are  appreci- 
ated, not  only  by  tlie  profession  of  America,  but  of  the  world, 
goes  without  saying.  His  work  is  frequently  quoted  by 
writers  on  historical  dental  subjects,  and  with  a  feeling  of 
security  as  to  fact,  hitherto  noticably  lacking  in  mucli  of  the 
previously  avaihible  data,  because  of  its  questiona))le  au- 
thenticit.v.  Much  of  the  contents  of  the  present  chapter  is 
based  eitlier  directly  or  indirectly  upon  Guerini 's  work. 

The  facts  as  presented  in  Guerini 's  History  lead  to  the 
belief  that  the  origin  of  dentistry  was  coeval  with  that  of 
medicine;  that  in  all  probalnlity,  in  very  ancient  times, 
dentistry  as  a  specialty  was  not  recognized  as  such,  and 
therefore  the  treatment  of  dental  lesions  came  properly 
within  the  domain  of  the  medical  practitioner. 

Although  the  statement  has  repeatedly  been  made  that 
teeth  filled  with  gold  and  various  substances,  and  prosthetic 
pieces  of  different  forms,  have  been  found  in  the  sarcophagi 
of  mummies,  in  the  pyramids  and  necroiJoli  of  Egypt,  the 
fact  has  not  been  substantiated.  Schmidt,  Ebers,  Virchow 
and  Mummery,  all  of  whom  devoted  considerable  effort  to 
this  phase  of  research,  failed  to  find  authentic  specimens 
of  the  classes  of  work  mentioned.  Neither  has  Guerini,  in 
his  examination  of  ancient  specimens  or  in  historical  re- 
search found  anytliing  to  indicate  that  the  very  early  Egyp- 
tians knew  "how  to  insert  gold  fillings,  and  still  less  to 
apply  pivot  teeth."  He  further  states,  however,  that,  al- 
though the  direct  proof  may  be  lacking,  he  beliercd  the 
Egyptians  knew  how  to  apply  artificial   teetli. 

He  bases  his  deduction  on  the  following:   "And  even 


1104  A     liKIWF     IIISTOKY    OK     i'UOSTUKTU'    DKNTISTUY 

tliouuli  it  in;i>-  iiol  lie  |i(issihlc  tii  dciiioiist  r;il  c  this  by  tlii'cct 
prddl',  (iiic  is  (M|ii.'illy  prdiic  to  atliiiit  it  when  one  coiisidcvs, 
on  tlic  one  hand,  the  remarkable  ability  of  tlic  ancient  K.nyi"- 
tians  in  all  j)lasti('  arts,  and,  on  the  other  hand,  the  great 
importance  they  attril)uted  to  beantii'yiug  the  human  body; 
so  much  so,  tliat  even  in  so  ancient  a  document  as  the  Fibers 
l)apyrus,  one  tinds  formula'  for  medicaments  against  bald- 
ness, for  lotions  for  the  liair,  and  other  kinds  of  cosmetics. 
Is  it  not  likely,  therefore,  that  so  refined  and  ingenious  a 
people  should  not  have  found  the  means  of  remedying  the 
deformity  resulting  from  the  loss  of  one  or  more  front 
teeth!"  " 

THE   PHCENICIANS 

The  ancient  Phu-nicians,  a  race  of  Semitic  origin,  were 
a  thrifty  nation  of  maritime  traders.  Their  country,  the 
nortliern  Palestine  Mediterranean  coast  land,  ^afterwal''ds 
known  as  Canaan,  consisted  of  a  strip  about  15  miles  wide 
and  150  long.  It  lay  between  the  Lebanon  Mountains  and 
the  sea,  on  the  borders  of  which  were  situated  the  populous 
cities  of  Tyre,  near  the  center,  and  Sidon  to  the  north.  All 
of  the  principal  ports  of  the  world  were  known  to,  and  vis- 
ited by  her  merchantmen,  whose  bartering  excursions  and 
voyages  of  discovery  lirought  them  in  contact  with  the  trad- 
ers, artisans,   and   scholars  of  many  lands. 

EFFECT  OF  EGYPTIAN   CIVILIZATION   ON   PHCENICIA 

P>eginning  about  17()(i  P.  (".  Kgypt  assumed  a  protector- 
ate over  Phoenicia,  which  was  maintained  for  about  three 
hundred  years.  This  political  bond,  coupled  with  mutual 
commercial  exchange,  brought  the  ])eople  of  the  two  coun- 
tries into  close  business  and  social  relations  with  each  other. 

Since  the  beneficent  influence  of  Egypt's  advanced  civili- 
zation was  felt  and  recognized  in  the  known  remote  cor- 
ners of  the  earth  in  those  times,  it  naturally  followed  that 
Phoenicia,  l)y  reason  of  the  connection  noted,  must  have 
benefited  thereby,  and  ai)propriated  to  herself  some  of  the 
advanced  ideas  of  the  older  country  in  culture,  fine  arts  and 
medical  science. 

ONE  OF  THE  MOST  ANCIENT  SPECIMENS  OF  PROSTHETIC  ART 

Now,  although  she  has  left  no  papyrus  scrolls,  no  pyra- 
mids, no  obelisks  to  commemorate  important  historical  events, 
Phamicia  has  left  what  P]gyi)t  has  not,  viz.,  a  well  preserved 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  IIO.J 

speeimeu  of  ancient  prosthesis.  How  old  this  piece  may  be 
no  one  can  tell,  but  that  it  is  very  ancient  there  can  be  no 
doubt.  The  outline  of  Guerini's  history  of  it  is  about  as 
follows : 

In  1862,  Dr.  Gaillardot.  (•(iniicclcd  with  Kenan's  Syrian 
Exploring  P]xpedition,  found  in  tlie  most  ancient  part  of 
the  necropolis  of  Sidon.  a  part  of  the  upper  jaiv  of  a  woman, 
in  which  the  six  anterior  teeth  were  united  together  with 
gold  wire.    A  central  and  ])roximating  lateral  incisor  appear 


I'HiEXiciAX     .U'ri,i^o;c-E    found     at 

SIDON,   AS  RErRESENTED  IN  A  CUT  OF 
RENAN'S     MISSION    DE    THENICE 

(GUERINI) 


THE    SAME    FIGURE    RE\ERSED.    AS    IT 

OUGHT    TO    HE     IF    THE    PIECE    FOUND 

AT  SinON  BELONGED  TO  A  LOWER  .TAW 

IGI'ERINII 


to  have  belonged  to  another  person,  and  from  the  manner 
of  their  attachment  were  sul)stitnted  for  lost  teeth.  This 
piece  is  now  in  the  Louvre  in  Paris.  In  addition  to  this 
prosthetic  piece  there  were  also  found  in  the  same  grave 
two  copper  coins,  an  iron  ring,  a  vase  of  most  graceful  out- 
line, a  scarab,  and  twelve  very  small  statues  of  Egyptian 
deities,  probalily  a  necklace  judging  by  the  holes  bored  in 
them. 

Concluding  his  remarks  on  "Dental  Art  Among  tht 
Egyptians,"   Guerini   says: 

"The  remains  discovered  in  many  of  the  Plia?nician 
tombs  would  of  themselves  alone  be  sufficient  to  demonstrate 
luminously,  the  enormous  influence  exercised  by  the  Egyp- 
tian civilization  on  the  life  and  customs  of  that  people.  Now, 
if  there  were  dentists  in  Sidon  capable  of  applying  false 
teeth,  it  may  reasonably  l)e  admitted  that  the  dentists  of  the 
great  Egyptian  metropoli,  Thel)es  and  Memphis,  were  able 
to  do  as  much  and  more,  the  level  of  civilization  being  with- 
out doubt  higher  there  than  in  Tyre  or  in  Sidon,  or  in  other 
non-Egyptian  cities." 

THE  ETRUSCANS 

The  I'ltniscaiis  were  a  iKMiplc  who  iiihahited  TT]ip('r 
Central  Italy  from' about  800  15.  C.  to  -JS:'.  15.  C.,  when  they 
wore  conquered  by  the  Romans.  One  author  has  said  of 
them:  "Ancient  writers  concur  in  rei)resenting  the  Etrus- 
cans as  the  most  cultivated   and  refined  peo])le  of  ancient 


1106  A    BnilOP    HISTORY    OF    PROSTHETIC    DENTISTRY 

Italy,  ami  as  especially  skillt'iil  in  (ii-]iaiiiental  and  useful 
arts,  in  which  1  he  ideas  and  patterns  used  singularly  re- 
semhh'  those  dl'  I'lgypt." — "They  made  groat  progress  in 
architecture,  sculpture,  and  i)ainting,  and  es])ecially  in 
bronze  work  and  gold  jewelry." — "They  excelled  in  agricul- 
ture, navigation,  engineering,  and  in  useful  jMililic  works." 
( Universal  J^ncyclopedia. ) 

Guerini  says:  "They  were  a  laborious  and  courageous 
race,  not  only  active  in  agriculture,  in  art  and  commerce, 
but  also  brave  warriors  and  hardy  navigators.  In  tlieir 
long  sea  voyages  tlie  Etruscans  frequently  visited  Egypt 
and  Phoenicia,  trading  especiall.y  in  the  more  flourishing 
cities,  which  were  at  that  time  Memphis,  in  Egypt,  and  Tyre 
and  Sidon  in  Phoenicia.  On  the  other  hand,  the  PlKPnicians, 
who  were  also  active  merchants  and  navigators,  not  only 
visited  Etruria  and  other  regions  of  Italy  very  frequently, 
but  also  established  numerous  colonies  in  many  islands  of 
the  Mediterranean,  and  especially  in  those  nearer  Italy. 

"This  continual  intercourse  between  I^truscans  on  one 
side,  and  Egy))tians  and  Pluimicians  on  the  other,  accounts 
for  the  great  influence  exercised  by  the  Egyptians  and  Phoeni- 
cian civilization  upon  the  later  developed  Etruscan  culture 
— an  influence  manifesting  itself  very  distinctly  in  the  works 
of  art  of  the  latter,  whicji  often  have  an  altogether  Oriental 
character,  and  not  seldom  re])resent  scenes  drawn  from  the 
domestic  life  of  the  Egy]itians  and  Phcenicians. 

ETRUSCAN  DENTAL  ART 

"As  to  what  concei-ns  dental  art,  everytliing  leads  up 
to  the  belief  that  it  was  ])racticed  by  tlie  Egyptians  and 
Plioenicians  earlier  than  l)y  the  Etruscans,  whose  civiliza- 
tion, as  already  hinted,  is  certainly  less  ancient.  Neverthe- 
less, in  comparing  the  dental  appliances  fovmd  in  the  Etrus- 
can tombs  with  the  sole  and  authentic  dental  appliance  of 
Phoenician  workmanship  known  at  the  present  day,  we  can- 
not but  be  struck  with  the  greater  superiority  of  the  Etrus- 
can appliances.  It  is  therefore  probable  that  the  Eltruscans, 
although  they  had  learned  the  dental  art  from  the  Egyptians 
and  Phoenicians,  had  subsequently  carried  it  to  a  much  higher 
degree  of  perfection  than  it  had  aiMi\-ed  nt  in  Egypt  or  in 
Phoenicia." 

A  number  of  specimens  of  ancient  prosthetic  appliances 
of  Etruscan  workmanship  have  been  found  within  recent 
years,  the  genuineness  of  which  are  unquestioned.  Most  of 
these  specimens  are  preserved  in  various  Italian  museums. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1107 

Some   of   them   arc   illustrated   in   Dr.    Guerini's   admirable 
work,  a  few  of  which  are  here  reproduced. 

In  an  excavated  tomb  at  Valsiarosa,  near  the  ancient 
Falerii,  was  found  an  ap]>lian('e  consisting  of  four  gold  rings 


HTlirSl'AX      AI'l'LlAXOB      FOUND 
AT    VALSLiVBOSA.     DESTINED    TO 
SUPPORT  AN  ARTIFICIAL  BICUS- 
PID,   NOW    DISAPPEARED 
((iUEKINI) 

soldered  together  and  fitted  to  the  cuspid,  tirst  bicuspid,  and 
first  molar.  The  ring  over  the  site  of  the  second  bicuspid, 
the  missing  tooth,  had  a  rivet  extending  through  it  from 
buccal  to  lingual,  evidently  intended  for  holding  the  sub- 
stituted tooth,  which,  however,  was  lost. 


ETRUSCAN      AI'PLIANCE       FOR       SUPPORTING      THREE 

ARTIFICIAL  TEETH.  TWO  OP  WHICH  WERE  MADE  PROM 

ONE    OX    TOOTH     (CIVIC    MUSEUM    OF    CORNETO) 

(GUEMNI) 


*5 


THE    SAME    APPLIANCE    REVERSED 


Guerini  suggests  that  the  substitute  tooth  may  have  been 
made  of  some  destructible  material,  and  had  disintegrated, 
or  that  it  might  liave  been  slotted  at  its  base  to  pass    on 


11(18  A   i!i;ii':i''   HISTORY   OK   ruos'riii'n'ii'   I)iontisti{Y 

eitlu!!'  side  of  llu'  I'ix'cl,  jiikI  not  haviiin'  hccn  i-i,i;i(lly  lixcd 
within  tlie  ring,  was  dislodged  jind  losl  during  the  cxcaN'atioii. 
Tliis  appliance  is  now  in  the  iiuisiMiiii  (if  i'upc  -liilius,  in  llonu'. 

Two  appliances  similar  in  character  to  the  one  just  de- 
scribed will  serve  to  illustrate  the  general  type  of  the  an- 
cient prosthetic  pieces  found  in  other  Etruscan  tombs,  and 
which  are  supposed  to  be  about  3000  years  old.  Botii  of 
these  specimens  repose  in  the  civic  museum  of  Corueto,  the 
ancient  city  of  Tarquinii. 

The  first  of  these  s]:)ecimens  to  be  described,  consists  of 
bands  of  pure  gold,  soldered  together  and  fitted  to  the  cus- 
pid and  lateral  on  the  right,  and  to  the  cuspid,  first  bicuspid, 
and  first  molar  on  the  left  side.  A  band  of  gold  con- 
taining a  rivet  extending  through  it  from  buccal  to  lingual, 
occupies  the  site  of  the  missing  natural  second  bicuspid, 
and  served  for  the  attachment  of  its  substitute,  the  latter, 
however,  having  become  disintegrated  or  in  some  manner, 
lost.  A  single,  elongated  band  of  gold,  occupying  the  space 
of  the  three  missing  anterior  teeth,  extends  from  the  right 
lateral  to  the  left  cuspid.  Fitted  within  this  band  and  filling 
the  entire  space,  was  a  wide  ox  tooth,  grooved  longitudinally 
in  its  center  to  represent  two  central  incisors.  The  space 
once  occupied  by  the  these  three  teeth,  having  closed  slightly, 
no  effort  was  made  to  reproduce  the  lateral  incisor.  This 
block  was  firmly  fixed  in  position  by  means  of  two  rivets. 
(Page  1107.) 

Whether  the  dentist  in  this  case,  recognized  the  prophy- 
lactic advantage  of  keejiing  the  gingival  ends  of  the  bands 
as  far  removed  from  the  gun  line  as  possible,  or  was  merely 


ETRrsc  w  \i-n  I  wii:  inu  si-r- 
rOETIw: 'I'wn  i\si:i;ti.ii  ihmaN 
TEETH.  ilXi.  IIK  W  llhll  IS  NOW 
WANTI.NC  icnic  .Ml  SKI  .\1  OF 
fOliXKTOl      (GlEIUXI) 


actuated  through  moti^'es  of  convenience  in  fitting  and  at- 
taching the  appliance,  cannot  of  course,  be  determined,  but 
the  fact  is  apparent  that  the  bands  occupied  a  position  well 
toward  the  incisal  and  occlusal  third  areas  of  the  anchor 
teeth. 

The  second  s]teciinen  consisted  of  two  strips  of  rolled 
gold,  adapted,  one   labially  and   the  other  lingually  to   the 


A    BRIKF    HISTORY    OF    PROSTHIOTIC     DKNTISTRY  llUli 

rL'maiuiiig  autL'iior  tei'tli,  and  soldfred  at  their  extremities 
to  form  an  elongated  band.  Four  small  sections  of  gold, 
spaced  and  soldered  within  this  elongated  l)and,  divided 
it  into  five  square  spaces.  Three  of  these  s))aces  were  oc- 
cupied by  supporting  natural  teeth.  The  otlier  two  spaces 
served  as  sockets  to  carry  the  sulistitutes,  which  in  this 
case  were  natural  teeth,  one  of  wliich  was  missing.  The 
same  method  of  anchorage  as  previously  described — the 
rivet — was  used  for  attaching  the  snlistitute  teeth  to  the  gold 
structure. 


ETRI'SCAX  .\P 

TEXDED  TO  A  \  i 
EFFECTS  OF  I  (IN 
PERHAPS.  Tn 
PURELY  nl;\  \  \l 
FICIAI.  K'  I'.si  I  r 
OF     COXTI        I'l:!  ■ 

xi:' 


Tliese  methods  of  wiring  and  banding  together,  with 
gold,  loose  natural  teeth,  and  of  applying  the  same  means 
for  the  retention  of  substitutes  for  missing  teeth,  in  the 
manner  described,  represent  C[uite  fully  the  lirst  etfoi'ts  of 
the  earlv  dentists  in  bridge  construction. 


The  addition  of  a  saddle  to  rest  ui>on  the  border,  and 
thus  furnisli  greater  support  and  security  to  the  substitute 
than  was  affordeu  by  ligating  or  ))anding  to  tlie  proximat- 
ing,  and  adjacent  teeth,  was  evidently  not  conceived  until 
a  much  later  period. 


1110  A    BRU'W    mSTOIlY    OF    PROSTHETIC    DKNTISTUY 

ANCIENT  CROWN  WORK 

The  first  and  only  specimen  of  ancient  gold  crown  work 
so  far  known  was  found  within  recent  years,  at  Satricum, 
near  Rome,  and  is  now  in  the  museum  of  Pope  Julius.  This 
crown  consists  of  two  pieces  of  gold,  stamped  to  represent 


ROMAN    APPLIANCE    FOUND    AT  THE    SAME    SEEN    FROM    liBf.OW 

SATRICCM.      CROWN    OF '  LOWER  (GUERINI) 

INCISOR    MADE    OP    C.mA) 

the  labial  and  lingual  surfaces  of  a  lower  central  incisor, 
and  united  along  the  mesio-inciso-distal  surfaces  witli  solder, 
just  as  the  Hollingsworth  two-piece  anterior  crown  is  joined 
together.  It  was  held  in  place  by  an  elongated  band  which 
embraced  the  proximating  and  adjacent  tootli  on  either  side 
of  the  crown.  The  attacliment  of  the  band  was  close  to  the 
gingival  margin  of  the  crown. 

FIRST  REFERENCES  IN  HISTORY  TO  PROSTHESIS 

Although  these  ancient  specimens  of  dental  prosthesis 
have  been  found,  and  somewhere  near  the  probable  time  of 
their  construction  determined  by  deductive  reasoning,  no 
written  records  of  such  or  similar  work  appears  until  about 
the  beginning  of  the  CHiristian  Era. 

In  Edersheim's  "Life  and  Times  of  Jesus,  the  Mes- 
siah," according  to  Dr.  W.  C.  Miller,  in  Dental  Cosmos, 
December,  1905,  the  following  statement  is  found:  "Speak- 
ing of  things  purchasable  in  Jeruslaem  in  the  time  of  Herod 
the  Great,  40  to  4  B.  C,  'And  then  the  lady  visitor  might 
get  anything  in  Jerusalem,  from  a  false  tooth  to  an  Arabian 
veil,  or  a  Persian  shawl,  or  an  Indian  dress.'  " 

Martial,  a  Latin  poet,  who  lived  in  Rome  during  the 
first  century  A.  D.,  in  a  number  of  his  epigrams  mentions 
artificial  teeth.  Gruerini  says:  "There  is  therefore,  not  the 
least  doubt  that  in  the  days  of  Martial,  artificial  teeth  were 
in  use;  and  that  these,  as  may  be  seen  from  the  epigram 
just  qiioted,  were  made  of  ivory  and  bone;  we  do  not  know 
whether  they  were  formed  of  other  substances.  The  ques- 
tion, however,  arises;  In  those  days  did  they  manufacture 
movable  artificial   sets,  or  was  the  dental  art  then  limited 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1111 

to  tixiug  the  artificial  teeth  immovably  to  the  neighboring 
firm  teeth,  by  means  of  silk  threads,  gold  wire  and  the  like  ? 
The  answer  to  this  question  may  be  found  in  anotlier  epi- 
gram of  Martial,  where  the  latter  ridicules  a  wanton  old 
woman,  telling  her,  among  other  things  still  worse,  that 
she  at  night  lays  down  her  teeth  just  as  she  does  the  silken 
robes. 

"It  is,  therefore,  beyond  all  doubt  that,  at  that  period, 
the  manner  of  constructing  movable  artificial  sets  was 
known;  and  most  i)robal)ly  not  only  partial  pieces  were  made, 
but  even  full  sets.  In  fact,  from  the  verse  quoted  above 
we  have  justly  the  impression  that  the  poet  means  a  whole 
set  rather  than  a  few  teeth.  From  the  words  of  Martial, 
it  may  also  be  concluded  that  these  dentures  could  be  put  on 
and  off  with  the  greatest  ease;  or,  as  we  may  say,  by  a 
iiiancuvcr  as  simple  as  that  of  removing  any  articles  of  wear- 
ing apjiarel;  they  must,  therefore,  have  been  extremely 
well  constructed." 

DENTISTRY  AMONG  THE  ANCIENT  HEBREWS 

In  Dr.  Koch's  "History  of  Dental  Surgery"  is  found  the 
following  from  the  pen  of  Dr.  H.  L.  Ambler:  "The  ancient 
Hebrews  did  not  have  any  large  amount  of  mechanical  in- 
genuity, and  dentistry  with  them  was  in  a  state  of  semi- 
cultivation,  but  they  replaced  natural  teetJi  with  false  ones 
more  than  two  thousand  years  ago.  A  law  of  the  Talmud 
allowed  the  women  'to  go  out  on  the  Sabbath  with  their 
false  golden  or  silver  teeth.'  Some  rabbis  allowed  their 
])eople  'to  wear  the  false  silver  teeth,  since  these  appeared 
natural,  but  the  use  of  golden  false  teeth  on  the  Sabbath 
was  ])roliibited.'  Many  teeth  were  made  of  wood,  and  later 
on  from  the  ivory  of  the  elephant's  tusk." 

SLOW    PROGRESS   OF   DENTAL    PROSTHESIS    IN    THE 
MIDDLE  AGES 

Passing  down  through  the  centuries  but  little  progress 
seems  to  have  been  made  in  denture  construction  until  within 
the  last  one  hundred  and  fifty  years.  It  is  true  that  various 
monographs  on  medical  and  dental  subjects  jirevious  to  the 
date  last  mentioned,,  contain  frequent  references  to  teeth 
carved  from  bone.-  or  ivory,  or  hippopotamus  tusks,  but  it  is 
more  than  likely  that  most  of  these  were  partials,  held  in 
]ilace  with  ligatures  of  silk  or  gold  wire,  in  the  manner  al- 
readv  described. 


1112  A     liHlEF    HISTOKV     OK     i'ROSTH  lilTIC     DKXTISTKY 

'I'lic  coiistriiclidii  dl'  siitisract(u-y  I'lill  upper  mid  lower 
dentures  imist  liave  been  u  coiiHiderahie  undertaking  in  the 
olden  time,  considerin.i''  tlie  manner  in  which  impressions 
of  the  moulh  weic  secured  and  casts  wei'e  derived  from  them, 
and  finally  the  de\-el(ipnient  i>\'  a(hii)tation  of  the  block  of 
hone  or  i\'ory  to  tlie  cast  by  carxiui;-  and  scra]Mni4'. 

FIRST  REFERENCE  TO  THE  USE  OF  MODELS 

Brief  as  it  is,  the  outline  of  technic  of  full  denture  con- 
struction as  given  by  Aratthias  Gottfried  Purmaim,  of  Bres- 
lau,  1fi48  to  1721,  is  the  most  complete  description  found 
u])  to  his  lime,  lie  was  the  lirst  to  refer  to  the  use  of  models 
in  dental  i)rostliesis,  but  he  does  not  state  how  they  were 
obtained.     Here  is  his   outline  as  given   by   Guerini : 

"The  front  teeth,  or  pronouncing  teeth,  ought,  when 
they  are  wanting,  to  lie  substituted  by  artificial  ones,  in 
order  to  avoid  the  defects  of  |jronunciation,  as  well  as  to 
obviate  deformity  of  the  mouth,  and  this  is  carried  out  in 
the  following  manner :  One  has  other  teeth  made  of  bone, 
or  of  ivory,  according  to  the  number,  the  size,  and  the  pro- 
portions of  those  wanting;  for  which  purpose  one  may 
previously  have  a  model  executed  in  wax,  reproducing  the 
particular  conditions  of  the  teeth  and  jaws,  in  order  after- 
ward to  make  and  exactly  adjust  the  whole  on  the  pattern 
of  it;  then  when  the  base  of  these  teeth  is  well  fitted  on 
the  jaw  and  small  holes  have  been  made  in  the  artificial 
teeth  and  also  in  the  natural  ones  next  to  them,  one  applies 
the  artificial  teeth  in  the  existing  void  and  fixes  them  as 
neatly  as  possible  with  a  silver  wire  by  the  help  of  pnn- 
cers. " 

Because  he  advised  the  perforation  of  the  natural  teeth 
for  the  passage  of  the  silver  wire,  a  method  which  would 
prove  exceedingly  painful,  and  invite  pathological  complica- 
tions as  well,  Guerini  concludes  that  Purmann  simply  de- 
scribed, "and  not  even  accurately,  a  prosthetic  method  al- 
ready in  use  among  specialists  of  that  period.  *  *  * 
On  examination  of  the  passage  cited  above,  which,  how- 
ever is  not  so  clear  as  might  be  desired — it  would  appear 
that  the  models  of  which  the  author  speaks  were  most  prob- 
ably' quite  different  from  those  in  use  now.  It  is  almost 
certain  that  the  specialists  of  those  days  first  made  a  sketch 
of  the  prosthetic  part  to  be  constructed,  using  for  the  pur- 
pose a  piece  of  wax,  which  they  modeled  jiartly  with  the 
hand  and  partly  carved ;  and  after  having  tried  on  this  model 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1113 

until  it  fitted  ]>('rt'ectly  in  tlic  inontli,  and  was  iu  every  way 
satisfactory,  they  probably  |)assed  it  on  to  a  craftsman  to 
make  an  exact  re]n'odnction  of  it  in  bone  or  ivory." 

FIRST   REFERENCE   TO    FULL    LOWER    DENTURES 

The  first  reference  to  a  full  lower  denture  is  found  in 
the  writings  of  Anton  Nuek,  an  eminent  Dutch  surgeon  and 
anatomist,  16M  to  l(i92.  He  says,  "In  the  case  of  all  of  the 
teeth  of  the  lower  jaw  being  wanting,  the  entire  dental  arch 
ought  to  be  framed  in  with  a  single  piece  of  ivory  or  tusk 
of  hipi^opotamus. "  From  this  we  infer  that  full  upper 
dentures,  being  more  difficult  to  retain,  were  not  frequently 
constructed,  else  they  also  would  have  been  mentioned  in 
this  connection. 

Nuck  further  recommends  that  artificial  teeth  be  made 
of  hippo])otamus  tusk,  specially  favoring  the  whitest,  which 
he  estimated  would  preserve  its  color  for  seventy  years,  in 
preference  to  ivory,  which  turned  yellow  from  the  action  of 
food,  drink,  and  the  saliva. 

FIRST   RECORD   OF   APPLICATION   OF   MINERAL   SUBSTANCES 
FOR  DENTURES 

Pierre  Dionis,  a  surgeon  and  anatomist  of  Paris,  in 
1690,  states  that  artificial  teeth  are  generally  made  of  ivory, 
but  may  be  made  of  ox  bone,  which  will  retain  its  color  bet- 
ter than  ivory.  He  also  states  that  Guillemeau  constructed 
artificial  dentures  from  a  composition  made  by  fusing  to- 
gether white  wax.  gum  elemi,  ground  mastic,  and  powder  of 
white  coral  and  of  pearls. 

On  this  Guerini  remarks:  "This  fact  is,  as  everyone 
can  see,  most  important,  for  it  constitutes  the  first  step  to- 
ward the  manufacture  and  use  of  mineral  teeth.  Dionis 
tells  us  that  the  teeth  made  of  Guillemeau 's  composition 
never  became  yellow,  and  that  it  was  also  very  good  for 
stop])ing  decayed  teeth.  It  would  seem,  therefore,  that  it 
could  be  used  as  cement  is  now  used." 

RETENTION  OF  PARTIAL  DENTURES  WITHOUT  THE  USE   OF 
LIGATURES  OR  WIRES 

While  it  is  i)ofsible,  and  in  fact  quite  probable,  that 
partial  dentures'liad  been  constructed  and  used,  which  were 
not  dependent  on  the  use  of  the  ligatures  for  their  reten- 
tion, yet  no  clear  statement  of  this  fact  has  so  far  appeared. 


1114  A     HIUKF    HISTORY    OK     I'ROSTHKTK'     DKNTISTRY 

The  first  attempts  to  construct  easily  I'ciiiovable  pieces,  .in 
all  probability,  consisted  in  longitudinally  i^rtxjving  the  ends 
of  tbe  partial  deulure  so  as  to  partially  embrace  tlie  prox- 
imating  teeth,  just  as  the  nativ(>s  of  the  Orient  now  do  in 
their  prosthetic  restorations.  II  will  therefore  be  interest- 
ing to  mention  tlie  first  record  of  such  practice. 

Lorenze  ITeister,  a  celebrated  surgeon,  in  1611  first  rec- 
ommends the  use  of  movable  jirosthetic  appliances  of  ivory 
or  liippopotamus  tusk  without  special  means  for  fixing  tliem, 
and  further,  that  they  should  be  removed  at  night  and  not 
be  returned  to  the  mouth  again  until  well  cleansed. 

Johann  Adolph  Goritz,  in  1725,  recommended  that  tlie 
natural  teeth  be  preserved  by  every  possible  means.  He 
discouraged  the  use  of  prosthetic  appliances  where  only  a 
few  natural  teeth  were  lost,  but  suggested  that  in  the  worst 
cases,  to  avoid  defective  "pronunciation,  or  for  some  other 
reason  (presumably  unsightliuess)  it  may  lie  filled  by  an 
imitation  in  soft  wood." 

Heinrich  Bass  of  Bremen,  1690  to  1754,  iirofessor  of  an- 
atomy and  surgery  in  Halle,  recommended  the  application 
of  "whole  dental  sets,  even  in  the  upper  jaw,  so  long  as 
there  be  two  natural  teeth  existing  to  fix  the  prosthetic  piece 
to."  From  this  we  again  infer  that  the  construction  of  full 
upper  cases  was  not  frequently  attempted,  on  account  of  the 
difficulty* in  securing  adequate  adaptation  and  guarding 
against  the  force  of  gravity  and  masticatory  stress. 

FAUCHARD'S  WRITINGS 

Pierre  Fauchard,  born  in  Brittany,  1690,  died  in  Paris 
in  1761,  has  been  called  the  "founder  of  modern  scientific 
dentistry."  He  published  a  work  in  1728,  entitled  "Le 
Chirurgien  Dentiste, "  consisting  of  two  volumes,  which 
was  by  far  the  best  exposition  on  dentistry  that  up  to  that 
time  had  ever  been  written. 

In  olden  times,  down  to  a  ])eriod  within  the  memory  of 
some  of  the  members  of  the  profession  still  living,  there  was 
a  tendency  on  the  ]iart  of  many  practitioners  to  jealously 
guard  with  secrecy  their  methods  of  practice,  especially 
prosthetic  operations,  and  thus  jireveiit  comjietitors  from 
profiting  thereby. 

Fauchard 's  writings  cover  a  wide  range  of  dental  sub- 
jects and  in  i^rosthetic  operations  he  is  particularly  explicit. 
He  recognized  the  existence  of  the  petty  jealousies  alluded 
to,  but  was  able  to  rise  above  them,  as  his  descriptive  details 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1115 

plainly  show.  In  roference  to  tliis  he  says:  "I  have  per- 
fected and  also  invented  several  artificial  pieces,  both  for 
substituting  a  part  of  the  teeth  and  for  remedying  their 
entire  loss,  and  these  pieces  substitute  them  so  well  that 
they  serve  perfectly  for  the  same  uses  as  the  natural  teeth. 
To  the  prejudice  of  my  own  interests  I  now  give  the  most 
exact  descriptions  possible  of  them." 

"While  Fauchard  did  perfect  some  of  the  prevailing 
forms  of  artificial  sulistitutes  and  invent  others,  the  greatest 
benefit  he  rendered  the  profession  and  posterity  consisted  in 
having  collected  and  included  in  his  work  "the  whole  doc- 
trine of  dental  art,  theoretical  as  well  as  practical,  thus  set- 
ting in.  full  light  the  importance  of  the  specialty,  and  giving 
it  a  solid  scientific  basis."     (Guerini.) 

Interesting  as  all  of  Fauchard 's  writings  are,  only  a 
few  of  the  ])iiiici])al  methods  he  describes  can  lie  here  in- 
troduced. 

TRANSPLANTATION  OF  NATURAL  TEETH 

He  mentions  that  iu  transplanting  a  tooth,  whether  re- 
cently extracted  or  not,  its  root  should  be  grooved  hori- 
zontally, so  that  when  ligated  firmly  in  position,  the  alveolar 
process  would  eventually  be  built  in  the  depressions  so 
formed,  and  as  he  expressed  it,  "the  tooth  will  remain  mor- 
tised and  may  be  preserved  for  a  considerable  length  of 
time. ' ' 

He  describes  several  methods  in  detail  for  replacing  the 
loss  of  two,  three,  or  more  contiguous  teeth.  One  of  these 
consisted  in  carving  from  ivory,  hippopotamus  tusk,  or  bone, 
each  tooth,  individually,  to  be  replaced  and  fixing  them  to- 
gether in  a  single  piece  by  drilling  holes  and  ligating  with 
wire.  This  was  then  bound  to  the  natural  teeth  with  gold 
or  silver  wire,  or  silk  or  linen  thread.  Another  method,  in- 
stead of  ligating  the  substituted  teeth  together,  consisted  of 
applying  a  strip  of  gold  fitted  into  a  horizontal  groove 
formed  in  the  lingual  surfaces  of  the  carvings,  and  to  which 
each  tooth  was  attached  by  means  of  two  rivets.  Again,  the 
teeth  to  be  re]ilaced  were  sometimes  carved  from  a  single 
block  of  the  materials  commonly  used  and  attached  in  the 
manner  ])reviously  mentioned. 

CROWN  WORK  IN  FAUCHARD'S  TIME 

Crowns  were  attached  to  roots  of  teeth  by  means  of  a 
metal  pivot  extending  into  the  root,  which  in  ease  of  enlarged 


IIIG  A    BRIEF     HISTOKY    OK     I'KUSTHETU',    DKNTlSTItY 

canal  had  ])revioiisl\  hcoi  lillcd  with  lead.  A  hole  drilled 
in  llio  load  i-eceivcd  the  root  end  of  tiic  pixnt,  while  I  lie  crown 
was  attached  to  the  iirojectin.n'  end  of  I  he  |ji\ol  with  a  cement 


J"-  fu 

c 


i-'ArniAitii-s   ii.i.rsTitATiox  df  a  riiowx  ok 

noitV    DIt    IIIIM'OI'OTAMIS    TUSK 
WITH    METAL   IJOWEI, 

composed  of  gnni  lac,  \'enice  tnrjientine,  and  jiowdered  white 
coral.  The  crown  of  a  natural  tooth  was  frequently  em- 
ployed in  such  cases. 

MEDIEVAL   BRIDGEWORK 

The  first  mention  of  fixed  bridgework,  although  not  so 
designated,  is  made  by  Fauchard,  wherein  he  describes  how 
a  prosthetic  piece  may  be  held  in  position,  in  case  the  crowns 
of  the  teeth  had  been  losl   but  the  roots  were  ])resent.     Two 


BBIDGE    CAR\ED    FROM    nf)RV.    RETAINED 

BY     TWO     SCREWS     FITTED     IN     ROOTS     OF 

I,\TEUAI,    INCISORS     (FAUCHARD) 


holes  were  made  in  the  substitute,  corresponding  to  and  in 
alignment  with  the  canals  of  two  roots,  through  which  pyra- 
midal screws  were  introduced  and  screwed  firmly  into  the 
roots. 

FULL    DENTURES 

Full  lower  dentures  were  recommended,  with  the  sug- 
gestion that  the  piece  should  be  so  formed  as  to  fit  the  irreg- 
ularities  of  the  arch   perfectly,  when,   with   the   aid   of   the 


A    BRIEF    HISTORY    OP'    PROSTHETIC    DENTISTRY  1117 

tongue  interiorly  and  the  cheek  and  lower  lip  exteriorly,  the 
substitute  would  be  held  steadily  in  place  and  the  patient 
would  be  able  to  masticate  with  it  after  becoming  accus- 
tomed to  its  ])resence. 

CONSTRUCTION  OF  FULL  DENTURES  BY  FAUCHARD 

Although  full  upper  dentures  were  constructed  long  be- 
fore Fauchard's  time,   it   is   evident  that  thev  were   seldom 


AN    I  I'l'Klt    DENTLRE    Kl  I'l'OliTEl)    BV    SriilXGS    FIXED    Til    A 

COED     APPLIANCE    WailCII    EMBKACES    THE     NATIRAI. 

TEETH  OP  THE   LOWER  JAW    (FAUCHARD) 

(GUBRINI) 

satisfactory.  One  case  is  mentioned  which  illustrates  the 
helplessness  and  inaliility  of  some  who  were  considered  other- 
wise well  qualiS.'^d  in  llie  construction  of  full  upper  cases. 
Pauchai'd  says:  "In  17;!7  a  huly  of  high  rank,  of  about  the 
age  of  sixty,  who  had  not   lost  any  of  her  lower  teeth,  Init 


1118  A    BRIKF    illSTOKY    OF    IMiOSTHETIC    DENTISTRY 

"was  deprivcil  entirely  nl'  llie  upper  mies,  jipplied  to  M. 
Caperon,  dentist  to  the  Kiiii;-,  who  was  riidst  ahh'  in  his  pro- 
fession, in  the  liope  that  he  ini^lit  he  alih'  to  furnish  her 
mouth  witli  an  upper  set.  But  lie  said  that,  'no  tooth  what- 
ever being  left  in  existence,  every  possible  point  of  attacli- 
ment  was  wanting,  and  it  would  therefore  be  as  difficult  to 
do  this  thing  as  it  would  he  to  huild  in  the  air.'  "  M.  Caperon 
referred  her  to  Fauchard,  who  after  some  delil)ei-ation  "suc- 
ceeded in  devising  a  means  of  applying  an  upper  set  of  teeth 
which,  in  fact,  entirely  satisfied  the  wishes  and  wants  of  his 
client."  (Gruerini.) 

The  apjiliance  in  this  case  did  not  include  the  full  com- 
plement of  teeth,  some  of  the  posterior  space  being  occupied 
by  the  springs,  by  means  of  which,  in  conjunction  with  a 
double  bow  frame  of  gold  lifted  around  the  lower  teeth,  the 
denture  was  retained  in  ]iosition. 

Mention  is  also  made  of  three  successful  cases  of  full 
upper  dentures  which  were  retained  without  the  aid  of 
springs.  Several  points  of  interest  are  seen  in  Fauchard 's 
own  description  of  these  cases,  which  is  as  follows: 

"One  can  adapt  an  entire  set  of  teeth  to  the  upper  jaw 
of  much  greater  sim]ilicity  than  those  described,  and  which 


r^ 

m   ^/^ 

P-^iJW 

B.          ■  W,   A 

41^ 

Li^^S 

is  maintained  in  its  ]>lace  by  tlie  sole  support  of  the  cheeks 
and  the  lower  teeth.  It  must  be  very  light  indeed  and  serves 
almost  solely  to  improve  the  appearance  and  the  pronunci- 
ation ;  but  when  the  individual  gets  used  to  it,  he  can  also 
masticate  with  it.  A  set  of  teeth  of  this  kind  ought  to  ad- 
here well  to  the  gums  and  to  be  constructed  in  such  a  man- 
ner  that   the   cheeks   may   afford    if    sufificient   ]iressure   and 


A    BRIEF    HISTORY    OP    PROSTHETIC    DENTISTRY  1119 

support,  together  with  the  aid  of  the  k^wer  teeth.  These 
latter  sometimes  bring  it  baclv  into  its  place  without  anyone 
perceiving  the  movement  except  the  wearer  liimself.  Not 
long  since  I  had  occasion  to  renovate  a  set  of  teeth  of  this 
kind  made  by  me  more  than  twenty-four  years  ago  and 
worn  by  the  owner  to  the  greatest  advantage.  I  have  since 
made  two  others  which  have  proved  most  useful  to  the  per- 


UPPER   DENTUKE   IX   IVORY.   AT    THE   END   OF   THE   ErcHTBENTH    CEN- 
TURY, roR  A  CASE  IN  WHICH  THE  LAST  MOLARS  AND  THE  FRONT 
TEETH  WERE  PRESENT   (GUERINI'S  COLLECTION) 

sons  wearing  them.  Tt  is  true  that  tliere  are  few  mouths 
adapted  for  wearing  tliese  sets,  so  much  so  that,  excepting 
the  three  referred  to,  I  have  never  made  any  others.  To  be 
able  to  construct  similar  sets  successfulh',  the  dentist  must 
be  possessed  of  skill  and  ingenuity.  Apart  from  this,  they 
are  tlie  most  suitable  for  poor  persons  wlio  cannot  sjicnd 
niiu'li,  as  they  cost  less  to  make." 

SUMMARY   OF  FAUCHARD'S  WORK 

Fauchard  made  use  of  both  flat  steel  and  coiled  gold  wire 
springs  for  the  retention  of  both  full  and  partial  dentures. 

Summed  up  briefi.y,  tlie  main  facts  of  prosthesis  which 
Fauchard  elaborated  upon  are  as  follows: 

The  transplantation  and  replantation  of  natural  teeth. 

The  application  of  both  carved  and  natural  crowns  to  the 
roots  of  teeth  l)y  means  of  metal  pivots,  or  by  binding  tliem 
to  proxiraating  natural  teetli  with  ligatures  of  gold  or  silver 
wire,  or  silk  or  linen  thread. 

The  ap])lication  of  a  crude  form  of  bridgework  consisting 
of  a  carved  replacement  rigidly  fixed  to  two  natural  roots  l)y 


1120  A    RHIIOF    HISTORY    OF    rROSTHKTIC    DENTISTRY 

means  of  two  tapcriiis;'  screws  passiiit;-  tln'ouiili  llie  siilislitut.e 
into  the  root  canals. 

Tlie  carving- of  jiailia I  and  I'lill  deiitiii-es  fioni  ivory,  hip- 
poyiotanins  tnsk,  or  hone,  1oi;e1  her  with  a  desci'iption  of  means 


OOMPI.ETl!    DKN'TtlRES    IFAlTHAHDl.     F'   RKl'ItESEN'TS   AX   ENAM- 
ELED   DENTURE    WITH    ARTIFICIAL  GUMS.    F<    AND    F-    STEEL 
SrniNGS    (GUERINIl 

of  attachment  witli  liii-atnres,  springs  and  metal   cril)s,   and 
adhesion. 

The  enameling  of  artificial  teeth  to  represent  the  varia- 
tions in  color  of  the  natnral  teeth,  and  the  staining  or  enam- 
eling of  the  gnm  portion  to  reju-esent  the  color  of  the  mucous 
tissues. 


A    BRIEF    HISTORY    OF    PROSTHKTU'    11KNTISTRY  1121 

'IMic  coiistructioii  <>(  (ilil  uijitnis  I'nr  (•(in-cclinu-  tlclVcls  of 
the  palate. 

Finally,  the  suggestion  Init  iiul  the  ilc\('li)|)incnt  ami  nsi', 
of  ])oivelain  for  teeth  ami  dentures,  as  not(Ml  in  the  clia])!!-!- 
on  ]iorcelain. 


DD 


A  SPRING   DEXTIRE  FOB  A   lASE    I.N    WHICH   THK    LOWER   FRONT 
TEETH  STILL  EXIST.      FIfiS.    1   TO   II    ILLI'STRATE  \'ARIOUS  PARTS 
OF  THE  APPARATUS    IFAUrilAROI    ((H'ERIXI) 


BENEFICIAL    INFLUENCE    OF    FAUCHARD'S    WRITINGS    UPON 
.      THE  PROFESSION 

rndouhtedn ,  the  exanijile  of  Fauchard  in  giving  freely 
and  uustintingly  to  tlie  profession,  the  henetits  of  his  knowl- 
edge, experienee  and  im])rovements,  exei'ted  a  widespread  and 


1122  A    liUlICK    HlSTOJtY    OK    J>l{OSTHKTIG    DKNTISTKY 

beneiicial  iiitluciicc  oii  his  coiilcinporarics  aiu!  llic  mi'ii  who 
followi'd.  This  is  cNidi^'iit  I'l-oiu  tiie  sijarsciicss  oT  ilctail  in 
previous  writings  and  tho  marked  tendency  oT  suhscciiiciit 
writers  to  more  fnlly  clalxiratc  tlicir  ideas. 

Tliat  till'  work  ot  l''iui<'har(l  was  up  to  date  and  in  some 
respects  in  advance  of  Ihc  tiiiics  is  apparent  from  the  fact 
that  altliough  other  works  appcai-ed  at  about  that  time  and 
at  intervals  afterward,  none  of  importance  was  presented 
until  eighteen  years  after  the  i)nl)lication  just  reviewed. 

FIRST  WORK   CONFINED  EXCLUSIVELY   TO   DENTAL 
PROSTHESIS 

In  1746  Mouton  i)iil)lished  the  first  work  of  record  con- 
fined to  dental  prostiiesis.  Most  of  the  methods  detailed  by 
Fauchard  were  included  in  this  later  publication,  and  some 
new  ideas  were  introduced,  among  which  may  l)e  mentioned 
the  application  of  gold  crowns  to  badly  decayed  front  and 
back  teeth,  the  front  crowns  being  enameled  to  correspond  in 
color  with  the  natural  teeth. 

For  the  first  time  mention  is  also  made  of  the  use  of 
spring  clasps  for  the  retention  of  partial  dentures. 

FIRST  MENTION  OF  PLASTER 

In  1756  Philip  Pfaff,  dentist  to  Frederick  the  (Ireat,  in 
a  work  confined  to  dental  subjects,  first  describes  the  use  of 
plaster  models.  Guerini  remarks:  "It  is  therefore  to  two 
Germans — Pfaff  and  Purmann,  the  latter  who,  as  we  have 
already  seen,  used  wax  models — that  one  of  the  greatest  pro- 
gressive movements  in  dental  prosthesis  is  indebted;  that  is, 
the  method  of  taking  casts  and  making  models,  of  which 
method  one  finds  no  trace  whatever  in  the  authors  of  anti(|uity, 
and  which,  it  would  appear,  was  not  known  even  to  Fauchard 
himself.  The  wax  casts  of  an  entire  jaw  were  taken  by  Pfaff 
in  two  pieces,  one  of  the  right  half  of  tlie  jaw,  the  other  of 
the  left,  which  were  then  reunited,  and  one  thus  avoided  spoil- 
ing the  cast  in  removing  it  from  the  month." 

FIRST  MENTION  OF  GOLD  BASES 

In  1757  Bourdet  described  the  use  of  gold  bases  for 
resting  upon  the  aheolar  process,  to  which  the  replaced  teeth 
were  attached  )iy  means  of  small  pins  and  the  whole  base 
overlaid  with  flesh  colored  enamel,  similar  to  the  continuous 
gum  pieces  of  today,     lie  also  described  another  dentui'e  in 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1123 

wliicJi  he  carved  the  three  back  teeth  on  either  side  from  tlie 
same  block  of  hippopotamus  tusk,  which  formed  the  base, 
while  the  ten  anteriors  were  human  teeth  fixed  to  the  carved 
base  by  means  of  rivets. 

IMPLANTATION  OF  TEETH 

The  first  mention  of  imiilantation  of  teeth  is  made  by 
Bourdet,  which  is  related  Ity  Guerini  as  follows:  "This  sel- 
ebrated  author  inveighs  bitterly  against  charlatans  and  quack 
dentists,  and  throws  light  on  all  their  impostures.  It  appears, 
however,  that  in  the  midst  of  this  despicable  class,  so  justly 
condemned  by  him,  there  existed  a  courageous  though  unscien- 
tific operator,  to  whom  posterity  would  have  attributed  due 
honor  had  his  name  been  handed  down,  for  he  was  the  first, 
in  all  probability,  to  try  the  implanting  of  teeth  in  artificial 
alveoli.  This  is,  at  least,  what  we  deduce  from  a  passage  in 
one  of  Bourdet 's  works,  in  which  we  read  that  a  charlatan 
sought  to  impose  on  the  public  the  belief  that  he  could  make 
a  hole  in  the  jaw  bone  and  plant  therein  an  expressly  pre- 
pared artificial  tooth,  which  in  a  brief  space  of  time  would  be- 
come firm  and  as  useful  as  a  natural  one.  Bourdet  adds  that 
an  attentive  investigation  led  to  the  recognition  of  said  tooth 
being  sim])ly  that  of  a  sheep.  It  would  appear,  therefore,  that 
the  operation  had  been  in  reality  performed,  it  matters  but 
little  whether  with  the  tooth  of  a  sheep  or  with  one  of  another 
kind." 

Adam  Anton  Brunner,  a  (reinuui,  in  1766,  described  a 
method  of  applying  pivot  teeth  by  screwing  the  pivot  into  the 
base  of  the  crown,  then  enlarging  the  root  canal  just  enough 
to  tightly  embrace  the  root  ])ortion  of  the  ]nvot  Light  ham- 
mer l)lows  directed  against  the  crown  forced  the  pivot  into 
the  root  canal  and  held  it  firmly  without  the  aid  of  cement. 

BERDMORE'S    REFERENCE    TO    ARTIFICIAL    DENTURES 

Thomas  Bcnlnioic,  dentist  1o  Oeorge  ill  of  England  in 
17()H,  makes  this  statement  in  regard  to  artificial  teeth:  "Al- 
though artificial  teeth  are  evidently  ornamental,  although  they 
give  a  juvenile  air  to  the  countenance,  imi)rove  the  tone  of  the 
voice,  render  pronunciation  more  agreeable  and  distinct,  help 
mastication,  and.  preserve  the  o]iposite  teeth  from  growing 
prominent,  yet  many  are  prejudiced  against  them  on  account 
of  some  inconveniences  which  are  often  fduiid  to  attend  the 
use  of  them.    For  thev  are  said  to  become  very  soon  yellow 


11^4  A     imilOK     IIIS'I'OKY     OK     I'UOSTI  1 KTIC     DKNTISTKY 

ami  tlirtv',  to  .i;i\('  a  stiiikiiii;-  hrcatli,  not  to  lit  easy  on  the 
i!,'uiiis,  selciom  to  slaml  linn,  and  to  loosen  after  some  time 
the  rieis>'hhc)rin,s>'  teeth  to  wliieli  they  are  t'asteneil,  or  the  hafd 
lij^'atiire,  which  i^  connnonlx  nscd.  is  often  seen  to  ent  \-ei\v 
deo])  into  the  soimd  teeth."  Il<'  la\s  tiiese  dil'tienlties  to  the 
fa  nit  of  the  "artist,"  the  ne^li.ii'enee  of  the  patient,  or  the  want 
of  proper  instrnetions.  lie  reeonmiemh^d  the  frei|nerit  nse 
of  the  brush  with  suitable  iiowders,  aud  to  axoid  the  use  of 
red  wines  and  stainiu,<>-  hKiuors,  and  the  use  of  silk  twist  in 
stead  of  wii'c  ligatures. 

"A  whole  set  of  artilieial  teeth  ma>'  he  made  for  one  oi' 
hotli  jaws,  so  well  litliMJ  to  admit  of  the  ueeessar>  motions, 
and  so  eonvenientiv  retained  in  the  proper  situation  li>'  the 
hel]i  of  spring's  of  a  ih'W  aud  peculiar  consti'uetiou  tiiat  they 
will  answer  e^•ery  purpose  of  natural  teetli.  ami  can  he  taken 


^^^BSi^ 


out,  cleaned  and  rejtlaced  by  the  ])atient  himself,  with  the 
greatest  ease.  I  say  si)i-ings  of  a  peculiar  construction,  he- 
cause  they  are  totally  different  in  shape  and  action  from 
those  whieli  have  Ijeen  used  by  my  predecessors,  because  they 
follow  all  the  various  motions  of  the  jaw  very  freely,  aud  be- 
cause the  ])ressure  which  they  give  is  always  e(|ual  and  gen- 
tle, whether  the  mouth  be  shut  oi-  not."  He  further  states 
that  dentures  made  from  soft  hone  or  ivory  discolor  readily, 
but  may  be  made  of  more  durable  materials  which  will  retain 
their  ])olish  and  whiteness  for  a  long  time.  Further,  that  the 
gum  ]»ortion  ma>-  lie  stained  so  ])erfectly  that  "nobody  in 
common  conversation  can  distinguish  the  artificial  from  the 
natural  gums," 

Jourdain,  in  17S4,  descrihed  a  full  ujiper  and  lowei'  den- 
ture sustained  in  ])i)sition  by  means  of  four  springs,  the  idea 
of  which,  he  states,  was  conceixcd,  hut  ]irol)ahlv  not  developed, 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1125 

by  Massez  in  177"_'.     Because  tliis  means  of  retention  was  com- 
])lieated  and  dil'licult  to  atlapt,  it  did  not  eome  into  i^eneral  use. 

PRINCIPAL   MATERIALS   USED   AS   DENTURE   BASES 

The  principal  materials  so  I'ar  mentioned  and  used  as 
substitutes  for  natural  teeth  were  hone,  ivory,  hippopotamus 
tusk,  wood,  gold,  silver,  white  wax,  mother  of  ])earl,  human 
teeth  and  those  of  animals,  all  more  or  less  i»ei-ishable  except 
the  metals  mentioned. 

The  effort  of  (Tiiillemeau,  mentioned  hy  Dionis,  in  KilMI, 
was  the  first  of  record  to  com])ound  a  substance  which  would 
more  nearly  fulfill  the  reciuirements  of  duraliility,  apyjearance 
and  ease  of  a])])lication,  for  prosthetic  sulistitutes,  than  did 
the  organic  materials  in  common  use. 

FIRST    SUGGESTION    OF    PORCELAIN    WORK 

Fauchard,  in  17l'S.  sng.ucsted  the  use  of  porcelain  for 
teeth  and  dentures,  but  did  not  follow  u]i  and  develop  what 
has  since  proven  to  be  one  of  the  most  inqjortant  as  well  as 
esthetic  i)hases  of  ])rostlietic  science.  It  seems  that  he  made 
use  of  enamels  for  staining  both  teeth  and  gums  to  resemble 
those  of  nature.  Hourdet,  in  175(3,  stated  that  he  "had  used 
the  pink  enamel  of  Fauchard."  This  enamel  must  have  been  in 
the  nature  of  a  jiaint  or  varnish,  and  so  applied  since,  if  of 
porcelain,  the  heat  necessary  to  fuse  the  latter  would  have  de- 
stroyed lioth  teeth  ami  base  of  bone  or  Ivory. 

DUCHATEAU'S   EFFORTS    IN   PORCELAIN   WORK 

In  1774,  Dnchateau,  a  French  chemist,  near  Paris,  who 
was  wearing  a  tlenture  made  from  hippo])ntanuis  tusk,  and 
which  had  accjuired  a  disagreeable  odor,  conceived  the  idea 
that  a  porcelain  denture  would  l)e  free  from  the  ol),iection  men- 
tioned. He  i)resented  his  idea  to  (luerhard,  a  i)orcelain  manu- 
facturer in  Paris,  and  together  they  proceeded  to  ex])erinient. 
The  first  denture,  on  account  of  the  contraction  of  the  ]iorce- 
lain  in  baking,  was  too  small.  A  number  of  others  were  con- 
structed, noni'  of  which  foi-  \arious  reasons  proved  sat- 
isfactory. 

THE  WORK  OF  DUBOIS  DE  CHEMANT 

Discouraged  by  the  many  failures  encountei-ed,  Dncha- 
teau apjilied  to  Dubois  de  Chemant,  a  well-known  dentist  of 
Paris,  for  ad\ice  and  assistance.      I>y  modifying  the  porce- 


1126  A    BRIKF    HISTOltY    OP    PROSTHETIC    DENTISTRY 

lain  ui'  Ducliatcau  willi  |ii|K'  clay  and  coldriiij;-  earth,  its  i'ns- 
ing  point  was  reduced,  the  color  improved,  and  contraction 
was  lessened.  Finally,  after  a  number  of  efforts,  a  denture 
was  produced  that  Dnchateau  was  able  to  use.  Although  he 
endeavored  to  ccmstruct  dentures  for  others,  Duchateau's  ef- 
forts resulted  only  in  failure,  his  general  knowledge  of  ])ros- 
thesis  being  insufficient  to  accom])lish  the  required  results. 

He  received  a  vote  of  thanks  and  an  honorable  mention 
from  the  Royal  Academy  of  Surgeons  of  Paris  in  177(i,  be- 
fore whom  his  process  was  laid.  The  failures  mentioned  dis- 
couraged Dnchateau  from  further  efforts  in  this  field,  nor 
does  it  appear  that  he  again  renewed  them. 

De  Chemant,  to  whom  the  success  of  Duchateau's  et¥orts 
were  largely  due,  continued  his  experiments,  and,  after  a 
number  of  years,  suc<'eeded  in  compounding  a  porcelain,  the 
contraction  of  which  could  be  determined  to  a  fairly  accurate 
degree,  of  modifying  the  shade  to  a  considerable  extent  as 
desired,  and  of  iminoviiig  the  sjirings  and  other  means  of 
attachment. 

Desirabode,  writing  in  18-18,  says  in  reference  to  the  in- 
troduction of  porcelain:  "Fauehard  seems  to  be  the  inventor 
of  porcelain  teeth,  then  Dnchateau  improves  the  manufacture ; 
De  Chemant,  by  accident,  gets  hold  of  the  secret,  which  he 
further  improves  and  gives  as  his  own  in  1788  when  he  imb- 
lished  the  first  edition  of  his  work.  De  Chemant  carried  the 
art  to  England,  where  he  obtained  the  exclusive  right  to  work 
the  invention  for  twelve  years. ' ' 

In  tlie  work  alluded  to  De  Chemant  shows  by  means  of 
engravings  the  various  types  of  prosthetic  substitutes  he 
could  produce  in  porcelain.  Among  these  were  included  a 
crown,  a  bridge,  full  dentures  and  an  obturator. 

With  few  exceptions,  Fauehard  being  a  notable  exainiile 
to  the  contrary,  the  writer  on  dentistry  in  those  days  pub- 
lished a  book,  not  so  much  to  enlighten  his  professional  breth- 
ren, as  to  impress  the  public  with  his  superior  attainments. 
De  Chemant  was  one  of  the  latter  class.  His  work  was  largely 
made  up  of  eulogistic  effusions  of  himself  and  the  new  process 
of  which  he  claimed  to  ))e  the  sole  inventor,  thus  denying  to 
Dnchateau  auy  credit  whatever,  in  either  the  conce]ition  or 
development  of  the  porcelain  idea. 

Furthermore,  he  studiously  avoided  giving  to  the  i)rofes- 
sion  so  much  as  a  hint  of  the  com]iosition  or  manner  of  work- 
ing the  paste  for  the  making  of  "indestructible  teeth,"  which, 
as  appears,  still  lacked  many  desirable  qualities.     Indirectly 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1127 

his  selfish,  commercial  attitude  resulted  in  l)enefit  to  the  pro- 
fession liy  instigating  others  to  enter  the  field  in  au  elTort  to 
find  something  as  good  or  better  tlian  that  which  he  had  dis- 
covered. 

Dubois  Foucou,  dentist  to  the  King,  was  one  of  the  jury 
appointed  by  the  French  Academy  of  Surgeons  to  examine  into 
the  merits  of  De  Chemant's  discovery.  He  was  at  first  op- 
posed to  the  idea,  but  later  mi  began  experimenting  and  suc- 
ceeded in  improving  both  the  ([uality  and  color  of  the  porce- 
lain over  that  used  by  De  Chomant.  While  this  was  indeed 
laudable,  the  greatest  benefit  resulting  from  Foucou 's  re- 
searches consisted  in  publishing  to  the  profession  all  of  the 
formulas  and  methods  he  had  discovered.  His  dentures  were 
jiroduced  in  three  shades,  bluish  white,  grayish  white  and  yel- 
lowisli  white,  in  varyins,'  gradations. 

INTRODUCTION    OF    SINGLE    TEETH    AND    BLOCKS    OF 
PORCELAIN 

Fonzi,  au  Italian,  practicing  in  Paris,  in  1808,  introduced 
for  the  first  time  single  teeth  and  blocks  of  teeth,  having  baked 
within  and  projecting  from  them  small  pins  or  hooks  of 
])latimim,  by  means  of  which  Ihey  could  be  attached  to  bases  of 
various  kinds.  This  was  a  decided  and  valuable  improvement 
in  itself,  for  it  encouraged  the  production  of  bases  of  more 
permanent  character,  such  as  gold,  silver,  and  platinum,  and 
the  consequent  development  of  teehnic  in  metallurgical  lines. 
The  porcelain  of  which  these  teeth  were  composed  was  some- 
what translucent  and  much  more  nearly  resembled  the  nat- 
nral  teeth  than  did  that  of  either  De  Chemant  or  Foucou. 
vStill  further  credit  should  be  given  Fonzi  from  the  fact  that 
these  teeth  were,  to  a  limited  extent,  manufactured  and  ren- 
dered available  to  other  members  of  the  profession,  and, 
further,  were  capable  of  comparative  ease  of  application. 

Til  us  when  the  facts  are  known  Fonzi  stands  out  as  a 
indiniiient  character  in  the  advancement  of  jtrosthetic  sci- 
ence, for  it  is  apparent  that  from  his  time  on  progress  in  the 
porcelain  field  shows  gradual  but  marked  improvement. 

The  jiroduction  of  dentures  carved  from  bone,  ivory  and 
similar  substances  continued  for  many  years  after  Fonzi 's 
time,  largely  becau'Se  of  imperfect  technical  methods,  and  the 
difficulties  encountered  of  fusing  porcelain  in  the  cumbersome 
furnaces  in  use  in  those  days,  some  of  this  material  reciuiring 
a  temperature  of  3,000  degrees  F.  to  vitrify. 


naS  A     HKIIOK     IIISTDKY     Oh'     I'liOS'l'l  I  lO'l'lC     HKNTIS'I'HV 

FIRST  INTRODUCTION  OF  PORCELAIN  IN  THE  UNITED 
STATES 

111  1S17,  I'laiitoii  111'  Paris  (■aiiic  to  I'hiladcliiliia.  liriii,i;iii,u' 
witli  liiiii  a  stock  v\'  iioirdain  Iccth  made  in  l''raiirc.  'riicsc 
liavc  been  descrilicd  as  Kciiiii  inrcridr  in  Imlli  (|iiality  and 
color,  somewhat  reseiiihliiii'-  a  split  bean,  liaviiii;-  a  liall'-round 
STOOve  in  the  back,  in  tlie  sides  of  which  were  inserted  small 


OI!()(l\  FJI     I'DKCKI.An 


i:ii    r.iiTH    Kill! 


\NI1     IIENTI   ItK     WORK 


stri))s  of  ])latinniii  for  bciidiiifj,'  over  and  sohlcTinn-  to  a  j^old 
wire  post  attached  to  the  deiitnre  base. 

The  arrival  of  Plantoii  ]iroved  an  incenti\'c  to  incinliers  of 
the  profession  in  this  country  to  enter  tlie  porcelain  field  in 
an  endeavor  to  improve  the  iiiiality  and  forms  of  the  teeth 
then  available. 


THE   FIRST  MANUFACTURE   OF   PORCELAIN   TEETH   IN 
AMERICA 

In  1822  Chas.  W.  Peale  began  the  manufactnre  of  ]iorce- 
lain  teeth,  in  the  backs  of  which  platinmn  ]nns  were  inserted 
and   baked  for  attachment   purpose. 

In  1825  S.  W.  Stockton  began  the  manufactnre  of  jiorce- 
lain  teeth  with  such  success  that  in  a  few  years  liis  business 
had  grown  to  ipiite  extensive  pro])ortions.  In  reality  he  was 
the  first  in  this  country  to  engage  extensi\-ely  in  the  produc- 
tion of  porcelain  teeth  for  the  jirofession. 

It  was  customary,  about  this  time  and  for  many  years 
later,  with  a  number  of  men  in  the  profession  to  manufacture 
teeth,  both  single  and  in  blocks  or  sections,  to  meet  the  re(|iiire- 
ments  of  individual  cases  in  practice. 

These  teeth  and  blocks  were  attached  to  bases  of  various 
kinds,  being  mounted  on  i^'ory  or  hi])po])otamus  tusk  l»y  means 
of  screws  or  rivets.  ]iassiiig  tliniiigli  hoh's  driih'd  through  Imtli 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1129 

ba.si'  and  ixn'celaiii,  wliilc  to  metal  liases  they  were  attaclicd 
in  the  same  manner  and  l)y  soUh'rini;-  a  liackinii'  to  pins  baked 
in  the  poreehiin. 

Ambler  states  that  "among  tliose  who  made  teeth  for 
their  own  nse  were  Doetors  Mellhennv  (182(i),  Ambkn-  and 
Spooner  (1828),  Fhigg  (1830),  S.  Spooner  (1831),  Harwood 
and  Tucker  (1833),  Aleock  and  AUen  (1835),  and  Wildman, 
who  began  liis  experiments  in  1837.  The  latter  made  pains- 
taking investigations  and  achieved  iiotabU'  results.  'Mis  work 
was  so  imjiortaiit  and  far-reaching  that  he  has  been  aecordei] 


I.AHIAL    AND    LINliUAL    VIFAVS    OF    DENTUHK    I'OX- 

STKICTED  BY  DR.   MclUlENXV  IN   ISJI.'i.     TOOTH 

ISIX)(KS    WERE   (■AR\En   BY    HAXI) 

till'  honor  of  baxiiig  been  iirst  to  ]ilace  tlie  manufacture  of 
teeth  on  a  scientitic  basis.'  " 

In  1844,  kSamuel  S.  White  of  Philadelphia  began  tlie  manu- 
facture of  teeth,  in  a  small  way  at  first,  but  liis  products  w^ero 
of  such  excellent  quality  that  the  business  soon  grew  to  large 
l)roportions.  r])on  the  foundation  which  he  laid  was  estab- 
lished tlie  S.  S.  ^Vhite  Dental  Manufacturing  Company,  which 
to-day  is  one  of  the  most  extensive,  il'  not  the  hirgest,  concern 
of  its  kind  i?i  Ihe  worlil. 

\'\)\-  uiany^vea'rs  the  i|ualit\-  of  porcelain  teetli,  both  for- 
eign and  domestic,  has  been  reasonablx-  satisfactory  in  color 
and  texture,  Imt  few,  if  any,  have  fullilled  anatomic  require- 
ments.    The  bicuspids  and  molars  are  usually  too  small  and 


1130  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

ai'c  rchitixcly  (lispropdrtioiifd  to  each  otliiM"  a8  well.  Laliial 
and  biUH-al  surfaces,  wliile  i'alling  short  of  ])erfectioii  in 
t'onii,  presented  a  nnieli  better  appearance  than  did  tlic  in 
cisal  edges  of  tlie  anterior  or  the  oeclusal  surfaces  of  bicusiiiils 
and  molars,  particularly  the  latter,  the  planes  and  surface 
markings  of  wliicli  oftentimes  in  no  way  resembled  in  form  the 
surfaces  they  were  supposed  to  represent. 

Within   recent    years,   since  mandibular  movements   are 
better  understood,  the  demands  of  the  profession  for  better 


TYPE    OF    (OKI      HIKNUE    I  OM 

M0NI1    I  sti)    [^     iHE    ^iRI^ 
Bws  roR  I  [  si\f  moi  k  tlftii 

\X1)      IO\ri\LIOt'f      (,l  M      DIN 
TUBl/S 


forms  of  artificial  teeth  iiave  been  and  are  being  met  by  the 
manufacturers  with  commendable  and  in  many  instances  ex- 
tremely gratifying  results. 

INTRODUCTION  OF  GOLD  FOR  DENTURE  BASES 

As  previously  stated,  Bourdet,  in  1757,  mentions  the  use 
of  gold  for  denture  bases.  It  was  not  introduced  into  the 
United  States  until  1780,  when  Dr.  James  Gardette  of  Phila- 
delphia described  and  used  it  for  this  purpose. 

Silver  and  platinum  were  also  employed  for  baseplates, 
but  the  use  of  all  of  these  metals  was  limited,  because  of  tlie 
difficulty  met  with  in  secnrimi'  ada|)tation  to  the  oral  tissues. 


DIES   FOR   SWAGING  METAL   BASES 

Dies  were  frequently  made  of  brass,  the  model  being  sent 
to  a  brass  foundry  for  casting,  no  laboratory  being  equipped 
with  furnaces  suitable  for  fusing  this  alloy. 


A    BRIEF    HISTORY    OF    PROSTHETIC     DENTISTRY  1131 

Ijutor  Oil  zinc  was  ciniiloyod  for  dies  heeanse  of  its  com- 
liaiativoly  low  fusibility  and  hardnoss.  Still  later,  about  1860, 
Babbitt's  metal  was  made  use  of  for  the  same  purpose,  it 
Ix'ina,'  almost  as  hard  as  zine,  fused  lower  and  contracted  less 


EXfir.ISH    XriiE    TEKTH    MOUNTED    ON    SWAGED 

GOLD    BASE.     CONSTRUCTED     ABOUT     1S44 

(LOANED    BY    C.     R.     SYKES.    OF    C. 

ASH    &    SONS) 

than  the  latter  metal.  Dr.  L.  P.  Haskell  is  largely  responsi- 
ble for  the  introduction  of  and  improvement  in  Balibitt  metal, 
which,  without  doubt,  is  the  best  alloy  available  for  die  pur- 
poses. 

As  late  as  1840,  De  Loude  of  London,  in  writing  of  his 
methods  of  technic,   says:   "Tlie  im]iression   is   ])(mred  with 


FULL    UI'I'Ell     AND     LOWlvIl     DENTURES.     GOLD    BASES.     WITH     SFIilNGS    FROM    FOX    AND 
HARRIS.    ED.     1855) 

plaster  and  the  model  sent  to  a  brass  founder  to  have  a 
similar  one  mgfde  of  brass ;  after  which  a  she-mold  of  lead  is 
made  on  the  one  of  brass,  then  plates  of  gold,  silver  or  ]ilatina 
are  swaged."     (Ambler.) 


1132  A     liini':K     IIISTOIiY    l)l'"     I'KOSTIIKTIC     DKNTISTKV 

FIRST   USE   OK   CAST   BASES 

Till  liases  made  li>'  rastiiii;'  llic  innllcn  metal  iiiln  a  matrix 
(•(iiitaillilii;-  llle  teeth,  and  directly  tn  tllelli,  was  ilil  rndllced  liy 
Dr.  Edward  Hudson  oi'  Pliiladelpliia  in  1S-J(I.  I''urtlier  wurk 
along  similar  lines  was  carried  mi  hy  Dr.  W.  A.  Koyce  of 
Newlmrgli,  X.  \..  in  IS.'KI,  and  hy  Dr.  (icorge  K.  Ilawes  of 
Xew  ^'ol■k  in   IS.IO,  hut  with  mure  or  less  indifft'i'ent  success. 

Di'.  A.  .\.  I^)landy  of  Baltimore,  in  1S5(),  greatly  imjiroved 
the  then  existing  nictliods  of  technic,  and  introduced  an  alloy 
for  denture  bases  wliicli  cast  more  sharply  than  tin.  The 
process  was  termed  "Cheoplasty, "    and    deiitui-es    so    con- 


(iflM)    HA.SK    llE-NTUUK.    SIN<;l,E    CUM    StX'TIOX    TKHTH. 

HACKKl)     ,\XD     SOLDERED.     WITH     PEHIPHEH.U,     UIM. 

CIINSTIU  ITED  BY  DR.   VV.   X.   MORRISON  .iBOI'T   I.<ili!l 

stiucted  were  called  chroplasfu-  dctit iiU's.  Harris'  Edition, 
187o,  states  that  "the  name  chosen  hy  him  (Blandy),  signify- 
ing the  making  of  ])lates  by  pouring  a  metal,  made  plastic  by 
heat,  is  equally  apjilicable  to  all  alloys  of  tin  noiv  nsed. 
Blandy 's  alloy  of  chcoplastic  metal  was  silver,  with  some 
bismuth  and  a  trace  of  antimony."  Tin,  combined  with 
bismuth  or  cadmium,  was  introduced  shortly  afterward,  and 
these  alloys  are  used,  more  or  less,  for  lower  weighted  den- 
tures at  the  ]n-esent  time. 

Hard   vulcanite,   although    discovei'ed    in    IH.')!.    had   not 
come  into  genei'al  use  as  a  denture  base,  and  the  teeth  used 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  11:1". 

ill  metal  liasc  ilciituii'  consl  i-nrtidii  were  not  suitcil  because 
of  their  foriii  and  type  oT  iiiiis,  for  linn  allaciinieiit  in  the  cast 
l)ases,  therefore  teeth  of  iimililieil  fonus  were  designed  and 
used  for  tliis  |mr[)ose. 


SPECIAL   FORMS   OF   TEETH    FOR    USE   WITH    CAST   BASES 

111  IS.")*).  \V    (i.  ()liver  and  Thomas  Harrison  introduced 
teeth  witli  uroii\es  and  holes  for  anchorage  purposes,  to  ho 


Ql^f 


,%>. 


used  in  the  casting  process.     These  teetli  were  phmiied  souk 
what  on  the  oi-der  of  tlie  present  diatoric  teetli. 


DENTAL  VULCANITE   LITIGATION 

In  1852  John  A.  ('uinmiiigs  of  Boston  filed  a  caveat,  an  1 
in  1855  ai)])lied  for  a  iiateiit  for  the  method  and  use  of  rnhiier 
in  denture  constiin-tion  in  i)ractically  tlie  same  manner  as  it 
is  used  to-day.  This  i)a1ent  was  granted  in  18(U,  and  there- 
upon liegan  a  long  and  drastic  siege  of  litigation,  on  the  part 
of  Cmnmings  and  others,  to  enforce  n])on  the  members  of  the 
profession  who  were  using  vulcanite,  the  pavment  of  ojpcc 
rif/hts,  or  roifiilfi/.  -for  the  i)ri\'ilege  of  using  rubber  for  tliis 
purpose. 

The  hiial  sunmiiiig  up  and  outcome  of  this  now  famous 
legal  battle  can  be  fiumd  in  the  Dental  Cosmns,  .\i)ril,  1S7;;, 


ii:m  a   \uukv  ]iis'1'()kv   ok   iMiosTiii'rnc    I)iontisti{y 

the  entire  issue  dl'  Ihiil  llKilitil  heilli;  (le\'()1eii  t(i  llie  court 
ti'aiisacliojis  in  tii<'  linal  case. 

The  followin.n'  pai'a.iiraph  hrietlx  explains  the  |uinei|ial 
])oiiits  of  history  of  the  vulcanite  litigation: 

"Letters  patent  were  granted  to  John  A.  ('uniinings  on 
June  7,  186-1,  for  an  'iiii])rovement  in  artificial  gums  and  pal- 
ates,' and  on  account  of  a  defect  were  reissued  January  10, 
18()5.  to  the  Dental  \'ulcanite  ('oin])any,  and  later  on  account 
of  a  defect  were  again  reissued  March  iM,  ]S(ir>.  to  said  com- 
])any. 

"The  Goodyear  Company,  by  assignment,  l)ecame  the 
legal  owners  and  issued  to  densists,  for  various  sums, 
'licenses  and  agreements'  to  use  its  process  only  in  their  own 
business,  the  license  not  to  be  assigned,  sold,  transferred  or 
otherwise  disposed  of,  and  the  licensee  not  to  encourage  in- 
fringements, and  if  he  found  any  one  infringing  he  was  to  re- 
port it  to  the  company  and  they  were  to  bring  suit  against  the 
infringer.  These  licenses  were  generally  given  for  one  year, 
and  were  signed  by  the  licensee,  the  agent  and  Josiah  Bacon, 
treasurer,  who,  on  account  of  his  arbitraiy  methods  and  mean- 
ness in  dealing  with  the  dental  profession,  was  shot  and  killed 
in  San  Francisco. 

"The  contest  as  to  the  validity  of  the  ])atent  between  the 
Groodyear  Company  and  the  whole  dental  profession  of  the 
United  States  was  long  and  bitter.  Finally  S.  S.  White  took 
up  the  cause  for  the  profession  and  spent  much  time  and 
money  and  in  the  end  won  the  case  and  wiped  out  the  abomina- 
tion."    (Dr.  H.  T.  Aml)lei',  in  Mistory  of  Dental  Surgery.) 

COLLODION   AND   CELLULOID   AS   DENTURE   BASES 

The  refusal  of  many  to  use  rubber,  on  account  of  pending 
claims  of  the  patentee,  led  to  the  introduction  of  collodion  as 
a  denture  base  in  1859,  by  John  Mackintosh  of  England. 

Dr.  J.  A.  McClelland  of  Louisville,  Ky.,  in  1860,  improved 
the  collodion  base  and  introduced  it  under  the  name  of  "Rose 
Pearl,"  but  this,  as  well  as  Mackintosh's  product,  proved  lui- 
satisfactory  on  account  of  contraction,  warpage  and  lack  of 
]H'rmanent  quality. 

Celluloid,  having  collodion  as  a  base,  was  invented  by 
Isaiah  S.  and  John  W.  Hyatt  of  Albany,  N.  Y.,  in  1870,  and 
for  many  years  was  used  extensively,  and  is  to  a  limited  ex- 
tent to-day  employed  in  denture  construction. 

Although  any  of  the  existing  forms  of  vulcanite  teeth 
can  be  used  in  conjunction  with  celluliod  as  a  base,  a  special 
form  of  tooth  having  a  constricted  cervix  and  of  more  natural 


A    BRIEF    HISTORY    OP    PROSTHETIC    DENTISTRY  tl35 

form  generally  was  designed  for  tiiis  }>uri)ose.  The  counter- 
suuk  piu  tooth  followed  closely  on  the  introduction  of  im- 
proved teeth  for  celluloid  work. 

Some  of  the  most  notable  attempts  to  reproduce  natural 
tooth  forms  were  made  by  Dr.  E.  T.  Starr  in  1869.  A  few  of 
the  molds  he  jn'oduced  are  scai'cely  eciualed  l)y  tlie  liest  efforts 
of  present-day  tooth  designers. 

Ash  &  Sons  of  London  liave  long  been  noted  for  the  pro- 
duction of  teeth  which,  in  both  form  and  color,  closely  resem- 
ble the  natural  organs  of  mastication.  Their  tube  teeth,  which 
were  introduced  al)out  1840,  are  capable  of  varied  applica- 
tion, both  for  dentures  and  single  crowns.  These  teeth  can 
be  reshaped  by  grinding  and  the  glaze  restored  by  polishing  so 
perfectly  that  the  moditication  cannot  be  detected.  Because 
of  the  materials  employed  and  the  mode  of  manufacturing,  the 
finished  product  is  very  dense  and  free  from  porosity. 

Most  of  the  manufacturers  of  teeth  have,  within  recent 
years,  improved  the  quality  of  materials  in  their  products,  and 
practically  all  of  the  present-day  teeth  can  be  modified  and 
re])olished  as  described. 

VULCANIZING  RUBBER  BETWEEN  METAL  SURFACES 

The  })rocess  of  vulcanizing  rubber  between  two  polished 
metal  surfaces  was  introduced  by  Dr.  Stuck  in  1868.  His 
method  consisted  in  forming  a  cast  of  the  mouth  in  tin,  de- 
veloping the  baseplate  in  wax  or  securing  the  recpiired  thick- 
ness and  form  of  the  model  denture  l)ase  with  several  layers 
of  tinfoil,  investing  the  case  in  the  flask,  and  on  opening  re- 
moving all  but  the  outermost  layer  of  tinfoil  from  the  matrix 
side.  This  resulted  in  the  formation  of  a  metal  matrix  in 
which  the  rubber  was  packed  and  vulcanized.  The  product 
was  much  denser  than  when  vulcanized  in  a  ])laster  matrix, 
and  in  addition  recjuired  no  polishing  except  where  the  sur- 
plus margins  were  trimmed  away.  A  similar  method  is  some- 
times resorted  to  at  present,  except  that  instead  of  the  tin 
cast  of  the  mouth  a  plaster  cast  as  ordinarily  constructed  is 
used,  to  which  a  thin  sheet  of  tinfoil  is  carefully  adapted, 
cemented  to  the  cast  with  a  thin  film  of  sandarac  varnish  or 
Le  Page's  glue,  which  thus  affords  a  metallic  surface  against 
which  the  vulcanite  is  molded. 

DENTURE    BASES    PRODUCED    BY    ELECTRO-DEPOSITION    OF 
GOLD  AND   SILVER 

Denture  bases  fonncd  li\-  electro-deposition  of  gold,  and 
also  of  gold  combined  with  silver,  have  at  various  times  been 


113(;  A    imilOK    HlSTOliY    OK     I'KOSTHI'rnC     IJKNTlSTItV 

tricil,  lint  Avitli  iiKlilTcrciit  success.  Metal  (le|insileil  l)y  this 
pi'ocess  lacks  tli(>  cohesiveness  of  either  casi  (ir  idlleil  plate, 
and  although  beautiful  results  and  gcxMl  adaptation  may  he 
secui'ed,  unless  the  hase  is  formed  \'ery  hea\y,  so  thick,  in 
fact,  as  to  he  ohject  ioiiahle.  it  will  fractui-e  rea<lil\'  under 
stress. 

ARTICULATORS 

The  i)!'o,iiress  of  improN'cment  in  articidntors.  or,  more 
correctly,  occliidnig  fruitn'ti,  is  extremely  interesting.  The 
development  of  this  appliance,  which  is  practically  indispensa- 
ble in  the  correct  occlusion  of  teeth,  has  been  retarded  because 
of  lack  of  accurate  knowledge  of  mandibular  movements,  or, 
more  exactly,  those  movements  of  the  mandil)le  concerned  in 
the  frictional  contact  of  the  lower  against  the  upper  teeth. 
Without  a  fundamental  and  exact  knowledge  of  these  move- 
ments, it  is  im])ossible  to  construct  an  a]ipliance  whicli  will 
rejiroduee  them. 

Even  with  present  estalilished  ihita,  there  is  no  appliance 
yet  devised  that  will  i-eproduce  all  of  the  varied  essential 
movements  discerned  in  every  individual  with  exactness,  but 
some  approach  very  closely  the  desired  re(iuirements.  ()\\\y 
a  brief  outline  of  those  appliances  most  familiarly  known  can 
be  given  here. 

A  metl'.od  of  building  a  distal  extension  to  eacji  cast,  the 
first  ha\'ing  notches  oj-  deiiressions  into  which  the  ))laster  of 


CASTS    lO.X'I'UNDEU    iHSTAl.l.V  T(l  FdKiM   AltTUM!  LATiXd   SUIU'WCES 

the  opi)osite  side  was  filled,  to  serve  as  guides,  constituted  the 
first  articulator. 

J.  B.  Grariot  is  ci'edited  with  having  invented  the  tirst  den- 
tal articulator  in  ISO.l.     An  extended  search  through  dental 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTKY  1137 

literature  by  the  writer   has  faih'd  to  (lisrh)se  more  than   a 
mere  mention  of  the  fact  as  stated. 

Ill  1840,  Dr.  Daniel  T.  Evans  of  Phihidelphia  patented  an 
articulator  in  which  an  eH^'ort  was  made  to  i-eprodnce  tlie  hit- 
eral  movements  of  the  mandilih'. 


THE     E\ANS     AXATOMU'AI.     ARTUTLATOIl 


The  distance  between  the  condyle  slots  of  the  frame  was 
less  than  the  average,  while  the  center  of  rotation  in  lateral 
movements  was  located  in  the  center  of  the  frame. 

In  185.S.  Dr.  W.  G.  Bonwill  introduced  his  "Anatomical 
.Vrticulator. "  and  presented  his  theory  of  the  equilateral  tri- 
angular relation  of  the  mandibular  condyles  and  the  lower 
central  incisors.  lie  claimed  that  by  such  an  arrangement  it 
was  clearly  Nature's  plan  to  thus  provide  a  more  perfect  bal- 
ance for  the  masticatory  app)aratus  in  lateral  movements ;  that 
these  movements  were  most  effective  in  the  reduction  of  food, 
and  that  dentures  should  be  so  constructed  that  the  mandibu- 
lar muscles  could  perform  their  functions  in  the  same  manner 
as  when  the  natural  teeth  were  present. 

Ilis  tlieories,  although  in  the  main  correct,  aroused  con- 
si(lei-al))e  antagonism,  because,  in  many  cases,  the  results  he 
claimed  couhl  be  dt>rived  fi'oni  the  use  of  bis  articnlator  were 
not  realized. 

Tins  was  largely  due  to  ignoring  the  variation  in  pitcli 
of  condyle  jniths  of  different  iiulividuals,  and  in  an  inaccurate 
metlioil  of  mounting  casts  on  the  articulator. 


1138  A    BRIKF    HISTORY    OK     I'KOSTHI'ITU:     DENTISTRY 

J)i-.  I)Oii\vill  \v;is  ii  iijitni'al  horn  ])r()slliotist  iiiid  in  tlio 
analomie  Held  overcame,  by  intuition,  the  obstaeies  resnltin,n' 
fidni  his  imperfect  appliance,      fn  liis  euthusiasm   he  failed 


I.    AiniriI.AT(JK 


to  recognize  the  limitations  of  the  articulator,  or  to  realize 
that  it  was  his  intuitive  skill  and  not  the  appliance  that  was 
resi)onsible  for  much  of  his  success. 

His  persistent  effort  in  tliis  field  for  more  than  forty 
years  finally  aroused  the  interest  of  various  investigators. 


PLAIN    LINE   OR    COMMON    ]IIN(!E   AltTUT  l.ATdl!    USEIi    I'dl!    MANY    YEARS 

with  the  result  that  to-day  the  problem  of  anatomic  occlusion 
has  almost  reached  solution.  The  anatomic  method  of  den- 
ture construction  is  a  reality,  established  on  a  practical  work- 


A    BRIEF    HISTORY    OP    PROSTHETIC     DENTISTRY  1139 

iiig  basis,  and  its  great  iiujiortaiicc  and  value  are  gradually 
becoming  recognized  by  the  profession  iu  general. 

In  1868,  Dr.  E.  T.  Starr  devised  an  articulator,  having  a 
latei'al  movement,  with  horizontal  condyle  initlis. 


THE    SiTAKU    ARTIClI.ATnlt 


In  1889,  Dr.  Richmond  8.  Hayes  introdnced  an  articula- 
tor having  a  lateral  movement  and  with  inclined  condyle  paths. 
From  the  Patent  Office  drawings  of  this  appliance  it  appears 
that  the  condyle  ]iaths  inclined  too  steeply  and  were  not  ca- 
pable of  adjustment. 


THE    HAYES    .iETICULATOK 


As  a  matter  of  fact,  a  practical  method  of  registering  the 
human  condyle  paths  had  not  yet  been  discovered,  nor  had  the 
importance  of  such  registration  been  recognized,  so  that  ad- 
justable conilyle  paths  were  not  even  considered.    Dr.  Hayes 


1140  A    BKIKK     HISTORY    OK    I'l{OSTHETI('     IJKNTISTIiY 

also  (l('\'is(Ml  a  cniilc  scirt  oT  I'acc  how  For  cslaMisliini;  I  lie  cor 
reel  disfancc  of  casls  rroiii  I  lie  rraiiH'  hinges. 

FIRST   SUGGESTION   OF   THE   FACE   BOW 

l'i-('\'i()iis  to  this  tiinr.  Dr.  'I'.  L.  (Jilmci-,  in  a  paper  |)r(' 
sented  before  tiie  Illinois  .State  Dental  Society,  in  1882,  sus'- 
gested  measurement  of  the  distance  from  condyles  to  tlie 
middle  of  the  npper  jaw  so  lliat  casts  miuht  lie  mounted  a  cor- 
responding distance  fi-om  (he  articulator  hinges,  thus  a\oid 
in:;-  disturbance  of  occlusion  in  fracture  cases.  'I'his  in  reality 
was  (Mpiivalent  to  the  use  of  a  face  how. 

STUDY    OF    CONDYLAR    IVIOVEMENTS 

In  188!»,  J)rs.  liowditch  and  Luce  of  Ihirvard,  Conn.,  con- 
ducted a  series  of  exjieriments  to  determine  detinitel.v  tlie 
condylar  movements  of  the  mandible.  The  results  of  these 
experiments  were  ])ul)lisheil  in  the  Boston  Medical  and  Sui'- 
gical  Journal  of  tiiat  year,  hut  imt  heiny  re])rinted  in  any  of 
the  dental  .iournals,  were  not  hrouuiit  ])romiuently  to  the  at- 
tention of  the  profession. 

WALKER'S  RESEARCH  WORK 

In  1895.  Dr.  W.  K.  Walker,  without  knowin,":  of  the  work 
of  Bowditch  and  Jjuce,  carried  out  a  similar  line  of  investiga- 
tion, and  arrived  at  i)ractically  the  same  results.  Just  what 
he  strove  to  and  did  accomplish  can  best  be  stated  l)y  (|Uot- 
ing  from  one  of  his  ))apers,  published  the  following  year: 

"Up  to  that  time  T  had  not  been  able  to  find  menti(m  of 
the  facts  which  I  had  observed  that,  in  the  movements  of  mas- 
tication, the  mandibular  condyle  moves  'not  only  forward, 
but  downwai'd  also,  causing  the  ramus  to  drop  in  the  anterior 
and  lateral  excursions  of  the  mandible, '  and  that  the  condyl<> 
on  the  side  toward  which  the  jaw  is  advancing,  in  the  lateral 
excursions,  does  not  merely  'rotate  on  its  axis,'  otherwise  're- 
maining stationary,'  as  we  are  taught,  ))ut  that  it  also  moves 
l)oth  upward  and  backward,  very  slightly,  it  is  ti'ue,  in  many 
subjects,  and  not  at  all  in  some,  but  iiuite  c()nsideral)ly  in 
others." 

The  discovery  of  this  fact  led  to  another  liitherto  unreco.g- 
nized  fact,  viz.,  that  the  lateral  rotation  centers  of  the  man- 
dibl(>  mav  or  mav  not  be  located  in  the  condvie  centers. 


A    BRIEF    HISTORY    OF    PROSTHKTIC     DKXTISTKY 


1141 


WALKER'S  ANATOMICAL  ARTICULATOR 

\\'alkcr  (li's'n;iic(l  ail  atiafoinical  articiilalor.  Iia\iii,i;'  Ixitli 
adjustable  condyle  patlis  and  varialilc  rotation  (■enters  wliieli 
could  1)0  set  in  aeeordanee  witli  records  olitained  in  each  in- 
dividual ease. 

'i'liese  records  were  secured  iiy  means  of  another  api)li- 
ance  he  devised  and  called  a  "facial  clinometer."  In 
the  light  of  our  present  knowledge,  a  prosthetist  familiar  with 
the  ])resen1  day  ap])liances,  if  given  the  AValker  articulator 


1       1*^ 

1 

■ 

A, 

1^1 

l^^^l 

■■^si^^^ 

— 

^                  ^    J^l^s^^l 

^n 

1      ^ 

' 

^^^      ''  m 

1 

1^ 

iM 

L' 

JHI 

\i,  .uiTini.ATdi; 


and  clinometer  and  a  Snow  face  how,  could  construct  anatomic 
dentures  e<jual  to  those  constructed  by  any  other  system. 

Practically  the  only  essential  ])oint  which  Walker  over- 
looked was  the  importance  of  and  necessity  for  setting  the 
casts  on  the  occluding  frame  so  that  their  alveolar  planes 
sustained  a  similar  relation  to  the  frame  hinges  that  the 
natui'al  alveolar  i)lanes  did  to  the  condyles.  Although  he  does 
not  exi)lain  how  he  mounted  the  casts  on  the  frame,  it  is  more 
than  likely  that  he  followed  Bonwill's  method  of  cali])ering — 
setting  them  so  that  the  calii)ers  registered  four  inches  from 
each   rotation   center,  to   the  i)osition   to   be  occupied   by  the 


1142  A    BRIEF    HISTORY    OP    PROSTHETIC    DENTISTRY 

iiH'sio-iiicisnl    angles    of    I  lie     Uiwcf     ccnli-al     incisors,     wiicii 
occluded.     This  inctliod,  alUioui^ii  decidedly   liellei'  tliaii  tlie 
usual  plan  of  qiiessirig  the  proper  position  oi"  tiie  casts,  pro- 
vided for  neitluM'  iMM'pcudicular  nor  horizontal  ))laiie  relation 
ship  and  tlievefore  led  lo  errors. 


WAUCEB'S   FACIAL   CLINOMETER 


Walker's  efforts  were  more  far-reaohing  and  valuable 
than  he  himself  or  the  profession  realized  at  the  time,  but  on 
the  foundation  which  Bonwill  laid,  and  he  strengthened  and 
added  to,  the  present  system  of  anatomic  occlusion  of  artifi- 
cial dentures  rests.  Three  valuable  papers  by  Walker  on 
mandibular  movements  and  methods  of  registering  them  ap- 
peared in  the  Dental  Cosmos,  in  1896-7. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 


In  189-1:  Dr.  C.  E.  Bixby  desigiied  an  attai-hincnt  for 
moiuitiiig  casts  on  a  plain  line  artieixlator. 

This  device  regulated  the  correct  antero-posterior  posi- 
tion. I)ut  j^rovided  no  means  for  establishing  the  horizontal 


THE    BIXISY    ATTACIIMlCN'l' 


])lane  relationship.    It,  however,  was  a  forerunner  of  the  face 
bow. 

GRITMANS   ARTICULATOR 

In  1899,  Dr.  A.  D.  Gritman  introduced  an  improved  form 
of  ai-ticnlator,  having  the  same  general  proportions  as  the 
Bonwill,  but  more  rigid,  and  with  condyle  slots  set  at  an  angle 


THE  liniTMAX   AltTKIT.ATdR 


of  al)ont  15  degi'ees  slant.  In  this,  as  in  all  articulators  hav- 
ing fixed  condyle  paths,  the  pitch  of  the  path  of  the  frame  was 
often  increased  or  decreased  in  moimting  the  casts  on  the 
frame,  depending  on  the  thickness  of  the  cast  and  the  care  used 
in  mouutini'-  them. 


144  A    BKIKK     lllSTOIiV     OK     l'K(  )STH  KTIC     DKNTISTHY 

SNOWS   FACE    BOW 

In  llic  saiiic  \c;ii-,  Di-.  (icoriAc  15.  Snow  (if  llic  I'liiNcrsitv' 
if  I'lilValo  inli'odiircil  llic  fdci'  linif.  a  calii)!'!-  likr  i|c\icc  used 


T 

^'IT^'*'^' 

c      f^     '6.   'd     i,^^^^.        "      'J,  c_    A 

H- 

\ 

'■   c. 

ill  inouiitiug  casts  on  the  occliidino-  frame.  This  device  is  one 
of  the  most  valualiU^  ac(|uisitions  in  the  anatomic  field.  By 
means  of  this  api)liance,  correct  antero-posterior,  as  well  as 


THE    KERI!    ANATdMlCAr.    ARTK  Tr.ATdR 


ix'rpeiidicuhtr  ami  liorizoiital  i)hiii(',  rehitioiislii]!  of  casts  to 
frame  hinges  can  be  estahlisiied.  As  a  result,  when  teeth  are 
arranged  on  occlusion  models,  clearance  paths  for  the  cusps 


A    RKIKF    HISTORY    OF    PROSTHETIC    DKNTISTKY  114.') 

(if  the  liiwcr  lncusi)i(ls  and  ludlai-s  hctwccn  tliosc  of  the  upper 
teeth  can  be  develoix'd,  so  tliat  in  latcnil  cxiairsidns  there  is 
no  marked  interference. 

THE    KERR   ANATOMICAL   ARTICULATOR 

In  IMOl'  th<'  Ken-  lirothei-s  of  Detroit  inti-odneed  an  an- 
atomical ai'tienhitor  haxint;'  adjustahh'  condyle  paths  and  a 
latftral  movement.  The  first  frame  was  arranged  witli  hinges 
about  on  the  same  plane  as  the  occlusal  plane  of  iii)])er  cast 
when  mounted,  the  idea  lieing  to  copy  the  c(Miter  of  rotation 
of  the  mandible  in  wide  open  movements. 

p'or  oltvious  reasons  this  was  found  incorrect,  and  the 
design  of  the  frame  changed  to  the  form  shown  on  page  1144. 

CHRISTENSEN'S  WORK 

111  lilOi'.  Dr.  Carl  Christeiisen  of  ( 'ojienhagen,  Denmark, 
disco\-ered  a  simjile  method  of  recording  the  condyle  i)alhs  in 


THK    rllTlI.STF.XSEX    AXATCIM  ll-.M.    A  It'l  UTI.ATOR 

the  living  subject,  and  devised  an  articulator  having  adjust- 
able condyle  paths  which  could  be  set  according  to  such  regis- 
tration.    (See  i)age  337.) 


SNOW'S  ANATOMICAL  ARTICULATOR 

In  1906.  Dr.  Snow  imtiroved  the  (iritman  articulator  by 
converting  the  fixed  into  adjustalile  condyle  jiatlis,  and  api)ly- 
ing  a  tension  si)ring  which  ])erniitted  a  greater  range  of  niov(»- 
ment  without  impairing  the  stabilitv  of  the  frame. 

riiristensen's  method  of  registering  the  cotkIvIc  jiatlis  in 


1146  A     HRIIOK    HISTORY    OK    I'KOSTIl  KTIC     DKNTISTKY 

coiijiiiicl  idii  witli  llic  use  (iT  the  Siiow  "Xcw  Cciitm-y  Arlicu 
hitor, "  and  llic  J'acc  1mi\v,  sni>i)ly  the  means  I'or  cunsl  rnctin.i;' 
dentures  anatomical iy  and   is  to  a  great  exicnl    Hie   system 
mosl   n'eiierallv  iti'aclii'fd  and  1aiif>iit  in  this  rniiii1i-\-. 


(TT    SUOWIXU    COllPEXSATINIi     ITTtVE     (criJilSTIiNSKX) 

Dentures  constructed  by  tliis  method,  when  introduced  in 
the  mouth,  will  perform  essentially  the  same  functions  as  the 
natural  teeth,  and  are  capable  of  I'educing  food  witli  less  effort 
tlian  are  those  in  which  hinge  action  alone  is  i)ossiljle. 
Furthermore,  they  are  much  less  liable  to  displacement  when 


THE    NEW    CENTURY    AIITII 'ULATOR     (SNOW) 


in  use,  as  haluncing  contact  is  one  of  the  essential  features  that 
in  jiractically  all  cases  can  be  attained. 

The  Snow  Articulator,  like  the  Ohristensen,  Walker  and 
Bonwill  appliances,  has  its  rotation  centers  placed  four  inches 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1147 

apart,  which,  arcordiiiy  to  rxjuwill's  measurements,  corre- 
sponds witli  tlie  average  distance  from  center  to  center  of  the 
human  condyles. 

Wahver  ch^arly  proved  that  the  lateral  rotation  centers  of 
the  mandible,  in  some  individuals  at  least,  were  located,  not  in, 
but  between  the  condyles  at  varying  distances  in  different 
cases.  Others  have  since  proven  the  truth  of  Walker's  find- 
ings, and  in  addition  have  shown  that  the  rotation  centers  may 
lay  outside  of  the  condyle  centers  as  well. 

Excepting  the  efforts  of  Ohristensen  as  noted,  this  de- 
scription has  been  confined  to  what  has  been  accomplished  by 
men  in  this  country.  It  will  now  be  in  order  to  mention  some  of 
the  contributions  to  this  subject  by  the  members  of  the  profes- 
sion in  Europe,  whose  interest  was  aroused  by  Bonwill's  work. 

In  1890,  Graf  von  Spee,  a  German  anatomist,  called  at- 
tention to  the  curved  arrangement  of  the  occlusal  planes  of 
the  natural  teeth  and  of  corresponding  curves  in  the  con- 
dyle paths.     (See  i)age  -302.) 

SCHWARZE'S  ARTICULATOR 

In  1900,  Dr.  Paul  Schwarze  of  Leipsic  constructed  an 
articulator  somewhat  on  the  order  of  the  Bonwill  appliance. 


TIIK    SCHWARZE    ANATIIMICAI.    AUTU'UI.ATOR 


but  having  both  a  'forward  and  downward  movement  to  the 
condyles. 

In  1901,  Tomes  and  Dolamore  made  a  series  of  records 
of  condyle  paths  as  disclosed  by  the  hinge  action,  or  opening 


1148  A     HIUKF    IIISTUKY    OK     I'ROSTUKTIC     DIONTISTUY 

and  closing  niiiiidilnilar  inoxcnicnts.  'I'liose  were  of  no  special 
value  in  a  ])ractii>ai  way,  I'lirther  tliaii  to  verify  the  research 
work  of  Walker  and  others  in  reference  to  the  downward  pitch 
as  well  as  variations  in  the  condyle  ])aths.     (See  pajije  275.) 

Parfitt,  Constant,  Cainpioii,  Warnekros,  Peckert  and  oth- 
ers have  contrihuted  in  various  ways  and  at  different  times 
to  this  most  interesting  suhject. 

Recently  Bennett  has  shown  that  there  is  an  actual  l)odily 
side  movement  to  the  mandihle,  which,  although  caused  by 
the  muscles  that  induce  lateral  rotation,  cannot  l)e  classed 
as  rotary.  This  is  a  most  important  recent  discovery  in 
mandibular  movements,  and  one  which,  in  some  cases,  miglit, 
with  profit,  be  reckoned  with  in  denture  construction. 

GYSrs  WORK 

In  1910,  there  appeared  in  the  Dental  Cosmos  a  series 
of  articles  bv  Dr.  Alfred  Gvsi  of  Zurich,  Switzerland,  de- 


<IIVI.K    ItlOCiSTKIt 


scribing  in  detail  various  registering  devices  for  recording 
mandibular  movements,  together  with  many  records,  secured 
by  means  of  them. 

The  principal  a])pliances  shown  are  an  (irticulator,  a  coii- 
(l/flc  path  rpfj'istef.  and  an  iiicism   ixtth   ref/isfer. 


A    BRIEF    HISTORY    OF    PROSTHETIC     DENTISTRY  114'J 

The  articulator  has  adjustahlc  (•(hkInIc  paths,  and  also 
adjustable  rotation  centers,  the  niaxinunu  distance  between 
which  is  tive  and  one-fourth  inches,  while  the  minimum  dis- 
tance is  about  two  and  three-fourths  inches. 

The  condyle  register  as  its  name  indicates,  records  the 
inclination  and  curvature,  if  any  exists,  of  the  condyle  |)aths, 
on  cardl)iiai(l,   in   such  manner  tliat  the  anyular  inclination 


I'ATH     RKcaSTKIt 


may  be  read  and  the  condyle  paths  of  the  articulator  set  ac- 
cordingly. 

The  condyle  register  also  fulfills  the  saiiK  purpose  as  a 
face  bow  in  mounting  casts  on  the  occluding  frame. 

The  incisor  ])ath  register  consists  of  a  metal  plate,  at- 
tached to  the  occlusal  surface  of  the  lower  occlusion  model,  the 
upper  surface  ol  which  is  covered  with  a  thin  film  of  carbon- 
ized wax.  A  small  steel  point,  l)acked  by  a  fine  spring  within 
a  socket,  and  attached  to  a  small  plate,  is  fixed  to  the  labial 


A    BRIKF    HISTOllY    OF    PROSTHETIC    DENTISTRY 


surface  of  the  upper  occlusion  model  in  such  manner  that 
when  tlio  mouth  is  closed  the  point  rests  upon  the  waxed  sur- 
face of  the  incisor  path  register,  which  extends  somewhat  for- 
ward of  the  labial  surface  of  the  baseplate.  In  lateral  and  pro- 
trusive movements  of  the  maiidil)le  the  point  marks  upon  the 
waxed  surface  the  lines  of  travel  of  the  mandible  in  the  in- 
cisal  region.  Later  on,  when  the  occlusion  models  are  returned 
to  the  casts  on  the  articulator,  the  rotation  centers  of  the 
frame  are  moved  to  such  position  that  the  marker  on  the  ujjper 
occlusion  model  will  follow  the  same  lines  it  marked  on  the 
waxed  register  during  mandibular  movements.  By  this 
means  the  lateral  rotation  centers  of  the  mandible  are  de- 
termined and  the  centers  of  the  articulator  set  accordingly. 

Since  1910,  Dr.  Grysi  has  devised  a  lateral  covdyle  path 
register,  which  records  the  bodily  side  movement  of  the  man- 
dible. The  articulator  condyle  j)aths  are  so  arranged  that 
they  may  be  set  to  reproduce  this  movement  to  a  fairly  accia- 
rate  degree.     (See  page  465.) 

The  Gysi  Adaptable  Articulator,  with  accessory  appli- 
ances enable  the  careful  prosthetist  to  register  more  of  the 
essential  mandibular  movements  than  can  be  accomplished 
by  any  other  available  means. 

Consequently,  with  such  registration  i)0ssible,  and  with 
the  generally  improved  methods  in  denture  construction  that 
have  recently  been  and  are  being  developed,  prosthetic  den- 
tistry is  rapidly  advancing  into  the  field  of  an  exact  scientific 
specialty. 


LOWER    SEOTIOX     OF    T.IK'K     A  Ullri    I.A  1  OK.     .SIHIUIM.        1K\CIN'0 
KNOBS"    IN   I'OSITION    ON    LOWER    OCCLUSION    MODEL 

Dr.  C.  E.  Luce  has  designed  an  articulator  in  which  cer- 
tain anatomic  movements  may  be  reproduced  as  follows : 

Round  liead  tacks,  or  ' '  tracing  knobs, ' '  are  pressed  into 
the  lower  occlusion  model,  the  wax  rim  of  the  upper  model 


A    BRIEF    HISTORY    OP    PROSTHETIC    DENTISTRY  1151 

softeiu'il,  and  introduced  in  tlic  nionlli  and  the  mandililc  snl)- 
jected  to  lateral  movements.  The  round  heads  of  the  pniject- 
iug  tacks  mark  lateral  paths  iu  the  upper  wax  rim. 


To  use  this  appliance  successfully,  tlie  casts  should  be 
mounted  on  it  by  means  of  a  face  bow. 

When  so  mounted,  the  hinge  pin  of  the  articulator  is 
removed,  the  eu]i  situated  immediately  in  front  and  between 


the  hinges  lilled  with  softened  modeling  compound,  the  upper 
bow  of  tile  frauie  carrying  the  cast  and  occlusion  model  is  set 
in  position  and  subjected  to  lateral  movements,  the  round- 
head tacks  guiding  tlie  direction  of  movement.     During  this 


1152  A     liUIIOK    HISTORY    OK    I'UOS'lM  I  KTlC     DIONTISTliV 

lateral  inoA'ciiiciit,  prnjcclions  on  the  nndcrsidi'  nf  llic  ii|ip('i' 
1)()W,  inini('(liat('l\'  (i\('i-  the  liiiiiic  cup,  rm-iii  pnllis  in  llic  niod- 
cliiiii'  coniiioiuiil. 

'^riiosc  i)atlis  in  tlic  cup  rcjircscnt  shorter  ares  of  circles 
than  those  in  tlie  ocelusion  rims.  They  inwe,  liowever,  coiii- 
moii  centers.  \iz.,  the  centers  of  rotation  of  the  niandilile. 

( »ii  I'emovinn' tin'  tacks  from  the  ocolnsion  rini  the  i)ins  of 
the  franu'.  restinn'  ami  nio\inn'  in  tln^  n'rooves  in  the  compound. 


UKTAIL.S  UK  .\RTIcrLATINi:   ITl' 


within  the  liinge  enp  gnide  and  control  the  lateral  movements 
of  the  k)wer  a^'ainst  the  njiper  ooclnsion  moth'!  on  nuich  tlie 
same  ])rinciple  as  a  ])anta,i>'raph  works. 

CROWN  WORK 

The  ])lacin!i'  of  ai'tilicial  crowns  on  the  roots  of  natural 
teetli  lias  been  practiced  for  hundreds  of  years,  yet  it  is  only 
witliin  the  last  half  century  that  much  advancement  has  been 
made  o\'er  the  lu■imiti^■e  methods  of  Fauchard's  time. 

PIVOT  TEETH  OF  DE  CHEMANT 

Pivot  teeth  of  ])orcelain  were  mentioned  hy  de  Chemant 
in  ^^()^2.  althoniJ.h  for  manv  vears  after  his  time,  teeth  c;ir\-ed 


from  hone,  ivory  and  various  substances  were  used  in  single 
crown  replacements.  Frequently,  sound  natural  tooth  crowns 
were  also  used  for  this  inirjiose. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1153 

THE    GROOVED    FLAT-BACK    FACING 

In  the  early  part  of  tlie  last  century,  a  porcelain  facing, 
grooved  on  the  back,  and  with  small  strips  of  platinum  baked 


in  the  porcelain  along  the  sides  of  the  groove  for  attachment 
to  the  wire  pivot,  was  used  both  in  Europe  and  this  country 
in  crown  work. 

THE  ASH   TUBE  TOOTH 

The  Ash  Tube  tooth,  introduced  about  1840,  was  used  in 
both  denture  construction  and,  to  a  limited  extent,  in  crown 
replacements.     (See  page  529.) 

The  recent  articles,  within  the  last  two  years,  by  Dr. 
Girdwood,  have  shown  the  modern  application  of  this  type  of 
tooth  to  prosthetic  restorations.    (Dental  Cosmos,  1914-1915.) 

THE  WOOD   PIVOT  TOOTH 

A  full  contoured  porcelain  crown,  with  a  circular  open- 
ing in  the  base  for  the  reception  of  a  wood  pivot,  was  intro- 
duced, probably  between  1850  and  1860.  This  crown  was  at- 
tached to  the  root  by  means  of  a  wood  pivot  which  fitted 
tightly  into  both  crown  base  and  root  canal.     The  pivot  was 


r  R  E  P  A  R  ATION  (IF 
ROOT  FOR  RECEPTIOX 
OF  r^ROWN  AJfD  DOW- 
EI-.       LABIAI,    VIEW 


forced  to  place  while  dry,  and  on  absorbing  moisture  swelled 
and  firmly  held  the  crown  in  position.  The  writer  a  number 
of  years  ago  removed  two  central  incisors  which  had  been 
set  in  this  manner  eighteen  years  i:)revionsly,  neither  of  which, 
in  that  time,  had  required  resetting. 

THE  SMITH  CROWN 

In  1844,  Dr.  J.  Smith  Dodge  devised  a  crown  which  was 
of  similar  form  to  the  one  just  described,  but  in  which  a  wood 


A    BRIIOF    HISTORY    OF    PROSTHKTIC    DIONTISTRY 


^rOOO  PLUG 


DI!.    J.    DODGE    SMITira    CRf)\VN 

pivot  containing  a  metallic  tube  for  a  core  to  strengthen  it 
was  used. 

THE  CLARK  CROWN 

In  1849,  Dr.  F.  H.  Clark  devised  a  removable  crown,  which 
was  attached  to  the  root  by  means  of  a  metal  dowel,  split  to 


form  a  spring,  for  bearing  against  a  metal  tube  firmly  fixed  in 
the  root  canal.  It  was  so  formed  as  to  afford  drainage  for  pus 
or  vent  for  gas  which  might  accumulate  in  the  pulp  chamber. 

THE  LAWRENCE-FOSTER  CROWN 

In  1849,  Dr.  Henry  Lawrence  invented  a  porcelain  crown 
having  an  opening  extending  through  from  base  to  lingual 


DR.    HENRY    I-AWTtKNTES 

CROWN.       AFTERWARD 

CALLED     THE     •■l.'dSTER" 

CROWN 


surface.    It  was  held  in  place  by  means  of  a  screw  anchored 
within  the  root  canal. 

This  crown  was  afterward  known  as  the  "Foster"  Crown. 


A    BRIEF    HISTORY    OP    PROSTHETIC    DENTISTRY  1155 

THE  DWINELLE  CROWN 

In  1855,  the  American  Jonrnal  of  Dental  Science  con- 
tained a  description  by  Ur.  W.  H.  Dwindle  of  a  gold  baud 
\\\t\i  floor,  iitted  to  a  tooth  with  vital  pulp,  and  held  in  place 


THE       D  WINELT-E 
CROWN      FOB      VITAl, 
TEETH       AND       NON- 
VITAL   TEETH 


by  means  of  two  screws  passing  through  the  floor  and  into  the 
dentin.  The  "tubbing."  or  gold-bound  cavity,  was  filled  with 
crystal  gold,  while  to  the  labial  or  buccal  surface  of  the  band 
a  porcelain  facing  was  affixed. 

This  same  principle  was  also  applied  in  the  crowning  of 
pulpless  teeth,  the  crown  being  held  in  position  by  means  of 


THE  DWINELLE  CEOWN  FOB  VITAL  TEETH 


a  screw  anchored  within  the  pulp  chamber.  The  five  cuts  show 
the  Dwindle  method  of  attaching  a  porcelain-faced  ferrule 
crown  to  the  stub  of  a  vital  tooth  with  crystal  gold. 

This  work  of  Dr.  Dwinelle  is  about  the  first  reference 
found  of  combining  gold  and  porcelain  in  the  restoration  of 
lost  natural  crowns. 

THE    WOOD    CROWNS 

In  1862,  Dr.  B.  Wood  describes  the  restoration  of  de- 
fective teeth  by  the  application  of  enamel  caps.     These  were 


B.    WOOD'S   -ENAMELED  CAP"  CROWNS 


formed  by  fusing  to  platinum  caps,  previously  fitted  to  the 
teeth,  some  form  of  enamel,  probably  such  as  jewelers  used. 


A    BRIEF    HISTOltY    OP    PROSTHETIC    DENTISTRY 


Willi 


•lili>ri( 


These  caps  were  cemented   in   \>\i\i 
or  attached  with  gutta  ix'iclia. 

Dr.  Wood  also  constructed  tliin  gold  crowns  with  interior 
staples  by  means  of  wliieh  anchorage  to  the  teeth  was  secured 


f*?" 


THIN  GOLD  CM'   t'llOWNS  DESCItlP.ED  ItY   DH.    li,    WOOD 

with  cement.    These  crowns,  because  of  their  thin  walls,  were 
more  or  less  unstable. 

THE  MORRISON  CROWN 

In  1869,  Dr.  W.  N.  Morrison  described  in  the  May  number 
of  Missouri  Dental  Journal  a  gold  shell,  two-piece  crown.  This 


GOLD     SHELL     CliOWX     CONSIIHlllD      \M> 
DESCniBED    P.V    DR.    W.    \     MOUniSO% 

IN    ISGO 


crown  was  substantially  the  same  as  is  constructed  to-day 
and  is  quite  generally  known  as  the  "Morrison  Crown." 

THE    BLACK    CROWN 

In  the  June  nuuilicr  of  the  same  journal.  Dr.  G.  V.  Black 
described  and  illustrated  the  construction  of  a  porcelain-faced 


crown  for  an  anterior  tooth,  held  in  place  by  means  of 
screw  passing  into  a  gold-lined  root  canal. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1157 

The  similarity  between  tliis  and  the  erown  Dr.  Richraoiid 
patented  years  afterward  is  obvions. 

THE   BEAN    CROWN 

In  the  duly  nuniher,  IS*)!),  of  the  American  donnial   of 
Dental  Science,  Dr.  J.  B.  Bean  described  a  porcelain-faced  re- 


CROViT^'  rONSTRU('TED 
AKD    DESCKIBED    BY 

DR.     J.     B.     BEAN    IN 
18G9 


mo\able  crown    tlie  dowel  of  which  was  split  and  received 
within  a  permanently  fixed  tube  in  the  root  canal. 


THE  MACK  CROWN 


In  1S72,  Dr.  (Hias.  If.  Mack  designed  a  pivot  tooth  liaving 
a  dovetailed  depression  in  the  base  of  the  crown. 


THE    MAIK    c'li<>\V> 


Metal  i)in"s,  roughened,  were  first  fixed  in  the  root 
of  the  tooth  and  the  crown  attached  with  cement  or  amal- 
gam. 


1158  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

THE   BEERS   CROWN 

In  1873,  Dr.  J,  B.  Beei-s  of  Oalifoniia  patented  a  gold  cap 
crown  practically  the  same  as  described  some  four  years  pre- 
viously bv  Dr.  Morrison. 


Till!   BEERS   CKOWN 


THE  GATES   CROWN 


In  1875,  Dr.  W.  H.  Gates  devised  a  "vertically  open  con- 
tour crown,"  composed  of  metal  and  porcelain,  designed  to 
be  held  in  place  with  cement.    In  this,  as  in  the  Mack  crown, 


THE    GATES     CHOWN' 


the  dowel  was  first  permanently  set  in  the  root  canal  and 
the  crown  adjusted  and  attached  later.  Manufacturing  diffi- 
culties, however,  prevented  its  introduction  and  use. 


THE  RICHMOND  CROWN 

In  1880,  Dr.  C.  M.  Bichmond  designed  a  porcelain-faced 
crown  backed  with  metal  and  held  in  place  on  the  root  by 
means  of  a  screw  similar  to  the  crown  designed  by  Dr.  Black. 

An  internally  and  externally  threaded  tube  was  fixed  in 
the  root  canal,  the  crown  formed  with  a  groove  in  its  lingual 
surface  for  the  passage  of  a  screw  which  entered  the  tube 
within  the  root,  and  by  means  of  which  it  was  lield  in  place. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  lloO 


THE   mcllMOND    CROWN 


THE    IMI'HOVEI)    RICHMOND    CROWN 


A  cap  diaphragm  rested  upon  the  root  end  and  over  this 
the  crown  hase,  also  of  ca]i  form,  telescoped. 


THE   GATES-BONWILL   CROWN 

In  1881,  Dr.  W.  CI.  A.  Boiiwill  desiiined  a  crown  wholly 
of  porcelain  having  a  central  opening-  slightly  enlarged  at 
either  end  fonr  the  reception  of  metal  dowel. 


/\mm 


THE    OATES-BONWILIi   CROWN 


These  crowns  were  set  with  an  amalgam  specially  pre- 
pared by  Dr.  Bonwill.  Both  three-sided  and  triangular  metal 
dowels  were  iised. 

The  specifications  of  the  Mack  patents,  issued  six  years 
previously,  were  so  broad  that  they  covered  the  principle  of 
this  crown.  Therefore,  when  placed  upon  the  market  it  was 
given  the  name  of  the  "Gates-Bonwill  Crown." 


1160  A    BRUOP"    HISTORY    OF    PROSTHETIC    DENTISTRY 

THE   BUTTNER   CROWN 

Til  1SS1,  "Or.  W.  II.   r.iiltiici-  pntcnlcd  a  scf  of  appliances 
i'oi-  rcdiiciinj;-  the  mmiI  iH'ii|ilici'\   (if  a  Idtith  \u  a  iiniroi'in  cylin- 


||1    111 


I  ji 


TUB   BUTTNKIl  SYSTEM   OF    CROWN  CONSTRUCTION 

dor.  fitting  a  doep-sided  doTvel  cap  to  same  and  root  canal  and 
attaching  a  porcelain  facing  to  tlie  base  so  formed. 

THE    HOW    CROWN 

In  1S83,  Dr.  W.  S.  How  designed  what  was  called  the 
"fonr-pin  crown."  These  pins  were  set  within  a  depression 
on  the  lingual  surface  of  the  facing,  were  folded  aronnd  a 


§ 


'"'i? 


tmi 


THE    HOW   FOUll-I'lN    CROWN 


threaded  dowel  fixed  in  the  root  canal  and  tlie  lingual   con- 
tour of  the  tootVi  developed  in   amalgam. 

Dr.  How  also  designed  the  Dovetail  Crown  in  1889. 


THE    WESTON    CROWN 

Tn  1883,  Dr.  Henry  Weston  designed  a  "porcelain  pivot 
crown"  having  two  pins  located  in  a  depression  on  its  lin- 
gual surface  for  the  reception  of  a  cross-head  dowel.  The 
dowel  and  facing  were  attached  with  solder  and  the  crown 
attached  to  the  root  by  gold,  cement  or  amalgam. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1161 

Another  form  of  ci'own  devised  by  Dr.  Weston  consisted 
in  a  more  fnllv  contoured  iiorcelaiii  faciiii;',  in  wliicli  the  (hiwel 


WESTOXS    ntdSS  lIKAli    DOWLI     I'BOWN 


WESTON'S    FIXED    IIOWEI,    IROWN 


was  baked.     This  crown  was  secured  to  the  root  in  the  same 
manner  as  was  the  preceding  crown. 

THE   LOGAN  CROWN 

In  1885,  Dr.  ]\I.  Ij.  I^ogan  devised  a  full  contoured  porce- 
lain crown  having  a  ]ilatinum  dowel  permanently  fixed  within 
its  base. 


THE    LOiiAX    I'liOWN" 


This  crown  has,  almost  from  its  introduction,  been  ex- 
tensively employed  and  has  proven  most  serviceable  as  a  sub- 
stitute of  the  fixed  dowel  type. 


THE  BROWN   CROWN 

In  18!M),  Dr.  E.  Painily  T.rown  designed  a  crown  very 
similar  to  tlie  "Logan,"  iiut  with  a  convex  instead  of  a  con- 
cave base. 


THE    E.    PARMf.V    P.I'.nWX    CIIOWX 


AVithin  recent  years  many  forms  of  detached  dowel 
crowns  have  l>een  introduced,  which,  because  of  comparative 
ease  of  adaptation,  are  fast  coming  into  favor,  both  as  crown 


1162  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

rfiplaceinents  and  lor  use  in  liriilgx'  and  di-nture  work  as 
well. 

Among  these  may  be  mentioned  the  Davis,  S.  S.  White, 
Justi,  Brewster  Twentieth  Century,  illustrations  of  which  are 
found  elsewhere. 

An  analysis  of  the  various  means  I)y  which  crowns,  Itotli 
ancient  and  modern,  are  fixed  to  natural  teeth  and  roots  shows 
but  two  general  principles  of  attachment,  viz.,  with  dowels, 
the  telescoping  principle,  or  a  comlnnation  of  tlie  two  methods. 

Much  of  the  material  contained  in  the  foregoing  history  of 
crowns  has  been  obtained  from  a  monograph  published  by 
the  S.  S.  White  Dental  Manufacturing  Company,  entitled 
"Origin  and  Development  of  Porcelain  Teeth,"  and  from  vari- 
ous articles  which  have  apjieared  from  time  to  time  in  the 
Dental  Cosmos. 

BRIDGEWORK 

Modern  bridgework,  of  a  practical  character,  is  of  very 
recent  origin  as  compared  with  dental  procedures  in  general. 

Dental  literature  of  modern  times  contains  scarcely  any 
reference  to  bridgework  previous  to  1869. 

In  addition  to  the  three  greatly  improved  crowns  pre- 
sented by  Drs.  Morrison,  Black  and  Bean  in  that  year,  Dr. 
Bennett  described,  in  the  Dental  Cosmos  of  October,  1869, 
a  method  of  bridging  in  the  space  of  a  single  missing  tooth  as 
suggested  by  Dr.  B.  J.  Bing  of  Paris. 

THE   BING  BRIDGE 

This  method  consisted  in  preparing  cavities  in  the  teeth 
proximating  the  space,  fitting  a  square  bar  across  the  space, 
its  ends  resting  within  the  cavities,  and  by  suitable  steps 


adapting  and  soldering  a  facing  to  the  bar.  The  appliance 
was  fixed  by  packing  gold  foil  into  the  cavities  and  around 
the  bar  ends. 


A    BRIEF    HISTORY    OF    PROSTHRTIC    DENTISTRY  11C2 

DR.    WEBB'S   WORK 

In  1873,  Dr.  Marshall  II.  Webb  suggested  a  modification 
of  the  Bing  method,  consisting  of  a  flattened  "two  stop  back- 
ing and  saddle,"  and  in  1879  a  "stop  post,"  consisting  of  a 


MODIFICATION    OF    THE   BING    BRIDGE    (WEBB) 

facing  attached  to  a  rigid  wire  staple,  the  ends  of  which  were 
anchored  within  the  root  canals  of  the  proximating  teeth. 

In  both  cases  the  stops  were  surrounded  by  and  anchored 
within  gold  foil  filling  in  the  cavities  of  the  adjoining  teeth. 

DR.  LITCH'S  WORK 

In  1880,  Dr.  Wilbur  V.  Litcli  suggested  two  modifications 
of  the  Bing  bridge.  The  first  was  called  a  "wing  plate,"  in 
which  the  backing  was  extended  beyond  the  dummy  so  as  to 
rest  upon  the  lingual  surfaces  of  the  proximating  teeth.  Per- 
forations were  then  made  in  the  wings  and  corresponding 


DK.    LITCU'S   FIRST  MODIFICATION  OF  THE  BING   BRIDGE 

holes  in  the  teeth,  through  the  enamel,  and  as  deeply  in  the 
dentine  as  practicable,  without  endangering  the  pulp. 

Headed  platinum  pins  were  passed  through  the  plate 
into  the  holes,  the  relation  between  backing  and  pins  secured, 
the  case  invested'  and  the  pins  soldered  to  the  wings.  The 
substitute  was  set  with  cement. 

The  second  modification  consisted  in  devitalizing  either 
one  or  both  teeth  and  extending  dowels  through  the  wings  into 


11fi4  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

tlic  n.ot  canals.     Ij   will  he  imrM-cd  llial   holli   Di's.   \Vel)!>  and 
l;ilcli  increased  ilic  anclioran'cs  of  ilic  diiiiiniics  li\'  root  dow- 


0''''h\^ 


DR     I.ITCirS   SECOXI)  JIUIUKUATll  LN  (IF  THK  lilXG   ISl'.IDGE 

els,  being  impelled  to  do  so  l)eeanse  of  failures  iu  their  first 
attempts. 

DR.  WILLIAMS'  WORK 

In  1884,  Dr.  J.  Leon  Williams,  in  the  Dental  Cosmos, 
called  attention  to  the  neeessitv  for  more  sta1)le  anchorage  for 


MODIFIED  KICHAEDSOX  CROWN    (WILLIAMS 


bridges  and  suggested  the  use  of  a  modified,  so-called,  Eich- 
mond  crown,  wliich,  in  a  general  way,  represents  a  common 
type  of  porcelain-faced  crown  of  to-day. 


FOUR-TOOTH  ANTERIOR  BRIDGE   (\VIMiI.\MS) 


""'"^  \s.^X^*^-^ 


This  article  was  followed,  the  next  year,  with  illustra- 
tions and  descriptions  of  two  very  practical  bridges  by  the 
same  writer. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1165 

Dr.  Williams  remarks,  in  Jamiarv  Cosmos,  1884:  "As 
the  single  crown  is  the  beginning  and  the  end  of  all  bridge- 
work,  a  description  of  that  particular  form,  which  is  of  the 
greatest  practical  value,  will  be  necessary.  This  is  known  as 
the  Richmond  crown,  though  not  the  crown  he  claims  as  his 
invention.  It  consists  essentially  of  three  parts — a  pin 
[post  .n  which  enters  the  root  canal;  a  root  cap  of  gold;  and 
a  porcelain  face,  which  is  the  ordinary  plate  tooth." 

It  is  evident  that  our  modern  system  of  bridgework  could 
not  have  been  possible  without  the  evolution  of  suitable  crowns 
for  supporting  the  same. 


DR.   STARR'S  WORK 

In  the  Dental  Cosmos,  188(i,  Dr.  R.  Walter  Starr  de- 
scribed a  difficult  case  of  restoration  in  which  two  removable 
l)ridges  were  successfully  applied.  The  telescoping  crown 
])rinci]ile  is  here  mentioned  for  the  first  time. 


EEMOVABLE  BRIDGES  BY  DB.    STARB.   ISSi; 

In  1887,  Dr.  Starr  suggested  a  modification  of  the  Bing 
bridge  tooth,  consisting  of  a  porcelain  tooth  with  two  parallel 
bars  extending  through  it  by  means  of  which  the  projecting 
ends  of  the  substitute  were  anchored  within  fillings  placed  in 
the  proximal ing  teeth. 

The  names  of  Drs.  Cryer,  Starr,  Ilodgkin,  E.  Parmly 
Brown,  EoUo  Knapp,  Stowell,  and  Rhein  are  associated  with 


1166  A    BRIEF    HISTORY    0I<"    PROSTHETIC    DENTISTRY 

the   early  history  of  recent  bridge  methods,  nearly   all   of 
whom  presented  modilications  of  the  Bing  bridge. 

Drs.  Williams,  Eichmond  and  Knapp  seem  to  have  been 
among  the  first  to   reeognize  the  necessity  for  the  use  of 


STARR'S  MODIFICATION  OF  THE 
BING   BRIDGE.    1887 


stronger  and  more  hygienic  abutments  in  bridge  appliance, 
although  no  doubt  many  others  were  coming  to  recognize  the 
same  fact. 

In  1888  Dr.  Sidney  S.  Stowell  described  an  extension 
stop-supported  bridge,  similar  to  those  frequently  constructed 


TWO-TOOXn  STOP  AND  SADDLE  BRIDGE 


to-day,  except  that  with  present  methods  the  stop  rests  in  a 
depression  within  an  inlay  instead  of  being  enclosed  within  a 
filling,  as  described  by  Dr.  Stowell. 


BASIS  OF  OUR  PRESENT  SYSTEM  OF  BRIDGEWORK 

The  crowns  of  "Wood  and  Dwinelle  in  the  "50's"  formed 
the  basis.    The  great  improvements  by  Morrison,  Black  and 


A    BRIEF    HISTORY    OP    PROSTHETIC    DENTISTRY  1167 

Bean,  in  crowns,  and  the  appearance  of  the  Biug  bridge  tooth, 
all  of  which  were  presented  in  1869,  although  crude,  furnished 
the  necessary  elements  which  had  previously  been  lacking. 

Further  improvements  in  crowns,  the  development  of 
various  forms  of  dummies,  together  with  simplitied' technical 
procedure,  gradually  followed,  but  only  after  many  failures 
and  a  considerable  lapse  of  time. 

It  is  singular  to  note  that  practically  all  of  the  pioneers 
in  bridgework  failed  to  recognize  the  heavy  stress  in  mas- 
ticatory effort  delivered  against  bridge  replacements.  Neither 
were  the  limitations  in  regard  to  resistance  of  stress  of  the 
materials  employed  well  understood. 

This  lack  of  knowledge  of  the  strength  of  materials  used, 
together  with  an  indefinite  or  exaggerated  idea  of  the  ca])acity 
of  natural  teeth  or  roots  for  performing  their  own  work  and 
carrying  the  additional  burden  imposed  by  the  replaced  teeth 
were  some  of  the  discouraging  features. 

Peridental  troubles,  the  splitting  of  roots  and  recurrent 
decay  of  the  abutment  and  pier  teeth  and  roots  were  of  fre- 
quent occurrence. 

A  recognition  of  these  facts,  which  could  only  be  gained 
by  experience,  led  to  further  improvements  in  crowns  of 
greater  strength  and  of  more  hygienic  form  and  in  more  judi- 
cious selection  of  cases  for  substitutes  of  this  type. 

PORCELAIN   BRIDGE 

Baked  porcelain  crown  and  bridge  work  went  through  a 
similar  jn'ocess  of  trial,  failure  and  development  before  the 
limitations  in  this  field  were  finally  determined.    The  principal 


PLATINUM  FRAMEWORK  FOR  PORCELAIN 
BRIDGE    (SCHWARTZ.    1902) 


failures  were  due  to  insufficient  strength  to  the  metal  sub- 
structure and  deficient  bulk  of  porcelain.  One  of  the  pioneers 
in  this  field  was  Dr.  G.  W.  Schwartz  of  Chicago,  who  was  en- 
gaged in  the  production  of  porcelain  crowns,  bridges  and  in- 
lays as  early  as  1893. 


1168  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

While  to-day,  tlie  application  of  fixed  bridgework  is  not 
as  extensive,  the  results  of  such  application  at  the  ])resent 
time  are  generally  far  more  satisfactory  than  in  the  past. 

REMOVABLE  BRIDGES 

Bridges  of  the  remo\'able  type,  and  partial  dentures  sup- 
ported by  saddles  resting  upon  the  alveolar  process,  retained 
in  position  by  some  of  the  various  forms  of  fractional  appli- 
ances, are  now  introduced  in  many  cases  where  formerly 
bridges  of  the  fixed  type  were  a])pli('d. 


INLAYS 

An  inlay,  in  its  dental  meaning,  refers  to  a  filling  com- 
posed of  some  dense  material,  constructed  outside  the  tooth 
cavity,  and  which  is  held  in  position  in  the  cavity  by  some 
adhesive  medium. 

FIRST  RECORDED  ATTEMPTS  IN  FILLING  TEETH 

The  first  attemi)ts  at  filling  teeth  must  naturally  have 
been  extremely  crude,  and  the  results  of  the  ])ioneer  efforts 
in  this  field  have  ])roved  but  temporary  in  character.  Be- 
cause of  the  difficulty  in  adapting  dense  materials,  the  first 
fillings  were  undoubtedly  of  the  ])asty,  plastic  or  pitchy  class. 

Mastic  and  alum,  a  substance  of  this  class,  was  recom- 
mended for  filling  carious  cavities,  by  Rhazes,  a  Persian  phys- 
ician, about  850  A.  D.  (Guerini).  Frequently  medicinal  agents 
were  incorporated  with  the  mastic  base  for  the  purpose  of 
arresting  the  progress  of  decay,  myrrh,  sulphur  and  tur- 
pentine being  mentioned  in  this  connection.  The  comfort 
derived  from  the  use  of  such  stoppings,  although  only  of  tem- 
porary nature,  gradually  led  to  the  general  practice  of  filling, 
and  the  use  of  more  permanent  materials. 

Mesu,  an  Arab  surgeon,  in  the  latter  part  of  the  eighth 
century  recommended  the  use  of  gold  foil  for  filling  teeth, 
while  from  the  thirteenth  century  on  various  writers  mention 
the  use  of  both  gold  and  lead  for  this  purpose. 

FIRST    MENTION    OF   INLAYS    IN    DENTAL    LITERATURE 

In  1()90,  Pierre  Dionis,  a  surgeon  of  Paris,  in  discussing 
the  filling  of  teeth,  says:  "For  this  purpose,  gold  or  silver 
leaf  is  made  use  of;  but  this  method  of  stopping  is  not  dur- 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1169 

able,  liecaiise  gold  or  silver  leaf  is  apt  to  become  loosened 
and  fall  out.  It  is  tberefore  preferable  to  make  a  stopping 
with  a  piece  of  gold  or  silver  corresponding  in  size  and  shape 
to  the  cavity.  Many  prefer  lead  on  account  of  its  softness, 
while  others  simply  use  wax."  (Guerini.)  This  is  the  first 
definite  reference  to  the  inlay  method  of  filling  teeth,  so  far 
as  the  writer  knows,  in  any  of  the  old-time  treaties  on  dental 
procedures. 

In  1718,  Lorenz  Heister,  a  German  surgeon  recommended 
the  filling  of  teeth  with  various  substances.  In  reference  to 
crown  cavities  in  molar  teeth  he  recommends  gold  or  lead  leaf, 
or  a  piece  of  the  latter  fitting  into  the  cavity.     (Guerini.) 

Unfortunately,  few  specimens  of  ancient  inlay  work  are 
in  existence,  and  the  genuineness  of  such  as  are  preserved  is 
questionable. 

PREHISTORIC    INLAY    WORK 

In  the  Peabody  Museum  of.  Harvard  University  is  a  pre- 
historic skull,  in  the  central  incisors  of  which  are  inlays  of 
green  stone.  This  specimen  was  found  a  few  years  ago 
among  the  Aztec  or  Toltec  ruins,  near  Copan,  Honduras,  by 
Professor  Owen.  Whether  these  inlays  were  placed  in  the 
teeth  to  correct  the  ravages  of  decay  or  merely  for  ornamental 
purposes  cannot,  of  course,  be  determined. 

THE  BEGINNING  OF  MODERN   INLAY  METHODS 

Authentic  records  of  inlay  work  in  modern  times  date 
back  only  about  one  hundred  years.  At  the  beginning  of  this 
period,  tin,  lead  and  gold,  in  the  form  of  foil,  were  the  only 
metallic  fillings  in  use.  Amalgam  had  not  yet  been  introduced. 
It  came  into  vogue  as  a  filling  material,  under  the  name  of 
"silver  paste,"  about  1825,  but  for  years  was  looked  upon 
with  disfavor  and  used  to  a  very  limited  extent.  Cohesive 
gold  was  not  introduced  until  1855,  and  therefore,  since  none 
of  the  foils  were  cohesive,  extensive  contour  restorations 
were  impossible.  Added  to  these  difficulties,  the  general  dis- 
like on  the  part  of  patients  to  the  display  of  metals  in  the 
mouth,  rendered  the  filling  of  teeth  a  discouraging  and  often- 
times unsatisfactory,  jirocedure. 

It  is  not  surprising,  therefore,  that  efforts  were  early 
made  to  find  a  material  for  filling  operations  less  obiection- 
able  in  appearance,  and  easier  to  manipulate  than  the  metals. 
The  records  of  these  attempts  are  scattering  and  difficult  to 


1170  A    BRIF^P"    HISTORY    OF    PROSTHETIC    DENTISTRY 

find.  Many  efforts  in  inlay  work,  and  probably  some  reason- 
ably successful  results,  were  without  doubt  never  disclosed, 
because,  as  a  rule,  the  pioneer  practitioner  kept  his  methods 
a  secret. 

Such  early  records  as  are  available  are  usually  found  in 
little  handbooks,  published  in  the  early  days  by  the  prac- 
titioner, and  intended  for  circulation  among  prospective  pa- 
tients. Later  on,  the  dental  journals  from  time  to  time  con- 
tained descriptions  of  inlay  methods,  as  they  developed. 

BRIEF  SUMMARY  OF  INLAY  WORK,  BEGINNING  WITH  1820 

In  1902,  Dr.  Walter  W.  Bruck  of  Breslau,  Germany,  in 
the  Items  of  Interest,  presented  an  outline  of  the  history  of 
inlay  work,  gathered  from  common  and  obscure  sources.  A 
portion  of  the  following  brief  description  of  the  progress  of 
this  work  is  based  upon  tlio  article  mentioned. 

In  1820,  C.  J.  Linderer  filled  teeth  by  the  "fournieren'' 
(inlaying)  method  and  the  "plattieren"  (veneering)  method. 
The  first  procedure  consisted  in  i)reparing  a  cavity  in  circu- 
lar form,  and  from  the  tooth  of  some  animal  shaping  a  cylin- 
drical rod  to  fit.  This  was  driven  into  the  cavity,  the  project- 
ing portion  cut  off  and  polished  even  with  the  tooth  surface. 
The  expansion  of  the  inlay,  due  to  absorption  of  the  oral 
fluids,  caused  it  to  swell  and  thereby  furnish  retention.  Some- 
times both  inlay  rod  and  cavity  walls  were  threaded  to  fur- 
nish positive  mechanical  retention. 

The  plattieren  method  was  adapted  to  shallow  cavities 
and  consisted  in  shaping  small,  flat  pieces  of  rhinoceros  teeth 
to  fit  the  prepared  cavity.  These  veneers  were  usually  held  in 
place  with  dowels  of  the  same  material.  Difficulty  in 
matching  the  shades  of  the  natural  teeth,  discoloration  from 
use  and  general  lack  of  permanency,  were  the  principal  objec- 
tions to  the  Linderer  inlays. 

In  1837,  Dr.  Murphy  of  London  conformed  a  platinum 
matrix  to  the  prepared  cavity,  and  in  this  matrix  a  glass  in- 
lay was  fused,  which  was  held  in  place  with  amalgam. 

In  1857,  Dr.  A.  J.  Volck  recommended  the  use  of  porce- 
lain for  filling  cavities  in  the  front  teeth.  The  inlays  so 
formed  were  held  in  place  by  packing  ropes  of  gold  foil  around 
their  peripheries. 

In  1862,  Dr.  B.  Wood  shaped  porcelain  blocks  to  tooth 
cavities  by  grinding  to  form. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1171 

In  1870,  Dr.  Hickman  formed  inlays  from  sections  of 
porcelain  teeth,  shaping  the  pieces  to  fit  the  cavities  by 
grinding. 


In  1870,  Dr.  Starr  designed  "cavity  stoppers,"  small 
pieces  of  porcelain  of  various  shapes  and  sizes,  which  were 
fitted  to  cavities  by  grinding.  The  pieces  were  provided  with 
platinum   pins   for   retention   purposes. 

DR.  C.  H.  LAND'S  METHOD  OF  PORCELAIN  INLAY  WORK 

In  1870,  Dr.  C.  H.  Laud  constructed  inlays  by  "fusing 
pieces  of  artificial  teeth  in  a  platinum  impression  of  the  outer 
borders  of  the  cavity."  This  method,  as  he  later  on  modified 
it  by  pulverizing  the  teeth  before  fusing,  represents  the  basic 
principle  of  our  porcelain  inlay  system  of  to-day. 


In  1876,  Dr.  Bogue  described  a  method  suggested  liy  Dr. 
Fisk  of  veneering  a  carious  tooth  with  small  gold  caps,  which 
he  likened  to  "little  gold  toadstools,  set  with  gutta  percha, 
somewhat  resembling  an  umbrella." 


DR.  BING'S  METALLIC 
FACING 


DR.   BING'S   METALLIC   FACING 

In  1877,  Dr.  B.  J.  Bing  recommended  the  use  of  "metallic 
facings"  for  protecting  fillings  of  cement  or  gutta-percha. 
These  facings  were  usually  made  of  pure  gold  or  platinum. 


1172  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

and  when  set  very  much  resembled  in  ;i}»i>eariiuce  tlic  metallic 
inlays  of  the  present  time. 

Dr.  Wilber  F.  Liteli  describes  llicsc  J'ac^ings  quite  fully  in 
the  American  System  of  Dentistr}-,  p.  IMU.  Of  their  practica- 
bility, he  says:  "In  large  crown  cavities  they  have  an  in- 
definite durability,  and  in  the  writer's  practice  large  numbers 
of  proximal  facings  have  been  in  use  for  three  and  four  years 
and  still  give  no  sign  of  failure."  This  system,  although 
crude,  proved  an  incentive  to  many  to  attempt  the  restoration 
of  badly  decayed  bicuspids  and  molars  by  these  or  similar 
means.  The  writer  constructed  and  placed  a  number  of  fac- 
ings of  this  type  for  patients  in  the  clinic  of  Washington 
University  Dental  School  in  1891.     (Mo.  Dental  College.) 

ROLLINS'  METHOD  OF  INLAY  WORK 

In  1885;  Dr.  W.  Rollins,  in  the  Archives  of  Dentistry,  de- 
scribed as  follows  a  method  of  inlay  work  employed  by  him- 
self for  a  number  of  years  previous  to  the  date  mentioned. 
An  impression  of  the  tooth  with  cavity  prepared  is  taken  in 
a  material  composed  of  two  parts  mastic,  one  part  paraffin, 
and  one  part  graphite.  The  tooth  and  cavity  surfaces  should 
be  previously  oiled  with  vaseline.  When  secured,  the  im- 
jaression  should  be  i^laced  in  a  bath  of  copper  sulphate,  and 
a  film  of  copper  deposited  by  electrolysis,  the  process  usually 
requiring  from  two  to  three  days  to  develop  a  sheet  about 
11/2  m.m.  thick,  or  sufficiently  rigid  to  obviate  distortion  in 
handling.  The  impression  was  then  removed,  and  a  hole  bored 
in  the  bottom  of  the  cavity  in  the  copper  reproduction  of  the 
tooth,  to  facilitate  the  removal  of  the  matrix.  Into  the  cavity 
a  piece  of  No.  .30  gold  foil  was  adapted  with  pellets  of  cot- 
ton. The  matrix  thus  formed  was  filled  with  enamel  powder 
and  fused  in  a  gas  muffle  furnace.  Before  the  mass  hardened 
it  was  pressed  into  the  copper  mold  with  a  platinum  instru- 
ment. After  cooling,  the  enamel  was  removed  from  the  mold 
by  pressure  through  the  opening  in  the  base  of  the  copper 
pattern,  and  the  gold  matrix  peeled  off.  It  was  set  with  a 
mixture  of  zinc  oxide  and  gutta-percha,  the  excess  being  re- 
moved with  chloroform. 

DR.  DUNN'S  METHOD  OF  INLAY  WORK 

In  1885,  Dr.  C.  W.  Dunn,  in  the  British  Journal  of  Den- 
tal Science,  described  a  method  practiced  by  himself  since 
1868,  of  taking  a  wax  impression  of  the  tooth,  and  cavity, 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1173 

from  whicli  a  modrl  iii  plaster  was  secured.  This  was  painted 
with  a  mixture  of  wax  and  rosin,  to  prevent  friability  of  the 
cavity  margins.  Into  the  cavity  a  filling  was  tittecl  by  re- 
peated grinding  and  trial,  until  satisfactory  adaptation  had 
been  secured,  after  which  it  was  set  with  cement  Various  sub- 
stances were  used  by  him  for  inlays,  such  as  mineral  and 
natural  teeth,  as  well  as  the  teeth  of  cattle  and  lambs. 

DR.  STOKES'  METHOD 

In  1887,  Dr.  J.  L.  Stokes,  in  the  Southern  Dental  Journal, 
described  a  method  of  first  making  the  inlay,  and  shaping 
the  cavity  to  receive  it.  After  setting,  he  removed  the  hard- 
ened cement,  from  the  joint  to  a  slight  depth,  and  tilled  be- 
tween the  cavity  walls  and  inlay  with  gold.  A  similar  method 
of  retention  had  been  previously  introduced  by  Dr.  Essig  of 
Philadelphia  some  time  in  the  seventies. 

DR.  AMES'  METHOD  OF  GOLD  INLAY  WORK 

In  1888,  Dr.  W.  V.  B.  Ames  of  Chicago  constructed  gold 
inlays  by  adapting  a  foil  matrix  of  platinum  to  the  tooth 
cavity,  and  fusing  in  it  gold  plate  or  solder  to  the  recpiired 
contour.  The  inlay  was  then  cemented  in  position.  Shortly 
after  this  he  demonstrated  the  method  at  a  meeting  of  the 
Illinois  State  Dental  Society,  a  description  of  which  is  found 
in  the  Proceedings  of  1890. 

So  far  as  the  writer  is  able  to  learn,  this  was  the  begin- 
ning of  the  gold  inlay  methods  by  the  matrix  system.  It 
demonstrated  the  practicability  of  fillings  of  this  type. 

VARIOUS   METHODS    OF   INLAY   PRODUCTION    IN    RECENT 
YEARS 

In  1889,  Dr.  W.  Storer-llow,  in  the  Dental  Cosmos,  de- 
scribed in  detail  the  method  of  constructing  inlays  by  gi'ind- 
ing  sections  of  ]iorcelain  teeth  of  suitable  shade,  to  the  de- 
sired form 

In  1889,  Dr.  ITerbst  descrilied  a  metiiod  of  making  glass 
inlays.  An  impression  of  the  tooth  with  cavity  prepared  was 
secured  in  Stent's  Compound,  from  which  a  plaster  model 
was  formed.  To  make  the  base  of  the  inlay  rough,  for  re- 
tention purposes,  grains  of  sand  were  jjlaced  in  the  bottom  of 
the  cavity  of  the  plaster  tooth,  and  the  latter,  while  moist, 
was  filled  about  two-thirds  full  of  powdered  glass.  Tlie 
moisture  was  then  absorbed  and  the  glass  fused.  This  was 
then  repeated  until  the  inlay  was  of  the  desired  contoui-. 


1174  A    BRIEF    HISTORY    OF    PROSTHRTIC    DKNTISTRY 

111  1890,  Prof.  Sachs  reeouiiiiciKlcd  making  a  matrix  of 
Williams'  gold  foil  No.  60,  or  of  platinum  foil,  and  fusing  the 
glass  direeth'  into  tiiis  reproduction  of  tlie  cavity.  Sachs  also 
described  an  excellent  method  of  making  inlays  from  porce- 
lain teeth  of  suitable  shade.  From  a  porcelain  tooth  a  piece 
nearly  cylindrical  in  form  and  slightly  larger  than  the  cavity 
was  cut.  This  cylindrical  section  was  mounted  with  melted 
sliellac  on  the  end  of  an  engine  mandrel.  The  mandrel  was 
revolved  in  the  engine  and  the  porcelain  held  against  the  face 
of  a  lathe  stone  revolving  in  the  opposite  direction.  The 
mandrel  was  held  at  a  slight  angle  to  the  face  of  the  lathe 
wheel,  so  as  to  form  the  mounted  block  into  a  slightly  tapering 
cone.  The  cavity  was  prepared  in  circular  form  by  means  of 
suitable  wheel  burs.  The  inlay,  still  mounted  on  the  mandrel, 
was  introduced  into  the  cavity  with  emery  powder  or  pumice 
stone,  and  revolved  rapidly  to  secure  close  adaptation  at  the 
margins.  When  closely  adapted  a  groove  was  cut  near  the 
peripheral  base  of  the  inlay  for  retention  purposes.  After 
setting,  the  surplus,  or  projecting  end,  was  reduced  to  a  level 
with  the  tooth  surface  with  stones  and  discs.  Copper 
trephines  charged  with  diamond  dust  were  also  used  for  cut- 
ting the  section  from  the  porcelain  tooth,  while  cylindrical 
burs  corresponding  in  size  to  the  section  cut  by  the  trephine 
were  used  for  forming  the  cavity. 

In  recent  years  the  supply  houses  have  introduced  rods 
of  porcelain  for  inlay  work,  of  varying  sizes  and  tints,  with 
trephines  of  corresponding  sizes,  for  cavity  preparation.  This 
system  obviates  grinding  the  periphery  of  the  inlay.  A  sec- 
tion of  rod,  slightly  longer  than  the  depth  of  the  cavity,  is  cut 
and  cemented  to  place,  and  the  surplus  reduced  with  stones 
and  discs. 


DR.  ALEXANDER'S  INLAY  METHODS 

In  1896,  Dr.  C.  L.  Alexander  described  a  method  of  in- 
lay construction,  the  substance  of  which  is  as  follows:    Pre- 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1175 

pare  cavity  with  definite  margius.  I\Iake  lioles  for  retaining 
pits  in  dentin.  Adapt  platiunm  foil  to  tootli  surface.  In- 
sert retaining  iiosts  through  matrix.     Take   impression   of 


PIN  INl-AY   FOR  JIOI.AR  TOOTH 


posts  and  foil;  rciuo\e,  invest  and  unite  with  \mve  gold.    Re- 
turn to  tooth  for  iiual  adaptation  and  trimming. 


YAKIOUS   VIEWS  OF  INCISOR  AND  MOLAR  INLAYS 

When  fitted,  a  wax  or  modeling  compound  bite  is  taken, 
occlusion  casts  are  formed,  the  bite  removed,  and  the  desired 
restoration  developed  in  wax. 


RESTORATIONS  FOR  THE  ANTERIOR  TEETH 


Over  this -restoration  in  wax,  gold  or  platinum  foil  is 
burnished. 

Invest,  leaving  one  side  open  for  removal  of  wax  with  hot 
water  and  into  the  metal-lined  matrix  thus  formed  gold  is 


n76  A    HHIIOF    HISTORY    OF    PROSTHKTIC    DKNTISTRY 


fused.     Tli(>  various   ilhistratimis    here   shown   ai'e    IVoiii   tli 
Dental  Cosmos. 


Ul'PER  BlilDGE  SL  I'l'OUTED   UY  THREE  I'lN   INLAYS 

lu  18!)7,  Dr.  M.  S.  Fiiiley  deseribed  a  similar  method  of 
restorinn'  the  occlusal  surfaces  of  hicnsiiid  and  molar  teeth 


Heavy  gold,  however,  instead  of  foil,  was  iised  for  adaptation 
to  tooth  surfaces.    When  swaged  on  a  die  and  adapted  to  the 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1177 

tooth,  tlic  cus]!  foi-nis  were  (Icveloiu'd  on  this  rigid  fouuda- 
tion. 

Gohl  inlays  were  made  liy  iircparinn'  tlie  cavity  without 
iiudereiits,  and  into  this  Watts'  crystal  gold  was  moderately 
condensed,  the  filling  being  built  to  general  contour  by  this 
means.  It  was  then  removed  and  the  cavity  surfaces  of  the 
inlay  were  painted  witli  rouge  and  alcohol  to  prevent  the 
solder,  which  was  afterward  flowed  into  the  interstices,  from 
spreading  and  modifying  tlie  form  of  the  inlay  The  origina- 
tor of  this  method  is  not  known  to  the  writer.  Dr.  W.  M 
Griswold  of  Hamburg,  Germany,  described  it  a  number  of 
years  ago,  and  stated  that  he  had  been  using  it  since  1898. 

SLOW   PROGRESS   OF  INLAY   WORK 

Inlay  work  advanced  slowly  because  of  the  prejudice  ex- 
isting in  regard  to  the  use  of  cement  as  a  retention  medium  for 
fillings  of  this  class.  The  objections  urged  against  inlays  in 
general,  both  porcelain  and  metallic,  were,  first,  the  liability  of 
the  cement  to  solution  liy  the  oral  fluids,  and  second,  the 
tendency  of  such  fillings  to  become  displaced  under  sti'ess. 

Three  factors  contributed  largely  to  the  production  of 
botli  classes  of  inlays  under  consideration:  First,  the  intro- 
duction of  the  Custer  electric  furnace  in  1894,  and  of  im- 
proved porcelain  bodies,  revolutionized  and  simplified  the 
making  of  jDorcelain  inlays;  second,  the  methods  of  cavity 
preparation  in  general,  suggested  by  Dr.  Black,  of  opening 
up  cavities  in  order  to  gain  access  to  all  parts,  and  of  de- 
veloping flat  seats  and  parallel  walls  so  as  to  furnish  resist- 
ance form,  largely  overcame  the  liability  to  displacement,  of 
inlays  of  both  gold  and  porcelain,  when  set  and  subjected  to 
stress;  third,  observation  of  cases  where  properly  adapted 
and  correctly  set  inlays  had  been  subjected  to  stress  and  the 
action  of  the  oral  fluids  for  a  considerable  length  of  time,  dis- 
closed the  fact  that  cement,  although  not  ideal,  was  a  reason- 
ably good  retaining  medium,  not  lial)le  to  solution  as  rapidly 
as  was  at  first  deemed  probal)lo,  and  that  under  favorable  con- 
ditions there  was  no  recurrence  of  decay. 

The  improvements  mentioned  in  porcelain  bodies,  and 
means  of  fusing  the  same,  together  with  the  beautiful  results 
accomplished  by  experts  in  this  field,  developed  a  widespread 
wave  of  enthusiasm  in  ceramic  dental  art.  Like  all  new 
things  which  promise  reasonably  good  results  ]iorcelain  be- 
came a  fad  and  was  grossly  misapplied,  not  only  in  the  con- 
struction of  inlays,  but  in  crown  and  bridge  work  as  well. 


1178  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

In  limited  bulk,  porcelain  is  inherently  weak,  friable  and  ex- 
tremely liable  to  fracture  luidor  stress.  These  facts  were 
overlooked,  or  not  recognized  by  many,  with  the  result  that 
many  discouraging  failui'es  occurred.  Warpage  of  the 
matrix,  resulting  in  imperfect  adaptation  of  inlays  to  cavities, 
dithculty  in  matching  the  tints  of  natural  teeth,  with  frac- 
ture and  displacement  of  the  fillings  imder  stress,  were  some 
of  the  discouraging  features  of  porcelain  inlay  work. 

From  flood  to  ebb  tide,  the  wave  of  enthusiasm  in  ceramic 
work  lasted  about  ten  years,  beginning  about  1895,  just  fol- 
lowing the  advent  of  the  Custer  electric  furnace.  It  reached 
its  highest  level  in  1903-4.  Since  the  latter  date  mentioned, 
as  time  and  service  disclosed  the  limitations  of  porcelain  as 
a  filling  material,  its  use  has  gradually  declined.  Its  value  in 
favorable  locations  is  unquestioned. 

PROGRESS   OF   GOLD   INLAY   METHODS 

Meanwhile,  although  less  desirable  from  an  esthetic  stand- 
point than  porcelain,  the  production  of  gold  inlays  rapidly 
increased,  because  of  their  great  inherent  strength  and  wide 
range  of  application.  During  the  period  from  1900  to  1907, 
the  method  of  gold  inlay  production  by  means  of  a  matrix 
gained  in  favor,  technical  steps  improved,  and  the  value  and 
permanence  of  this  system  of  filling  teeth  was  practically 
established. 

One  of  the  greatest  difficulties  met  with  in  the  making  of 
gold  inlays  by  the  methods  then  in  vogue  was  in  warj^age  of 
the  matrix  while  fusing  the  gold  in  it  to  the  desired  contour. 
In  1905,  Dr.  Barnes  of  Cleveland,  Ohio,  demonstrated  that 
by  substituting  1-500  platinum  foil  for  the  1-1000  gold  or 
platinum  foil  then  in  use,  warpage  could  be  practically 
eliminated. 

While  the  matrix  method  of  inlay  production  had  ap- 
proached a  stage  bordering  on  perfection,  the  technical  steps 
involved  were  at  times  tedious  and  sometimes  compli- 
cated, depending  on  the  form  and  location  of  the  cavity  to 
be  filled.  The  production  of  the  matrix  itself,  although  much 
less  trying  on  both  patient  and  operator  than  tedious  filling 
operations,  required  time  and  skill  to  secure  the  desired  re- 
sults.    Some  easier  method,  therefore,  was  sought. 

INCEPTION  OF  THE  WAX  MODEL  METHOD 

The  idea  presented  of  making  a  model  of  the  filling  by 
pressing  wax  into  the  tooth  cavity,  or  a  reproduction  of  it. 


A    BRIEF    HISTORY    OP    PROSTHETIC    DENTISTRY  1179 

This  model,  wlieu  properly  carved  and  contoured,  was  in- 
vested and  cast  in  metal.  Where  or  when  this  idea  originated, 
or  to  wliom  credit  for  it  helongs,  cannot  now,  and  probably 
never  will,  be  determined. 


AN  ANALYSIS  OF  THE  CASTING  PROCESS 

By  analysis,  the  casting  process,  as  applied  to  dental 
operations,  may  be  set  forth  as  follows  -. 

First,  forming  in  a  plastic  material  as  wax,  or  in  wax  and 
metal,  a  model  or  pattern  of  the  ol),iect  it  is  desired  to  repro- 
duce by  casting. 

Attaching  to  the  model,  before  investment,  a  wax  or  metal 
sprue  former  to  form  a  pouring  gaine,  or  sprue,  for  the  injec- 
tion of  the  metal  into  the  mold. 

Enclosing  the  pattern  with  sprue  former  attached,  in  a 
single  mass,  or  a  sectional  mass  of  refractory  material,  capa- 
ble of  setting  in  a  short  time  and  of  withstanding  heat  with- 
out material  change. 

Eliminating  the  wax  from  the  investment  by  some  form  of 
applied  heat,  thus  freeing  the  mold  for  the  introduction  of  the 
metal. 

Fusing  the  metal  in  a  crucible-like  depression  in  the  in- 
vestment, which  is  connected  with  the  mold,  through  the 
sprue;  or  melting  the  metal  in  a  crucible  and  pouring  it  di- 
rectly into  the  enlarged  outer  extremity  of  the  sprue,  through 
which  it  is  conducted  into  the  mold. 

Applying  pressure  to  the  molten  metal  to  force  it  into  all 
parts  of  the  mold,  to  insure  the  production  of  a  sharp  cast- 
ing. 

Some  of  these  various  processes  will  now  be  considered 
in  detail,  after  which  their  application  in  the  production  of 
prosthetic  restoraticms  of  different  kinds  will  be  presented 
somewhat  in  chronological  order. 

FORMING    MODELS   IN   WAX    OF   THE    CASTING   TO    BE 
PRODUCED 

The  construction  of  a  plastic  model,  usually  wax,  of  the 
object  it  is  desired  to  reproduce  in  metal. 

This  princi]ile'is  centuries  old  among  artizans,  and  even 
among  uncivilized  peo])le,  with  some  of  whom  it  was  customary 
to  form  in  wax,  a  model  of  an  implement  and  enclose  it  in  a 
clav  investment.    On  heating  the  clay,  the  latter  was  hardened 


1180  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

and  the  wax  dissipalcd,  tliiis  lca\  iiii;-  a  matrix  oi-  mold  into 
wliicli  the  molten  metal,  usually  copper,  was  cast. 

METHODS  OF  FORMING  A  SPRUE  OR  POURING  GATE 

A  siirue  is  delined  as  follows:  "In  castin.i;-  metal,  one  of 
tile  passages  leading  from  tlie  'skinmiing  gale'  to  the  mold; 
also,  the  metal  wliicli  (ills  tlie  sprne  oi-  sprue  gate  after  solidi- 
lieation,  same  as  dead-iiead."  (('entnry  Dictiiuiary.)  "A 
piece  of  metal  or  wood  used  hy  a  molder  in  making  the  ingate 
through  the  sand."     {K.  IT.  Knight.) 

For  many  years,  in  ))rostlietic  jiroeednres  it  was  custom- 
ary, and  is,  even  at  the  present  time,  in  two-piece  molds,  to  cut 
the  sprue  after  investment  of  the  model.  More  often,  how- 
ever, a  piece  of  wax  is  attached  to  the  patteru  leading  exter- 
nally to  the  outside  of  the  investment  flask,  so  as  to  form  a 
groove  in  both  parts  of  the  investment.  When  the  matrix 
is  separated  and  the  wax  removed,  tlie  groove  thus  formed 
may  be  enlarged  if  necessary  for  the  injection  of  the  metal. 
In  single  investments,  a  piece  of  wax,  metal  or  wood,  of  suit- 
able size  for  the  sprue,  is  attached  to  the  model  before  invest- 
ing, and  removed  after  the  investment  has  hardened.  When 
wax  is  used,  its  removal  is  effected  liy  heat. 

In  Harris,  Ed.  1873,  the  first  suggestion  of  "small  cylin- 
drical wax  gates"  are  mentioned  in  connecticm  with  the  Bean 
process  of  casting.  These  wei-e  enclosed  in  a  single  invest- 
ment to  serve  as  sprue  formers  through  whicli  the  nu'tal  was 
cast  in  attaching  the  teeth  to  the  aluminum  base. 

In  Richardson,  Ed.  1880,  mention  is  made  of  a  tapering- 
sprue  former  of  wax,  in  connection  with  Reese's  cast  base  den- 
tures. The  name  pouring-gaine  is  there  api)lied  to  it.  In  the 
final  investment  of  a  pattern,  the  wax  S2:»rue  form<M'  was  en- 
tirely enclosed,  and  subse(|ueidly  dissipated  in  heating  the 
case. 

ENCLOSING  THE  WAX  MODEL  IN  A  SINGLE  INVESTMENT 

The  object  in  enclosing  a  wax  model  in  a  single  invest- 
ment rather  than  in  a  sectional  matrix  is  to  prevent  fracture 
of  the  margins  of  the  mold,  which  nearly  always  occurs  in 
opening  a  matrix  formed  in  two  or  more  pieces. 

Rough  margins  of  the  mold  result  in  rough  castings,  while 
oftentimes,  even  though  the  margins  may  not  be  fractured, 
slight  contraction  in  the  investment  material,  or  failure  of  the 


A    BRIEF    HISTORY    OP    PROSTHETIC    DENTISTRY  1181 

several  sections  of  the  matrix  to  register  correctly,  will  permit 
the  fused  metal  to  escape  into  the  joint  areas. 

This  fact  has  been  recogiiized  by  many  and  for  the  past 
twent}^  years  or  more  the  single  investment  has  been  gradu- 
ally coming  into  favor. 

ELIMINATING  THE   PATTERN  BY  HEAT 

This  is  a  logical  ontcome  of  the  use  of  wax  for  a  pattern 
and  of  its  enclosure  in  a  single  investment. 

FUSING  THE  METAL  IN  CLOSE  PROXIMITY  TO  THE  MOLD 

The  principal  cause  of  failure  in  casting  operations  is  due 
to  the  metal  when  fused  of  becoming  chilled  and  more  or  less 
sluggish  in  injecting  it  into  the  mold.  This  difficulty  is  spe- 
cially noticeable  when  the  metal  is  melted  in  a  separate  re- 
ceptacle from  which  it  is  poured  into  the  mold. 

To  cast  sharply,  a  metal  or  an  alloy  must  be  superheated 
sufficiently  so  that  after  injection  into  the  mold  it  will  be  in  a 
liquid,  conformable  condition,  in  order  to  become  adapted  to 
irregular  surfaces. 

APPLYING    PRESSURE    TO    THE    FUSED    METAL    TO    INDUCE 
SHARPNESS   OF  DETAIL   IN   THE   CASTING 

Tlie  necessity  for  applying  pressure  in  some  manner  to 
the  fused  metal  to  insure  sliarpness  of  detail  in  castings  was 
recognized  by  Blandy  in  1855,  and  many  others,  since  his  time. 

The  manner  of  api^lying  pressure  to  eliminate  the  air  in 
the  mold  and  permi■^t•he-metaltafillit  perfectly  varies  greatly, 
as  will  subsequently  be  seen. 

Briefly  summed  up.  some  of  these  methods  are  as  follows : 
Gravity,  vibration,  mechanical  pressure,  compressed  air  or 
gas,  partial  vacuum,  centrifugal  force  and  steam. 

PIONEERS   IN   THE   PRODUCTION    OF    CAST   WORK 

The  casting  of  denture  bases  of  tin,  as  stated  on  page 
1132,  was  first  attempted  by  Dr.  Edward  Hudson  of  Phila- 
delphia in  1820,  liy  Dr.  W.  A.  Royce  of  Newbnrgh,  N.  Y.,  in 
1836,  and  by  Dr.  George  E.  Hawes  of  New  York  in  1850. 

Tin  does  not  cast  sharply  by  the  ordinary  or  crude 
methods  employed  in  those  days  and  therefore  the  production 
of  dentures  by  this  method  was  not  very  satisfactory. 

The  introduction  by  Dr.  A.  A.  Blandy  of  an  improved  tin 
alloy  gave  a  decided  impetus  to  casting  methods  since  his  time. 


1182  A    BRIEF    HISTORY    OP    PROSTHETIC    DKNTISTRY 

THE  ^LANDY  CAST  BASE  DENTURE 

The  Blandy  Process  of  casting  metal  base  dentures,  which 
was  presented  in  1856,  was  described  in  Harris,  Ed.  1873,  in 
substance  as  follows : 

A  wax  model  of  the  required  denture  was  formed  in  which 
the  teeth  were  arranged,  mueli  as  for  vulcanite  cases,  a  special 
tooth  being  used  for  this  purpose. 

The  waxed  case  was  enclosed  in  a  two-piece  investment 
composed  of  plaster  and  feldspar.    On  separating,  the  larger 


n  r^? 


rrr" i '  I'l 


TEETH  DESIGNED  FOR   DSE   WITH   THE   BLA^•DY  PROCESS.    1S55 

portion  of  wax  was  removed,  but  the  smaller  portions  between 
the  teeth  were  allowed  to  remain,  being  subsequently  dissi- 
pated in  the  heating  process. 

A  channel  was  cut  in  the  back  of  the  case,  at  least  two 
inches  long,  to  serve  as  a  sprue,  and  on  either  side  vents  for 
the  escape  of  the  air  were  formed.  A  deep  sprue  was  sug- 
gested so  that  when  filled,  the  weight  of  the  metal  therein  con- 
tained would  insure  density  in  the  casting.  In  addition  to  this 
means,  it  was  suggested  that  jarring  the  flask  as  soon  as  the 
metal  was  poured  would  aid  in  tlie  production  of  a  sharp 
casting. 

BEAN'S    METHOD    OF    CASTING    ALUMINUM 

In  1867,  Dr.  J.  B.  Bean  of  Baltimore  formed  denture  bases 
in  wax,  arranged  gum  section  teeth  in  occlusion  and  alignment 
and  carved  the  denture  to  required  form.  The  gum  sections 
were  then  removed  and  a  recess  of  dovetailed  form  was 
carved  in  the  wax  baseplate  to  the  lingual  of  the  pins  to  af- 
ford anchorage  for  the  ,gum  sections  in  final  attachment. 

The  wax  model,  minus  the  teeth,  was  then  enclosed  in  a 
special  flask,  in  an  investment  composed  of  plaster  and 
pumice  stone  previously  boiled,  so  treated  to  form  a  denser 
mass  than  would  result  from  an  ordinary  mix. 

When  the  investment  was  hardened,  the  flask  was  opened, 
the  wax  removed,  the  flask  again  closed  and  thoroughly  heated 
to  evaporate  the  moisture. 

The  flask  was  su])plied  with  three  openings,  one  centrally 
located  to  serve  as  a  sprue  for  the  introduction  of  the  fused 
metal,  and  a  smaller  one  on  either  side  for  the  admission  and 
exit  of  hvdrogen  gas  at  the  moment  of  casting.    At  the  time  of 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 


clearing-  tlio  matrix  of  wax,  grooves  were  cut  from  these  open- 
ings to  the  interior  of  the  mold. 

The  terminal  end  of  tlie  the  sprue  on  the  flask  was  cone- 
shaped,  to  receive  an  extension  sprue,  some  six  inches  long, 
which  was  heated  and  set  in  position  just  before  pouring  the 
metal. 


HI      V.LW    Al'i'LIANC'lO    FOR    CASTING 
ALUMINUM   (REPRODUCED  FROM 
HARRIS  ED.   ISrS) 


When  the  aluminum  was  fused,  hydrogen  gas  was  inti'o- 
dueed  in  the  mold  through  one  of  the  lateral  openings  in  the 
flask,  to  expel  the  air  and  thus  prevent  oxidation  of  the  heated 
metal,  the  extension' sprue  set  in  position  and  the  metal  cast 
into  the  hydrogen  filled  mold. 

As  the  metal  filled  the  mold,  the  hydrogen  escaped  through 
the  other  lateral  opening.  Both  lateral  openings  were  par- 
tially olistruf'tod  by  fine  wire  wliich,  although  permitting  the 


1184  A    mUEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

introduction  of  gas  in  one  and  I  he  escape  of  gas  and  air 
tlirougli  the  otlier,  i)ievented  tlie  escap(!  ol'  tlie  metal  under 
pix'ssure  of  tliat  contained  within  the  hjng  sprne. 

When  cast,  the  baseplate  was  finished,  the  porcelain 
bloclcs  adjusted  in  i)osition  and  attaclied  by  a  second  casting 
process  in  wiiich  a  more  fusible  alloy  was  injected  into  the 
dovetailed  groove  previously  mentioned,  and  iiround  the  jjins 
of  the  teeth. 

In  this  second  step  the  use  of  "small  cylindrical  wax 
gates"  were  mentioned.  These  served  the  purpose  of  sprue 
formers,  were  enclosed  witli  the  baseplate  and  teeth  in  a  sin- 
gle investment,  subsequently  dissipated  by  heat,  and  through 
them  the  low  fusing  alloy  was  cast  under  gravity  pressure 
into  the  groove  and  around  the  pins  of  the  teeth. 

In  these  two  operations  described  by  Dr.  Bean  are  pre- 
sented several  of  the  fundamental  processes  of  casting,  viz., 
in  the  first  steps  are  mentioned  a  wax  pattern ;  its  investment 
in  a  sectional  matrix  of  refractory  material;  injection  of  the 
molten  metal  into  the  mold  under  gravity  jiressure;  in  the 
second  steps  are  mentioned  "cylindrical  wax  gates,"  or  sprue 
formers,  a  single  investment,  or  one  piece  matrix,  and  dis- 
sipation of  the  wax  by  heat. 

SAUER'S  METHOD  OF  CASTING  ALUMINUM 

On  page  630  of  the  Dental  Cosmos,  1873,  is  illustrated 
an  apparatus  designed  by  C.  Saner  of  Berlin,  for  casting  alum- 
inum denture  bases.  This  appliance  resembles  in  manj'  re- 
spects the  Bean  apparatus  which  had  been  introduced  a  few 
years  previously. 

The  points  of  interest  in  this  article  are  the  use  of  an 
alloy  of  aluminum,  recoimiiended  because  it  cast  more  sharply 
than  the  pure  metal,  the  application  of  a  deep  si^rue  to  the 
flask  to  increase  the  pressure  on  the  metal  within  the  mold, 
and  the  casting  of  the  fused  metal  directly  against  the  teeth. 

REESE'S   METHOD    OF   CASTING  TIN   ALLOYS 

In  1879,  Dr.  Gr.  F.  Reese  introduced  a  new  alloy  of  greater 
hardness  than  that  previously  in  use,  which  was  designed  for 
upper  denture  bases.  A  special  flask  of  his  own  design  was 
recommended  for  the  investment  of  the  case. 

HAYFORD'S  METHODS  AND  APPLIANCES 

In  1884,  Dr.  J.  W.  Hayford  of  Xenia,  0.,  patented  an 
appliance  for  casting  Watt's,  Weston's  and  other  fusible  al- 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1185 

loys  then  in  use.  This  ajipliance  consisted  of  a  press  and  a 
flask  having  an  opening  in  its  upper  side  through  which  tiie 
fused  metal  was  poured  into  the  sprue  and  mold. 


DK.    HAIKIKI) 


By  means  of  a  lever  a  plunger  was  pressed  downward 
into  the  flask  and  against  the  fused  metal  and  in  this  manner 
it  was  forced  into  all  parts  of  the  mold  by  mechanical  pressure. 

THE  WATT'S  FLASK 

In  the  latter  part  of  the  80 's,  Dr.  Geo.  E.  Watt  designed 
a  flask  having  two  extensions  in  which  the  sprues  were  formed. 
When  the  cast  metal  was  injected  into  the  mold  the  weight  of 
that  contained  within  the  sprues  condensed  that  within  the 
mold  by  gravity  ])ressnre.     (See  page  224.) 


DR.  MARTIN'S  METHOD  OF  CASTING 

Beginning  about  1889,  and  for  a  num))er  of  years  follow- 
ing. Dr.  G.  M.  Martin  of  Indiana  demonstrated  and  taught  tlie 
method  of  casting  inlays,  crowns  and  bridges  in  the  Indiana 
Dental  College,  and  in  post-graduate  work  in  Indianapolis. 

The  method  was  substantially  as  follows : 

Formation  of  the  pattern  in  wax,  investment  in  refrac- 
tory material  within  a  cuplike  receptacle,  eliminating  the 
wax  with  heat,  melting  the  metal  in  a  crucible-like  depression, 
which  was  connected  with  the  mold  by  a  sprue,  and  casting  the 
fused  metal  by  mechanical  and  later  by  centrifugal  force.  No 
matrix  was  used  in  forming  the  jiattern  in  wax  for  an  inlay. 

The  crucible  and  sprue  were  formed  by  attaching  a  piece 
of  wire  in  case  of  inlays,  or  a  strip  of  metal  plate  in  bridge- 
work,  to  the  curved  side  of  a  section  of  cork,  mounting  the 


Il8t;  A    BRIEF    HISTORY    OF    I'ROSTHKTIC    DENTISTRY 

pattern  at  the  outer  ('xti-ciiiit\  of  the  siii'uc  t'oniu'i-  and  ai)l>ly- 
ing  the  investment  ai-dund  lhe  |iatteni  and  over  tiie  curvf'd 
cork  base. 

THE  CARROLL  METHOD  OF  CASTING  ALUMINUM 

In  1888,  ])r.  ( ".  ('.  Carroll  patented  an  apparatus  i'or 
casting  alnniinnni  deiilure  liases,  bridges  and  crowns.  The 
principal   inipi-oveiiient   <>\'  tlie   method   ovei-   those   in-eceding 


it  was  in  the  use  of  a  sealing  cai)  for  closing  the  crucible,  and 
casting  the  metal  by  ine^ns  of  compressed  air. 

Dr.  Carroll  demonstrated  his  appliances  and  method  of 
casting  aluminum  at  the  World's  Columbian  Dental  Congress 
in  Chicago,  in  ]89;>,  as  well  as  at  ]irevious  times. 


THE  ZELLER  CASTING  APPLIANCES 

In  1891,  the  Zeller  aiipliances  were  introduced.  These 
consisted  of  a  tlask  for  investment  of  the  case,  burners  for 
heating  the  flask  and  fusing  the  aluminum,  and  a  suction  tube 
by  means  of  which  a  partial  vacuum  could  be  created  in  the 


A    BRIEF    HISTORY    OF    PROSTHFTIC    DENTISTRY  1187 

mold.    When  tlie  ease  was  licated  and  the  iiit'tal  fused,  it  wan 
drawn  into  the  mohl  li>'  inoutli  suction  (W  a  suction  bulb. 

THE   FENNER  CASTING  APPLIANCES 

In  1893,  the  Fenuer  appliances  were  introduced.  These 
consisted  of  a  flask  with  attached  crucible  for  investment  of 
the  case  and  holding  the  metal  while  fusing,  of  a  stove  and 
jacket  for  heating  the  case,  a  sealing  cap  fitted  with  a  packing 
by  means  of  which  the  metal  could  be  forced  into  the  mold  by 
compressed  air.  The  writer  used  and  demonstrated  both  wax 
and  metal  s])rue  formers  with  this  aiipliance  as  early  as  1895. 

DR.  HARPER'S  CAST  CROWNS   AND   BRIDGES 

In  1894,  Dr.  W.  E.  Harper  of  Chicago  constructed  cast 
aluminum  bridges  by  the  following  method,  one  special  type  of 
abutment  of  which  will  be  outlined : 

A  molar  tooth  having  a  }n'oxiiuo-occlusal  cavity  was  pre- 
pared by  reducing  its  occlusal  and  axial  surfaces  in  the  usual 
manner  recjuired  for  the  receipt  ion  of  a  shell  crown. 

The  cavity  in  the  tooth  was  prepared  as  for  the  reception 
of  a  tilling,  but  without  undercuts,  the  axial  walls  flaring  out- 
ward slightly. 

An  axial  liand  of  alnminuiu  was  then  fitted  to  the  tooth,  be- 
ing carried  slightly  under  the  gingiva,  the  occlusal  end  being 
left  open. 

Wax  was  i)ressed  into  the  open  end  of  the  band,  directly 
into  the  cavity  against  its  various  walls,  and  over  the  reduced 
occlusal  areas  of  the  tooth,  without  the  interposition  of  a 
matrix. 

The  patient  was  instructed  to  bite  into  the  wax  to  de- 
velop occlusion,  after  which  the  cnsps  were  carved  to  re- 
quired form. 

This  wax-nu'tal  abutment  was  then  united  to  the  dummies, 
which  were  of  wax,  or,  in  some  cases,  of  wax  aud  porcelain 
combined,  a  wax  sjjj-ue  former  attached,  the  whole  piece  in- 
vested in  a  Zellcr  flask,  and  heat<'il  to  dissi])ate  the  moisture 
and  wax. 

The  alumiiuim  was  then  fused  in  the  attached  crucible 
and  drawn  through  the  sprue  into  the  mold  by  partial  vacuum 
force. 

In  sjtecimens  shown  the  writer  in  18i)6  and  subsequently, 
there  api>eared  to  be  perfect  union  between  the  cast  metal  an  1 
the  band. 


1188  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

This  abutment  might  appropriately  be  termed  a  crown 
inlay,  since  it  constituted  not  only  a  crown,  Imt  an  accurately 
iitting  inlay  as  well. 

Dr.  Harper  frequently  demonstrated  and  described  this 
method  of  crown-inlay  construction  at  various  clinics  and  to 
different  individuals  as  well.  He  stated  to  the  writer  as  early 
as  1896  that  he  had  been  successfully  following  this  plan  of 
bridge  construction  in  liis  practice. 

By  analysis  this  metliod  embodies  the  pressing  of  wax 
directly  into  the  tooth  cavity,  and  against  various  tooth  sur- 
faces, in  the  formation  of  the  crown-inlay  pattern,  without  the 
interposition  of  a  matrix,  the  use  of  a  sprue  former  of  wax, 
investment  of  the  pattern  in  refractory  material,  dissi])ating 
the  wax  by  heat,  casting  tlie  fused  metal  into  tlie  matrix  by 
vacuum  force. 

THE  ALEXANDER  METHOD  OF  CASTING  INLAYS 

Reference  has  previously  been  made  to  Dr.  C.  L.  Alex- 
ander's method  of  forming  inlays.  His  first  paper  on  "Cast 
ing  Fillings  and  Abutments  for  Bridges"  was  reported  at  a 
meeting  of  the  Southern  Dental  Association,  held  at  Asheville, 
N.  C,  in  July,  1896.  The  discussion  which  followed  clearly 
brought  out  the  fact  that  the  durability  of  the  cement  by  which 
inlays  were  held  in  place  was  still  a  point  not  yet  determined 
by  experience,  and  many  in  the  profession  opposed  the  ap- 
plication of  inlays  on  this  ground. 

The  "casting  of  fillings,"  however,  was  "in  the  air,"  and 
the  possibilities  in  this  field  were  beginning  to  be  recognized. 

THE  HOLLINGSWORTH   METHOD  OF  CASTING 

In  the  American  Text  Book  of  Prosthetic  Dentistry,  pages 
669-70,  Ed.  1896,  is  described  the  Hollingsworth  method  of 
casting  bridge  dummies,  the  patterns  of  which  were  composed 
of  wax,  wax  and  paraffin,  or  wax  and  gutta  percha. 

The  pattern  after  being  carved  to  correct  occlusion  and 
form  between  the  two  abutments,  was  removed.  To  one  end 
was  attached  a  cylindrical  piece  of  wax  about  one-eighth  of  an 
inch  in  diameter,  to  serve  as  a  gate  or  sprue  former. 

A  shallow,  oblong,  sheet  iron  pan,  to  which  a  handle  was 
attached,  was  used  as  a  table  on  which  to  invest  the  case. 

The  investment,  composed  of  a  mixture  of  plaster  and 
marble  dust,  was  mixed  to  medium  thin  consistency,  the  pan 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1189 

filled  with  it  and  the  wax  pattern  with  sprue  former  attached, 
laid  on  it  near  one  end,  and  covered  over  to  the  depth  of  about 
one-half  inch. 

The  investment  in  the  other  end  of  the  pan  was  not  con- 
toured hut  left  flat,  and  when  hardened  a  depression  or  shal- 
low crucible  was  formed  in  this  surface  and  connected  by  a 
groove  with  the  exposed  end  of  the  sprue  former,  tlie  invest- 
ment around  which  was  removed  to  form  a  funnel-shaped 
opening  for  the  ready  entrance  of  the  gold  into  the  mold. 

All  surfaces  were  cleared  of  debris  and  the  case  heated  to 
dissipate  the  moisture  and  wax. 

In  the  crucible  depression,  gold  scrap  or  plate  was  placed 
and  with  a  blowpipe,  brought  to  a  thoroughly  li(|uid  condition, 


THE    KIKST  HOLLINGSWORTH    ArPLIANCK    FOR    lASTI.NU    GOLD    DIJIMIES 

when,  by  tipping  the  pan  in  an  upright  position,  the  gold  was 
cast  into  the  mold  by  gravity. 

In  1902,  Patent  No.  708^811  was  issued  to  Dr.  M.  W.  Hol- 
lingsworth  for  a  machine  for  forcibly  casting  dental  bridges. 
The  fundamental  principle  of  this  machine  resembled  some- 
what his  first  crude  appliance,  previously  described. 

This  appliance  consisted  of  a  base  provided  with  a  hinged 
table,  on  which  the  investment  rested.  Through  the  bottom  of 
the  table  projected  a  sprue  former  of  brass,  having  a  reduced 
upper  extremity  to  which  the  wax  model  was  attached.  A 
metal  hood  for  supporting  the  sides  and  outer  end  of  the  in- 
vestment was  adjusted  to  the  table,  and  which,  being  adjust- 
able, permitted  the  investment  to  be  closely  applied  to  the 


A    BRIEF    HISTORY    OF    PROSTHP^TIC    DENTISTRY 


pjittcrii  and  thus  exclude  the  air,  at'tei'  wiiirh,  wliihr"  tlu;  invest- 
ment, was  still  soft,  the  IukxI  was  adjusted  and  filled. 

When  hardened,  the  sprue  former  was  removed  and  a 
stick  of  carbon  of  corresi)onding  size  was  inserted  into  the 
opening. 

In  investing  a  ease  in  tliis  ajipliance,  tlie  crucible  for  melt- 
ing the  gold  was  formed  in  one  end  of  the  table,  being  con- 
nected with  the  sprue  by  a  lateral  groove  and  opening. 

When  the  investment  was  thoroughly  dry  and  heated,  and 
the  wax  dissi])ated,  gold  was  placed  in  the  crucible,  where  it 
was  fused. 


THE    Hor.l.INXiSWOUTII     I'll] 


By  means  of  a  lever  device  the  hinged  tal)le  was  raised  to 
an  upright  position.  This  movement  cast  the  gold  into  the 
si)rue  and  mold  liy  gravity. 

When  the  table  was  in  nearly  an  upright  position  the  outer 
end  of  the  carbon  was  brought  in  contact  with  a  cam  surface 
of  the  base,  thus  pressing  it  forward  into  the  sprue  and  forcing 
the  gold  into  the  mold  by  mechanical  pressure. 

These  processes  involve  a  wax  model,  enclosed  in  a  sin- 
gle investment  of  refractory  material,  a  removable  metal 
sprue,  formation  of  a  crucible  depression  in  the  investment, 
dissipation  of  the  wax  model  by  lieat,  fusing  and  casting  the 
gold  under  both  gravity  and  mechanical  iiressure. 


A    BRIEF    HISTORY    OF    PROSTHP^TIC    DKNTISTRY  1191 

FLASK   DESIGNED  BY   THE  WRITER 

In  litOO,  the  writer  designed  a  flask  for  casting  aluiniiuun 
in  wliicli  a  metal  sprne  former  was  used  in  conjunction  witli  a 
wax  model  enclosed  in  a  single  investment. 

Tlie  metal  was  melted  in  an  attached  crucil)le  and  forced 
into  the  mold  with  a  metallic  piston  which  fitted  the  interior 
of  the  crucible.  Because  of  difficulty  at  times  resulting  from 
tiie  piston  becoming  locked  within  tlie  crucible  chamber,  a 
sealing  cap,  with  tube  attached,  was  substituted  and  l>y  tliis 
means  the  fused  metal  was  injected  into  the  mold  with  com- 
pressed air,  and  also  steam  pressure.  These  flasks  were  used 
for  some  time  in  the  teclinic  laboratories  of  the  Northwestern 
I'niversity  Dental  Scliool  l^y  Dr.  Wahlhcrg,  Dr.  Mctlivcn  and 
the  writer. 

DR.   PHILBROOK'S    METHOD    OF    CASTING    INLAYS 

Between  189(5  and  liH)."),  Dr.  H.  F.  IMiilhi-ook  of  Hennison. 
la.,  developed  a  system  of  casting  inhiys  whicli  in  substance 
was  as  follows: 

In  his  first  efforts,  l)etween  the  jieriod  from  1896  to  about 
18.9S,  he  formed  a  model  of  the  desired  filling  by  pressing  wax 
into  the  cavity  of  a  tooth,  reprcnluced  in  the  usual  way,  in 
plaster.  This  is  known  as  the  indirect  method.  From  1898 
and  thereafter  he  formed  the  filling  by  pressing  the  wax  di- 
rectly into  tlie  natural  tooth  cavity,  without  the  interjiosition 
of  a  matrix,  and  carved  it  to  the  required  form. 

To  each  extremity  of  the  inlay  a  cylindrical  piece  of  wax 
was  attached,  one  to  serve  as  a  sprue  former,  the  other  to 
form  a  channel  thi'ongh  which  to  clear  out  the  wax. 

'I'lie  pattern  and  extensions  were  then  invested  in  refrac- 
tory material  in  a  ring  in  such  manner  as  to  exclude  the  air, 
the  sprue  former  occupying  a  central  position,  the  other  ex- 
tension situated  near  one  side. 

When  the  investment  had  set,  it  was  trimmed  out  aroniul 
the  sjirue  former  to  form  a  crucible-like  depression  in  which 
to  melt  the  metal. 

With  a  bulb  syringe,  hot  water  was  forced  iuto  the  sprue 
aiid  mold,  and  out  the  side  channel,  thus  freeing  the  mold  and 
openings  leading  to  it  of  the  greater  bulk  of  wax. 

The  invested  case  was  heated  to  ex])el  the  moisture  and 
any  remaining  wa-x  present,  the  metal  placed  in  the  crucible, 
fused  with  a  blowpipe,  and  forced  into  the  mold  as  follows: 

A  sealing  cap  consisting  of  a  metallic  disc  of  larger  diam- 
eter than  the  investment  ring,  having  attached  an  asbestos 


1192  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

packing  for  sealing  against  the  escape  ui'  air,  was  pressed 
firmly  and  evenly  down  upon  the  upper  end  of  the  ring. 

Through  a  tube  of  metal  which  was  attached  to  the  upper 
central  side  of  the  disc,  air  was  forced  by  moutli  pressure  into 
the  crucible  containing  the  fused  metal,  thus  injecting  it 
through  the  sprue  into  the  mold. 

By  1904,  several  important  modifications  in  tlic  al)i)v<' 
methods  were  made  b.y  Dr.  Philbrook,  viz.,  tiie  use  of  a  metallic 
sprue  former,  the  designing  and  use  of  a  metallic  crucible 
former,  dissipation  of  the  wax  by  dry  heat  or  fiame,  a  sealing 
cap  containing  moist  asbestos,  the  steam  from  which,  wlien 
heated  and  confined,  injected  the  fused  metal  into  the  mold. 

The  methods  and  ap]iliances  employed  l)y  Dr.  Philbrook. 
from  1896  to  1905,  inclusive,  may  he  briefly  summed  up  as 
follows : 

A  model  formed  without  a  metal  matrix ;  both  liy  the  in- 
direct method  of  pressing  wax  into  a  plaster  model  of  the  pre- 
pared tooth  and  cavity,  and  by  the  direct  method,  by  pressing 
the  wax  directly  into  the  natural  tooth  cavity ;  the  use  of  both 
wax  and  metal  sprue  formers;  a  metallic  investment  ring; 
metal  as  well  as  wax  sprue  formers  for  supporting  the  pattern 
and  forming  the  sprue;  investment  of  the  wax  ]iattern  in  a 
single  mass  of  refractory  material ;  dissipation  of  the  wax  by 
hot  water  in  some  cases,  dry  heat  or  flame  in  others ;  fusing 
the  metal  in  the  crucible  depression  of  the  investment  in  the 
upper  end  of  the  ring;  injecting  it  into  the  mold  Ity  com- 
pressed air  or  by  steam  pressure. 

DR.   SCHLOTTER'S   CLINIC 

In  1904,  Dr.  Jacob  Schottler  at  Manitowoc,  Wis.,  gave  a 
clinic  before  the  Wisconsin  State  Dental  Society  on  cast  gold 
inlays,  in  which  successful  castings  were  shown,  made  by  grav- 
ity pressure.  This  clinic  demonstrated  the  method  he  em- 
ployed in  his  practice. 

THE  LENTZ  CASTING  PROCESS 
In  August,  1905,  Dr.  John  A.  Lentz  of  Pluenix,  Ariz., 
applied  for  a  patent  for  a  "process  for  forming  dental  struc- 
tures," which  patent  was  granted  in  October,  1906.  Briefly 
described,  his  processes  are  outlined  as  follows:  "My  inven- 
tion relates  to  such  dental  work  as  making  inlays,  onlays, 
crowns,  bridges,  artificial  dentures  and  other  dental  structure, 
or  certain  parts  of  the  foregoing." 

He  iTientions  specifically  his  method  of  preparing  a  molar 


A     BRIKF    HISTORY     OF    PROSTHETIC    DENTISTRY 


1193 


tooth  for  a  crown  in  tlie  usual  manner,  to  which  was  fitted 
a  properly  contoured  band.  A  iilastic  impression  material 
was  then  placed  on  the  occlusal  end  of  the  band,  forced  between 
its  inner  walls  and  the  axial  surfaces  of  the  tooth  and  against 
its  occlusal  surface  as  well,  without  the  interposition  of  a 
metal  matrix.  By  closing  the  jaws  in  various  positions,  clear- 
ance paths  for  the  opposing  cusps  were  developed,  after 
which  the  cusps  were  carved  to  desired  form. 

The  crown  was  then  removed  and  inclosed  in  a  suitable 
investing  material  in  a  two-])iece  i-iiig.    On  wanning  and  sep- 


THE  I.ENTZ  l-ASTIXG    APPUANTE 

arating  the  latter,  the  plastic  material  which  lined  the  in- 
terior of  the  band  and  of  which  the  cusps  were  formed  was 
removed.  In  one  portion  of  the  ring  the  root  sides  and  end, 
reproduced  in  investment  material,  were  thus  exposed  within 
the  enclosed  gold  band,  while  in  the  other  part  of  the  ring  the 
investment  presented  the  reverse  of  the  carved  cusp  surfaces. 
The  casting  was  accomplished  by  drying  and  heating  the 
investment  in  the  two  halves  of  the  ring,  placing  an  excess 
amount  of  gold  in  the  cusp  depressions,  where  it  was  fused, 
while  i)ressure,  sufficient  to  force  it  into  all  parts  of  the  mold, 


ll'.M  A    BRIEF    HISTORY     OK    I'R(JSTHETIC    DENTISTRY 

wjis  (lc\('l()j)('(l  by  dropiniiii'  the  Icxcf  ol'  the  iiioldiiii^  nuu'hino 
down  until  the  two  liaKcs  of  the  riii^  touched  and  registered. 
By  this  process  the  fused  gold  was  adapted  to  all  the  in- 
e(|nalities  of  the  root  surfaces,  as  rejiresented  in  the  investment 
material  within  the  ring-,  and  when  properly  linished,  lilted  tiie 
root  closely.  Modelini;'  comiiouml  or  wax  was  used  as  the  im- 
pression material. 

THE  OLLENDORF  CASTING  PROCESS 

In  1906,  or  previously,  Dr.  OUendorf  of  Breslau,  Ger 
many,  presented  appliances  and  described  a  system  for  cast- 
ing crowns,  bridges  and  dentures  under  pressure.  He  used  the 
disa])pearing  wax  model,  enclosing  it  in  an  investment  of  silex 
and  i)laster.  Gravity  force  for  producing  jiressure  on  the  gold 
in  casting  was  employed,  as  in  some  of  the  ])receding  methods 
mentioned.  This  method  was  described  by  Dr.  Sachs  in  a 
pai)er  read  before  the  American  Dental  Society  of  Kurope, 
August,  1906.     (Dental  Review,  March,  1907.)  " 

SUMMARY   OF  PROGRESS  IN  CASTING  OPERATIONS 

Thus  it  a])pears  that  the  live  fundamental  principles  in- 
volved in  the  casting  i)rocess  as  practiced  to-day  were  widely 
known  and  utilized  prior  to  1907  in  crown,  bridge  and  denture 
construction,  and  the  casting  of  inlays  was  practiced  by  a  con- 
siderable number  of  individuals  with  greater  or  less  success. 

That  experiments  had  been  and  were  being  conducted 
along  these  lines  by  a  considerable  number  of  individuals  is 
uni|uestioned.  The  results  of  these  efforts  were  frequently 
gratifying,  but  sometimes  disappointing,  due  largely  to  a  lack 
of  exact  knowledge  of  the  physical  properties  of  materials 
employed. 

CAUSES  OF  FAILURE  IN   CASTING  OPERATIONS 

In  the  light  of  present  knowledge,  the  causes  of  failure 
in  some  of  the  pioneer  efforts  with  cast  inlays  were  due  to 
dimensional  changes  in  the  wax  model  during  and  after  form- 
ing it,  this  material  being  very  susceptible  to  temperature 
variations,  to  impurities  present  in  the  wax  which  remained 
as  a  residue  in  the  matrix,  and  failed  to  volatilize  on  heating; 
to  changes  in  the  investment  under  heat ;  but  principally  in 
failure  to  render  the  gold  suliliciently  plastic  to  cast  sharply. 

Although  it  is  possible  to  superheat  gold  to  a  sufficient 
degree  to  cast  sharply,  by  means  of  the  ordinary  ))lowpipe, 
still,  under  some  conditions,  it  is  a  difficult  task. 


A    i,RlEF    HISTORY    OF    PROSTHETIC    DENTISTRY  liy^ 


THE   OM.ENDORF    CASTIXC    APIMJAXCES 


1190  A     BKIP^F    HISTORY    OF    I'KOSTHETIC    DENTISTRY 

Had  the  pioneers,  in  llic  castin.iz,'  of  ]irostlietic  substitutes 
in  gold,  recognized  the  great  value  and  effieieucy  of  the  Knapp 
nitrous  oxide  and  gas  blowpipe  which  was  introduced  about 


l.l.dUI  II  L 


1890,  work  in  these  lines  would  have  progressed  rapidly,  and 
the  problem  of  casting  inlays  and  various  prosthetic  appli- 
ances would  have  been  practically  solved. 


DR.   TAGGART'S    METHOD   OF   CASTING   INLAYS 

In  1907,  Dr.  AV.  H.  Taggart  of  Chicago  made  application 
for  patents  on  various  processes  and  "Apparatus  for  making 
models  for  the  casting  of  dental  inlays  and  the  like,"  "Method 
for  making  models  for  dental  inlays  and  the  like,"  "Method 
for  making  dental  inlay  fillings  and  the  like,"  "Apparatus  for 
making  castings."  The  first  two  patents  were  granted  in 
1907,  the  last  two  mentioned  in  1911. 

Briefly,  the  steps  of  producing  an  inlay  by  the  Taggart 
method  are  as  follows: 

A  pattern  of  the  desired  filling  is  made  by  pressing  wax 
directly  into  the  prepared  tooth  cavity,  without  the  interposi- 
tion of  a  matrix,  and  carved  to  required  form. 

The  pattern  is  mounted  on  a  metallic  sprue  former,  which 
rests  in  and  is  supported  by  a  metallic,  dome-shaped  crucible 
former. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1197 

A  mix  of  refractory  investment  material  is  made  and 
carefully  ai)plied  around  tlie  wax  model  in  such  manner  as  to 
eliminate  the  air. 

The  investment  ring  or  flask  is  then  set  on  the  crucible 
former  and  its  interior  filled  with  investment  material,  thus 
surrounding  tlie  previously  coated  model. 


17         -        15 

THE  TAGGART  CASTING  .yPI.IAXCKS 


Wlien  the  investment  lias  hardened,  the  crucible  former 
and  sprue  former  are  removed. 

The  invested  case  is  then  heated  to  expel  the  moisture  and 
dissipate  the  wax. 

The  flask  or  investment  ring  is  then  set  in  the  depressed 
base  of  the  casting  macliine.  the  metal  placed  in  the  crucible 
depression  of  the  investment  and  fused  with  the  flame  from 
an  attached  blowpipe  of  the  nitrous  oxide  and  gas  type. 

When  fused,  the  i^lunger  which  carries  a  sealiug  cap  ou 
its  lower  end  is  brought  forcibly  down  upon  the  upper  end  of 
the  flask,  thus  preventing  escape  of  the  nitrous  oxide  gas. 


lUlS  A     liRlKK    HISTORY     OK    I'UOSTHIOTK;    DIONTISTRY 

wliicli   is  autoiiiiiticjillx-   ;i(linittc(l   at    llic   time  (if  scaling'  tlic 
enu'ible  space. 

TTnder  coinprcssioii  of  the  ,i;as,  the  fiiseil  metal  is  forced 
through  the  sjirue  into  the  mold. 

The  essential  principles  iii\dl\cd  in  this  i)i-ocess  iriay  l)e 
Itriefly  summed  uj)  as  follows: 

A  wax  model  formed  with  or  without  a  metallic  matrix, 
an  investment  ring,  a  metallic  sprue  former,  a  metallic 
crucible  former,  a  sealing  cajj  for  confining  the  compressed 
gas,  a  single  investment  matrix,  dissipation  of  the  wax  i)attern 
by  heat,  injecting  the  fused  metal  into  the  mold  by  com 
])ressed  gas. 

The  discovery  by  Dr.  Taggart  that  in  order  to  cast 
shar])ly  gold  must  be  superheated,  constitutes  the  most  valu- 
able contribution  to  the  casting  i)rocess  introduced  within  re- 
cent years. 

This  he  accomplished  and  demonstrated  by  means  of  his 
casting  appliances  to  which  a  blowpipe  of  the  Knapp  pattern 
was  adapted.  With  the  Taggart  appliance  or  the  Knapp  blow- 
pipe, gold  in  small  quantity  can  be  readily  heated  several  hun- 
dred degrees  above  its  melting  point. 

In  using  either  of  these  appliances,  care  must  be  observed 
not  to  overheat  the  gold  or  hum  it.  When  excessively  over- 
heated, even  pure  gold  is  slowly  but  gradually  dissipated, 
while  if  composed  of  an  alloy  some  of  the  lower  fusing  con- 
stituents will  be  oxidized  or  volatilized,  thus  impairing  the 
quality  of  the  metal  for  specitic  j^urposes. 

Again,  in  superheating  the  gold  excessively,  the  invest- 
ment deteriorates,  resulting  in  rough  surfaces  in  the  mold, 
change  in  form  of  the  latter,  and  in  some  cases  intimate  union 
of  the  investment  with  the  casting. 

By  means  of  an  ordinary  gas  blowpipe,  with  a  free  inlet 
for  both  gas  and  air,  and  means  for  controlling  the  same,  to- 
gether with  a  strong  pressure  of  air  such  as  can  be  developed 
with  a  large  foot  bellows  or  power  pumjj,  equally  good  results 
may  be  accomplished  without  danger  of  dissipating  the  gold 
or  impairing  the  investment.     (See  page  1050.) 

RECENT   APPLIANCES 

Within  recent  years  many  devices  in  which  some  of  the 
older  methods  of  pressure  mentioned  were  employed  have 
been  introduced,  two  of  which  will  be  described. 


A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY  1199 

THE  SOLBRIG  CASTING  PLIERS 

'I'his  devic'i^  consists  of  |ilit'i-  liainllcs;  to  the  shorter  (MkI 
of  one  is  attaolied  a  pad  coiitainiiiu,'  moidiiu'  or  moist  asbes- 
tos. 'Pile  ojii)osite  beak  coiitains  a  depression  in  whioli  rests 
the  investment  ring'.    When  t'liseil,  the  metal  is  foreed  into  tlie 


LURKi    CASTING    AI'PLIANCE 


mold  by  closing  the  plier  handles,  thus  Ijringing  the  pad  at- 
tached to  the  opposite  beak  in  contact  with  the  ring  margins 
and  sealing  the  crucil)le  chamber.     (Ash's  Quarterly,  1910.) 

THE  BIBER  CASTING  APPLIANCE 

This   consists   of  a   base  for  snjjporting  tiie   investment 
ring,  and  a  cup  device  containing  moldine  or  clay. 


THK  IJIBEU  CASTI.NG  APPLIANCE   (ASH'S 
(lUARTERLT.  1910.  SLIGHTLY  MODIFIED) 


When  the  gold  is  fused,  the  caj)  is  applied  to  the  ring  and 
the  metal  forced  into  the  mold  liv  hand  pressure. 

From  this  brief  outline  of  casting  operations  in  the  past, 
the  names  of  a  number  of  men  who  engaged  in  this  work,  to- 


l:iOO  A    BRIEF    HISTORY    OF    PROSTHETIC    DENTISTRY 

gether  with  a  description  of  their  methods  and  appliances, 
have  been  omitted  for  laclc  of  time  and  space. 

The  writer  has  attein])ted  to  present  in  a  concise  and  dis- 
passionate manner  those  facts  which  lie  has  been  able  to  care- 
fulh^  gather  from  reliable  sources,  pertaining  to  the  inception 
and  growth  \\\)  to  present  development  of  the  five  funda- 
mental principles  of  the  casting  jorocess. 

That  the  science  of  precision  casting  is  yet  imperfect  is 
evident  since  the  control  of  dimensional  changes  in  tlie  ma- 
terials used  lias  not  yet  been  accomplished. 

By  simplest  means  and  with  crudest  appliances  some  arc 
able  to  secure  results  equal  to  the  best.  Others,  ecpiipped  with 
the  most  convenient  and  improved  apparatus  meet  with  fre- 
quent failures.  Personal  equation  in  this  as  in  many  other 
fields  largely  determines  the  (piality  of  results  attained. 

From  this  outline  it  will  also  be  seen  that  the  development 
of  the  five  fundamental  principles  of  casting  as  practiced  to- 
day is  the  result  of  the  composite  effort  of  many  men,  extend 
ing  over  a  period  of  many  years.  Practically  all  of  the  proc- 
esses had  become,  and  most  of  them  were  long  ago  recognized, 
as  heritages  of  the  profession,  since  time  and  use  had  rendered 
them  more  or  less  common  methods  of  ]>rocedure. 


INDEX 


Absorption    of   alveolar    borders. ..  .18-22 

irregular    191 

under   stress    497 

unequal 320 

Abutments,     in    engineering     bridge 

construction    783 

in    dental    bridgework 781) 

preparation      of      roots      and 

teeth   for    795 

selection     of     suitable     roots 

and    teeth   for 790 

Acid    for    pickling    169 

Adaptation,      denture,      comparative 

results    with     different    bases 126 

Adhesion,    physics   of 24 

useful    in   denture    retention 24 

Adjusting    the    face    boiv    to    occlu- 
sion models  and  face 330 

to   occluding   frame 332 

Affinity   of  metals   for   each  other...  1000 

Alabaster     43 

Alexander,    Dr.    A.    C,    denture    re- 
pair        573 

Alexander,  Dr.  A.  C,  method  of  re- 
pairing   vulcanite     673 

Alexander,    Dr.    C.    L.,    inlays.  .1174-1176 
Allen,    Dr.    John,    continuous   gum... 

590,    901,   902,  905 

Alloys     999 

affinity  of  metals  for  each  other.lOOO 

binary    1014 

copper  amalgam   1O02 

dental    amalgam    1001 

eutectic    1001 

for     crown,     bridge     and     plate 

work    1026 

for   inlay   casting    1030 

for  prosthetic   casting    1028-1029 

for  tempering   1067 

Matthiessen's    theory    of 9i)9 

specific   gravity   of 1002 

triple     135 

Alloying    metals,    object    in 1000 

Alpha    rays   of   radium    963 

Alumino-thermy    992 

Aluminum     1079 

denture    bases     120 

cast    191 

swaged     212 

physical    properties    of 1080 

Alveolar  borders    IS 

absortion    of    18-22 

adapting  base  plates  to 313-320 

reduction  of  flabby 19-20 

selecting  and  fitting  trays  to....     64 

Amalgam     1001 

dental,  history  of 1169 

dies,   In  crown  work 664 

restoi-ation     of     badly     decayed 

teeth  with   736 

Ambler.    Dr.    H.    L 1111 

Ames,   Dr.   W.  V.   B.,  inlays 1173 

Ansesthetics.    local 630 

Analysis  of  the  casting  process 1179 

Anatomic     and     esthetic     forms     of 

teeth    631-633 

Anatomic    method    of   denture    con- 
struction      , 304-463 

masticatory   mechanism    269 

Anchorage,      of     te^th     to     various 

bases    525 

of    plastic    substances    to    metal 

bases    174 

In   restorations   for  crowns 736 

for    Inlays    934 


Ancient,    prosthesis    history    of 1101 

records    of    1110 

prosthetic  appliances    1105 

Anderson,  Dr.   C.   L.,  bridge 796-840 

Angle,    Dr.    E.    H.,    impression    trays     73 

Annealing    metals    168-984 

An  outline  of  metallurgy 960 

Anterior,   teeth,    bridges   for 792-807 

cla.ssiflcation    of    807 

crowns    for    640 

palatine    foramina    11 

typal    forms    of     362 

."Antimony     1090 

Antiquity    of    Ebers'    papyrus 1102 

Aphrodite    facial    outlines 371 

Appliances,     in    die    and    counterdie 

construction     128 

anatomical,     Gysi 465-1148-1149 

Snow     308-1144-1145 

Application,     of    bridge    restorations  786 

of  crown   replacements 625 

of  full  dentures 304 

of  heat  in   soldering 995 

of  occlusion  rims  to  base  plates  314 

of   porcelain    609-SSS-S96-922 

of   face   bow 330 

Aqueous  solutions,   separating  medi- 
ums          94 

borax   and    shellac    94 

soap     95 

Arch,   alveolar    291 

bar,     palatal 522 

in  engineering  783 

palatal     10 

Argol    1058 

Arranging    and    occluding    the    teeth 

in    full    dentures    382 

Arrhenius,      Prof.      Svante,      nebular 

temiperatures     976-994 

Articulation,    tempero-mandibular. . .   274 

of     sound 401 

Articulators 

Bonwill    1138 

Christensen      1145 

Evans     1137 

Gariot      1136 

Gritman    1143 

Gvsi     465 

Hayes     1139 

Kerr    1144 

Luce     1150-1151 

Plain    line    1138 

Plaster     1136 

Schwarz    1147 

Snow     1146 

Starr     1139 

Walker    1141 

Artificial,     dentures,     physical     and 
mechanical    problems    involved    in 

their   construction    23-304 

stone     110-495 

Artistic   judgment   necessary   in   de- 
veloping   wax    model    dentures....   396 

Asbestos,    for    investment 689 

Ash's  tube  teeth   529 

Assembling   bridge,    structural   parts 

of    a    829 

crown      687 

.atmosphere     24 

aid    in    denture    retention 1'i 

pressure    exerted    bv    25 

Atomic     weight .' 980 

unit  of  980 

Atomic  relation  of  elements  to  each 

other     971 

Atoms     969 

vibration    of     969 


1201 


Attaching,    bite     fork    to    occlusion 

model     ;i26 

ancliorage    loops    to    metal    base 

dentures    177 

casts  to  occluding  frame 333 

clasps  to  baseplate 188-268 

facings    to    crowns   and    bridges, 

in  repairs   863 

peripheral      shoulder      wires      to 

metal  bases   175-4S9 

teeth   to   baseplate,    by  soldering  188 
Attachments,  for  retention  of  partial 

dentures    233 

clasps 236-500 

specialized         frictional        appli- 
ances     305-525 

for  bridges    S32  to  858 

Carmichael     832 

modified    836 

Corcoran     835 

Goslee,     inlav     clasp 851 

Heddy    840 

split  dowel   crown    845 

St   John   inlay    936 

telescoping  crown  . . . : 844 

Autogenous    soldering,    (sweating) . .   995 
Automatic,   blowpipes,    Knapp,    Tag- 

gart     958 

flask    closing    devices 446-454 

gas  regulators    452 

safety   valve    453 

Babbitt    metal    134-1087 

Backing,  porcelain  facings,  in  crown 

and    bridge    work    682 

Bailey    flask    129-156 

Bak  iiig,  of  porcelain 

615-878-885-888-897-926 

Balancing  contact    

299-307-317-334-391-404 

Banded,    crowns    

. . .      640-721-733-735-S44-S48-S73-S81-8S3 

Bar,   forms   of  lingual  bars 491 

contact     506 

lingual,  combined  with  gold  sad- 
dles       496 

palatal    arch    622 

Barium      968 

Barns.    Dr.,    inlay.s 1178 

Bartlett.   Dr.   Walter  M 38-622 

Base    metals     980 

Baseplates    118 

celluloid     123 

ideal    126-230 

metal    119-126-166-1S0-208-222-588 

requirements    of    313 

Bases   for  artiflcial   dentures lis 

alu!ninum     120 

alloys  of  tin    120 

celluloid     125 

comparative    results    in    adapta- 
tion     126-127 

gold     lis 

platinum      119 

vulcanite      121-127 

Basic    ingredients   of   porcelain 904 

constituents  of   rubber 436.439 

Bean,    Dr.   .1.   B 218-1157,    1182 

Beautv.    science    of 360 

Beeswax    59-946 

Bennett,  Dr.  N.  G 299-1148 

Benson.    Dr.    C.    W 750 

Bequerel     Radium 963 

Berdmore    1123 

Beryllium     967 

Bessemer    steel 1066 

Beta    rays    903 

Bevan,   Dr.,   experiments   in   vu)can- 

izlng     43S 

Beveling    681 

Biber    1199 

Bilious     356 

Binary    1014-1026 

Bing  ' 1162-1167-1171 

Birkland,  Dr.   J.   W 769 

Birmingham    wire    gauge 1094 

Bismuth     1089 


Bite     fork     326 

modified     675 

Bite,  meaning  of  term 327 

difficulty    in    taking     327 

practical   method   for   securing. .  329 

various    methods    of    such 327-330 

Black,    Dr.    O.    V 

IS,   125,  278,  305,  306,  931,  1156 

Blanch    Barkley,    nugget 1005 

Hlandy,  Dr.  A.  A 227-1182 

Blocks,    porcelain. 532-620-621-622-1127 

Blowpipe 

flame,    structure   of 996-1198 

Knapp's    nitrous    oxide 958 

Stiver's    gas    692 

Bodily     functions 7 

impairment    of    8-397 

Bogue,    Dr.   E.  A 1171 

Bonwill,  Dr.  W.  G.  A : 

. .  238-273-308-1137-1138-1141-1142-1159 

Borax     1057 

Boron     967 

Boser's    rule    1010 

Bowditch     283 

Brantt    436 

Brass    1078 

Bridgeford,     Dr.,     rubber    paste    for 

repairs     586 

Bridges    (Engineering) 783    to    7S6 

arch     783 

cantilever     785 

girder     784 

Howe    truss    784 

pontoon      785 

suspension    785 

Bridges    (Dental)    786    to    856 

fixed    786 

classification     of 786-798 

extension 789,    1166 

saddle     787 

.sanitary     789 

removable     841 

repair  of  856 

Bridgework   (dental) 786  to  856 

fixed    786    to    841 

abutments   and    piers 790 

preparation  of  teeth  and 

roots     for 795 

selection      791 

constructive     technic 823 

factors    to    be   considered    in 

planning    790 

history    of    1162 

means    of    attachment    other 
than    crowns 

Oarmichael     832 

modified      835 

Corcoran     835 

Heddy      840 

inlays     797,    939 

St.    John     936 

removable    841  to  856 

attachments    842 

inlay     851 

lingual     half     crown 852 

split    dowel    845 

telescope    crown    844 

modifications   of    ....   855 

repair    of     856    to    872 

Brief  outline  of  recent   discoveries..   962 

Britannia     35-1090 

Bromine    967 

Bronze      1079 

Brophv,   Dr.  R.   C 220 

Brown,  Dr.  E.  P 1161 

Brown  and   Sharp    1094 

Briick,    Dr.    W.    W 1170 

Bryant    repair   system 861 

Buckingham.     Dr 54 

Bunsen    burner    997 

Burchard.  Dr.   H.   H 19 

Bush,     Dr.     A.     .T..     classification    of 
bridgework     798 

Cadmium    1084 

Caesium     967 

Cajaput   954 


Calcar     129 

Calcium     968 

Calipers     460-654 

Calorie,  the  unit  of  heat  energy 121 

Candle,  flame   996 

Cantilever    bridge    7S5-7S9 

Caoutchouc,   tlie  basis   of  rubber....   436 

Cap,    in    crown    work 651 

construction   of    651-662 

direct    method    651 

indirect    method 662 

Carat,   use  of  term 1010 

Carbon     967 

Carmichael    attachment    832 

modified 835 

Carroll,    Dr.    C.    C,    casting    alumi- 
num       219-1186 

Case,    Dr.    C.    S.,    enamel    cleavers..   644 

Cassius,   purple  of 900 

Cast,    definition     33 

crowns 770 

cusp    of     769 

denture    bases    120-190 

aluminum     120-190-1182 

Watts  metal    120,   222 

trays.  Impression    38 

iron      1065 

Casting     Counterdies 159-759-760-761 

clasps     264-851-852 

crowns     770 

dies     153-256 

inlays     957 

materials    used    in    inlay    work.. 

944    to    953-1047 

plaster     , 33 

rings   for   molding    129 

root    restorations    737 

Casts,   production  of 90 

change  of  form  under  stress....   100 

construction   of    100 

distinction  of  term,  from  model.     33 

forms    for 96-98 

materials     used     for 101 

necessity    for    use    of    resistant 

materials    101 

partial   cases    104 

removal  of  iinpn-s.-^inns   from.... 

106,    107,    109 

strengthening  isolated   teeth  on.   105 
treating  surfaces  of,  for  vulcan- 
ite       432 

treatment  of  impressions  for 105 

warpage     106 

Cavitv    preparation    for    inlays 912 

gold 931 

porcelain     912 

Celluloid      551 

dentures    550 

casts  for   97,   560 

technic     of     construction.... 

555-559 

Cement,   as   an   Impression    material    57 
as  a  medium  for  setting  crowns 

and    inlays     694-910-913-930-959 

general    composition    of 117 

shadow   problem    in    inlay    resto- 
ration      92S 

Cementation    process    1066 

Cementum      625 

Cerium     968 

Change  of  volume   in   rubber  during 

vulcanization     447 

color,    in  porcelain  due   to   metal 

backing    6S2 

dimensional      in     material     em- 
ployed in  casting   944 

Chase's   molding  sand    129 

Chaser    183,   763 

Character      of       emanations       from 

radio-active  substances 963 

Chemical   constituents   of  rubber. . . .   440 
changes   in    ru'bber   due    to   vul- 
canization        441 

formulae   of  wax   and  paraffin... 

946-917 

of   plaster  of   Paris 43 


Chemistry    of    vulcanization 441 

photograpliy     1075 

Chlorination    process    1008 

Chlorine     956 

Christensen,  Dr.  Carl.. 275,  308,  337,  1145 

Chromium     968 

Cicero,   facial  outlines 369 

Cinnabar     1087 

Clamps,   soldering 185,   186 

Clapp,    Dr.    G.    W.,    color    analysis..   379 

Clark,  Dr.  F.  H.,  crown  1154 

Clark,  F.  W.,  unequal  distribution  of 

elements    970 

Clasp    metal    10.S3 

formuUe    for    (Weinstein)     1034 

gauges  commonly  used  241 

Clasps 236 

advantages   and   objections 236 

application    of    246-249 

indications     and     contra-indica- 

tions    governing    246 

requisites    of    T.'," 

technic    of    construction 250-264 

t.N'pes    most    commonly    used .... 

"242-249-500-505 

Classification,    bridgework     (Bush)..   798 

natural    teeth    (Williams) 362 

temperaments     356-357 

Clay    902 

Clearing,   matrix  of  wax  in  vulcan- 
ite  work    414 

mold   of  wax   in   cast   base  den- 
tures        204 

in    inlay   work    956 

Cleavers     644-645 

Cocaine     630 

Coefficient   of  expansion 989 

Coin  gold    1010-1018-1060-1061 

Coke  furnace,   for  baking  porcelain.  1130 

Collodion     93-1134 

Colloids      4::6-437-969 

Color  problems  in  tooth  .selfction 373 

compleinentary     377 

principles,    syhop.sis    of 374 

primary,    secondary,    iiitrnx 

'    chart'  of   .'. ....  .  .  !■  i..niisi,i,-ce 

Columbium      96S 

Compensating  curve,  meaning  of  the 


tert 


300 


development     of,    on     occlusion 

models      343 

fundamental    principles    of..   344 

omitting    353 

practical  steps  in   348 

Ulsaver's  method    352 

Wilson's    method    354 

modification    of    302 

Composition,  alloys  of  gold  plate.... 

1011-1026-1027-1038 

artificial    stone    HO 

Babbitt's   metal   (Haskell's)  .134-1087 

beeswax     946 

celluloid     551 

clasp    metal    1012-1034 

dental    rubber    439 

Hux,    oxidizing     1059 

reducing    1058 

soldering     1056-1060 

gold,     for     casting 1029-1030-1032 

investment   materials.  .1044-1046-1047 

Melotte's  metal    135-136-1089-1090 

modeling   compound    58 

plaster     43 

porcelain    continuous    gum    body  904 

gum    enamel     906 

solders    gold    1011-1036-1038 

platinum     1012 

silver     1075 

tinner's    1086 

Compressibility  of  plaster 56-428 

Condit,    Dr.,    attachment 512 

Conductivity,   denture  base   material  121 

electricitv     S87 

heat     ..." 986 


Condyles,  articular  surfaces  of  man- 
dible        274 

form    of    -72 

location  of   272 

patiis  of   274 

lateral    297-472 

methods   of  registering. .  .336-466 

protusive     296-466 

variation  In  pitch  of 275 

Conic     forms    of    natural    bicuspids 

and    molars     633 

method  of  band  construction. 635-745 

Constitution,   Kinetic,   of   matter 968 

Construction   of,   dentures 304 

aluminum     190-208 

celluloid     551 

contiiluous   gum    588 

wax  model 405 

weighted   221 

vulcanite     304-463-476 

bridges     783-849-891-900 

casts     96-97-100 

counterdies" '.'.'139-159-165-759-760-761 
crowns.. 625-7S2-S44  to  856-873  to  893 

dies  139-153-165-256 

inlays     901-959 

occlusion    models    314 

Continuous    gum,    body    and    enamel 

608-904-906 

dentures    583 

advantages     588 

disadvantages     588 

sequent  step  in  construction 
5SS-619 

Contouring,    shell   crown    band 749 

cast    crowns    770 

continuous    gum    dentures 588 

occlusion    models     322 

patterns    for   seamless    crowns..  773 

pliers    25S-750-751-900 

wax  model  dentures 395 

Contour  models  in   anatomic  worlc..   313 
construction    of     314 

Copper     1077 

alloys    of    1078 

amalgam     1002 

as    a    hardening    agent    in    gold 
alloys      1026 

Corcoran   attachment   in   bridgework 
787-835-838 

Cores    99-142-147 

Coronium     976 

Counterdies     159 

construction   of,    by   casting 159 

dipping    161 

metals   and   alloys 136 

fusing  points   of    136 

for    partial    denture    bases 164 

partial     162 

requirements    of    136 

Countersunk,    pin    teeth 528 

retention  holes,  aluminum  bases 

210-218 

root   cap    669 

Cradle    in    placer    mining 1006 

Crowns,   artificial,  various  forms. 625-7S2 

banded,    baked    porcelain 874 

Bean     1157 

Beers     1158 

Black      1156 

Bonwill      1159 

Brown    1161 

Buttner     1160 

cast     770 

Clark,    F.    H 1154 

Davis,   plain    725 

banded     733 

cast  base   731 

DeChemant    1152 

Dwlnelle     1155 

Foster    1154 

Fouchard     1116 

Gates     1158 

How      1160 

Johnson    &    Lund    716 

Justl     730 


Crowns — Continued. 

Logan,    plain    717-1161 

banded      721 

Land,  jacket   885 

lingual  half  852 

Mack    1157 

Morrison     735-1156 

porcelain    faced    640 

jacket     880 

Richmond     1159-1164-1165 

shell,   two  piece    735 

seamless     772 

shoulder    771 

Smith     1153 

split    dowel    845-849-1154 

telescope     844 

tube.   Ash's    529-1135 

Twentieth   Century    716 

Weston    1160 

White,  S.  S 1162 

Wood      1155-1156 

wood   pivot    1153 

replaceable   porcelain    teeth    and 

facings   for    696   to   725 

diatoric    715 

Dimelow    857 

Evslin     702-703-704 

flat   back,    Ash's    529-531 

grooved     1153 

Gardiner     712-713-714 

Goslee    707 

long    pin    700 

Merker     714 

Steele     697-698-858 

technic    of    construction    697 

cap   and    dowel    641-662-663 

cast    base     731 

plain   base    '726 

shell      739 

various    repair    methods    for 856 

crown    slitter 870 

post    puller,    Skinner 868 

White,  S.   S 869 

systems.   Bryant    862 

Steele's     858 

Crucible,    in   steel  production 1066 

chamber    1199 

former    201 

space    in    investment    1198-1199 

Crystallization,     of    plaster 47 

effect  of  cohesiveness  on  metals 

983-984-985 

Crystals  of  plaster,  size  of 48 

Cupellation     1074 

Curie,     Madame 963 

Curve,    compensating 300 

Spec,     Graf    von 302 

Cushing.    Dr.    George    H.,    clasp....   241 
Cusps,     development     of     in     crown 

work      755-772 

adapting  to  axial  band 763-766 

developing  in  plaster 754 

metalline    compound     761 

wax     755-764 

reproducing  in   gold,   casting 769 

swaging     759 

Custer.    Dr.   L.    E.,    furnace 926-1177 

Cutting,  bands  in  crown  work. ..  .651-744 

conic     method     635-746 

compensating  curve  on  occlusion 

models      343 

Cyanide  process .1008 

David    (facial    forms) 371 

Davis    crown    725 

Debasement  of  elements    964 

DeChemant,    early    porcelain    work.. 1125 
Decomposition,    oxides    of    aluminum  993 

radium     compounds 963 

Deglutition,   the  tongue  as  an  aid  in     14 

Dental    amalgam    alloy 1001 

alloys     1072 

arch     291 

bridgework     786-872 

organs 288 

Dentimeter  for  root  measurement...   649 
Dentin     625 


Dentures,    anatomic    method.  .304    to    475 

full    cases    304 

Gysi   system    465 

technlc     465-475 

Snow-Christensen     method..   304 

technlc   of    304-465 

partial     475 

technlc    of    475    to    525 

repairing     561-5S7 

Developing,    balancing    contact 391 

cusps  In  gold    759 

metalline   compound    761 

plaster     754 

wax 764-765 

Devitalization,    in    crown    work 641 

Diatomaceous   earth    1044 

Dies,    definition    33 

for    clasp    construction    256 

for   denture    construction 153 

metals    used    for 132-134-136 

purpose  of   126 

Differential    limit     299 

Digestion    7-8 

Dimelow  facing  529-530-531-857 

Direct    method    of    casting    denture 

bases    200 

counterdie     construction 759-761 

inlay,     matrix    and     wax     model 

formation     920-942-953 

root    cap    construction 659-661 

Discoloration    of    pink    vulcanite    in 

repair     567-571 

Discoveries,      recent,      in     chemistry 
and    metallurgy-.. 962,    969,    976,    992-993 

Dispersion    of  light 374 

Displacement      

Distal     margins    of    upper     denture, 

outline    form    of 30-312 

Distribution    of    elements,    unequal..   970 

Dobereiner,     triads    of 372 

Donham    flask    spring 433-434 

Dovetailing,  preliminary  in  vulcanite 

repair   work    576 

Drawing   split    dowels i<47 

Draw    plate     847 

Du     Chateau,     first    efforts    in    por- 
celain      1125 

ITuctility     9S3 

Duff.   Prof,  A.  Wilmer,   Kinetic  con- 
stitution of  matter    970 

Dummies,    various    forms    of 

825-826-827-828 

Dunn.    Dr.    C.    W.,   inlays    1172 

Dwindle,  Dr.  W.  H.,  crown 1155 

Early    efforts    in    porcelain 1125 

records    of    dental    prothesis. . .  .1110 
specimens     of     denture     replace- 
ments  1105   to    1110 

Edge   tools,   table   for   tempering. ..  .1067 
Effect    of    X-ray    on    various    sub- 
stances        965 

Eka-alumlnum     976 

Eka-boron    976 

Eka-silicon    976 

Elasticltv    in    metals    986 

modulus   of    986 

rubber    439 

Electricity,   conductivity  of  metals..   987 

exceptions      988 

Electrons    969-970-976 

Electro-welding     991 

Elemental   gases 962 

eleotricitv     

Elements     961 

outline  of  recent  discoveries....   962 
table  of,   in  order  of  discovery..   966 

atomic    weight    .  .•. 967 

periodic  table  of  975 

their    atomic    reli-tion    to    each 

other     971 

Elgin   casting   machine    959 

Eliminating  wax  patterns  in  casting 

204-225-956-1179-1181 

Emery  lathe  bands   457 


Eminentia    articularis    274 

Enamel,   removal  of  from  roots 

644-739-741 

Enameling,  metal  caps  in  crown  re- 
placements       1155 

Engineering,     principles     of     bridge.   783 

Enlarged    raphe    11 

Equalizing     denture     bearing 105 

Equilateral    triangle    of    Bonwill 273 

Esthetics   of   denture   construction..       2 

tooth    selection    355 

Etching     porcelain    inlays' 930 

E'thereal  solution    93 

Etruscans     1105 

dental  art  of 1106 

Eucaine     630 

Eutectics     1001 

Evans,    Dr.    Daniel   T 1137 

EVslin    tooth    in    crown    and    bridge 

construction     702-703-704 

Expansion,    coefficient   of 989 

compensating  for    29-133 

control  of  53 

of  investment  materials 

949-1040-1047-1048-1053 

of  plaster   51-52-1043 

silex      1044 

wax     945-1053 

Expression,  muscles  of   279 

Extension,    bridge    ((see    cantilever) 

785-789-1166 

Extraction  of  gold   1007 

metals    960 

Eye,    color    functions    of 377 

Face    bow    309-1140-1144 

adjusting   to    occlusion    models..   330 

occluding  frame    332 

bite  fork  of   326 

application         to        occlusion 

models     326 

object    accomplished    by    its    use  309 

Facer,   root,   Ottolengui 659 

Roach     660 

Facial    outlines 360 

proflle     322 

Facing  gum  porcelain. 532-534-608-617-906 

granular    440 

protesyn      537 

vulcanite,    pink    439 

in    repairs    567 

Facings,    teeth,    Dimelow. 529-530-531-857 

Evslin      702-703-704 

flat    back.    Ash's 531 

grooved      1153 

long    pin    680,    715-863 

Steele     697-698-858 

Enactors   to   be   considered   in  crown- 
work      625 

bridgework     790 

denture    construction     23 

Fact.-!,      hypotheses,      theories      and 

speculations     961 

Farragut,    Admiral    367 

Fauchard,    bridgework 1116 

crown    work    1115 

dentures      1117 

summary    1119 

Feldspar    903 

Fenner     1187 

Ferrite     999 

Fine,    Dr.    W.    M 459 

Finishing,    bridges    830 

crowns    693,    725,    767,    781 

dentures    456-461 

Inlays     959 

Finley,    Dr.    M.    S 1176 

First  reference  to  prosthesis 1110 

Fixed     dowel     crowns 640-716-721 

Flame,    structure    of 995-998 

Flare   of  axial  surfaces   of  bicuspids 

and   molars    633 

average   634 

greatest    634 

least    634 


F.asks,   casting   11 

Bean's    1183 

Carroll's    1186 

Fennel's    1187 

Havford's     .' 118r> 

Watts     224 

molding     129 

Wood's      203 

Zeller     11S6 

Bailey     129-156 

Hawes'     129-156 

Lewis'    129-157 

rings,  nest  of  129 

vulcanite     4ns 

Flasking,     aluminum,      wax     models 

for     196-201 

celluloid     556 

vulcanite,   full  cases    410 

partial   cases    481 

Flexure,  elasticity  of   239 

Flow   of  metals  under  stress 986 

Fluorine    968 

Flux,     oxidizing     1059 

reducing    1058 

soldering     1056 

Fogg's    interstitial    gum    facings.  .480-620 

Fonzi,     teeth     1127 

Force  of  mastication    271-306-806 

Forms  of  matter    979 

F'ormuUe      for     casting      gold      "A," 

"B."     "C,"     "D" 1029-1032 

clasp    gold     1012-1034 

dental    alloy    1072 

amalgam  alloy   1001 

gold     solder     1011-1038 

gold     plate    No.     1-2 1026-1027 

investment      compounds      (cast- 
ing)       1052 

investment    compounds     (solder- 
ing)     1046 

oxidizing    flux    1059 

platinum    solder    1012 

reducing  flux    1058 

silver    solder     1075 

soldering    flux    1056 

specific    gravity     981 

Foster   crown    1154 

Fracture    of    enamel 645 

Fractured    bridge     S71 

vulcanite    dentures    561 

Freezing   of  metals 981-1031 

French's    impression    plaster 52-101 

Friability    of    porcelain 909 

F'rictional     or    working    surfaces    of 

the     teeth     288 

Full  dentures   (see  dentures) 

Furlong's    plastic    rubber    586 

Furnaces,     porcelain     613-614-897-898 

Fusible    metals     (Hall's    formulas) .  .1090 
Fusing    point    of    metals 981 

Gadolinium    967 

Gallium      967 

Gardiner,     replaceable     facings 712 

Gariot,    Dr.    .T.    B 1136 

Garretson    bite    guide    328 

Gas   and   nitrous    oxide   blowpipe. . . .   958 

regulator     451-452 

Gasoline     furnace     898 

Gates    crown     1158 

Bonwill    crown    1159 

Gates,    for    surplus    rubber 417 

(gauges,    steam    450 

Gauging   amount    of    rubber 427 

General   classification   of   bridgework  786 
Genese.       Dr..       developing      lingual 

forms    of    teeth    in    vulcanite 459 

German    silver    trays 39 

Germanium     968 

Gilmer,     Dr.    T.    L.,    suggestion    for 

correct    mounting   of    casts 1140 

Gllmore,     Dr.     Steele,    frictional    at- 
tachment       514 

Gingival,    termination    of    cementum  626 

Girder,    in    bridge    engineering 784 

Glaesenapp,    Prof.    M.,    plaster 45 


Glands,   salivary,   function  of l.'i 

Glass    inlays     1070-1073 

Glazing  porcelain    618-928 

Glenoid   fossa   274 

Gold    1004  to  1063 

alloys    of,    see    index 

carat,   meaning  of  term lOlO 

extraction     1007-1008 

formula,   see  index   

raining     1005 

preparation    of    pure 1009 

reduction   of   I  Hosci'.s   rule) 1010 

.Sdlrt.TS.    .S.'C     toiiiiulie 1011 

treatment    i)f    .■fi-iap 1009 

Goldschmidt,     I'rof 993 

Goslee,    Dr.    H.    J 193,851,954 

tooth     707 

technic    of    application 70S 

Graphite    949-1053 

Gravity,    specific,    formula    for    esti- 
mating       981 

casting    

222-1182-1184-1185-1188-1194 

Greene,     Dr.     J.     W 27,     87 

Grinding   porcelain    crowns 717,    728 

facings     680-693-887 

Grinding    to    correct    occlusion 388 

Griswold    attachment     524 

Grlswold,     Dr.     W.     M 1177 

Gritman,    Dr.    A.    D 1143 

Groove,    rectangular 288-290 

Ground     gypsum     44 

Guerini,   Di".   Vincenzo    1101 

history     of    dentistry 1103 

Gum,    sandarac    93 

Gutta    percha     62 

Gysi,    Di-.    Alfred 308.    460-465.   1148 

Half   band    crown 845 

crown     852 

round    wire   clasps 243 

for    split    dowels S46 

Hammond    furnace    614 

Hancock.    Thomas,    vulcanite 438 

Hard,    bite    wax 60 

solder     995 

Hardening   steel    1066 

Harmony    defined     358-374 

laws   of,    applied    in    tooth   selec- 
tion        360 

Harper,   Dr.   W.   E 741-1187 

Haskell,    Dr.    L.    P 134-135-1087 

Hawes,    Dr.    G.    E 129-148-1184 

Hayes,    Dr.    R.    S 1139 

Hayf ord.    Dr.    J.   W 1184 

Head,    Dr.    Joseph 306 

Heat      986-988-98! 

Heating,  flask  in  vulcanite  work 4U 

investment    for    soldering 1054 

for    casting    inlays 956 

Hebrews,       dentistry       among       the 

ancient    1111 

Heddy,    Dr 840 

Helium     967 

Heinrichsen    appliance     504 

Herbst,    Dr 1173 

Herder,    reference    to    mouth 3 

Herodotus,      reference      to      ancient 

dentists    5 

Hickman,    Dr.,    inlays 1171 

High    and    low    fusing   porcelains....   907 

lip    line    324 

temperatures    993 

Hindu    prosthetic    specimens 1109 

Hinge    tray    677 

Hippopotamus,  dentures  of 1110-1114 

Histology    626 

History  of  dentistry  (Guerini's) 1103 

Holder,    cotton    roll 76S 

crown     767 

Hollingsworth,    Dr.    M.    W 1188 

Horn,    mallet    171 

pene    hammer    262 

Hot   and   cold   molds    

957-1049-1050-1054-1087 

How.    Dr.    W.    S.,   crown .....1160 

Hutchinson,    Dr.,    on   temperaments.   356 


Hj'dro-carboii,     rubber 140 

Hydrogen,   debasement  of  other  ele- 
ments   into    964 

Hygienic    requirements    of    crowns..   63!) 
Hyperaemla,   due  to  mechanical   irri- 
tation        124 

Hypotheses     in     reference     to     ele- 
ments       961 

Impression   3:i 

materials     42 

beeswax    59 

beeswax    and    paraffin 59 

cements     57 

classification    of    42 

gutta    percha    61 

modeling   compound    5S 

plaster    43 

of   clasp,    teeth   and    baseplate..   267 

of   root   in   crown  work 663 

of   teeth    to   be    clasped 252 

rebuilding     254 

relieving     27-31 

technic    of    taking.  .63-68-69-71-72-74 

difficult    cases    79 

modeling   compound    Sl-86 

partial    cases    73-495 

plaster     63 

tray     34 

fitting     36-3S-64 

hinge    677 

nomenclature    35 

special    3S-39-40 

treating  and   tilling  of   90-105 

Incisor    teeth    28S 

path     295 

registering     469 

India   rubber    (.see   caoutchouc) 436 

Indirect    method    of   constructing.... 

cast    aluminum    193 

counterdie    760 

inlay  matrix  and  wax  model. 942.  943 

root   cap    662-S36-SS0 

Indium     967 

Individual    saddles     78S-S26 

Infection,  the  mouth  as  a  focus  of..  S 
Inflammatory    mucous    tissue    under 

vulcanite     122 

Inlays     901-959 

gold,    cast    944 

cavity  preparation   931 

matrix     method     of     produc- 
tion      942 

direct    942 

indirect    943 

technic    of    construction 953 

physical       properties      of 

materials    employed    . .  944 

porcelain     901-908 

basic   ingredients    902 

properties     904 

cavity    preparation    913 

technic    of    construction.  .919-931 

Insoluljle   constituents   of   rubber 440 

Inter-articular     fibro-cartilage 274 

Interchangeable   teeth    706 

diatoric    715 

Evslin,   (posterior) ....:..  702 

Gardiner     712 

technic  of  application  712 

Go.slee     707 

technic  of  application  708 

Merker     714 

Steele,    posterior 697 

tooth    facings    697 

Ash     531 

nimelow    530,  857 

Evslin     702 

long   pin 700 

Steele's    697 

application       697 

Internal    lateral    ligament 286 

Investing,     aluminum,     wax     pattern 

for    196.  203 

banded,    I>ogan    724 

bridge,    for    soldering 830 


Investing — Continued. 

cap    and    dowel 672 

celluloid     556 

continuous  gun,    for  soldering...   600 

Richmond    crown    890 

vulcanite,     wax     model    denture 

for     410 

wax    model    inlay    for    casting..   955 
wax  model  foi"  weighted  lower. .    223 

Investment,    compounding   of 1052 

compounds    for    casting 1047 

soldering   1040-1044 

directions    for    use 1053 

for    aluminum    rases 203 

heating  of    1054 

Iodine     631 

Iridio-platinum 1023 

Iridium    1023-1072 

Iron    ores    1062 

hama?tite      1063-1064 

magnetic     1063 

occurrence    1063 

pyrites    1064 

reduction   of    1064 

spathic     1064 

forms  of   1063 

cast    1065 

steel    1065 

wrought    1065 

Ivoiy    appliances    1110-1114 

Ivory.    Dr.    J.    W 644.768-843 

Jacket    crowns,    porcelain 880 

Land     885 

Jenkins'    porcelain     907 

Jewelers'    gauge    1095 

gold    plate    1011 

Johnson   and   Lund   crowns 716 

Joint,   tempero   mandibular 274 

bevel   in  vulcanite  repairs. ..  .564-565 

Juno,    facial    outlines 371 

Justi    crown    730 

impression    trays    65-74-87 

porcelain    body    90'7 

teeth,    gum    sections 621 

plain      526 

Justi.    H.    D..    teeth    526-621 

K    plier    for    inlav    %vork 924 

Kaolin    902 

Kelly    attachment    523 

Kennedy,    Dr.    E..    modified    Uarmi- 

chael     835 

Kerr  articulator    1144 

impression    trays    82-85-88 

metal  forms  for  casts    96 

soldering  tweezers   766 

Kieselguhr    1044 

Kinetic,   constitution   of  matter 968 

Kingsley   alloy    227 

scrapers     29-458 

Knapp.   Dr.   J.   Rollo.   blowpipe.  .958,  1196 

bridgework    1166 

Knight.  E.   H.,  definition  of  a  sprue.  1180 
Koch.   Dr.    C.  R.    E.,    history  of  den- 
tistry      nil 

Krypton,    discovery  of 961-962 

Labial.       contouring      of      occlusion 

models      316 

Ladles,    melting    131-256 

Land.    Dr.    C.    H..    porcelain    inlays.. 1171 

jacket   crown    885 

Lane,    Dr.    J.    G..    silica 1048 

Lanthanum    967 

Lathe,    polishing    456.    457-461 

Lavater.  discourse  on  the  mouth....       3 

Lawrence-Foster  crown    1154 

Lead    method    in    silver    reduction.  .  .1074 

physical   properties   of 1085 

Le   Gro.    Dr.    A.    L..    cavity   prepara- 
tion       941 

Lever,    the    mandible    as    a 271 

Leverage  on  denture  bases   25 

Lewis  fla.sk  for  molding 129-:157 


Ligaments,    the    mandibular 284 

capsular    285 

lateral    286 

external     286 

Internal    286 

spiieno-mandil)Uiar    2S6 

stylo-mandil3ular     2S6 

Lime   bloclj,    in    fusing    platinum ....  1071 

Lingual  muscle.s    14 

marginal     ridges     ;!S8 

Lips   as  a   feature   of   the   face 9 

as  a  guide  in  establishing  plane 

of  occlusion    320 

Liquation      1000 

Liquid  silex   in  vulcanite   work.. 417.  432 

Lithium     967 

a  product  of  debasement  of  cop- 
per        964 

Litigation,    dental   vulcanite 1133 

Lixiviation,    in    recovery    of   gold....  1008 
Locating   high   and    low   lip   lines. 318-324 

median    line    318-324 

outer  ends  of  condyles 318-325 

Logan.    Dr.    M.    L..    crown 1161 

Loop    clasps    500-501-503-504-505 

Loose  pin  anchorage  for  inlay  abut- 
ments        941 

Lower   jaw    (mandible) 270 

Luce.     Dr.     C.     E..     condyle     move- 
ments,   and    articulator 283-1150 

Lymphatic   temperament    356 

Magnesium     966 

chloride      113 

in     alumino-thermy     992 

Magnetic     iron     1063 

Malleability    983 

Mallet,    horn    171 

horn    pene    262 

Mallett,  Dr..  experiments  in  vulcan- 
izing         438 

Mandible     270 

analysis  of  iatei'al  movements.  297 
articulation  with  temporal  bone.    274 

auxiliary   functions    271 

centers  of  notation 297 

governing  factors  in   movements 

of    295 

muscles  whicli  control 282-284 

Mandibular   ligaments    284-286 

governing  factors   in   movements  295 

Manganese     968 

Manufacture    of   celluloid 552 

dental  rubbers    436-441 

gutta    percha    61 

plaster     44 

porcelain    902-907 

steel    1066 

wrought   iron    1 065 

Marble    dust    129-1043-118S 

Martin.    Dr.    G.    M..    castins: 11S5 

Mash    bite    lSS-478-576-.i79-673 

Mason    spacing    calipers 683 

Mastication,    muscles   of 284 

restoration   of    function    of 1-304 

Masticatory    apparatus    269 

mechanism     269 

movements     273 

muscles    of 277-284 

Matrix,    counterdies    163 

contour.      in      continuous      gum 

cases    598 

direct  method  of  production ... .  942 
Indirect  method  of  production..  943 
packing     in     vulcanite     denture 

construction    418-426 

production    of   platinum,    in    por- 
celain inlav  work   911-929 

sand     139 

seamless    crown    method 773 

Matter,    forms    979 

mutability   of    961 

Matthiessen's    theory    of    alloys 999 

McClelland.    Dr..    rose   pearl 551 

McLeod,    Dr.    W.    Bowman,    expan- 
sion  of   plaster    54 


Measurement,  angular  divergence  of 
axial      walls      of      bicuspids      and 

molars    634 

compressibility    of    plaster 56 

cutting    band    according    to.. 651-745 

expansion    of    plaster 52 

plate    and    wire 1092 

root,  in  crown  work 649-743 

width   of  band 744 

Mechanical     and    physical    problems 
involved   in   denture  constiuction. .     23 

Medieval     bridgework 1116 

Mediums,    separating    92-95 

Melotte's     135-1090 

Melting   point,    explanation   of 981 

Mendeleeff     Dimitri.     periodic     sys- 
tem of   974-976 

Mercury     1087 

Merker.    Dr.    M.    E..    tooth 714 

Metabolism     7 

Metals,    alloys    of 999 

a  new  series  of 1'  25  to  1040 

binary    1014    to    1025 

alloying     999  to  1002 

base    980 

native     980 

noble    980 

physical    properties    of.... 980  to  998 

Metallography    960 

Metalloid     979 

Metallurgy    960 

Methven.    Dr.   H.    F 838 

Meyer.    Lothar    974 

Michaels,     Dr.     W..      translation     of 

Glaesenapp's    work    45 

Micro-structure    of    metals 999 

Micrometer  caliper    1097 

Micron    969 

Miller.    Dr.   H.    C.   celluloid   Hask 556 

Millimeter    970 

Mineral,  first  reference  of.  for  teeth. 1113 
Minerals,  occurrence  of.   in  nature..   9*9 

Mixing   cement    694 

investment     955 

plaster    66 

porcelain     923 

Model,    use    of    term 33 

wax    contour    and    occlusion 313 

denture    313 

for    inlay    953 

nf     looth     for     seamless     crowns 

773-777 

Modeling   compound    58 

composition    58 

manipulation     81 

Molar    tooth    forms 288-293 

typical    forms    of 756-757 

Mold,    eliminating    wax    from. ..  .956-1181 

variation    in    method    of 956 

expansion  of  951 

formation  of  single 1180 

Molding    sand     129 

Molecular    tension    169 

disturbance    211 

theory    of    matter 968 

Molecule    968 

Molydenum    966 

Morgan     attachment 509-510-511-512 

Morrison.    Dr.    W.    N..   crown.  ..  .735-1156 

Mouth,   a   focus  of  infection 8 

examination   of    18 

Mucous  membrane  of  the  palate....      12 

plaques    124 

Muscle     marking    impressions 

37,     67-71-85 

Muscles    of    mastication 277  to  284 

action,    summary    of 284 

Native    metals     980 

Natural   denture    288-289-290 

Necessity  for  use   of  face   bow.. 309.    330 

Neodymlum     967 

Neon     967 

Nero,     facial     outlines 372 

Nervous    temperament    356 

New   elements    962-976 

Newlands.   octaves   of    974 


Newtonium      976 

Nickel     10S9 

Nltrog'en      967 

Nitrous    oxide    blowpipe,    Knapp's.. 

958,     1196 

Noble   metals    980 

Nomenclature    tray     35 

Nonconductivitv     of     vulcanite 122 

Noyes,  Dr.  Frederick  B.,  histology.10-626 

Occlude,    definition    of    the    term 288 

Occluding    frame    307-308 

adjusting  condyle  paths  of 342 

applying    face    bow    with    occlu- 
sion   models    attached    to 332 

arranging      teeth      to      occlusion 

models    on    382    to    390 

Gysi    and    appliances 465-1148 

mounting    casts    on 332 

removing   casts    from 406 

Snow,    and    appliances 

308-332   to   353.   3S2   to  393,    1146 

various   types    of   the 1136-1152 

Occlusal  plane,  meaning  of  the  term  293 

curvature     of 293 

determining    correct 319 

Occlusion,     anatomical,     of     natural 

dentures      289-290-294-301 

models     313 

adjusting  bite  fork  and  face 


bow    to 


330 


arranging   the   teeth   on 382 

construction    of    314 

developing  compensating 

curve     on 343 

restoring      disturbed      facial 

contour  by  means  of 322 

rims,    approximate   depth    of  31."i 
bucco-lingual  relation  of. 

to   borders    315 

establishing      height      of 

individual    319-320 

i-eiiuirements    of    314 

trial   of,    in    the    mouth 318 

points     determined     b,\' .  . 

318    to    327 

retainer     412 

Occurrence   of  metals   in    nature.  .  .  .   979 

Octaves    of    Newland    974 

Offset    crowns    632 

dowels      727 

Ollendorf    casting    appliances 1194 

Onlays    1192 

Opaque  porcelain    929 

quality   of  cement    928 

vulcanite  gum    facing    440 

Oral    cavity     9 

boundaries   of    9 

contents    of    9-14 

teeth     9-2S8 

tongue      13-14 

mucous   membrane  of    10 

epithelium    of     10 

palatine    vault     10 

bony    structure    of    10 

foramina   of    11 

rugse    of    13 

vestibule   of    9 

cul  de  .sacs  of 9 

Ores     980 

Osmium     968-1024 

Ottolengui,    Dr.   R.,   root-facers 659 

Outline,    an,    of   metallurgy 960 

Overbite      301-535 

Owen,     Prof.,    prehistoric    inlays. ..  .1169 

Oxides,    reduction   of,    with   flux. 99.'i- 1055 

(See    noble    and    base    metals)..   980 

Oxyacetylene   blowpipe    994 

Oxvchorid    of    magnesium 110 

zinc 20-117 

Oxygen      : 967 

Oxyhydrogen    flame    994 

Oxyphosphate    of    zinc 20 

Packing  rubber  in  vulcanite  cases.. 

418   to  42S 

Palatine    vault     10 

epithelium    of    10 


Palladium.  .968.     1021-1026-1027-1029-1034 

Papyrus,    Ebers'    1101 

antiquity    of    1102 

Parabolic   arrangement   of  the   teeth 

in  the  dental  arches   292 

Paraffin     59-946-947 

Parker  shot  swager    163-164 

Partial    dentures    476 

baseplates   for    476 

gold,    technic    of .  .180-189-488-490 

lingual    bar    496 

vulcanite     477-484 

lingual   bar    490-491 

flasking    of    481 

planning  of    476 

protrusive  bite    for    478 

retention    of    187-233-236-476 

settling   of.    from   use 497 

specialized    frictional    appliances 

for   500  to  524 

Pathological    conditions,    oral 628 

treatment    of    629 

Peeso,    Dr.    F.    A.,    removable  bridge 

methods     ,';42-1013-1047-1056-1061 

removable      crown      and      bridge 

work     1013 

Pepperling,  Dr.    T.   L 955 

Peridental  membrane 625 

Periodic  table  of  the  elements  (Men- 

deleeft)      974 

law      978 

Peripheral  outlines  of  dentures 

Perlite  in  micro-structure  of  steel.  .   999 
Permanent  dentures,   when  to  intro- 
duce         21 

Philbrook,    Dr.    B.    F.,    inlays. .  .1191-1192 

Phoenician    dentistry    1104-1105 

Phosphor    bronze    107i) 

Phosphorus     968 

Photography,    chemistry    of 1075 

Physiological   relations   of  teeth   and 
sun-ounding     tissues. .  .627-801-805-806 

Pickling,    acid    bath    for 169-170 

Pier,   definition   of    783 

Piers    and    abutments 790 

preparation    of    teeth    and    roots 

for     795 

selection    of     790 

Pig   iron    1065 

Pigments     375 

Pink   gum    facing,    porcelain 608-906 

protesyn     537 

granular     440 

vulcanite     439 

Pivot  crowns.  De  Chemant  1152 

Fauchard    1116 

wood     1153 

Placer  mining    1005 

Plain    line    articulator 1138 

Plaster    models   to    arrest   expansion 

of     133 

Plaster  of  Paris,  accelerators  for..  101 
advantages  of,  for  impressions..  56 
as  a  binder  in  investments. .  .97-1043 

chemical    composition    of 43 

compressibility    of    56 

contraction   of    52 

deleterious     properties     of 101 

deterioration     when     heated 101 

expansion    of    51 

control    of    51 

warpage  as   result  of 5:i 

indications    for    use    in    impres- 

sit)rrs      63 

influence  of  mixing  on   quality..     51 

manufacture    of    44 

setting,    time    required    for 45 

size  of  crystals   48 

use    in    cast    production     103 

Plate    and    wire    gauge.- 1099 

gold  for  denture  bases 167 

annealing     168 

carat    of   used    167 

for   crown,    bridge    and    plate 

work     1026 

gauges    used     168 


I'latinum     1067 

alloys    of    1019-1072 

fusing    of,    Custer's    method 1070 

in    clasp    metal    1033 

physical  properties  of   106!i 

uses    1071 

I'liers    used    in    crown,    bridge,    den- 
ture  construction    258-750-751-900 

Plumpers    for    facial    contour   restor- 
ation      317,    323 

Polisliingr    vulcanite    dentures 456 

Polyprene-india    rubber    441 

sulphides,   formation   of,    in   vul- 
canization         442 

Ponton    bridge    (engineering) 785 

Porosity    in    porcelain 619-928 

in    vulcanite    441    to    445 

Portland    cement    101 

I'dssilil.'     sU'llar    temperatures 994 

I 'Mta,~,--iniri    sulphate    as    an    aocelei-- 

;iiu,      101 

PuuTiiij;   ;;;iine    1180 

Melotte's     metal     256 

metal   dies    154 

counterdies     160 

Watts     225 

Powder,    glass    1170,    1173 

silex     1044 

talcum    352 

Praseodymium     967 

Prehension     296 

Preliminary  considerations  in   crown 


Pulp  devitalization   in   crown   woik. 


Pumice    

Punch,     anchorage     loop. 


■Vi  i> 


jrk 


.625 


736 


dovetailing    of    denture    base    in 

repairs     576 

steps    in    flask    closing 428 

impression     taking     64 

packing    the    matrix 41S 

securing   anchorage   of   teeth 

to   metal   bases 174 

Preparation    of  cavit'es.    special 936 

continuous   gum    body    608 

pure    gold     .' 1009 

roots   or   teeth    for   abutments.. 

642-739-771-79D-S91 

Preparing   impression    for   cast    pro- 
duction          74 

ingredients    for    porcelain. ..  .903-904 

Pressure,    atmospheric 25 

applied  in  flask  closing 428 

metal    casting    1181 

Price,   Dr.    W.    A 907-951-1091 

Prime    object    of    crown    and    bridge 

application    799 

Principle,    object    sought    in    denture 

construction    1  to   6-304 

Principles,   a  synopsis  of  color 374 

Primary     colors     375 

Prismatic     colors      374-375 

Pritchett.   Dr.   T.   W 1-290 

Production     of    casts 90 

aluminum    bases    by    casting....    2"0 

swaging     212 

Profile,    facial 320-321 

Proportionate  parts   of  teeth 534 

Proposed   law   In   bridge    work 804 

Prosthetic    dentistry,    definition    and 

scope    of     ..■■       1 

Protesyn   as  a  gum   facing 537 

method   of   application. ..  .537    to    545 

Prout's    hypothesis    971 

Providing  for  escape  of  surplus  cel- 
luloid        556 

rubber      417 

settlement     of     dentures     under 

stress  497-517 

uniform   bearing   of   dentures  on 

issues     27    to     30 

Proximal    cavities    for   inlays   prepa- 
ration of    914   to   919-932  to  941 

contact    restoration    of 632-738 

surfaces    reduction    of    479 

views    of    bicuspids    and    molars 

766     to     769 

Pruyn,    Dr.    C.    P 20 

Pterygoid     muscles     278-280-284 


ry    plate     

pcrloj-ating     

riveting     

Young     

Purpie   of   Cassius    

secondary    color    

Pyrometer    furnace     

Pyroxylin,    basis    of    celluloid. 


460 
217 
684 
866 
217 
865 
684 
906 
375 


Radio-active    substances 963 

Radium      963 

Ramsey,    Sir  "SViHiam 

961-962-964-965-970 

Ransom      and      Randolph,      vacuum 

casting  machine    959 

Raphe     11-18 

Rawlinson,    Dr.    John,    dentures    for.    458 

Ra.vleigh,    Lord    962 

Ravs,    alpha    963 

beta    963 

gamma     963 

X    962-963 

Reaming     667 

Rebuilding    an    impression     for    die 

casting     254 

Recent    discoveries,    a   brief    outline 

of 962 

Recording  tlie  condyle  paths 336 

Red,    color  principles    375 

rubber     439 

Reducing    flame    998 

flux      1057 

Reduction,    alloys    of    mercury lOSS 

aluminum     1080 

copper     1078 

gold     1010 

rule    for    (Boser's) 1010 

iron     1064 

lead    1085 

silver    1073 

tin      1086 

Reenforcing     partial     baseplates     of 

gold     180 

detailed   methods    180-181 

platinum   bases    591-594 

Reese,   Dr  C.   N..   pin   shaver 687 

Reese.    Dr.    G.    N.,    casting 1184 

Refining  gold    1009 

Reflection    gold    base    against    teeth  182 

Refractory    materials    1040 

Registering  condyle  path 336 

Regrinding   of    teeth 462 

Reheating    modeling    compound    im- 
pressions      83-84-85 

Relation,    atomic,    of    elements 971 

securing      of,      between      clasps, 

teeth     and     baseplates. 266-267-483 
root     cap    and    dowel    in    crown 

work    671 

Relief  of   dentures   over   hard    pala- 
tine  areas    27 

border    crests    of    lowers 31 

Removable     bridgework 841 

attachments    842 

Removal  of  a  banded  dowel  crown . .   866 

dowels    from    root    canals 868-869 

natural   crowns    642 

shell    crowns    by    leverage    force  870 

slittinsr     869 

tempoi-arily    set    crowns 69r 

Removing    the    enamel     from    teeth 

and    roots    644-739 

wax   from   matrix    in   inlay   work  9^)6 

vulcanite   cases    414 

dowels   from    root    canals 868 

Repairing   crowns   and    bridges 857 

dentures    of    vulcanite 561 

Repilacing  crown  and  bridge   facings 

.  857    to    867 

Replacable  teeth   and   facings 696-734 


Reproducing    cusp    surfaces    in    gold 

in    crown    work     759-769 

gum   surfaces   in   porcelain 617 

protesyn      537 

natural      denture      in      porcelain 

teeth    and    wax 545 

Reproduction  of  natural  tooth  forms 

in  porcelain   364 

of  wax  model  dentures  in  perma- 
nent   materials 407 

Requirements  of  an  impression  ma- 
terial          42 

of    a    partial    denture 233 

of  a  base  plate , 313 

of  an  occlusion  rim 314 

Requisites   of  die    metal 131 

counterdie   metal    136 

clasps     237 

models     97 

denture   bases US 

Residual    ridges    18 

Resiliency   of  clasps 23S 

Resistance,  to  stress  of  casts,  neces- 
sity  for   110-42S 

dies    132 

Restoration    of    facial    contour 322 

masticatory    function 1-269,    463 

Reswaging    partial    gold    bases 1S6 

platinum    bases   plates 595 

Retainer    occlusion    412 

Retention     of    dentures,     full 23 

partial    233 

Rhodium   96S-1024 

Kichmond.    Dr.    C.    M.,    crown.  .1158-1159 

Rideout,   J.   B 856 

Ridge    lap    535-536 

Rigid    baseplates    necessity    for.. 118-313 
Rim    occlusion,    requirements    of....  314 

Ringer's    solution    630 

Roach,    Dr.    P.    E 235-265-500 

attachment    .  .503-505-508-660-769-842 

Roentgen,    Prof.    William 962 

Rollins.    Dr.    W.    H.,    inlays 1172 

Rolling   mill   for   gold 1093 

Roman,    lady,    facial    outlines 372 

history    of    prosthesis 1110 

prosthetic    specimen 1110 

Root  preparation    for   dovyel.    crowns 

in    to    1)50 

shell     73B-743 

porcelain   jacket    S80 

Rouge   and   alcohol  as   an  anti-flux.  1177 

as    a  polishing  agent 693 

Rubber,    composition  of  dental 439 

derivation     436 

vulcanization   of    454 

chemistry  of 441 

Rubidium 967 

Ruthenium     967 

Saddle    bridges     787 

individual    for   dummies 788 

with    ling;ual    bar 496 

Sali\-a,    function   of    15 

Salivary  glands   15 

Salts     of    radium 963 

Samarium     968 

Sand,   molding    129 

Sandarac  varnish 93 

Sanford    378 

Sanguine     temperament 356 

Saphira   facial   outlines 36S 

Sauer.  Dr.  C.,  casting 1184 

Scandium      967 

Schimmelpennick,  Mme.,  facial  forms 

360-361 

Schottler,   Dr.   Jacob,    inlay 1192 

Schwartz,    Dr.    G.    W 62^-1167 

Scrapers,    vulcanite    457-458 

Screw   estimating,    force  of.  in   flask 

closing     428 

presses     '.    433-434 

Seamless  crowns,  matrix  method....  772 

die   method    776 

Sectional  m.olds  in  vulcanite  work..   407 

Watts'     metal     casting 223 

seamless    crown     wor'.c 777 


Second   vulcanization    effect   on   pink 

vulcanite     567 

Secondary     contraction     in     gold     in 

casting    operations    952 

Selection  of  impression  trays 36-64 

teeth,   esthetics  of 355 

suggestion   in    380-537 

Selenium     968 

Sense  of  harmony    359 

taste    11 

Sepai-ating   mediums    92 

Separation  of  impressions  from  casts 

106-107-108-109 

die   and    counterdie 161 

Setting    crowns    and    bridges. 767-S31-S50 

inlays    930,    959 

Shade    guide   in    tooth    selection 536 

Shadow  problem   in  inlay  work 9iS 

tooth    selection 379 

Shears  for  crown  and  bridge  teehnlc  658 

Shot    swager,    Parker's 164-165 

Shoulder   crowns,    cast    gold 771 

porcelain  jacket    880 

Shrinkage  of  metals  in  passing  from 

liquid   to   solid   state 132 

Shut    (proportionate   parts   of   teeth) 

534-335-536 

Sieve  in   molding    130 

Silex,   powdered  as  an  ingredient   in 

investments     949-1044 

Silica,    fused    utensils    of 1044 

Silicate    cements,    protesyn    537 

Silicon    96S 

Silver,   alloys  of    1074 

conductivity   of    987 

ores    of    1073 

photographic    uses    of 107.5 

solders      1075 

reduction   of    1073 

Slag    in    iron    smelting    1064 

Slow,    mutation    of    elements 971 

Sluice    in    placer    mining 1006 

Smelting  of  copper  ores 1078 

Smith,    Prof.    Alexander 965-970 

Smith,    Dr.    J.    Dodge,    crown 1153 

Snow,  Dr.  Geo.  B.,  anatomical  appli- 
ances     30S-309-:;:;S-:^.3:i-1 144-111;; 

Soapstone  in   fusing  porcelain    926 

In   smoothing  models    130 

Sodium     96S 

Soft  palate,  extent  to  which  denture 

should    rest    upon     30 

Solarizing    pink    vulcanite 440 

Solbrig     casting    pliers 1 199 

Solder,    gold    


silv 


.1036 
.107 


soft      -lOSB 

Soldering     ■  •  •   994 

conditions  essential  to  successful  995 
temperatures     applied     =n     some 

cases     •   ^^2 

Soldering    jack     •■'"^"°i„ 

Solutions,    alcoholic    varnishes 93 

aqueous     94 

ethereal     ■ 93 

Sonorousness-  in  bell  metal i"m 

Spar,   fluor,    in  alumino-thermics 993 

Spathic  iron  ore    1064 

"Special"    Ideal    baseplate 230 

Specialized    frictional    appliances 

_ 235-500    to    o2.T 

Specific    gravity    981 

heat "89 

f^^?f;:sr':^.::::::::;:::96i:963:9?U?? 

Spence.    Dr.    Stewart   J..    bla_«te^r. . .  ._^^^ 

Spiral  springs  for  denture  retention 

1117-ll-l-ll"l 

Sol'it '  dowel    ". 845.    1061 

Spillers    resin     4q  |i 

Spongy    borders    ViSn 

Sprue,    definition    of   118I' 

Staining    fluids ^91 

Staining  porcelain  teeth il8 

Starr.  Dr.  E.  J.^ }]f--]\ll 

Starr,  Dr.  R.  W II60-II66 


1212 


INDEX 


steam    pressure,    table    of 450 

Steel,   hardening   and    tempering   of.  1066 

Steele,   teeth  and  facings 697  to  700 

repair    outfit     858 

Stellar    bodies,    temperature    of    the 

larger     994 

Stiver,    Dr.    D.    S.,    blowpipe 692 

Stomatitis     17 

Stokes,     Dr.     J.     L, 1173 

Stowell,     Dr.     Sidney     S..     extension 

bridge     1166 

Strontium     968 

Structure    of    flame 996 

Stuck,    Dr.,    vulcanizing    rubber    be- 
tween  metal   surfaces    113.=; 

Submaxillary  glands   15 

Sublingual  glands   15 

Substituting  artificial  for  lost  natural 

teeth    in   repairs    578 

Substitution      of      a      baseplate      in 

repairs     579 

Substructure  of  a  bridge 783 

application    of    stress    to 783 

Sulphur    968 

Sulphuric  acid  pickle 169 

Summary,  brief,  of  recent  discoveries  965 
Superheating  gold  in  casting  opera- 
tions  952,    1049-1050-1051-11S1-1198 

Superstructure     783 

Support  for  continuous  gum  case...   612 

Suspension    bridge    785 

Swaged    crowns,    seamless 772-776 

cusps  for  crowns    759  to765 

Swager,    Parker  shot    164 

Swaging    denture    bases 

.166-178-180-208-590 

Sweating     995-1028-1061 

Sykes,    C.    A 458 

Synovial  sacs   274 

Table  of  alloys,  binary   (Weinstein)  .1014 
casting  gold,  "A",   "B",   "C", 

••D"      1029-1032 

clasp    metal     1034 

hardness    and     elasticity 

of    1036 

gold    and    silver    1017 

copper      1019 

palladium      1023 

platinum    1020 

plate    No.     1 1026 

No.     2     1027 

solders     1038 

melting      points      of       "New 

Series"     1060 

triple    (fusible    metal) 136 

color,   analysis  of  individual  face  379 
conductivity  of  heat  and  electri- 
city      987 

constituents   of    dental    rubber. .   439 
gum    body    and    enamel.  .905-906 

coeffiicient    of    expansion    990 

divergence  of  bicuspid  and   mol- 
ar   crowns    634 

elastic     force     of     steam 451 

elements    in    the    order    of    dis- 
covery       966 

for       estimating      thickness       of 

doubled   gold    baseplate 182 

high   and   low   fusing   porcelains.   907 

mandibular    muscles     284 

masticatory    action    on    food....   306 
oxides  used  in  coloring  porcelain  905 

shrinkage   of  metals 132 

specific    heat    988 

screw   force    in   flask   casting...!   428 

steam   pressure    450 

temperature      as      displayed      by 

color      982 

temperaments     356 

tensile    strength    of    metals....!   986 
thermal      conductivity      of     sub- 
stances        122 

unequal  distribution   of  elements  970 
welding   under  pressure    991 


Table   of   the   periodic   law 975 

thermal     conductivity     of     sub- 
stances       102 

measured  in  calories  ...!!!!!'     122 

fusible    alloys !   136 

the    temperaments    355 

screw    force    in    flask    cloilng...     428 
unequal   distribution   of  the  ele- 
ments        97Q 

the   triads  of  Dobereiner    !!!!!!!   973 

welding    under    pressure 991 

Taggart,  Dr.  W.  H.,  Inlays 

. . .      9,-)0-954-957-958-1051-1196-n97-1198 

Taking    bites    327-329 

impressions     63    to    79-495 

Tantalum     ggg 

Taste   sense    14 

Technic   of  bridge  construction.  .823!   891 

crown    work     641    to    782 

full  denture  construction.  .308  to  475 
partial    denture    construction. 476-524 

celluloid     651 

continuous    gum    !  588 

repairing    dentures    561 

crowns  and  bridge  repairs. 856  to  872 

Teeth,    fonnula    of    human 288 

natural    form    of 755 

porcelain     forms     of 525 

Telescope     crowns     844-845 

Tellurium      968 

Temperaments,    table    of   the 356 

Temperatures    common    and     extra- 
ordinary         993 

Temporary  dentures 21 

Tempero-mandibular    articulation...  274 

Tenacity      985 

Tensile    strength    985 

Terbium      968 

Testing    balancing    cnntac  t 391 

base  plates  and  ocrUi.si.m  models  318 

impressions      S5 

occlusal     surfaces     of     teeth     for 

working  efficiency   387 

root   preparation   in   crown   work 

649,  743 

parallel    relation    of    crown    and 

bridge    abutments    843 

Thallium     968 

Theoretical   belief  in  regard   to   new 

elements    976 

Therapeutic  methods  of  treatment..   629 
Thermal      conductivity      of     various 

denture  bases   12I 

Thompson,   Prof.   J.   J.,   experiments 

in  the  debasement  of  elements 965 

Thorium      968 

Three     point     contact,     in     denture 

construction     393 

Thulium    ! ! !  958 

Time  a  factor  in  fusing  porcelains!!  614 

Tin     _  _  .1086 

Tint,     definition     !,.!!!   374 

Titanium    oxide ! !!  !965-968 

Tolstoi,    statue    of    398 

Tone    definition    374 

Tongue.    mu.scles    of 14 

Tongs,    muffle    92."; 

Tooth,    natural   forms   reproduced    in 

porcelain     352 

shade    guide    535 

Tray  nomenclature    35 

selection 36 

Treatment    of    diseased    conditions..   629 
after  setting  crowns  and  bridges 

631-695 

Triads    of    Dobereiner    972 

Trial    base    plates    311 

Truss   in    bridge    engineering 784 

continuous  gum  dentures 605 

porcelain    bridge    work K93-1167 

Tube   teeth.    Ash's 529-113.".     1153 

Tungsten .1091 

Turner   gasoline   furnace    898 

Tweezers   K,    for   inlav   work 924 

Types    of    True    Bite    Teeth 363-364 

Tynal       forms       of      natural       teeth 
(Williams)    362 


Ulsaver,   Dr.   E.   S.,  method  of 352 

developing      the      compensating 

curve    

Ultra-microscope    of    Zsigmondy. . . .   969 
Undercut  areas,  use  of  cores  in...     99 

swaging  gold   In    179 

Unetiual  distribution  of  the  elements  970 
Uniform  bearing  of  dentures  essen- 
tial           26 

Unilateral    mandibular    movements..   297 

Unit    of   thermal   conductivity 122 

Upper   dentures,    retention    of 26-27 

outline  form  of  distal 30 

margin     of     30 

Uranium    oompojnds    of 963 

the  initial  element  in 

the    debasement    scale     965 

Use  of  the  face  bow 330 

Utility   one   of   the   three    pri^me    ob- 
jects   in    denture    construction....       1 

Vacuum     caisting     machine 959 

chamber     28 

Vanadium     968 

Vanderpoel,    Emilv.    the    relation    of 

color  to  light   373 

Van  Horn,  Dr.  C.  S 1048 

Van    Woert,    Dr.    F.    T S78-943 

Variations    in   the   pitch   of    condyle 

paths    275 

lateral   paths  of  the   condyles...  474 

Various  forms  of  teeth 525 

Varnish   for  impressions 93 

Vault,     palatine     10 

Vegetable   bases    551 

Vein  gold    :1007 

Veneers  for  denture  gums,   granular 

facing     4  440 

pink     vulcanite     439 

porcelain    608 

prote.'i\n    537 

inlay,    Linderer's    1170 

Vestal  virgin,   facial  outlines 370 

Von     Wardroff,     Prof.     R.,     thermal 

conductivity    121 

Voick,   Dr.   A.    J.,   Inlays 1170 

Vulcan    facial    outlines 368 

Vulcanite,     conductivity    of    thermal 

chan^-es     121 

denture    bases     121 

advantages     and     disadvan- 
tages of 121 

double  vulcanization   process 

227    to    4S6 

inflammatory    conditions    re- 
sulting from  use  of  122 

dentures,    full    upper    and    lower 
sequent    steps    in    construc- 
tion   of    310    to    475 

partial    477  to  48S 

repairs  of   561  to  587 

finishers    (Wilson)     457 

lathe   burs    456 

Vulcanization    of   rubber,    chemistry 

of     441 

dimensional    changes    during. ...   447 

contraction 447 

expansion      447 

in   automatically    closed    flasks..   454 

closed   and   bolted    flasks 454 

time   of    455 

Vulcanizers.    danger    from    Improper 

handling     449 

safety    devices    for    449 

gas    regulator    451 

safety   valve    452 

steam  gauge   450 

thermometer     449 

time    regulators    451 

Walker,  Dr.  W.   E 

Ward.     Dr.     M.     A • 911-1041 

Warming   oven    for  flask   separation  413 


Warpage  of  casts  and  impressions. 53-55 
Watts'   flask  and   metal. 223-224-227-1185 

Wax,    bees    69 

and   parafflne    59-946-947 

rosin      60-1173 

composition  of   946 

hard   bite    60 

ijilay      946-947 

eliminating    from    mold 956 

temperature  required  to  ren- 
der plastic    954 

Weaver    cleavers     644 

Webb,    Dr.    Marshall    H.,    bridge 1163 

Webber,    Carl    O.,    Ph.    D 441-443 

Wedge    of    vulcanite    484 

Wedging  to  regain  lost  contact 738 

Weighted  lower  dentures 221 

of  vulcanite 221 

with    metal    core 221 

cast    metal    bases    222 

Weinstein,  Dr.  L.  J.,  artificial  stone 

495-1047 

refractory    materials     951-1040 

some     recent     work     concerning 

gold  alloys   1013  to  1063 

spring  for  absorbing  shock 500 

Welding    of    metals 990 

copper  to  iron   (new  process) 992 

alumino-thermy     892 

temperatures,    common    and    ex- 
traordinary      993 

Weston,     Dr.     Henry,     crown 1160 

metal   for   cast  bases 227 

Wet  method  for  recovering  silver.  .1073 
Whetting  hone,  aluminum  as  a... 1082 
White,  Dr.  J.  D.,  platinum  frame  for 

crown      8 '  ° 

White,    Samuel    S.,    vulcanite   litiga- 

tion     1134 

tooth    manufacture    1129 

White,  S.  S..  AVhite  Dental  Mfg.  Co. 
monograph  on  origin  and  develop- 
ment   of   porcelain    teeth 1162 

Wildman,    Dr.   E 439-905 

AVilliams,    Dr.    E.    Lloyd 58 

Williams,     Dr.    J.     Leon 

362-364-365-396-795-1164-1165-1166 

Wilson,   Dr.  George  H 

35-312-354-360-433-454-457 

Wire   and    plate    gauge   table 1099 

Wiring   denture   bases,    full   gold 17.5 

partial    4S9 

platinum     S93 

Wood.     Dr.    B.,     crowns 1155 

inlays    1171 

metal,  fusible   1 090 

Wood,    pivot,    teeth 1153 

Wood,  Dr.  W.  W.,  casting  appli- 
ances        200 

Wrinkles,      removing      from      metal 

bases     l^J 

platinum  matrix    920 

Wrought    iron    1065 

X    (Newtonium)    976 

Xenon    962 

X-ray   (Roentgen)    962 

Yellow   (primary  color) 375 

Yittrium      968 

Young  plate  perforator 6»4 

Zeller    casting    appliances 1186 

Zero.       absolute,       conductivity       of 

metals  at    988 

Zmc     1082 

for  dies    132 

Zitrconium      968 

Zslgmondy.    ultra-microscope    of 969 

Zygomatic  arch,  muscular  attach- 
ment to   278 

Zylonite   551 


f^ 


Date  Due 

1  ' 

■■,'.  -  .   ., 

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«^ 

OECl 

91949 

' 

(f) 

<ienti< 


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